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How do i build an oscillator circuit to drive camera transformers to charge my capacitor bank?

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jpoopdog

Thu Aug 16 2012, 09:10AM

Registered Member #6188 Joined: Wed Aug 15 2012, 08:34AM
Location:
Posts: 23

Hello im new to the forum,

I have spent allot of time researching different methods of making a coil gun capacitor bank charger, first one i came across was in the coil gun hand gun instructable which said to use camera charger circuits and flash capacitors (330v , 100uF), and it works Ok, given i was charging 8 capacitors with 9 parallel chargers, but unfortunately the chargers and capacitors simultaneously began to break down, and my first, although weak, coilgun ceased to work.

Since then, and for the most part during the time it still worked, ive been seeking out other means of charging a capacitor bank , looking for a charger circuit which would work, that i could also build, the next one i came across was int he same tutorial guide, which involved using a coilcraft 390uH power inductor, the only thing i couldnt acquire, since coilcraft required both a credit card, and wanted $40 in postage, which was unacceptable. incidentally i have not been able to find an even remotely similar inductor i could get my hands on to use in that circuit. later i discovered the uzzors2k schematics for a charger circuit, which i bought all the parts for except for the inductor, then i bought myself an expensive new multimeter to read inductance values. i found inside a radio, a toroid, with the exact inductance i needed, however when i tried to use the completed circuit for the 450v boost converter, it charged extremely slowly, 5 seconds from 0 to 250v, then another 7-8 to reach 300v, and that was for a single 330v 100uf capacitor, whats worse is that the capacitor was leaking current really bad, going down to 100v within 10 seconds, also, the voltage detector wouldn't turn off the 555 timer when the target voltage was reached, instead it would turn it on and off really fast, and the difference between the cutoff high and turn on low, was about 50v. overall, useless, though i feel the inductor had something to do with it.

Now, recently, while looking for a suitable inductor to build the first charger circuit i had been searching for, i realized that i could just use a bunch of mini transformers used in cameras!
My only problem is i dont know what a suitable frequency for them oughta be, since ill be using them at a fixed frequency rather than a changing one.

I need to know, what frequency and PWM should i use, given i am oscillating them with a 555 timer to charge a 400uF 400v capacitor bank.
also, does anyone know what may have been causing my problems with my attempt at uzzors2k's 450v boost converter, in regards to the fact it wouldnt turn off at the target voltage?

thanks.

ConKbot of Doom

Fri Aug 17 2012, 03:30AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Are you sure it was reaching the target value? I used the uzzors2k boost charger for a ~5000uF 330V bank, and was going from zero to charged in ~15-20 seconds. I'm not sure of your location, but all the parts can had for reasonable prices on mouser or digikey. The frequency does raise as it nears the target voltage. But it still cuts off. Perhaps given the slow charging and the rapid leak down the circuit cant keep up with the leakage.

Also, dont slowly adjust up your charging voltage with the power on, as it keeps the circuit in the high frequency range and I noticed a lot of excessive heating of the mosfet if you do. (i.e. beads of solder coming out of the mosfet between the plastic and metal tab sort of excessive heat)

The toroid in the radio may not be suitable for a boost converter, as youre looking for something to store energy, not a filter or something that is meant for a transformer and wont store energy as well.

If youre using the camera transformers, just use the flyback circuits as is, I cant imagine that they designers would over-spec the components in a disposable camera too much. Its a single transistor flyback circuit, and the transformer has a primary, secondary, and "feedback" winding to drive the oscilator. and imo is a decently easy circuit to reverse engineer and breadboard up. IIRC the fujifilm cameras had pretty simple boards, and the kodak cameras had rather annoying boards with a surprising amount of SMD components etc.

Forty

Fri Aug 17 2012, 06:07PM

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

coilcraft will send you free inductor samples ya know.

jpoopdog

Mon Aug 20 2012, 01:43AM

Registered Member #6188 Joined: Wed Aug 15 2012, 08:34AM
Location:
Posts: 23

coilcraft wants to charge me $40 in postage.
also, i will keep searching for a different inductor to use in the uzzors2k circuit.
However, i still do want to try and use the camera transformers. i found out they are only 15% efficient, i know how to use them in a flyback circuit, i was more so asking, how do i get the frequency to rise when i am oscillating the transformer with a 555 timer, sincce the on off needs to change as the cap charges. through trial and error i can find out what the most effective PWM and frequency works, i just dont know how to get the frequency to change, and if compatible, how would i use the feeback output along with the 555. i have no intention of using the old circuit, this is more a personal goal, to try and make an effective charger using that transformer.

Ben Solon

Mon Aug 20 2012, 02:25AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

You're using the tiny inverter xmfr from the flash charger? Do you notice any heating at those inefficiencies? I would suspect that you're saturating the core. Plus thisntype of charger is inherently lossy. I would recommend eiriks zvs charger, I've never built it myself but the mazzilli circuit is very nice.

And as for the boost converter slow charge and draining: I suspect some dielectric punch throughs to be at fault.

brandon3055

Mon Aug 20 2012, 05:32AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

I agree with ben123324 on the boost converter there us ether a problem with th. Cap being charged or the circuit and the fact its turning on and off means the shutoff is working but the cap isn't holding charge also uzzer has a circuit for a 50w zvs capacitor charger with auto shutoff

jpoopdog

Mon Aug 20 2012, 10:51AM

Registered Member #6188 Joined: Wed Aug 15 2012, 08:34AM
Location:
Posts: 23

ben123324 wrote ...

You're using the tiny inverter xmfr from the flash charger?

i havent tried using them yet, thats the thing, i was reffering to the circuit inside the camera which i simply cut out. heating was never an issue with them, not in the transformer anyway.

also, i have given much thought to that 50w charger as well, but im having a bit of difficulty locating the ferrite, though once i have one ide certainly take the time to wind my own transformer.
i think the problem i had was simply a weak toroid and maybe unequal resistors in the voltage divider, i dont think i recall checking if the had exacly identical values though they did come from the same strip. the one used by uzzor2k certainly had more windings than mine did, and as said before, i think mine was just a filter one.
im still unsure though about what caused the fast draining, i did at one point replace every single part just to be sure, but it didnt work.
once i source a proper inductor, ill have to try it again, and hope it works. i might need to start looking in other places for the right inductor, other than coilcraft.

brandon3055

Mon Aug 20 2012, 01:33PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

For the 50w zvs charger uzzer used the core from a flyback transformer can you get your hands on an old tv?

Ben Solon

Mon Aug 20 2012, 02:59PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Yes, tvs and monitors are extremely easy to get your hands on. The recycler who mans the recycling center near me let me and my friend sit in tballot with all the tvs and retrieve flybacks. But for a lower power you don't need he exact type. Any gapped chunk of ferrite will do.

Did you say you where using a toroid for your boost? The operating principle of a boost converter is that it builds up energy in an em field. Torroids don't do that. Because the material caries all the flux. I guess iron powder might work to degree, but if you want a good amount if power(fast charge) you are going to need a proper inductor.

Forty

Mon Aug 20 2012, 04:16PM

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

where are you located that coilcraft wants to charge that much for shipping?

this is a good source of flybacks but if you've got the same shipping problems then it wont help.

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