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Ideas for a Charger for These Capacitors

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LAN_403

nerdywarrior

Tue May 26 2009, 01:26AM

Registered Member #2139 Joined: Mon May 25 2009, 07:54AM
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Posts: 8

Transformers at hand: Flyback transformer from a tv I no longer needed and a 3kv neon transformer from information unlimited.

Capacitors to be charged: ( 7 ) 12,000uf 400V Caps -

Using either the flyback or the neon transformer - or if you have a better idea - please post circuits/advice/tips on a build that should be adequate to charge them up. It doesnt need to charge them super fast - I just need the job to get done

This capacitor bank is for a rail gun project (6.7kj)

rp181

Tue May 26 2009, 01:50AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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neither, use a voltage tripler, running of mains (in
US)

That is what i use, charges 5.6kJ in under 10 seconds.

hotcrazyfruit

Tue May 26 2009, 02:37AM

banned on 5/26/2009
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you do realize those transformers put out tens of kilovolts right? use what RP sent, as using a fly back or NST is running to high a risk to destroy your capacitors .although keep em around, in case you even come by a pulse capacitor XD

Arcstarter

Tue May 26 2009, 02:45AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

hotcrazyfruit wrote ...

you do realize those transformers put out tens of kilovolts right? use what RP sent, as using a fly back or NST is running to high a risk to destroy your capacitors .although keep em around, in case you even come by a pulse capacitor XD

Yes, but even so, the caps would not die. You just have to watch the voltage. It will be very limited current, so...

Indeed a tripler would work, but you need to use some big current limiting resistors, otherwise you might kill diodes or trip breakers. You can use capacitive limiting, and just use small tripler capacitors though, that will limit the current. Unless i am wrong, of course. Someone else have something to say about it?

nerdywarrior

Tue May 26 2009, 02:56AM

Registered Member #2139 Joined: Mon May 25 2009, 07:54AM
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thanks everyone

Myke

Tue May 26 2009, 02:57AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Use a lamp for resistive ballasting? That seems to be the easiest way to limit the charging current. The lamp will dim as the capacitor charges. There is no need for using a capacitive or inductive ballast in this case because efficiency isn't much of a concern. Also there isn't a whole lot of current coming out of the multiplier so you don't need a huge lamp as far as I know.

Hazmatt_(The Underdog)

Tue May 26 2009, 03:13AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I'd have to agree with the triplier. That's what I did for my cap charger on my ring toss. Worked perfectly. My resistors get pretty warm, but if you use a lamp on the mains side you'd get the same result. Be prepaired to wait 10 minutes though.

Killa-X

Tue May 26 2009, 04:26AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
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Hey. If I wanted to charge a smaller bank say 300J to 400uf... Despte the 15 stages, can I just connect my transformer (26VAC) to a tripler in 15 stages to get 40V to charge my caps? I tested a few camera caps on it to get 80v and it seems to work. I just wonder if I could get a 400v multiplier to charge 400v 300 joules of capacitors. Yet the transformer is rated 400ma, I don't mind the wait. I'm sure it's faster than my 7 camera transformers in parallel which charged 100J in 1 min. On 3AA in parallel

Backyard Skunkworks

Tue May 26 2009, 04:52AM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

As I said in the other thread, I'd go for the step up transformer. The tripler, however, is a much easier to build option. You could really use either, but as previously pointed out, stay away from HV sources for cap charging in the real world.

Can't wait to see a video of that railgun, the kinetic energy is going to be crazy if you acheieve even modest efficiency.

Z28Fistergod

Tue May 26 2009, 12:10PM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

You don't need any current limiting with this circuit, it is "built in." Like Arcstarter said, the ac reactance of the tripler capacitors will limit the current. The larger the capacitors the more current that is available. 10uF sounds like it would be pretty good for your application, maybe a little bigger but that's just guessing. I would avoid the resistors because they will dissipate a lot of power.

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