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Capacitor sizes
In my car I have a bluetooth phone kit that plugs into an auxiliary
cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith |
Capacitor sizes
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith This is not a good idea, as you'd need a capacitor the size of atlantis plus the V_out would ramp down not stay steady. If youre deterimned to do this you could just wire the lighter to an always on fuse, disconnecting the old feed. But this wont really work either, since system v drops heavily during cranking. NT |
Capacitor sizes
In article . com,
Trevor Smith wrote: In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Wouldn't it be easier to either re-wire the cigar lighter to the ignition circuit or provide a second outlet so wired? -- *Speak softly and carry a cellular phone * Dave Plowman London SW To e-mail, change noise into sound. |
Capacitor sizes
wrote in message ups.com... Trevor Smith wrote: In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith This is not a good idea, as you'd need a capacitor the size of atlantis .... That reminds me of the power supply I made for my first high level language computer - a UK101 - a kit that involved soldering hundreds of connections by hand. I decided I wanted to make the supply really smooth, so I put a 10,000 microfarad capacitor across the outlet. It was big, but it would run the TTL based computer for several seconds after I disconnected the power. Colin Bignell |
Capacitor sizes
Dave Plowman (News) wrote:
In article . com, Trevor Smith wrote: In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Wouldn't it be easier to either re-wire the cigar lighter to the ignition circuit or provide a second outlet so wired? -- *Speak softly and carry a cellular phone * Dave Plowman London SW To e-mail, change noise into sound. Thanks for your replies, I hadn't realised it would have to be that big so I think I will take Dave's advice and hook it into the ignition circuit instead. Regards Trevor Smith |
Capacitor sizes
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Capacitor sizes
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Capacitor sizes
Trevor Smith wrote:
In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith If you dig-out your old school physics books you'll find that CV=IT so for particular values of load current (I), hold-up time (t) and acceptable voltage droop (V) you can work out the size of C ... but much more practical to feed the phone kit from somewhere else. Dave |
Capacitor sizes
Trevor Smith wrote: In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith Wire it direct to a permanent live with its own fuse, much easier than having to hide a "coke can" somewhere!! |
Capacitor sizes
Trevor Smith wrote: give the phone kit enough juice to keep it powered up during the time it takes to start the engine I'd use 3 capacitors in parallel. 22uF (which is probably adequate), then a 1uF and a 100nF all in parallel, because I'd be worried about filtering high frequency electrical noise from the starter. Feed them from a diode. If 22uF isnt enough, then either fix the engine to start more quickly, or parallel up another one. As we don't know just how much the bluetooth gadget draws for current, it's not practical to calculate this beforehand. |
Capacitor sizes
wrote in message
ups.com... I'd use 3 capacitors in parallel. 22uF (which is probably adequate), then a 1uF and a 100nF all in parallel, because I'd be worried about filtering high frequency electrical noise from the starter. Does that actually work? My rather simple understanding of capacitors was that if you stick them in parallel, they just behave like one larger one. Or is the resistance of the wiring somewhere providing a useful effect? cheers, clive |
Capacitor sizes
No ammount of rewiring the sockets will get round the fact that voltage
on the main bus drops to a few volts during cranking This is the scheme I used for the radio and GPS in my last but one car. The NICAD supplies the voltage when the supply is less than 9volts and even when the main battery is removed. The Nicad trickle charges through the 330R resistor SUPPLY LOAD ----------|-------||-------------- / | \ 330Resistor | / | \ | |-------||----+ | ------- --- 9 VOLT ------- NICAD --- ------ --- | | GROUND |
Capacitor sizes
In article . com,
dcbwhaley wrote: No ammount of rewiring the sockets will get round the fact that voltage on the main bus drops to a few volts during cranking So what? It's unlikely the phone needs more than 10 volts. -- *All generalizations are false. Dave Plowman London SW To e-mail, change noise into sound. |
Capacitor sizes
On 27 Sep 2006 15:57:13 -0700, "Trevor Smith"
