Douglas Reid wrote:
  Try TECCOR triacs instead.  Had more than 10 times the
failure rate with BTA's on 8x8 (64 triacs per card) lamp
driver modules.  The T4000 series is a much better triac for
the same ratings in our experiences..
Alan




> In fact, the Mk I version of this design used MOC3021 opto-triac drivers
> driving
> BTA06 600BW triacs.  A snubber network using two resistors (360R and 470R)
> plus a 50nF/ 400V cap was used between the driver and the triac.  This was
> used in the first of our 3 installations and whilst it worked well for a
> time, was subject to catastrophic failure. On two occasions triacs failed
> (in fact, as I recall, all 4 triacs on the card
> were found to have failed).  It had been considered that the triacs were
> adequately specified - clearly, transient effects were not properly
> considered!  Given that we needed the system working quickly, we