Multi fridge "alternator".

Hi people!

I'm installing solar power with a grid tied system and I would like, at least during the day, to prevent my both fridges to work at the same time in order to be able, when possible, to feed them with the solar energy.

My idea is a small autonomous circuit with two relays that works like this:

At start the two relays are closed (passing current) to both fridges, but as soon as one of the fridges starts working (for example when power exceeds 30W or 130mA) the circuit opens (disconnects) the other relay for the other fridge and only closes it again when the consumption stops.

My both fridges consume about 60 to 90 W, one turns on about 15-20 minutes one time per hour and the other about 20-25 minutes one time per hour, so this schema would prevent grid consumption most of the times because would keep this two devices always under 100W when without a system like this they would go up to 120-180W, in association with other home appliances, consuming more then the production.

What do you think about this idea?

Is there an easy approach with little circuitry, mostly passive, to obtain this?



Robert Wall's picture

Re: Multi fridge "alternator".

If it works, it sounds like a good idea, BUT you need to be very careful to ensure that both fridges keep their contents at a safe temperature at all times. So in that respect you need to design your control scheme so that it fails safe, and that almost certainly means that if anything goes wrong, both fridges will be enabled and turn on if their thermostats demand it.

"My both fridges consume about 60 to 90 W..." They might do when running, but you must not forget the inrush current, and the fact that you have an inductive load. Ensure that your relay contacts have adequate rating for both voltage and current.

You also need to nominate one as the 'priority' device, so that in the event of both trying to start simultaneously, they don't both attempt to cut the other one off.

Without re-manufacturing relays with coil windings that carry the operating current of your fridge, and that is something that could be both difficult and potentially dangerous, I cannot think of a way to do this without active components.

CidiRome's picture

Re: Multi fridge "alternator".


I understand your fail safe, If one of the devices goes bad and never stops working the other one will be keept off, this is not good, some kind of of timer must be put in action and if one hour with the relay off is reached to turn in on even if the other one is still off.

It has the have some kind of active components to control things.

I think a regular 5V ou 12V coil and 10A can do the job, but has to be controlled with some electronics.

My first idea was to use a simple clock that would alternate every half an hour or 45 minutes... Then I came with this one because it wouldn't be good to turn the fridge off before the cooling cycle was finished in case it was only started close to the end of the clock change...


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