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#1
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Super Capacitor Voltage Protection Circuit
When connecting "super capacitors" in series to increase the working
voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill |
#2
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Super Capacitor Voltage Protection Circuit
On 08 Aug 2014 15:50:31 GMT, EngineeringGuy
wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill Need more details. What does "...when the power supply is disconnected" mean? Schematically show us the configuration... show with equalizing resistors. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#3
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
EngineeringGuy wrote:
When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon |
#4
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit - scan0002.png
On 08 Aug 2014 15:50:31 GMT, EngineeringGuy
wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? The relays are all Normally Open (Form A) with 24 volt DC coils. John Fields |
#5
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
In article ,
EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill You can probably find just the right color of power LED that can shunt 700mA. Just make sure they don't get thermal runaway faster than they can drain the cap. If you don't like all the glow, shunt voltage references and trickle charger shunts have current consumption that's low compared to ultracapacitor leakage. But there's a catch... The capacitors will eventually loose equalization through self-discharge. When you apply power again, shunts on less-leaky caps could be exposed to the full power supply current. It's not a big deal from a solar trickle charger but imagine trying to make practical shunts if your supply is over 10 Amps. That's why resistors are simpler when you need balancing. |
#6
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Super Capacitor Voltage Protection Circuit - scan0002.png
On Fri, 08 Aug 2014 18:16:22 -0500, John Fields
wrote: The relays are all Normally Open (Form A) with 24 volt DC coils. --- Oops... The circuit latches when +V is disconnected. :-( John Fields |
#7
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
Jon Elson wrote:
EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. |
#8
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit - scan0002.png
John Fields wrote:
On 08 Aug 2014 15:50:31 GMT, EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? The relays are all Normally Open (Form A) with 24 volt DC coils. John Fields OOOh...a completely solid-state solution. |
#9
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
On 08 Aug 2014 15:50:31 GMT, EngineeringGuy wrote:
When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill Supercap data sheets are universally terrible. And various "supercaps" are very different. You might measure a leakage vs voltage curve and decide whether they might be OK in series without external equalization. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation |
#10
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Super Capacitor Voltage Protection Circuit
On 8/9/2014 6:09 PM, Robert Baer wrote:
Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. -- Rick |
#11
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
On Sun, 10 Aug 2014 16:19:02 -0400, rickman wrote:
On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#12
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
In article ,
Jim Thompson wrote: On Sun, 10 Aug 2014 16:19:02 -0400, rickman wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. Late generation high efficiency LEDs have incredibly sharp conduction knees, amazing matching between components, and low internal resistance. LED manufacturers have put lots of black magic into those chips to break past normal efficiency limitations. Their only imperfection as a shunt regulator is that the voltage drops with temperature. The problem of handling full inrush current after the caps have self-discharged to different voltages remains unresolved. I still think resistors would balance the best. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson |
#13
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
rickman wrote:
On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. Err..any (reasonable) silicon diode reverse polarity connected WRT the cap will conduct in the region of 620mV; one certainly does not need to have more in series. And the diode reversed biased (capacitor forward biased) will will have essentially zero current. Now,if 620mV is a bit much for these soup-er-boop-a-doop capacitors, then instead of sand power, go for flower power (Ge) at about 320mV. Unfortunately, they are not exactly the bees' knees and are a bit leaky of the electronic honey. |
#14
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
On 8/11/2014 12:44 AM, Robert Baer wrote:
