SSR question... switching a freezer on and off

10 years ago i made a chest freezer temperature controller with a BASIC Stamp. It uses an Opto 22 240D45 zero crossing, 45A SSR to switch on and off a freezer to keep the temperature between -5 and +5C. It has been working perfectly for 10 years (however it is not used all the time, only about 20% of the year).

Now I am building another one but this time with an Arduino. I was reading a Crydom app note about SSR’s and it says do not use zero-crossing SSR’s for inductive loads. I don’t understand… what is the reason to not use zero crossing SSR’s for inductive loads? When you connect a freezers plug to an outlet it is going to be “random-crossing”.
Why have I not had a problem in 10 years… is it because the compressor in the freezer isn’t a very large inductive load?

Thanks for any help!

Dunno - with an ac inductive load the current taken lags the voltage - if you switch at zero voltage , it will either not switch off or generate a voltage spike ( which might kill it ?) .
With an on off switch , it will spark until the current reaches zero or create a spike - but as it’s mechanical,apart from de rating it , no one will know.

lkz7786:
10 years ago i made a chest freezer temperature controller with a BASIC Stamp. It uses an Opto 22 240D45 zero crossing, 45A SSR to switch on and off a freezer to keep the temperature between -5 and +5C. It has been working perfectly for 10 years (however it is not used all the time, only about 20% of the year).

Now I am building another one but this time with an Arduino. I was reading a Crydom app note about SSR's and it says do not use zero-crossing SSR's for inductive loads. I don't understand... what is the reason to not use zero crossing SSR's for inductive loads? When you connect a freezers plug to an outlet it is going to be "random-crossing".
Why have I not had a problem in 10 years... is it because the compressor in the freezer isn't a very large inductive load?

Thanks for any help!

Because! An inductive load will have the voltage and current sine waves out of phase by some amount. If you switch the relay when the voltage crosses zero, the current will still have a large value. That is where the stored magnetic field will collapse and produce a very large voltage.

I suspect very strongly that your freezer has a relay that you were controlling, not the compressor directly.

Paul