Help with Triac based Temerature Controller

May 20, 2007 8 Replies
A

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


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S

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

"it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
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D

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.
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H

Check the magazine web site for updates.

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P

"Homer J Simpson"

** Nothing in the notes and errata of interest.

BTW The article is called:

" Coolmaster Fridge/Freezer Temperature Controller ".

....... Phil

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D

Oh yea, the alternistor !!

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

formatting link

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P

"Donald" <

** Called " snubberless triacs " by many makers.

...... Phil

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A

That's easily tested.

How do I prevent contact arcing?

Cheers, Antony.

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R

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

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