Robert,

You are correct about the temperature not being 80 degrees K, however
that is how the part is marked, it could be 80 degrees centigrade and
the /K could be a tolerance. However, at room temperature the part
should read as a short, and on the defective one the case is physically
burnt up. The one in the other channel is OK, though I do not have a
temperature probe to see at what temperature it trips open.

Regards,
Tim Schwartz
Bristol Electronics


Robert Gault wrote:

Tim Schwartz wrote:
Hello all,

I'm trying to find a replacement thermal circuit breaker (Schematic
location TB1 and TB2) for a Hafler DH-500 the part number is SF-024 in
the earlier manual, or 332002 in the later manual. The part is no
longer available from Hafler.

The original is made by Elmwood Sensor, a division of Honeywell and is
a 2450 series (the number is molded into the plastic on the top of the
sensor). Other lettering around the side of the defective one is
"87-232 L167 80/K", where 87-232 is likely the date code (232nd day of
1987), no idea about the L167, and 80/K the temperature where it trips.

I've contacted Elmwood and the part is still available, with a $750
minimum order, so that is not one of my choices. I believe the DH-120,
DH-200, DH-220 and DH-500 all use the same part. Does anyone have a
parts unit that might have a good thermal circuit breaker that they
would be willing to part with? (Please note that on the DH-500 there is
also a thermal sensor to turn on the fan, which is NOT a substitute.)

Thanks for your time,
Tim Schwartz
Bristol Electronics

Whatever 80/K stands for it is not 80 deg K. A temp of 80 deg. K would
be -193 deg C or -316 deg F!

While the K is curious, 80 deg C at least would be a more reasonable
temperature. Perhaps you can short out the bad sensor and measure the
operating temperature of the heat sink during use with a thermocouple.
Add some factor say 20% to the number and compare that to the
temperature limit for the output MOSFETs. That would give you a
temperature range for a substitute thermal sensor.