How do I charge capacitors to full charge?

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Old 04-21-11, 10:14 AM
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How do I charge capacitors to full charge?

I'm having problems with my capacitors in a circuit.

What I'm doing: converting AC into DC using diodes, then boosting the voltage using capacitors which are wired in a series. My desired end voltage for the load is 2,000v.

Before I go on, here is a link to three diagrams of circuits I've tried - all very similar. Click on each to enlarge. Yes, I drew these up on a word processor and they are extremely non-professional :0) Sorry to all you professionals. But pictures help.
My Photos

Some details: I'm using 120v AC. Using forward biased diodes (2,000v) on the white ("hot") wire I essentially created a half wave rectifier. This positive wire then goes to 5 electrolytic capacitors wired in a series, each at 400v x 470uf. I've tried running the negative side of the caps to both a negative lead on a 12v battery as well as the black wire on the AC. Both times my caps only charge to 158v.

What's the problem? My capacitors are only putting out voltage of a steady 158v (checked using a multimeter). I am no expert, but shouldn't five 400v caps wired in a series produce 2,000 volts? In all of the diagrams in the link above, the caps only charge to 158v. If I discharge them, they quickly recharge to 158v.

I also built a full wave rectifier, which did not help since with the fully DC current the caps simply charge to about 12v, start blocking the DC, and discharge - as caps do in DC. Maybe I just wired it wrong with the full wave, but I doubt it. I think the full wave would just charge faster, not stifle the cap charge at 158 (I think...).

Not sure if my circuit is wrong. Or maybe my caps are broken? Maybe I'm going about this all the wrong way? Do I need to just build an old school Cockroft-Walton voltage multiplier? And if I do that, will the caps be able to as quickly charge to and discharge 2,000 volts?

Yes - I realize I'm working with rather high voltage and nobody posting on forums wants a potential law suit for giving misinterpreted advice. Don't worry. Post anyways

Any help would be greatly appreciated.

Thanks
 
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Old 04-21-11, 11:02 AM
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Originally Posted by isaaca View Post
My desired end voltage for the load is 2,000v.
To increase voltage you need either an AC transformer or a DC voltage multiplier circuit made of a network of diodes and capacitors. A very common one is a voltage tripler found on the flyback transformer of CRT televisions. Just about every electronics site on the net has a sample of one of these. They are dangerous to work on if you don't have safety equipment for HV applications.

Both times my caps only charge to 158v.
You're charging them to the peak of the AC sinusoid voltage, appx 168V plus or minus a bit.

What's the problem? My capacitors are only putting out
Caps only put out what you put in, they do not produce anything.

I am no expert, but shouldn't five 400v caps wired in a series produce 2,000 volts?
No, a 400V rating on a cap is the maximum voltage it can be exposed to without failing.

Do I need to just build an old school Cockroft-Walton voltage multiplier? And if I do that, will the caps be able to as quickly charge to and discharge 2,000 volts?
That is one option, but what you intend to do with the 2kV is important. The output of a voltage multiplier has limited usefulness because of the significant ripple.
 
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Old 04-21-11, 02:13 PM
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thaaaaaaaank you.

I'll try a microwave transformer :0)
 
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Old 04-21-11, 02:27 PM
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I suppose we will get some "how to defeat this interlock" questions shortly....
Just see if the U of F lightning lab will let you borrow their big voltage source. Good for a few feet of arc.
 
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Old 04-21-11, 03:52 PM
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This may be possible if you charge the Cap's individualy , then connect then in series.

Possibly you could experiment with X number of Cap's and a battery of X volts. You will have to arrange terminations for each C so when all are charged , the terminations are linked together with jumpers , and each terminal should have a Positive / Minus Polarity mark for conecting the C to the battery Positive / Minus terminals , and for the correct series connection.

The proceedure for say 2 C's and a 12 volt battery -- connect C 1 to the battery, charge the C to 12 volts , isolate C 1 , then charge C 2 . There is Zero current from the Bat to the Cap when the Cap is fully charged , so an ammeter would help in determining the fully-charged condition.

Connect the Minus ( - ) terminal of C #1 to the Positive ( + ) terminal of C2 , and check for 24 volts across the open terminals. You will need a voltmeter with a very high impedance input that will not be a discharge -path.
 
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Old 04-21-11, 03:55 PM
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You guys should know what he's doing from what he asked in his other thread. And given his admitted knowledge level vs what he's messing with, he's more than likely going to electrocute himself trying to build this 'free energy machine'. This thread is just asking for trouble.
 
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Old 04-21-11, 04:07 PM
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Closing this....not DIY repair type stuff...other sites are out there. It's making me a bit apprehensive of the possible results.
 

Last edited by Gunguy45; 04-21-11 at 04:57 PM.
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