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dc-dc converter
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat |
dc-dc converter
On 6/17/2013 8:43 AM, Pat wrote:
Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat I've no experience w. dc-dc converters but wonder why you just didn't tap one of the 12v batteries to run your lights, etc. while still leaving them series connected for the boat motor. |
dc-dc converter
On Mon, 17 Jun 2013 09:14:23 -0700, Bennett
wrote: On 6/17/2013 8:43 AM, Pat wrote: Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat I've no experience w. dc-dc converters but wonder why you just didn't tap one of the 12v batteries to run your lights, etc. while still leaving them series connected for the boat motor. I want to keep the 48V bank balanced rather than having one of them discharged further than the others. I am currently using a 5th (smaller) 12V battery for the lights to avoid using one of the four from the 48V bank. Adding the DC-DC converter keeps me from having to manually charge that 5th battery periodically. |
dc-dc converter
On Mon, 17 Jun 2013 11:43:53 -0400, Pat wrote:
Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat That behavior is normal. The DC-DC converter almost certainly has a capacitor across the input, and certainly has a capacitor across the output. There will be a high initial current draw when power is applied. Aftehr that it draws enough to provide the required output current plus a small amount for the circuitry. With no load it's output will rise until an overvoltage clamp shuts down the control IC. I'd use a 5A slow blow fuse in the input line with a switch to control the lights. PlainBill |
dc-dc converter
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dc-dc converter
On 17/06/13 23:43, Pat wrote:
Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat Apart from the inrush current to the cap which has been discussed already, being nav lights I would be inclined to use the converter to charge the dedicated 12v battery and keep it as a fail safe device for the nav lighting should the converter fail. |
dc-dc converter
Pat wrote in message
... Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat Could you not rewire the boat lighting so 4 lamps are in series, with some sort of LED failure indicator or something to show which lamp/wiring has failed , when it does. One for red, one green and 2 riding lights, about 4 are used together , never separately. Then for at anchor. and just one light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing. |
dc-dc converter
On Tue, 18 Jun 2013 08:12:54 +0100, "N_Cook"
wrote: Pat wrote in message .. . Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat Could you not rewire the boat lighting so 4 lamps are in series, with some sort of LED failure indicator or something to show which lamp/wiring has failed , when it does. One for red, one green and 2 riding lights, about 4 are used together , never separately. Then for at anchor. and just one light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing. Thanks to all for your comments and suggestions. I'll do some testing to see what minimum load will keep the output at 12V. I may also add a small resistor in series with the input to keep the inrush current down a little. I realize that will lower the overall efficiency, but I hate that snaping sound the switch makes with nothing limiting the inrush. Regarding the suggestion of putting the lights in series, I thought of that, too. However, the lights (4 of them total) are not even close to being matched loads. The red and green only draw 60 mA each. The anchor light draws 175 mA. The spot light used for docking draws 1.75 A all by itself. (All these are LEDs with their own internal current limiting resistors). Anyway, thanks again for your comments. Pat |
dc-dc converter
On Tue, 18 Jun 2013 11:00:16 +0800, Rheilly Phoull
wrote: On 17/06/13 23:43, Pat wrote: Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat Apart from the inrush current to the cap which has been discussed already, being nav lights I would be inclined to use the converter to charge the dedicated 12v battery and keep it as a fail safe device for the nav lighting should the converter fail. Sorry to burst your bubble, but you can't use a 12.31 supply to charge a 12V lead-acid battery, unless you run it through ANOTHER DC-DC converter PlainBill |
dc-dc converter
On Tue, 18 Jun 2013 10:46:29 -0400, Pat wrote:
On Tue, 18 Jun 2013 08:12:54 +0100, "N_Cook" wrote: Pat wrote in message . .. Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat Could you not rewire the boat lighting so 4 lamps are in series, with some sort of LED failure indicator or something to show which lamp/wiring has failed , when it does. One for red, one green and 2 riding lights, about 4 are used together , never separately. Then for at anchor. and just one light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing. Thanks to all for your comments and suggestions. I'll do some testing to see what minimum load will keep the output at 12V. I may also add a small resistor in series with the input to keep the inrush current down a little. I realize that will lower the overall efficiency, but I hate that snaping sound the switch makes with nothing limiting the inrush. Regarding the suggestion of putting the lights in series, I thought of that, too. However, the lights (4 of them total) are not even close to being matched loads. The red and green only draw 60 mA each. The anchor light draws 175 mA. The spot light used for docking draws 1.75 A all by itself. (All these are LEDs with their own internal current limiting resistors). Anyway, thanks again for your comments. Pat Rathe than using a low valure resistor to limit inrush current, use an ICL. Your input current into the module will be in the order of .5 - 1 amp. Cantherm's MF72-010D7 is available from Digi-key for $.36. At no load it looks like a 10 ohm resistor, under load it looks like a ..5 ohm resistor. Digi-Key has no minimum order; specify USPS First Class Mail and shipping would run under $3.00 PlainBill |
