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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
You could use a few small package SCRs in parallel. I used 5 SK065K ( ) in parallel for a 624 joule bank (800v 1950uf) which i could short directly across the SCRs. I have shorted it, and i have exploded foil and components and shot disks, and the SCRs all still work. I used a AAA cell and a push button to trigger, no need to limit current when the voltage is already perfect!
Registered Member #3785
Joined: Sat Mar 26 2011, 03:37PM
Location: Surrey, UK
Posts: 16
Reviving a dead thread a little here, but I suppose a small update would cancel out the negative karma? I took some photos to document progress today, and I will have a snap about in the lab *cough shed cough* tomorrow to get anything I missed. I have 10 1000uF 450V capacitors ready to be hooked up, and beyond that its just a case of troubleshooting my mazilli circuit (which of course, decided not to work first time :P ) and piecing the gun together.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Arcstarter wrote ...
You could use a few small package SCRs in parallel. I used 5 SK065K ( ) in parallel for a 624 joule bank (800v 1950uf) which i could short directly across the SCRs. I have shorted it, and i have exploded foil and components and shot disks, and the SCRs all still work. I used a AAA cell and a push button to trigger, no need to limit current when the voltage is already perfect!
I thought you aren't supposed to parallel SCR's...
Registered Member #3785
Joined: Sat Mar 26 2011, 03:37PM
Location: Surrey, UK
Posts: 16
Inducktion wrote ...
Arcstarter wrote ...
You could use a few small package SCRs in parallel. I used 5 SK065K ( ) in parallel for a 624 joule bank (800v 1950uf) which i could short directly across the SCRs. I have shorted it, and i have exploded foil and components and shot disks, and the SCRs all still work. I used a AAA cell and a push button to trigger, no need to limit current when the voltage is already perfect!
I thought you aren't supposed to parallel SCR's...
From what I know, without a balancing resistor in series with each you risk one SCR hogging the current and blowing. Luckily I've acquired a huge stub type SCR rated @ 285A continuous :P (What sort of application needs that level of current!)
Registered Member #2915
Joined: Fri Jun 11 2010, 10:41AM
Location: Malaysia!
Posts: 101
In my coilgun I paralleled 4 SCRs and they worked like a charm! But I was only using 150j... Buy some of those super cheep no-brand SCR's and give them a try! No resistors or anything, just a nice solid heaztsink. These are the ones I used: FS2510NH SCR 25A 800V TO-220 IPeak:270A
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
In theory, paralleled diodes or SCRs will start to share current unevenly as they heat up. However, in practice, it works just fine for coilguns since they tend to fire at a very low frequency and can cool off between shots before thermal runaway can take place.
Use equally valued resistors on each gate so they share the gate current nicely, and you'll be fine. FastMHZ paralleled SCRs on his monster coilgun and it worked beautifully.
Registered Member #3785
Joined: Sat Mar 26 2011, 03:37PM
Location: Surrey, UK
Posts: 16
Saz, you might be able to help me here, I'm having trouble with my charging circuit and i know you used one on your monster gun. I've constructed a copy of uzzors mazilli driver, but when I connect everything up, both LEDs illuminate simultaneously. As far as I can tell from the schematic, one should only light when the reference voltage is reached? The driver itself wont draw any current nor work, I think the mosfets are being held off...
Any pointers for where I should begin troubleshooting?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Just an idea, but if you want a cheap (ish) rechargable 14.4 supply, both Argos and Homebase sell bettery drills for £9.99.
The battery pack could be incorporated into the grip. You get a charger as well, but not a very good one, it doesn't appear to have a current limiter or to switch off when fully charged.
You'd also have a battery drill which may come in useful!
(EDIT: My mistake, they are 12V, not 14.4V, but still useful as high current rechargable compact 12V supplies.)
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
BenB wrote ...
Saz, you might be able to help me here, I'm having trouble with my charging circuit and i know you used one on your monster gun. I've constructed a copy of uzzors mazilli driver, but when I connect everything up, both LEDs illuminate simultaneously. As far as I can tell from the schematic, one should only light when the reference voltage is reached? The driver itself wont draw any current nor work, I think the mosfets are being held off...
Any pointers for where I should begin troubleshooting?
I'll post pictures etc later.
Cheers Ben
The best thing to do is to test it one part at a time. Start by disconnecting the control circuitry and try to get the Mazilli part to work. If the problem is with your transformer, it should at least charge a little bit, so I'd guess either you wired something wrong or your mosfets are bad. Try testing your mosfets on a separate circuit (a simple LED blinker or something) to make sure they are functioning.
Registered Member #3785
Joined: Sat Mar 26 2011, 03:37PM
Location: Surrey, UK
Posts: 16
I managed to coax some life out of the circuit earlier, in the form of some current drawn and a loud buzz from the ferrite core of the inductors. I took some turns off, and curiously current draw increased. In frustation, I sliced the diodes connecting the mazilli from the voltage detector and the caps started charging, but stalled at 25 volts. In the spirit of bigger is better, I grabbed a high discharge rated 18V drill battery, and voila! 425V in my cap bank. Haven't had a chance re-test the voltage comparing circuit, but for the moment watching the voltmeter carefully will do! :P
Edit: Forgot to mention, interestingly one MOSFET is becoming Luke-warm, but the other has remained cool. Both are wired identically, and are the same spec #. Edit edit: the 393 just dramatically exploded :) what could cause that to happen? Data sheet specifies input voltage up to 36V... Would the circuit function without it? ICs really aren't my strong point :/
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