I am looking to use an Solid State Relay (SSR) to turn the power on/off for a small 120V AC chest freezer.
*** Current situation ***
I have cut the hot line of an extension cord (leaving the neutral and ground intact) and attached each end of the cut to the high side of the SSR. The control side of the SSR is connected to an Arduino 5V digital out pin and ground.
I can turn the SSR on and off fine with the Arduino, and can have it power a decent sized load okay (I can have it turn on and off a heat gun plugged in to the SSR controlled extension cord just fine).
*** Challenge ***
When I try to power the chest freezer it turns on for a few seconds, and then turns off. I know about inrush surge current when a compressor starts but it should be well within the limits of the SSR. Monitoring it with a Kill-a-watt device, it surges to ~500 watts, then drops down to ~200W before shutting off. When I plug the chest freezer in directly to the mains electricity it draws about 55W on a continuous basis (when running and after the startup surge), which indicates that the inrush surge is about 10x the continuous current, which is about what is expected.
The SSR is rated for 25A, so the 500W peak at 120V should be ~4.2 A, so well within the rated amount of the SSR. But it shuts off after a few seconds.
Why?
Note: I am not sure if the SSR is real or not, and some reports that there are fake ones that are underrated. Even if it actually a 10DA, the SSR should be able to take it as it is rated for 10A and the current at surge is less than 50% of that.
MorganS,
Nothing is overheating. That was my first thought, but the SSR just stays cool.
terrryking228,
The Ardunio is powered via the USB cable to my computer, with the SSR connected to a digital pin and ground of the Arduino. I have also tried just putting it on the 5V pin just to lock it up, but can try it completely separated with a 5V walwart or the like.
Hi,
Yes, just to separate some cause and effect, plain 5V right to the SSR would be interesting.. Or you can use a 9V battery.. the SSR's usually rated up to 20V or so on input..
You said
(I can have it turn on and off a heat gun plugged in to the SSR controlled extension cord just fine).
That is a resistive load and the freezer motor is quite inductive. That SSR is supposed to be Zero-crossing On-Off but maybe the inductive load is confusing it...
WARNING. Fotek SSR-25DA.
Dont leave it where it possibly could start a fire. I used one for a hotwater boiler @230V /10A. Arduino controlled on/off by thermostat.
A few weeks OK - then a terrible smell. The SSR totally burnt.
It's highly possible you have a counterfeit product. Many of the 25A and 40A have crippled ratings. You'll need an SSR rated for inductive load, usually a random triggered type (not zero-cross type). An RC snubber or MOV is necessary.
I have no experience of SSRs but I do have a fridge controlled with an Arduino using an electro-mechanical relay. I think the present relay is rated at 16A or 20A AC (230v system). This A rated fridge runs from a quasi-sine-wave inverter and the inrush current has overloaded 2 x 800w inverters even though they were supposed to have overload protection.
it is working happily (touch-wood) with a 1kW inverter with IIRC a brief 2400kW peak capability. When it is running I see a 12v current of about 6 amps but at startup I regularly see 50 or 60 amps for a few seconds.
Do not underestimate the size of the inrush current.
Fridge motors are induction motors, you need an SSR rated for such a highly inductive load (with the
right snubber circuitry). They also take large currents at start up so the current handling must be up
to scratch.
