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I think I now know what the SAC722 is and the function of the board.

Started by Jamie July 8, 2012
   Earlier I asked if any one had some data on a
Motorola part "SAC722" and I have not had any response to
it, however, I think I now have it all under the hood.

   These units appear to be TRIACs, and there are two of them
in series, maybe for redundancy? Any way, there is a REED contact 
envelope in there with a couple of turns on it that monitors an 1/2 HP 
AC capacitor start motor.

   What this does apparently is when current is high, it closes the 
switch, turns on these two TRIACS which connects the starting cap. When 
motor RPM's are up a bit, current drops back and the REED switch opens,
thus, disconnecting the starting cap.

   This is a neat little trick so not to worry about a centrifugal
switch in the motor, and hard to access capacitors however, this
unit failed while being operating on a Honda Generator? personally,
I think it could of been low voltage? The water pump may be been doing
a lot of restarts and there are no heat sink on the triacs.

   What's your take on that? Do you think a low voltage event could of
caused over heating on the triacs? I have not tested them for the 230
volt break down yet and gate trigger levels.

   I was asked if I could come up with a better circuit that works more
reliable because apparently, this unit is no longer made and the 
replacement kit does not work as well from what I under stand.

  Jamie

Jamie wrote:


> > What this does apparently is when current is high, it closes the > switch, turns on these two TRIACS which connects the starting cap. When > motor RPM's are up a bit, current drops back and the REED switch opens, > thus, disconnecting the starting cap. >
These are called "sinpac switches" and have replaced a range of starting relays in all sorts of devices.
> > What's your take on that? Do you think a low voltage event could of > caused over heating on the triacs? I have not tested them for the 230 > volt break down yet and gate trigger levels. >
Most likely you had low voltage and the motor drew greater than normal current to compensate. This tricked the starting circuit to stay on all the time, frying the triacs.
> I was asked if I could come up with a better circuit that works more > reliable because apparently, this unit is no longer made and the > replacement kit does not work as well from what I under stand.
Go to a refrigeration or motor shop and ask for a sinpac switch or Stearns starting switch or electronic starting relay, they should recognize it under one of those names. Jon