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Old 01 April 2005, 05:17   #1
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Secret question, so mumís the work

Question for any electronics experts on the forum, would it be possible to use a capacitor to trickle charge a small battery Ideally, what would happen is that a supply would turn on for a moment (5 sec), the capacitor would be able to store sufficient power to slowly charge a battery over a longer period (30 min) Donít ask why cos itís a secret but if it is successful free ones to all that help Des
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Old 01 April 2005, 05:39   #2
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Capacitors discharge over a very brief period as a rule - ie in a flashgun for example.

Capacitors also have to be really huge to store a worthwhile charge.

To store the equivalant power of ONE AA battery you would need about 10,000 farads.

A 1 Farad capacitor is about the size of a 1 litre pop bottle and costs about £40.
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Old 01 April 2005, 07:29   #3
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How about something like this?

http://www.elektor-electronics.co.uk...Power%20Supply

(Showed a work colleague and he suggested this might help - Thanks Chris)
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Old 01 April 2005, 08:20   #4
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How about something like this?

http://www.elektor-electronics.co.uk...Power%20Supply

(Showed a work colleague and he suggested this might help - Thanks Chris)
Thanks Interesting I take it that this is something you build yourself Des
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Old 01 April 2005, 08:28   #5
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Yeah it is, might be able to get someone to help build it for a fee if required
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Old 04 April 2005, 21:45   #6
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Originally Posted by codprawn
Capacitors discharge over a very brief period as a rule - ie in a flashgun for example.

Capacitors also have to be really huge to store a worthwhile charge.

To store the equivalant power of ONE AA battery you would need about 10,000 farads.

A 1 Farad capacitor is about the size of a 1 litre pop bottle and costs about £40.
thats dead right, caps are typically used for smoothing in power supplys as they can reduce a ripple or dip for a momentary lapse... almost the opposite of what ur asking of them
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Old 05 April 2005, 07:20   #7
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A 1 Farad capacitor is about the size of a 1 litre pop bottle and costs about £40.
The 7.5Kv one we had wasn't & cost a bit more than 40 quid
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Old 05 April 2005, 21:35   #8
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The 7.5Kv one we had wasn't & cost a bit more than 40 quid
in general 12v ones are a lot more money than HV ones, our three phase big buggers we use at work cost pennies in comparison to the one on my car stereo.

remember ohms law. v = i.r so less voltage = more current = more money!! its a bit like sayin the word boat during a purchase, the shop attendant just presses the x3 button on the total!!
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Old 07 April 2005, 15:57   #9
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Originally Posted by Scary Des
Question for any electronics experts on the forum, would it be possible to use a capacitor to trickle charge a small battery Ideally, what would happen is that a supply would turn on for a moment (5 sec), the capacitor would be able to store sufficient power to slowly charge a battery over a longer period (30 min) Donít ask why cos itís a secret but if it is successful free ones to all that help Des
Hardly an expert, though I used to build avionics.

Two problems with your idea: First is leakage. Capacitors all have some inherent leakage. To charge one to a voltage suitable for charging a battery (i.e. about 20% more than the battery's rated voltage) would yield that voltage for a relatively short period of time.

Second is that as you draw off that current, the voltage will drop (giving you the same problem as in the first scenario.)

To overcome those effects, you'd need a really large capacitor array, and a pretty good size power supply to charge them quickly.

You'd probably be better off looking for a longer lasting battery in the first place.

My opinion only;

jky
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Old 07 April 2005, 17:19   #10
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Once built some very big caps using some plastic dustbins and sheets of polythene - filled the whole lot up with oil - fortunately got caught by my parents before I could do any REAL harm!!!
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