Hi folks,

A small problem.

We have a pilot chilling plant in which we need a much finer control over the cooling cycles. The standard method of Thermostat switched compressor does not offer the required control band.

I have devised a plan to replace the thermostat with an LM35 and feed the output after amplification to an 8 bit ADC. OK once here, I have full control when to start the compressor and when to stop it precisely with an MCU.

Issue however is with the relay - once I do away with the thermostat I need to provide for a means to switch the compressor. I thought I will use a SSR in place of a normal relay ( mainly the switching -audible noise is objectionable ).

The compressor draws 9 A at full load on single phase 230 Vac. I have decided on Omega's SSR330DC25. This has an inbuilt snubber shown in the data sheet - but there is no information as to what extent this would serve as a protection. And conveniently they have shown only a heater load as sample.

What I want to know is : Should I plan for some more snubbering for safety sake ? Or plan to live with the snubber inside the unit ? Any more tips on such replcements of mechanical relays with SSR is welcome. ( OK the basic differences on output isolation, bleed resistors, surge protection and I2T fuse back are all known - some other than that based on practical experiences are welcome)

Thanks

Raghu