Help with Triac based Temerature Controller

I've built a kit (Silicon Chip June 2005 "Tempmaster Temperature
Controller") to run my a fridge as a wine fridge.

The fridge is a 240v (Australia) commercial "cool drink" type fridge
drawing about 600W. I've replaced the old 'mechanical' thermostat with
this new electronic one to run is at a higher and more accurate
temperature.

The "output" is essentially a MOC3021 opto coupler driving a BT137F
triac.

However when the controller switches on the condenser / fan it often
clicks a few times (like its taking a few attempts to start it).

I've already tried incorporating a LC line filter without luck. A TVR
fitted between the active / switched active gets really hot (obviously
dissipating quite some power).

Any ideas what else I should be looking at?

Cheers, Antony

 

Can you post a link to a schematic? It's almost surely electrical
noise getting back into the control circuitry, although if the power
supply is not robust enough it could also be the dip in supply voltage
due to the surge when the compressor turns on.

This kind of thing is not good for the compressor.


Best regards,
Spehro Pefhany

 

You should probably use a mechanical relay to switch the refrigerator. Triacs
are rather poor choices for highly inductive loads.
If you're intent on using solid state switching, I recommend that you switch
from a triac to an alternistor, which is essentially a couple of
inverse-parallel connected SCRs, which avoid the commutating problems of the
triac.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.

 

Check the magazine web site for updates.

 

"Homer J Simpson"

** Nothing in the notes and errata of interest.

BTW
The article is called:

" Coolmaster Fridge/Freezer Temperature Controller ".




........ Phil

 

Oh yea, the alternistor !!

Never made it in the market place, I wonder why ??

http://en.wikipedia.org/wiki/Alternistor

 

"Donald" <

** Called " snubberless triacs " by many makers.




....... Phil

 

You should probably use a mechanical relay to switch the refrigerator.

That's easily tested.

How do I prevent contact arcing?

Cheers, Antony.

 

With a snubber. Designing an actual snubber is somewhat of an arcane black
art - I've seen people just pick values out of the air, but I've also
heard that the resistance should be equal to the inductive reactance of
the load, but I'm not sure how to choose a cap value - I'm sure someone
will chime in here.

Cheers!
Rich