wrote: In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. Well it would do that. snip Any advice would be appreciated Forget the capacitor idea it's ridiculous. Rewire the socket or add another one suitably fused directly back to the battery. Or you could just not use the phone while driving or alternatively chuck the whole lot away and use a phone box. -- |
Capacitor sizes
Clive George wrote:
wrote in message ups.com... I'd use 3 capacitors in parallel. 22uF (which is probably adequate), then a 1uF and a 100nF all in parallel, because I'd be worried about filtering high frequency electrical noise from the starter. Does that actually work? My rather simple understanding of capacitors was that if you stick them in parallel, they just behave like one larger one. Or is the resistance of the wiring somewhere providing a useful effect? More that the coiled up-ness of the big capacitor puts substantial inductance in series with it. Also electrolytic capacitors have a measurable internal resistance. cheers, clive |
Capacitor sizes
Staffbull wrote:
Trevor Smith wrote: In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith Wire it direct to a permanent live with its own fuse, much easier than having to hide a "coke can" somewhere!! Trouble having to remember to switch it off when I leave the car, memory not as good as it used to be. No I will wire it into a ignition feed as I only really need it when driving not parked up with the engine off. Thanks again for the feedback. Trevor Smith |
Capacitor sizes
Staffbull wrote:
Trevor Smith wrote: In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith Wire it direct to a permanent live with its own fuse, much easier than having to hide a "coke can" somewhere!! Trouble having to remember to switch it off when I leave the car, memory not as good as it used to be. No I will wire it into a ignition feed as I only really need it when driving not parked up with the engine off. Thanks again for the feedback. Trevor Smith |
Capacitor sizes
On Thu, 28 Sep 2006 12:49:04 UTC, "dcbwhaley" wrote:
This is the scheme I used for the radio and GPS in my last but one car. The NICAD supplies the voltage when the supply is less than 9volts and even when the main battery is removed. The Nicad trickle charges through the 330R resistor I have a Pama handsfree kit that does exactly that.... -- The information contained in this post is copyright the poster, and specifically may not be published in, or used by Avenue Supplies, http://avenuesupplies.co.uk |
Capacitor sizes
The Natural Philosopher wrote:
More that the coiled up-ness of the big capacitor puts substantial inductance in series with it. DC Volts + Inductance ? Not really an issue is it. Also electrolytic capacitors have a measurable internal resistance. Yes, to a DC voltage a Capacitor has infinite resistance because it is open circuit! I presume the OP was querying strapping 3 capacitors of the same value in parallel i.e. 3 x 22 uF instead of a single 66 uF cap. -- http://gymratz.co.uk - Best Gym Equipment & Bodybuilding Supplements UK. http://trade-price-supplements.co.uk - TRADE PRICED SUPPLEMENTS for ALL! http://fitness-equipment-uk.com - UK's No.1 Fitness Equipment Suppliers. http://Water-Rower.co.uk - Worlds best prices on the Worlds best Rower. |
Capacitor sizes
On Thu, 28 Sep 2006 16:21:10 UTC, "Pet @ www.gymratz.co.uk ;¬)"
wrote: The Natural Philosopher wrote: More that the coiled up-ness of the big capacitor puts substantial inductance in series with it. DC Volts + Inductance ? Not really an issue is it. Also electrolytic capacitors have a measurable internal resistance. Yes, to a DC voltage a Capacitor has infinite resistance because it is open circuit! His point, I think, is that an electrolytic capacitor does not have infinite resistance. (actually, no capacitor has infinite resistance....) -- The information contained in this post is copyright the poster, and specifically may not be published in, or used by Avenue Supplies, http://avenuesupplies.co.uk |
Capacitor sizes
In article ,
"Pet @ www.gymratz.co.uk ;¬)" wrote: Yes, to a DC voltage a Capacitor has infinite resistance because it is open circuit! Eh? -- *If love is blind, why is lingerie so popular? * Dave Plowman London SW To e-mail, change noise into sound. |
Capacitor sizes
Bob Eager wrote:
On Thu, 28 Sep 2006 16:21:10 UTC, "Pet @ www.gymratz.co.uk ;¬)" wrote: The Natural Philosopher wrote: More that the coiled up-ness of the big capacitor puts substantial inductance in series with it. DC Volts + Inductance ? Not really an issue is it. Also electrolytic capacitors have a measurable internal resistance. Yes, to a DC voltage a Capacitor has infinite resistance because it is open circuit! His point, I think, is that an electrolytic capacitor does not have infinite resistance. (actually, no capacitor has infinite resistance....) The issue is RF suppression in the original comment about paralleling capacitors. To preserve a low impedance across a broad range of frequencies it is usual to have up to three capacitors - a large electolytic, which is reaosanbly low impedance in the audio and kilohertz sort of arena then something like a mylar layered capacitor, which will do well up to a Mhz or tow and then something like a ceramic disc, which can absorb frequencies in the 10-100MHz range, or higher. Beyond that you are into black magic...every mm of wire will do SOMETHING. |
