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Registered Member #215
Joined: Sun Feb 19 2006, 09:14PM
Location:
Posts: 30
Alright, so I've been doing CG's for a while now, and am trying to get into solid state switching (SCR's). I need help figuring out what my SCR and protection diode should be rated at. I understand this is dependant on my capacitors, so here is my current bank:
330v (only going to charge to 300 for safety) 3420uF Coil resistance is 1 ohm, so Ohms Law dictates it will pass 300 amps.
Yeah, they're photoflashes Whatcha expect? They're FREE! Working on getting more soon, though. Any help will be gratefully accepted. I dont want to spend a ton of $$$ on an SCR and then overcurrent it. I also dont want to spend $$$ on a protection diode and have it blow up. Thanks all! (BTW New forum is hottt)
Registered Member #177
Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214
Try this in order to calculate maximum discharge current.
300A will be the maximum, for the case that your coil has no inductivity. In reality you coil of course has some inductivity, so the current will be less.
A SCR with 300A peak rating will be fine. The Diode on the other hand has to withstand a current of the same magnitude but also possibly a larger induced voltage comming from the coil. If the protection Diode is underrated, you will possbly fry your SCR and your charger circuit too. (If you have the charger still connected of yourse.)
Registered Member #215
Joined: Sun Feb 19 2006, 09:14PM
Location:
Posts: 30
Alright, well I bought a 110 amp 600v SCR the other day (10$!! Can you beleive?!) which has a surge of roughly 1kA. I was all worried it wouldnt work
Ok, so now for the anti-parrellel diode. Approximatly what should the diode be rated at? Unfortunatly, larger diodes start to get costly. Can I use a crapload of 1N4007's wired in parrellel?
Registered Member #32
Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549
One big set of 1N4007s in parallel isn't reliable for pulse work. The current generally won't go through all the diodes. It can be made to work if you use a resistor on each diode, as in the "dump and quench" circuit.
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
ive been using 4 1n5408 in parallel with no problem at all mine current system is 1050v peak charge to 950v for safety around 1kj at 950v scr is a semikron skkt 132/12e 1.2kv 4.7ka for 10ms surge and 4 1n5408s in parallel for CEMF 5408s are rated for 1kv 3a cont forgot the surge but i blew my 1.5ka peak stud when i put the diode pack in reverse, so they must have a surge of atleast 400a each... oh and no equalizing resistors at all
Since the ratings is covered, just a few some device examples. Some of the diodes are naturally larger in size hence current rating due to the case type. I use those reqularly and buy them from digikey. As for SCRs, try some to-218 or just smaller to-220 case of surge ratings about 800A to 500A. Those run about $3 - $5 and are good for small space requirements.
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Need some help with ratings
Whatcha expect? They're FREE! Working on getting more soon, though. Any help will be gratefully accepted. I dont want to spend a ton of $$$ on an SCR and then overcurrent it. I also dont want to spend $$$ on a protection diode and have it blow up. Thanks all! (BTW New forum is hottt)
) I should be set. Thanks all!