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Registered Member #1327
Joined: Mon Feb 18 2008, 12:13AM
Location: North Ridgeville, Ohio.
Posts: 38
Camel:
are you switching the Positive or Negative through the SCR? I have found that switching the Positive has a damaging effect on my SCRs and fries my triggering circuit too. D.L
Registered Member #1694
Joined: Sat Sept 13 2008, 09:13AM
Location: Australia
Posts: 108
When I say fail short, I mean there is continuity between anode and cathode, my caps don't charge at all because the current simply goes through the coil and through the SCRs.
David, I'm not sure what you are asking . . . I'm putting positive to the gate if thats what you mean.
Registered Member #1327
Joined: Mon Feb 18 2008, 12:13AM
Location: North Ridgeville, Ohio.
Posts: 38
Camel wrote ...
David, I'm not sure what you are asking . . . I'm putting positive to the gate if thats what you mean.
I have had bad luck connecting the positive of my cap bank through the scr. thanks Barry , your scr is a little different, but I think the theory applies.
Registered Member #1819
Joined: Thu Nov 20 2008, 04:05PM
Location:
Posts: 137
Camel wrote ...
I've put it down to excessive gate current.
Actually, I think that the real cause of these SCR failures is too little gate current. With only 24mA of gate current, the SCR might be turning on too slowly and is absorbing current during the trigger phase. (Note that the SCR doesn't even have to feel hot to fail in this way. The junction temperature may rise above the absolute maximum before the heat reaches the case, internally melting the SCR and probably causing a short.) A better triggering method would be to discharge a small capacitor (0.01 to 0.1uF) through a current-limiting resistor at the gate for a short gate pulse of 1A to 5A.
Also, do you know the inductance of your coil? The inductance may be causing a higher peak current than you expect.
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Shorting SCRs
