John said:
It has been a few years since I worked in motor controls. I accede to your
more recent knowledge.
In any case, the OP should be able to get the locked-rotor rating from the
manufacturer.
That's a good one!
I quickly looked up a triac on Mouser, the T1620W made by ST. The I2t is
given. I know this does not mean that the I2t is given for all (toy) triacs
and thyristors, but it seems likely that the info is available for most. I
designed motor control power stages from 1980 through 2000 and I never ran
across a thyristor data sheet which did not have I2t given. However, my work
was with Westinghouse, Westcode, and, later, Powerex thyristors. We never
used triacs.
I'm doing two projects with toy thyristors at the moment.
TIC106 - no. and a ratshit datasheet
BTA/B10 - yes.
BTW67/69 - yes.
I think the conclusion we can draw here is that lousy thyristor
datasheets dont include IIt.
However its a different story when we look at FETs, IGBTs & diodes. I
havent seen a toy diode, FET or IGBT spec IIt yet, but its pretty common
with the big stuff. interestingly enough, none of the Semikron miniSKiiP
datasheets have IIt.
but everyone has Ifsm, and there is a relationship between the two; an
IIt value based on Ifsm is lower than the actual fusing IIt, so it gives
a reasonable safety margin.
If only manufacturers would tell us the die dimensions!
OP: what triacs are you using? What are the motor nameplate ratings?
John
Cheers
Terry