Capacitor sizes
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Capacitor sizes
The Natural Philosopher wrote:
The issue is RF suppression in the original comment about paralleling capacitors. To preserve a low impedance across a broad range of frequencies it is usual to have up to three capacitors - a large electolytic, which is reaosanbly low impedance in the audio and kilohertz sort of arena then something like a mylar layered capacitor, which will do well up to a Mhz or tow and then something like a ceramic disc, which can absorb frequencies in the 10-100MHz range, or higher. Beyond that you are into black magic...every mm of wire will do SOMETHING. Apologies. My mistake. Your explanation above clears up the error of my confusion. :¬) -- http://gymratz.co.uk - Best Gym Equipment & Bodybuilding Supplements UK. http://trade-price-supplements.co.uk - TRADE PRICED SUPPLEMENTS for ALL! http://fitness-equipment-uk.com - UK's No.1 Fitness Equipment Suppliers. http://Water-Rower.co.uk - Worlds best prices on the Worlds best Rower. |
Capacitor sizes
Dave Plowman (News) wrote:
In article , "Pet @ www.gymratz.co.uk ;¬)" wrote: Yes, to a DC voltage a Capacitor has infinite resistance because it is open circuit! Eh? But if the 'DC' voltage changes a current will flow, so you can no longer describe it as presenting infinite resistance - although of course energy is being stored or released, rather than dissipated as heat as it would be in a resistor. For a perfect capacitor i = C * dv/dt, for a practical capacitor there's always some additional loss present which does result in heat being dissipated. This is usually thought of in terms of an equivalent series resistance, ESR. There's no such thing as DC really, unless you've been hanging around since before the big bang. -- Andy |
Capacitor sizes
In message . com,
Trevor Smith writes In my car I have a bluetooth phone kit that plugs into an auxiliary cigar lighter socket that is controlled by the ignition switch, which means it turns off when you turn the key to the start position. I would like to put an electrolytic capacitor across the terminals of the socket to give the phone kit enough juice to keep it powered up during the time it takes to start the engine but I'm not sure how they are rated, ie: a high number uF a lower number. I know the current that the kit draws will be needed to get the right capacitor for the right time but I haven't checked this yet, and I wouldn't the formula to work it out any way so I was going to go for the biggest. Any advice would be appreciated Regards Trevor smith Buy Drivel's rusty old Prius it's got a big battery in it -- geoff |
Capacitor sizes
So what? It's unlikely the phone needs more than 10 volts. -- But the main bus voltage can fall below 6 volts when cranking the engine, especially if it is very cold. |
Capacitor sizes
In article . com,
dcbwhaley wrote: But the main bus voltage can fall below 6 volts when cranking the engine, especially if it is very cold. No it can't. -- *I wonder how much deeper the ocean would be without sponges* Dave Plowman London SW To e-mail, change noise into sound. |
Capacitor sizes
In article ,
Nick2 wrote: But the main bus voltage can fall below 6 volts when cranking the engine, especially if it is very cold. No it can't. Why not? 6v gets you max power delivered from the battery... I've got an accurate voltmeter sitting across my car battery at all times the ignition is on, and I can assure you it never drops under nine point something volts even on the coldest day when starting. Usually the high 10s. If you think about it, old cold start ignition systems are designed for 9 volts minimum. -- *Verbs HAS to agree with their subjects * Dave Plowman London SW To e-mail, change noise into sound. |
Capacitor sizes
dcbwhaley wrote:
So what? It's unlikely the phone needs more than 10 volts. -- But the main bus voltage can fall below 6 volts when cranking the engine, especially if it is very cold. you won't even start a modern car on 6v. I had two batteries die on me this year on different cars. Around 9v was the startable limit. I stuck a meter on them to see. |
Capacitor sizes
Nick2 wrote:
On Fri, 29 Sep 2006 00:20:42 +0100, Dave Plowman (News) wrote: In article . com, dcbwhaley wrote: But the main bus voltage can fall below 6 volts when cranking the engine, especially if it is very cold. No it can't. Why not? 6v gets you max power delivered from the battery... And enough power absorbed inside it to explode it. |
Capacitor sizes
