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Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Short question: Is it possible? I know that current sharing is not equal and because of that max. current max. surgeis not the amount of SCRs multiplied by their rating. I have 3.3kA SCRs and i need switch for ~10kA. So maybe 7 or 8 in parallel to be safe?
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Kizmo, first of all, are you sure that you cannot use a single SCR? In a previous post I told you that it's not the current rating but the action integral of the SCR that matters, did you consider that?
IF you really need to parallel SCRs, yes it can be done. The current/voltage graph of an SCR is fairly tame, so current sharing will not be a big problem. By manufacturers spec, you only need to derate the devices by 20% or so.
Registered Member #853
Joined: Thu Jun 21 2007, 03:08PM
Location:
Posts: 14
I did it in my guns, since it was cheaper to buy many lower rated scr than big ones. One important thing was that all the gates should have a resistor in serial before they are connected together to the gate-driver, so that not one of the gates should draw away so much of the gatecurrent so that some of the others will not trigger. I destroyed a fair ammount before i did that. One good thing about parallelling is that if the coil-load is to high (too much current drawn or whatever), only one cheap scr will be destroyed, since it then will short the capacitor and save the other ones. And, in multistage you can dimmension the number of parallelled scr's per stage. The most parallelled I have done is 6 pieces by the way, which I discovered when using 3 pieces: one of them was destroyed everytime. Using some more gave reliable switching.
Well, parallelled SCR's worked for me, with some work.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
In theory, parallel SCRs work fine. (I'm pretending for a moment that I haven't read all the above posts by all these other people who've successfully done it. )
The curves on these devices will share current just fine. Their use in a coilgun application is not like paralleling BJT devices which can suffer thermal runaway in some designs. If you have thermal runaway in a single-shot coilgun, then you have much bigger design flaws to worry about.
Cheers, Barry Never use a long word where a diminutive one will suffice.
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SCRs in parallel
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