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jnbrex

Thu Aug 11 2011, 01:11AM

Registered Member #3950 Joined: Wed Jun 15 2011, 12:45AM
Location:
Posts: 51

Will this charger work? I am completely new to electronics and this is my first attempt to design a charger. Another question, would I need a charging resistor of some sort? Otherwise the device might draw too much current and blow the diodes and transformer.

1313025053 3950 FT0 Capacitor Bank Charger

Edit: The diodes are 1N5406's, and the transformer is a 1:3.3 ratio. The first capacitor is 400v, 330uF and the second is 330v, 3470uF.

Legit_bacon

Thu Aug 11 2011, 01:48AM

Registered Member #4034 Joined: Thu Jul 28 2011, 10:41PM
Location: somewhere in the Southern hemisphere
Posts: 138

Yes i would use a charging resistor, and/or a fuse. The charging resistor would have to be of a high wattage, though I am unsure of the value. Good luck!

Bjørn

Thu Aug 11 2011, 02:21AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

A lightbulb might be a good choice for a series resistor, since it is cheap and gives visual feedback.

Remember that the end voltage will be the AC voltage multiplied by the square root of two so you will end up at over 500V and ruin your capacitors unless you turn off the charger in time.

rp181

Thu Aug 11 2011, 02:57AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

If you are powering of off mains, you can use a crockroft-walton multiplier:

With mains input, the out put is something like 450-500v. Use small capacitors for a slower charging time, but its always a good idea to use a series resistor.

When charging a 400v bank (156,000uf), I used 3900uf capacitors and had 12.5 ohms of series resistance.

jnbrex

Thu Aug 11 2011, 03:20AM

Registered Member #3950 Joined: Wed Jun 15 2011, 12:45AM
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Posts: 51

Thanks for the feedback! Where on the circuit would the charging resistor be? And what kind of lightbulb would you recommend for a slow charge time of 20-30 seconds? (Long enough to shut of the circuit before voltage caused the caps to explode.)

To rp181, wouldn't the ac current destroy the capacitors? I have access to photo-flash caps which are 330v 120uF, and anything that can be found on an old pc crt monitor. I'm not sure that I understand what is going on in the crockroft-walton multiplier, though I'm sure it works.

Forty

Thu Aug 11 2011, 03:21AM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

you won't want to charge to a voltage any higher than your lowest voltage rating capacitor. Mains straight to a voltage doubler would probably work out just fine (you'll need a protection element like a light bulb, series resistor, or beefy ntc thermistor, or you'll hear the faint click of your circuit breaker when you plug it in)

jnbrex

Thu Aug 11 2011, 04:04AM

Registered Member #3950 Joined: Wed Jun 15 2011, 12:45AM
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Posts: 51

I would like to build the circuit a little higher than needed just in case I find a good opportunity to get a nice 450v cap. Is there any way to build a voltage detecting attachment for this circuit, in addition to my earlier questions?

Legit_bacon

Thu Aug 11 2011, 05:02AM

Registered Member #4034 Joined: Thu Jul 28 2011, 10:41PM
Location: somewhere in the Southern hemisphere
Posts: 138

Here is a nice bar graph circuit, just take the last led's output and put it on a relay to switch of the circuit.

Killa-X

Thu Aug 11 2011, 05:51AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
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Posts: 1039

I'm in with rp181 on this one. When it comes to capacitor banks that i plan to use as a "Around the house" not portable, I always use mains doublers/triplers/quads. Capacitor size will debate how fast/slow it charges, and its current draw. This is the same system i did for a school demo with 1KJ, i did a voltage quad for a high-range use charger, and used a voltage divider (with a resistor to set the trigger) to fire a transistor, which kicks a relay on, killing the charge.

My first charger used 330V 80uF camera capacitors, but for my bank, it was too slow. ended up going with 250V 470uF capacitors for my bank. First time, I forgot my charge resistor, and didnt disconnect it, and one of the dioded exploded due to reverse polarity spikes. Probably because I had no charge resistor at all, or anti-parallel diode =)

Good luck!!!

Dr. ISOTOP

Thu Aug 11 2011, 06:35AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

If you have a big iron 1:3.3 transformer sitting around somewhere, that charger works great, though you should probably add overvoltage shutoff of some sort to prevent your 'lytics from going poof.
Otherwise, a voltage doubler for 120V mains gives you the voltage you need, and doublers aren't hard to make, and only need two diodes, and are lightweight.
Also, if your diodes die, there is a small chance that they will fail in such a way that lets the AC through -> 'lytics going poof.

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