rickman wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. Err..any (reasonable) silicon diode reverse polarity connected WRT the cap will conduct in the region of 620mV; one certainly does not need to have more in series. And the diode reversed biased (capacitor forward biased) will will have essentially zero current. Now,if 620mV is a bit much for these soup-er-boop-a-doop capacitors, then instead of sand power, go for flower power (Ge) at about 320mV. Unfortunately, they are not exactly the bees' knees and are a bit leaky of the electronic honey. I don't follow your reasoning at all. The OP wants to work at increased voltages by using multiple super caps in series. Why would you think 620 mV would be a high enough voltage? The way resistors work to equalize the voltage on the caps is to provide a small leakage current around the cap, higher when the voltage is higher reducing the charge on that cap relative to the others. The difference with the diodes is that they conduct much less current when the cap is in its normal working range. Only when it exceeds the working range by some margin does the diode start to conduct significantly bypassing a significant portion of the charging current. There has to be some headroom between the working voltage and the damage voltage since the diodes won't have a highly stable knee voltage. But given enough margin this should work well. If there is not enough margin then something with a better regulated knee would need to be used like a voltage regulator. -- Rick |
#15
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
rickman wrote:
On 8/11/2014 12:44 AM, Robert Baer wrote: rickman wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. Err..any (reasonable) silicon diode reverse polarity connected WRT the cap will conduct in the region of 620mV; one certainly does not need to have more in series. And the diode reversed biased (capacitor forward biased) will will have essentially zero current. Now,if 620mV is a bit much for these soup-er-boop-a-doop capacitors, then instead of sand power, go for flower power (Ge) at about 320mV. Unfortunately, they are not exactly the bees' knees and are a bit leaky of the electronic honey. I don't follow your reasoning at all. The OP wants to work at increased voltages by using multiple super caps in series. Why would you think 620 mV would be a high enough voltage? The way resistors work to equalize the voltage on the caps is to provide a small leakage current around the cap, higher when the voltage is higher reducing the charge on that cap relative to the others. The difference with the diodes is that they conduct much less current when the cap is in its normal working range. Only when it exceeds the working range by some margin does the diode start to conduct significantly bypassing a significant portion of the charging current. There has to be some headroom between the working voltage and the damage voltage since the diodes won't have a highly stable knee voltage. But given enough margin this should work well. If there is not enough margin then something with a better regulated knee would need to be used like a voltage regulator. I guess that you cannot read hat i said. |
#16
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
On 8/11/2014 11:20 PM, Robert Baer wrote:
rickman wrote: On 8/11/2014 12:44 AM, Robert Baer wrote: rickman wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. Err..any (reasonable) silicon diode reverse polarity connected WRT the cap will conduct in the region of 620mV; one certainly does not need to have more in series. And the diode reversed biased (capacitor forward biased) will will have essentially zero current. Now,if 620mV is a bit much for these soup-er-boop-a-doop capacitors, then instead of sand power, go for flower power (Ge) at about 320mV. Unfortunately, they are not exactly the bees' knees and are a bit leaky of the electronic honey. I don't follow your reasoning at all. The OP wants to work at increased voltages by using multiple super caps in series. Why would you think 620 mV would be a high enough voltage? The way resistors work to equalize the voltage on the caps is to provide a small leakage current around the cap, higher when the voltage is higher reducing the charge on that cap relative to the others. The difference with the diodes is that they conduct much less current when the cap is in its normal working range. Only when it exceeds the working range by some margin does the diode start to conduct significantly bypassing a significant portion of the charging current. There has to be some headroom between the working voltage and the damage voltage since the diodes won't have a highly stable knee voltage. But given enough margin this should work well. If there is not enough margin then something with a better regulated knee would need to be used like a voltage regulator. I guess that you cannot read hat i said. Ok, I understand now. -- Rick |
#17
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
Kevin McMurtrie wrote in
: In article , Jim Thompson wrote: On Sun, 10 Aug 2014 16:19:02 -0400, rickman wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. Late generation high efficiency LEDs have incredibly sharp conduction knees, amazing matching between components, and low internal resistance. LED manufacturers have put lots of black magic into those chips to break past normal efficiency limitations. Their only imperfection as a shunt regulator is that the voltage drops with temperature. The problem of handling full inrush current after the caps have self-discharged to different voltages remains unresolved. I still think resistors would balance the best. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill |
#18
Posted to alt.binaries.schematics.electronic
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Super Capacitor Voltage Protection Circuit
EngineeringGuy wrote:
Kevin wrote in : In , Jim wrote: On Sun, 10 Aug 2014 16:19:02 -0400, wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. Late generation high efficiency LEDs have incredibly sharp conduction knees, amazing matching between components, and low internal resistance. LED manufacturers have put lots of black magic into those chips to break past normal efficiency limitations. Their only imperfection as a shunt regulator is that the voltage drops with temperature. The problem of handling full inrush current after the caps have self-discharged to different voltages remains unresolved. I still think resistors would balance the best. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill ....with NOTHING to protect each one from reverse voltage? |
