g8on at fsmail.net
Tue Feb 11 04:02:35 EST 2014
My gut feeling is that there is a voltage transient at turn off causing the problem. Maybe a Transzorb or MOV would help. Personally, I prefer good old fashioned contactors, although the buzz you sometimes get when operating on AC can be annoying.
I worked some 20+ years ago with a guy whose first job after graduation was assisting in commissioning railway locos running off 25kV 50 Hz. They had just moved from steel tank mercury arc rectifiers to silicon, and his stories of the problems due to unexpected transients killing them was interesting, to say the least - including having blocked the main line with a failed loco, they had to get an old steam loco out to haul the test train out of the way! So transients and semiconductor problems aren't new...
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