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Danielle

Wed May 23 2007, 06:18AM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

I recently built a coilgun and voltage boost convertor I can charge my capacitor (33,000uf 400V) to 400V in 3 seconds my SCR is a hockypuck $300 1600V 5000A I was able to shoot a sharpened metal projectile 2.3g through 2 cans and into my wall after 20 shots I blew my capacitor i will bw posting pics but right now its a table top version.

uzzors2k

Wed May 23 2007, 06:30PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

800W boost converter, not bad. Could you post some info on it too? Were you able to measure the speed of the projectiles? Next time use inductive spike protection diodes to save your capacitor, I can't imagine a 400V, 33mF capacitor being cheap...

Danielle

Wed May 23 2007, 11:34PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

The capacitor was used and had some cracks in it I think the comparitor I used failed and the voltage shot up blowing my cap and I did use a diode it was also still intact 1000V 80A

I also have 10 600V 300A IGBT modules do you think I can use those for this I could charge 2 banks of capacitors and discharge one through one and the other through the other. they are modules halfbridge. FMG2G300LS60E

[Edit: Fixed double post]

uzzors2k

Thu May 24 2007, 03:23PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Were you charging a 400V rated cap right up to 400 volts each time? If so, stop, only charge them to 10-20 volts under their rated voltage to ensure that they survive. Especially if they were used. Your multimeter might be off by a few volts remember? FMG2G300LS60E! what a monster, 300A continuous... Those will work for a coil gun, the peak current is 600A repetitive, so it might take even more in a single shot. Those should make a powerful multi-stage coil gun.

Danielle

Fri May 25 2007, 03:14AM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
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Posts: 267

I was charging it to 400V and while it was charginh the meater was giving me weird readings. Also I am running it off the wall with a transformer rated at 5A 18vAC then to 24v DC. I just got a new bridge rectifyer reted at 32A 1000V its
1.5" by 1.5" and is rated at 300A surge and is isolated with really good thermal resistance. my question is though, I built a loltage multiplyer for my DRSSTC and its output is 360VDC can I use this to charge it the rectifyers on that are 80A rated. can I do this or will I blow up something when trying to charge a verry large cap bank?

uzzors2k

Fri May 25 2007, 12:55PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Your meter should read a constant voltage rise because any spikes are absorbed by the massive capacitance. When charging a capacitor, the capacitor acts as a dead short for a while, then it represents less of a load with time. See RC time constant. If using a constant current source, like the boost converter charger, then the capacitor is a short the whole time. In the case with the boost converter, current is limited by the inductance, so it can supply power the whole time without exploding. But with a wall charger the capacitor will pull unlimited amounts of current when the cap is empty, and slowly draw less and less current as it fills -So use a current limiter, like 500W light bulb, lower wattage, slower charge.

Steve Conner

Fri May 25 2007, 02:30PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Sure it wasn't a 3300uF cap? You can't charge 33000uF to 400v in a few seconds with a circuit running off a 5A, 18v supply. It needs way more power than the supply can give.

Danielle

Fri May 25 2007, 02:34PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

I am sure it is 33,000uf ill send a pic when I have time I could even send a vid of it charging but I need a new cap that one blew up.

Electroholic

Sat May 26 2007, 12:10AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

rocketry76, please, check your numbers...

A 33,000uf 400V lytic? its either a typo or BS.

Danielle

Sat May 26 2007, 06:05PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

Ok I was rong here is my pics of the setup it is 3300uf 450V. I have one thing to say to everyone who is staarting making coilguns, SCRs make a world of a diffrence.

*mod edit for oversized images*

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