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Super Capacitor Voltage Protection Circuit
On Tue, 12 Aug 2014 22:16:35 -0700, Robert Baer wrote:
EngineeringGuy wrote: Kevin wrote in : In , Jim wrote: On Sun, 10 Aug 2014 16:19:02 -0400, wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. Late generation high efficiency LEDs have incredibly sharp conduction knees, amazing matching between components, and low internal resistance. LED manufacturers have put lots of black magic into those chips to break past normal efficiency limitations. Their only imperfection as a shunt regulator is that the voltage drops with temperature. The problem of handling full inrush current after the caps have self-discharged to different voltages remains unresolved. I still think resistors would balance the best. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill ...with NOTHING to protect each one from reverse voltage? Reverse polarity protection is important too, but what he is asking about is individual cell overvoltage protection, for which he needs a 2.7 volt shunt regulator across each cell, which will bypass a fully charged cell while allowing the rest of the string to fully charge. The forward polarity diode string others have suggested is a crude, high tempco shunt regulator of sorts when used as suggested, but a much more precise and stable voltage limit could be set with IC shunt regulators. By replacing the resistor string with any variety of shunt regulator you do also need to consider replacing the other feature of a resistor string: preventing individual cell reverse polarity when the capacitor string is fully discharged. |
#20
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Super Capacitor Voltage Protection Circuit
On 13 Aug 2014 04:31:20 GMT, EngineeringGuy
wrote: [snip] In article , Jim Thompson wrote: [snip] This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill HOW the "25 volts is removed, turned off, disconnected, not charging" matters. It seems to me that "over voltage" would be managed across the whole stack, with equalizing resistors across each cell. Perhaps making the charging voltage sufficiently large that the OVP is always active during charging. When the charging voltage is removed, "something" in the OVP, because it is inactive, disconnects the equalizing resistors/elements?? What "leakage" current can you tolerate? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#21
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Super Capacitor Voltage Protection Circuit
On 13 Aug 2014 04:31:20 GMT, EngineeringGuy wrote:
Kevin McMurtrie wrote in : In article , Jim Thompson wrote: On Sun, 10 Aug 2014 16:19:02 -0400, rickman wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. Late generation high efficiency LEDs have incredibly sharp conduction knees, amazing matching between components, and low internal resistance. LED manufacturers have put lots of black magic into those chips to break past normal efficiency limitations. Their only imperfection as a shunt regulator is that the voltage drops with temperature. The problem of handling full inrush current after the caps have self-discharged to different voltages remains unresolved. I still think resistors would balance the best. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill Do you know how much voltage is safe for those caps? Do you have a voltage:current curve? -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation |
#22
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Super Capacitor Voltage Protection Circuit
On Wed, 13 Aug 2014 18:02:27 -0700, John Larkin
wrote: [snip] This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill Do you know how much voltage is safe for those caps? Do you have a voltage:current curve? Do you have a clue? Not likely :-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#23
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Super Capacitor Voltage Protection Circuit
Glen Walpert wrote:
On Tue, 12 Aug 2014 22:16:35 -0700, Robert Baer wrote: EngineeringGuy wrote: Kevin wrote in : In , Jim wrote: On Sun, 10 Aug 2014 16:19:02 -0400, wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. Late generation high efficiency LEDs have incredibly sharp conduction knees, amazing matching between components, and low internal resistance. LED manufacturers have put lots of black magic into those chips to break past normal efficiency limitations. Their only imperfection as a shunt regulator is that the voltage drops with temperature. The problem of handling full inrush current after the caps have self-discharged to different voltages remains unresolved. I still think resistors would balance the best. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill ...with NOTHING to protect each one from reverse voltage? Reverse polarity protection is important too, but what he is asking about is individual cell overvoltage protection, for which he needs a 2.7 volt shunt regulator across each cell, which will bypass a fully charged cell while allowing the rest of the string to fully charge. The forward polarity diode string others have suggested is a crude, high tempco shunt regulator of sorts when used as suggested, but a much more precise and stable voltage limit could be set with IC shunt regulators. By replacing the resistor string with any variety of shunt regulator you do also need to consider replacing the other feature of a resistor string: preventing individual cell reverse polarity when the capacitor string is fully discharged. A resistor does NOTHING to prevent cell reverse polarity. |