The Natural Philosopher wrote: Indeed. One reason that aircraft used to use (and may still do) rotary converters so that huge electrical drains like lowering undercarriages or flaps do not result in instrument blackout. A big heavy rotor spinning at many thousand RPM stores a lot more energy than the same sized capacitor. This is completely wrong. Although aircraft certainly did (and some still do) use rotary converters, they didn't use them to supply the high power loads. The high power system was fed by engine generators (DC, then later AC) at 100V and above and the rotary inverters were used to supply the older 28V standards for existing instrumentation systems. Nor do these rotaries have particularly massive rotors with appreciable stored energy in them. I posted a summary of aircraft electrical power to this ng a while ago. http://groups.google.co.uk/group/alt...a7213ccfd91f85 |
Capacitor sizes
Andy Wade wrote: Yes, to a DC voltage a Capacitor has infinite resistance because it is open circuit! But if the 'DC' voltage changes a current will flow, If it changes, then it isn't DC (for the purposes of reactive theory), you've imposed some AC component upon it. It may be of very low frequency, but it's still an AC component and thus the impedance of the capacitor is no longer infinite. |
Capacitor sizes
dcbwhaley wrote: But the main bus voltage can fall below 6 volts when cranking the engine, especially if it is very cold. If the terminal voltage of a lead acid car battery falls below about 9V, the effective internal resistance (for high currents) will also have become so high as well that they're no longer capable of supplying starter-levels of power. Try it and you'll find that voltage at the starter might be 6V when off, but drops to approximately zilch when you pull starting current. There's also the problem that trying to start at low voltages can burn the starter windings out. The engine is often cold and reluctant to start anyway, so the cranking time goes up. As the efficiency of a DC motor (mechanical power out / heat wasted) drops dramatically at lower voltages, then the temperature rise in the starter is significantly worse when trying to start from depleted batteries - even if they're not even delivering the same power. This is one reason why the Swedes were so keen to switch to permanent magnet starters. In their cold winters it was one less source of failure - it's not that they work significantly better, it's that they don't kill themselves when trying to. |
Capacitor sizes
The message
from The Natural Philosopher contains these words: you won't even start a modern car on 6v. The neighbour's Kia got upset with me jumpstarting it. Had to charge the battery even though it was cranking over easily fast enough for a petrol engine. I didn't actually measure the voltage, but it was damned annoying. -- Skipweasel Pay no attention to that man behind the curtain. |
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Nick2 wrote:
On Fri, 29 Sep 2006 09:47:58 +0100, The Natural Philosopher wrote: 6v gets you max power delivered from the battery... And enough power absorbed inside it to explode it. A few hundred watts for several seconds? I doubt that would result in much of a bang. About 5Kw...and guess what, enough hydrogen coming off the plates.. |
Capacitor sizes
Nick2 wrote:
On Fri, 29 Sep 2006 09:41:03 +0100, Dave Plowman (News) wrote: I've got an accurate voltmeter sitting across my car battery at all times the ignition is on, and I can assure you it never drops under nine point something volts even on the coldest day when starting. Usually the high 10s. If you think about it, old cold start ignition systems are designed for 9 volts minimum. I wonder how responsive it is to transitions? I think you are right though, most modern cars never seem to really load their batteries on starting. Doesn't always apply to diesels though... many a time I've heard a diesel van start up after barely turning over. We bought a second hand diesel, and tha battery was duff..I had to jump it. Even at 10v it would not 'catch' - gloplugs too cold probably. I had to fire up the 'donor' vehicle to get the volts up enough for it to fire, and the bloody thing ran a bit rough for half a minute till the volts came up on the battery. I had a meter on and that was about 10.5 volts that DIDN'T start it. Strangely enough I had traded it for a jaguar with also a dead battery. That fared even worse. Half the electronics didn't work properly even with the engine running (finally) and I drove it to the garage with the ABS and power brakes warning lights on, and the bloody windows wouldn't stay closed till I got there and rebooted them.. Its not a question of the starter motor these days as much as the likelihood that half the computers in the thing are designed for some voltage above 10v at least. Old cars are a lot more tolerant. |
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