dc-dc converter
"Pat" wrote in message ... On Tue, 18 Jun 2013 08:12:54 +0100, "N_Cook" wrote: Pat wrote in message . .. Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. Anyone else ever buy one of these things? Is the above behavior normal? I guess you get what you pay for and $25 isn't much. It is nicely potted so water resistance isn't an issue. But that also means I can't take it apart to see what's inside. The label says "TOBSUN THJ4812C120Z 120W DC-DC CONVERTER". Pat Could you not rewire the boat lighting so 4 lamps are in series, with some sort of LED failure indicator or something to show which lamp/wiring has failed , when it does. One for red, one green and 2 riding lights, about 4 are used together , never separately. Then for at anchor. and just one light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing. Thanks to all for your comments and suggestions. I'll do some testing to see what minimum load will keep the output at 12V. I may also add a small resistor in series with the input to keep the inrush current down a little. I realize that will lower the overall efficiency, but I hate that snaping sound the switch makes with nothing limiting the inrush. Regarding the suggestion of putting the lights in series, I thought of that, too. However, the lights (4 of them total) are not even close to being matched loads. The red and green only draw 60 mA each. The anchor light draws 175 mA. The spot light used for docking draws 1.75 A all by itself. (All these are LEDs with their own internal current limiting resistors). Anyway, thanks again for your comments. Pat Given that the currents of the running lights are so low, and the one that draws a bit more is only used for docking, I think that you are making things needlessly complicated for yourself. The original suggestion that someone made of just tapping the feed from one battery up the stack, is the perfect and sensible solution. With a total current draw of less than 300 mA (excluding the docking spotlight) this will not cause any significant 'unbalancing' of a high current-capacity lead acid stack at all. If it did, then there would be something seriously wrong ... Every time you add any kind of electronics to a simple wiring scheme, you are introducing a further layer of potential unreliability. Bear in mind also, that this is exacerbated in a marine situation by the intimate presence of corrosive seawater. Any kind of simple electronic 'dropper' from 48 down to 12 volts, is going to dissipate significant power and run hot unless it is a switch-mode type, in which case, it ceases to be simple, opening the way for even lower reliability. If you really *don't* want to use a single battery solution, then the other simple way to do it, given that you've now told us that the nav lights are LEDs with an appropriate internal resistor for 12 volt operation, is to hang the lights across the full 48 volts, but quadruple the series resistor. Or if you can't easily get to the resistor to replace it, add an external one of three times the value in series with each light. Arfa |
dc-dc converter
On Thu, 20 Jun 2013 02:12:21 +0100, "Arfa Daily"
wrote: If you really *don't* want to use a single battery solution, then the other simple way to do it, given that you've now told us that the nav lights are LEDs with an appropriate internal resistor for 12 volt operation, is to hang the lights across the full 48 volts, but quadruple the series resistor. Or if you can't easily get to the resistor to replace it, add an external one of three times the value in series with each light. Arfa Interesting idea. I hadn't thought of that. You are correct that I can't easily get to the internal resistors, but adding external resistors would be easy enough. However, If I add the appropriate external resistors to drop the additional 36 volts, I will be creating a lot of wasted heat. The nav light resistors would be dissipating 2 watts each while the anchor light R would be dissipating over 6 watts. The spot light R would be dissipating 62 watts! I think I'll stick with the (switching type) dc-dc converter. Your comments about added complexity are well taken, though. Pat |
dc-dc converter
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dc-dc converter
"Pat" wrote in message ... On Thu, 20 Jun 2013 02:12:21 +0100, "Arfa Daily" wrote: If you really *don't* want to use a single battery solution, then the other simple way to do it, given that you've now told us that the nav lights are LEDs with an appropriate internal resistor for 12 volt operation, is to hang the lights across the full 48 volts, but quadruple the series resistor. Or if you can't easily get to the resistor to replace it, add an external one of three times the value in series with each light. Arfa Interesting idea. I hadn't thought of that. You are correct that I can't easily get to the internal resistors, but adding external resistors would be easy enough. However, If I add the appropriate external resistors to drop the additional 36 volts, I will be creating a lot of wasted heat. The nav light resistors would be dissipating 2 watts each while the anchor light R would be dissipating over 6 watts. The spot light R would be dissipating 62 watts! I think I'll stick with the (switching type) dc-dc converter. Your comments about added complexity are well taken, though. Pat 2 Watts is nothing. A 4 or 5 watt wirewound resistor would barely get warm at 2 watts dissipation, and could be easily encased in a bit of heatshrink tube in line with the feed cable. Similarly, you could use three equal value resistors of 4 watts each, all in series and again in heatshrink tubing, for the higher demand anchor light. With a couple of watts being dissipated in each resistor, again there would be no issue with excess heat. The 'parking' spotlight is in use for only a short time, and I would not even bother trying to do anything with that one. I would just run that from the battery at the bottom of the stack for the relatively brief period that it was needed. Try as I might, I really can't come up with a 'practical' reason not to do that. Even with it pulling a couple of amps, it is not going to have any significant effect on the performance of the battery stack overall, or drain that bottom battery by any amount that wouldn't be equivalent to acceptable variations in battery performance anyway. What is the capacity of these batteries ? 100 AH apiece ? More ? Even running that light for an hour would not represent consuming more than say 1.5% of the battery's fully charged capacity, and if the system cannot cope with that, then I would be worried anyway, as once those batteries are more than about six months old, the variation in their capacities - and thus their potential to be 'unbalanced' - will probably exceed that figure anyway ... Arfa |