#24
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Super Capacitor Voltage Protection Circuit
In article ,
Robert Baer wrote: Glen Walpert wrote: On Tue, 12 Aug 2014 22:16:35 -0700, Robert Baer wrote: EngineeringGuy wrote: Kevin wrote in : In , Jim wrote: On Sun, 10 Aug 2014 16:19:02 -0400, wrote: On 8/9/2014 6:09 PM, Robert Baer wrote: Jon Elson wrote: EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Well, a couple diodes across each cap would not leak a whole lot when forward biased below the forward conduction voltage. With plain Si diodes, that might be 5 diodes in series. they would start leaking somewhere below 3 V, and conduct pretty strongly at 3.5 V. You could also look a Schottky diodes and see what values of Vf you see. If they start to conduct at .4 V, then 7 in series would give you 2.8 V turn-on. You can get surface mount SOT23 dual diodes wired in series, so that would only take 4 parts. Jon Sounds silly to me; why use the diodes in the forward bias mode,when the reverse bias mode seems far better? That way, the capacitors are always reverse polarity protected. Because the reverse breakdown voltage is not well specified. It is guaranteed to be above some value, but where exactly will that be? How many diodes do you know of that will protect a 2.7 volt cap when the diode is reverse biased? LEDs might be a good choice for forward biased protection. Some of them work at 2.7 volts or so. Add a single Si diode and you will get a very small amount of current flow in the cap working voltage range with the knee in the I/V curve somewhere above 2.7 volts depending on the color used. You're whistling somewhere inappropriate if you think diodes are going to match and track well enough. Late generation high efficiency LEDs have incredibly sharp conduction knees, amazing matching between components, and low internal resistance. LED manufacturers have put lots of black magic into those chips to break past normal efficiency limitations. Their only imperfection as a shunt regulator is that the voltage drops with temperature. The problem of handling full inrush current after the caps have self-discharged to different voltages remains unresolved. I still think resistors would balance the best. This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill ...with NOTHING to protect each one from reverse voltage? Reverse polarity protection is important too, but what he is asking about is individual cell overvoltage protection, for which he needs a 2.7 volt shunt regulator across each cell, which will bypass a fully charged cell while allowing the rest of the string to fully charge. The forward polarity diode string others have suggested is a crude, high tempco shunt regulator of sorts when used as suggested, but a much more precise and stable voltage limit could be set with IC shunt regulators. By replacing the resistor string with any variety of shunt regulator you do also need to consider replacing the other feature of a resistor string: preventing individual cell reverse polarity when the capacitor string is fully discharged. A resistor does NOTHING to prevent cell reverse polarity. Actually, resistors do. You're missing the point of why resistors are recommended. The capacity of ultracaps is reasonably well matched. What's not well matched is the internal leakage. Here's where you're in trouble: - All 10 series caps are at 0V - 25V is applied - All caps charge to 2.5V +/- a tiny amount - Disconnect charge/load and let them sit for a few days - The voltages become extremely unbalanced from varying leakage - Charging or discharging will cause OV or UV, possibly with enough current for damage Resistors would have brought them all down to 0V, a safe state. -- Astraweb posts are filtered as spam |
#25
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Super Capacitor Voltage Protection Circuit
On Wed, 13 Aug 2014 18:37:24 -0700, Jim Thompson
wrote: On Wed, 13 Aug 2014 18:02:27 -0700, John Larkin wrote: [snip] This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill Do you know how much voltage is safe for those caps? Do you have a voltage:current curve? Do you have a clue? Not likely :-} ...Jim Thompson You're repeating yourself, without content, as usual. And if you want to design an elaborate protection circuit for an expensive part that you don't understand, do that again, too. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com |
#26
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Super Capacitor Voltage Protection Circuit
On 13 Aug 2014 04:31:20 GMT, EngineeringGuy
wrote: [snip] Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill How much shunt resistance across each cell is tolerable when _not_ charging? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#27
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Super Capacitor Voltage Protection Circuit
On 08 Aug 2014 15:50:31 GMT, EngineeringGuy
wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill Food for thought, see... http://www.analog-innovations.com/SED/ChargeLimiter_SuperCap.png Obviously the charging current doesn't need to go thru the LED's in the OptoCouplers, but some means is needed to tell the TL431's to turn off. Perhaps parallel the LED's (with ballast resistors)? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#28
