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Resonant DC charger for capacitor banks

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PSCG

Tue Aug 30 2011, 10:27AM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136

Is it possible to use the DC resonant charging topology for a 450VDC / 4000 uF capacitor bank?

It is usually used for charging capacitors, but only high voltage and small capacitance as i've seen (2 - 3 Kv / 10 - 200 uF).

Forty

Tue Aug 30 2011, 03:56PM

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

might be possible, but the frequency would have to be pretty low. I'm unclear on any advantage you would gain using such a topology, and don't have the time right now to go searching/reading about it.
so give me a reason why you'd want to use it and i'll get back to you later.

PSCG

Tue Aug 30 2011, 05:22PM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
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Posts: 136

First reason is that (except the boost type converter) all other capacitor bank chargers are too difficult for me to construct.

Second reason is that i've tried approximately 52 times to make my boost type converter (Uzzor's design) to work without any success.

Third reason is that no one has tried it before as a coilgun capacitor charger, so it has not been evaluated for such a system.

I'm not asking from anyone to try it, just some thoughts about the general concept.

Forty

Tue Aug 30 2011, 07:18PM

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

I've had only limited success with various boost converter designs as well (FET always melts,) but every zvs I've made has worked great (except for the regulator bit, but i'm working on that.) I suggest you try making one, they're really quite easy to do point-to-point style.

Once I finish modifying uzzors' charging regulator for the zvs (separate supplies, 250v to 450v adjustment range, and most importantly, getting it to work reliably) then I'll post schematics and pcb layouts that you can use.

what problems have you had with the boost converter?

PSCG

Wed Aug 31 2011, 07:07AM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136

Everything you can imagine (and not): NE 555 oscillator working on a frequency completely different than the R and C values calculated for, IRFP 450 not switching, boost converter coil overheating and many other problems that i don't exactly remember. I also had problems with the rectification diode but i salvaged from a computer supply a very good HFA08TB60. But the most frustrating was that it worked, once, but it only reached 200 VDC (instead of the designed 450VDC with auto cut off circuit regulator).

The only thing that worked the first time was the voltage level regulator for protecting the capacitors from overcharging (design from Another Coilgun Site). I have used it many times again without any quirks.

Artikbot

Sun Sept 04 2011, 11:59PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

PSCG wrote ...

First reason is that (except the boost type converter) all other capacitor bank chargers are too difficult for me to construct.

Second reason is that i've tried approximately 52 times to make my boost type converter (Uzzor's design) to work without any success.

Third reason is that no one has tried it before as a coilgun capacitor charger, so it has not been evaluated for such a system.

I'm not asking from anyone to try it, just some thoughts about the general concept.

1) If you can find a transformer ferrite core (off eBay, p.ex) a Mazzilli ZVS is terribly easy to do. I'm currently doing one for a high power coilgun I'm designing.

2) Uzzors' has a problem driving the MOSFET. If you have high enough power, it won't be noticeable (the MOSFET won't have time to heat up), but if you run high iductances to keep heat down, it will fail due to a MOSFET driving issue. My first adaptation of it failed (ask Forty, he knows about that), blowing up an IRFP450, flames and all included.

3) I have no answer to that, but saying good luck with it. But I'd rather go with a ZVS driver. Efficiency is terribly high, and it can drive virtually any voltage, as long as the windings are properly calculated.

Dr. Slack

Mon Sept 05 2011, 12:42PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The cap bank will be storing 400J (400v/4mF).

A DC resonant charger requires an inductor to store 25% of the final cap energy. You'll need quite a lot of iron to store 100J during the charging pulse. You will also need a stiff 200v power supply to drive it.

So yes, it's possible, if you've got those things.

The topology of choice for capacitor charging is the flyback. Amongst its many advantages are

a) you can use it pulse by pulse (easy to start, stop and debug)
b) it retains near 100% efficiency into a wide range of voltages on the capacitor it's charging
c) it's easy to get large or small voltage step-up with the same topology
d) it's current output, so well suited to driving a low impedance load like a capacitor
e) you can get galvanic isolation across the transformer, very handy for safety

PSCG

Tue Sept 06 2011, 07:58AM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136

OK, as i see resonant DC capacitor charger is not possible for a portable coilgun. Also i have many ferrite cores from TV flybacks (+20) so i imagine that will not be too difficult to try the ZVS topology.

I have 2 IRFP 450 MOSFET's. Usually the ZVS uses IRFP 250 MOSFET's (0.085 Ohms - 33A) instead of the 450 (0.31 Ohms - 14A). Can they work in the circuit?

Forty

Tue Sept 06 2011, 03:03PM

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

the 450's will work, but they're not the best. I have used them before and they heat up if you run them too long (which you won't be doing for a charger.)
their breakdown voltage is just too high i think.

PSCG

Sat Sept 10 2011, 09:57AM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136

OK, i have ordered the IRFP 250 MOSFET's but i have a question: the inductor (as shown in Uzzors2k schematic) must have a specific value or just any inductor between 47 - 250 uH?

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