dc-dc converter
On Fri, 21 Jun 2013 00:01:26 +0100, "Arfa Daily"
wrote: "Pat" wrote in message .. . On Thu, 20 Jun 2013 02:12:21 +0100, "Arfa Daily" wrote: If you really *don't* want to use a single battery solution, then the other simple way to do it, given that you've now told us that the nav lights are LEDs with an appropriate internal resistor for 12 volt operation, is to hang the lights across the full 48 volts, but quadruple the series resistor. Or if you can't easily get to the resistor to replace it, add an external one of three times the value in series with each light. Arfa Interesting idea. I hadn't thought of that. You are correct that I can't easily get to the internal resistors, but adding external resistors would be easy enough. However, If I add the appropriate external resistors to drop the additional 36 volts, I will be creating a lot of wasted heat. The nav light resistors would be dissipating 2 watts each while the anchor light R would be dissipating over 6 watts. The spot light R would be dissipating 62 watts! I think I'll stick with the (switching type) dc-dc converter. Your comments about added complexity are well taken, though. Pat 2 Watts is nothing. A 4 or 5 watt wirewound resistor would barely get warm at 2 watts dissipation, and could be easily encased in a bit of heatshrink tube in line with the feed cable. Similarly, you could use three equal value resistors of 4 watts each, all in series and again in heatshrink tubing, for the higher demand anchor light. With a couple of watts being dissipated in each resistor, again there would be no issue with excess heat. The 'parking' spotlight is in use for only a short time, and I would not even bother trying to do anything with that one. I would just run that from the battery at the bottom of the stack for the relatively brief period that it was needed. Try as I might, I really can't come up with a 'practical' reason not to do that. Even with it pulling a couple of amps, it is not going to have any significant effect on the performance of the battery stack overall, or drain that bottom battery by any amount that wouldn't be equivalent to acceptable variations in battery performance anyway. What is the capacity of these batteries ? 100 AH apiece ? More ? Even running that light for an hour would not represent consuming more than say 1.5% of the battery's fully charged capacity, and if the system cannot cope with that, then I would be worried anyway, as once those batteries are more than about six months old, the variation in their capacities - and thus their potential to be 'unbalanced' - will probably exceed that figure anyway ... Arfa If it was me I'd try to figure out a way to place the resistors someplace where any heat they generate could keep something dry. I wonder, do DC-DC converters emit much RF? I'm really surprised that the original poster doesn't want to go with the most simple and robust solution. Especially on a boat. And it would be much easier to carry and wire in spare resistors than a spare DC-DC converter. ERS |
dc-dc converter
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dc-dc converter
snip ERS This is my last post on this subject as we have drifted off topic. Such is the nature of usenet ... more snipping ****End of Thread*** Oooooohh ! :-) Arfa |
dc-dc converter
Pat wrote:
Does anyone here have any experience with dc to dc converters? I need a unit that takes approximately 48 volts input (Four 12V Lead-Acid batteries in series) and provides 12 volts out at a few amps. This will be used on a pontoon boat to supply 12V for navigation lights from the 48 V battery bank that drives the electric motor. I found a module on the Internet that can handle 10 A output at 12 volts and only costs $25 (USD). Many no-name websites offer it anywhere from $22 to $40. All use the same exact picture. I picked a site that seems less scary than others and ordered one. It arrived very quickly. At first, it seemed defective, but after playing around a little, I think I figured it out. Now to my questions: 1) It is normal for such a device to draw high current when first connected? It draws quite an arc when the 48V line is connected but then only draws 31 mA with no load. Removing power for just a second starts that process over - ie, draws an arc with a loud snap when connecting it. I was using a switch when I first tried it and heard the snap from inside the switch. I then changed to a jumper wire and could see the arc. 2) Do these things normally have a minimum load spec? With no load, the voltage starts at 12.34 V and then drops to 4.7 V or so over a period of 30 to 40 seconds. It then jumps back to 12.34 and starts the process over. The instructions don't mention a minimum load, but I tried adding a lamp that draws a few amps. The output was then steady at 12.31 Volts. I don't have a scope, so I have no idea what's going on over timeframes shorter than a second or so. This sounds perfectly normal. I presume it is a switching power supply, and needs capacitors to buffer the switching pulses. So, the capacitor draws a large current at turn-on. You may need a high current relay to handle the turn-on surge without damage. Yes, your unit apparently needs a small load to continue regulating properly. Definitely put a fuse in the 48 V input to it. Jon |
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