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Super Capacitor Voltage Protection Circuit
On Thu, 14 Aug 2014 12:36:24 -0700, Jim Thompson
wrote: On 08 Aug 2014 15:50:31 GMT, EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill Food for thought, see... http://www.analog-innovations.com/SED/ChargeLimiter_SuperCap.png Obviously the charging current doesn't need to go thru the LED's in the OptoCouplers, but some means is needed to tell the TL431's to turn off. Perhaps parallel the LED's (with ballast resistors)? ...Jim Thompson As in... http://www.analog-innovations.com/SED/ChargeLimiter_SuperCap_v2.png ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#29
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Super Capacitor Voltage Protection Circuit
In article ,
Jim Thompson wrote: On 13 Aug 2014 04:31:20 GMT, EngineeringGuy wrote: [snip] Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill How much shunt resistance across each cell is tolerable when _not_ charging? ...Jim Thompson I've seen ratings of 2 to 10 microamps internal leakage per farad at 25C after holding the voltage for 72 hours. That's around 0 to 0.5V per day self discharge? The working voltage depends on temperature so getting them hot can take them 0.5V down from a full charge quickly. I've used them to keep mobile solar devices working as they pass through shade. They're hardly ideal capacitors since you're moving charges around in two films of carbon gel soaked with electrolyte. Their voltage fluctuates for a while after sudden charging or discharging. Some models have an ESR so crazy low that 0.1V of residual charge can weld the pins together. -- Astraweb posts are filtered as spam |
#30
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Super Capacitor Voltage Protection Circuit
On Wed, 13 Aug 2014 18:37:24 -0700, Jim Thompson
wrote: On Wed, 13 Aug 2014 18:02:27 -0700, John Larkin wrote: [snip] This is one of those annoying cases where the OP has vanished after the initial post and is not answering questions. Without more info, it's a wasted effort. Something along the lines of Field's relay method post... maybe with MOSFET's... is most likely to succeed... just needs the right controls :-} ...Jim Thompson Jim... I haven't vanished, just out of town. I don't quite understand what clairification you require... 10 caps in series to give 27VDC total operating voltage.. each with "something" in parallel to prevent over voltage... overvoltage will cause "super capacitors" to short and fail.. that "something" must be such that it will not discharge the capacitors when the 25 volts is removed, turned off, disconnected, not charging, etc. Bill Do you know how much voltage is safe for those caps? Do you have a voltage:current curve? Do you have a clue? Not likely :-} ...Jim Thompson Look at some supercap data sheets. On most, the only spec is operating voltage and ESR. I've never see a voltage vs leakage current curve. Seems to me that if you want to protect these things, you should know something about them. And if it's not on the data sheet, measure a few. If I had any, I'd measure them myself. If they are charged by a modest constant current, do they go POP like a film-foil cap, or do they just level off, like a wet electrolytic? [1] I'd suspect the latter. Would a series string self-equalize? A v:i curve might answer that question. You seen to be promoting ignorance. Nothing new there. [1] polymer electrolytics go POP! -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation |
#31
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Super Capacitor Voltage Protection Circuit
On Thu, 14 Aug 2014 12:52:10 -0700, Jim Thompson
wrote: On Thu, 14 Aug 2014 12:36:24 -0700, Jim Thompson wrote: On 08 Aug 2014 15:50:31 GMT, EngineeringGuy wrote: When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill Food for thought, see... http://www.analog-innovations.com/SED/ChargeLimiter_SuperCap.png Obviously the charging current doesn't need to go thru the LED's in the OptoCouplers, but some means is needed to tell the TL431's to turn off. Perhaps parallel the LED's (with ballast resistors)? ...Jim Thompson As in... http://www.analog-innovations.com/SED/ChargeLimiter_SuperCap_v2.png ...Jim Thompson Less sensitivity to OptoCoupler CTR (current transfer ratio)... http://www.analog-innovations.com/SED/ChargeLimiter_SuperCap_v3.png ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food. |
#32
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Super Capacitor Voltage Protection Circuit
On Fri, 08 Aug 2014 15:50:31 +0000, EngineeringGuy wrote:
When connecting "super capacitors" in series to increase the working voltage above the level of the individual capacitors, does anyone have an active voltage clamp that would not discharge the capacitors when the power supply is disconnected? Most "super" capacitors have a working voltage of 2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25 VDC capacitor stack. Most suggestions call for connecting equalizing resistors in parallel with each capacitor, but I would rather have a circuit that would not discharge the capacitors when the power is off... anyone have any ideas? Thanks, Bill There are commercial products for this purpose, for example: http:// www.aldinc.com/pdf/ALD8100xx.pdf. These also have a reverse diode built in but they don't give any specs on it so you may need to be concerned about that. -- Jim Mueller To get my real email address, replace wrongname with dadoheadman. Then replace nospam with fastmail. Lastly, replace com with us. |
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