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Old 10-28-2012, 07:05 PM   #1
pithed
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Default Question on relays for fridge fermentation control

Hi all,

I am converting a wine cooler (vinotemp vt24) to be controlled with relays by a microcontroller using some of the excellent builds on this site. I am using the standard solid state relays by Fotek (the ones I have are rated 25 amps). The trouble is that they work fine when I use them to interrupt the AC at the power cord, using a receptacle in a job box etc.., as has been detailed on this site, but when i use one in place of the mechanical thermostat it works for a minute or so then kicks in the compressor overload protection switch (clicking sound).

I have tested the current draw when using each setup and the power cord setup consistently draws 1.5 amps after an initial 5-6 amp start up. When i switch to the thermostat setup it draws 5-6 amps until it shuts down. Anyone have any idea why this is? I admit that I have almost zero experience with AC circuits and much much more with DC so I am using this as a learning tool but am frustrated that I can't figure out what is going on. Do the relays have too much voltage drop when used in that part of the circuit? Since the power cord version works ok I will use it but it would have been a much cleaner build without.

Any insight at all would be greatly appreciated as I am spending too much time on this right now and not enough time brewing. Thanks!

edit: pictures of build/problem:

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Old 10-29-2012, 09:55 PM   #2
FlatcapBrew
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Your wiring is missing the start winding of your compressor causing the high amp draw maybe?

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Old 10-29-2012, 10:50 PM   #3
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[edit]Nevermind, I just took a look at the control circuits on my two brew fridges and the keezer and there ain't no sign of a transformer anywhere. So all of that startup and run current goes through the thermostat points. Woof!

Cheers!

[another edit] What's the ON resistance for that SSR?

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Old 11-01-2012, 03:45 AM   #4
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I could not find any on resistance info and I am now going through a tutorial on AC circuits to figure this out. The on voltage value is given as >3 v if that helps? I will just go ahead a keep it plugged in to the job box circuit until I can make sense of it.

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