Appliance Toggle Switch to reduce peak power

beachdreamer

I am planning how to build a grid tie backup system with a Magnum inverter. The inverter has a max output of 4000W. I am monitoring the power consumption on my backup panel and the peak is higher than that. I am thinking if I could make a toggle switch of some kind that would ensure that the refrigerator and freezer are never powered at the same time it would reduce my peak power. I have not found any simple systems to do that. The only thing close I have seen is the priority loads in the Generac backup systems. Any better solutions for an automatic priority or toggle load switch?
Thanks.

waynefromnscanada

Re: Appliance Toggle Switch to reduce peak power

beachdreamer wrote: »

I am thinking if I could make a toggle switch of some kind that would ensure that the refrigerator and freezer are never powered at the same time it would reduce my peak power.

Hi Benchdreamer, welcome to the forum.
Actually I've done what you're looking for.
In my case I used a relay, who's coil is powered by the supply to the compressor of the fridge. When the fridge thermostat calls for cooling, it energizes the compressor and at the same time, a Normally Closed (120 volt coiled) relay that then pulls in and cuts power to the freezer until the fridge stops again. Freezers can wait, so I gave the fridge priority. Been working fine that way since Sept 2007.

BB.

Re: Appliance Toggle Switch to reduce peak power

In general, a refrigerator or freezer takes around 120 watts to run, ~600 watts to defrost, and >~1,200 watts to start...

A properly wired and designed 4,000 watt inverter should support an ~8,000 Watt (VA) surge. So--setting up a relay (for example), does not really help much unless you are trying to run two refrigerators from one ~1,200 watt AC inverter.

So, the first question, is the >4,000 Watt load last longer than a few cycles (or a few minutes, depending on inverter)?

Next, there is an issue with your selection of Refrigerators and Freezers... The "old fashion" frost full type of refrigerators and freezers--You could just hook up the thermostate from one (say freezer)--When freezer needs to run, relay shunts load to freezer. Otherwise, refrigerator gets power.

If you have a frost free refrigerator/freezer, there is (usually) some sort of timer that runs a ~1-2 hour defrost cycle every 12 hours. My "cheap" freezer has a mechanical timer--If I give it AC power only 50% of the time (the other 50% to run the freezer) would cause the timer to run on a 24 hour cycle (and upwards of 2-4 hour defrost cycle)--Not sure that is a good thing. And you need to do a defrost cycle every 12-24 hours or the evaporator will ice up and start blocking airflow.

The newer/fancier refrigerators may use an electronic defrost timer--And every time you turn on the AC power, the refrigerator may enter a defrost cycle (not useful if you are giving 30 minutes to the freezer and 30 minutes to the refrigerator every hour).

All of these can be worked around--But you might wish to revisit your loads and figure out who is sucking down 4,000 watts at a time... For my suburban home, I draw that sort of power only when running an air compressor+microwave+toaster oven+the rest of the house all at the same time (no AC/Electric heat).

-Bill

Blackcherry04

Re: Appliance Toggle Switch to reduce peak power

I run a couple Air Conditioners with a similar set up. One is set up as the Master and the other is the Slave. I'd make up a " Y " cord and use a Current Sensing Relay ( switch ) in the " Y ". The refrigerator in the Master and the freezer the Slave. They have a adjustable threshold, so say someone opens the door the light would not cut the freezer off and right back on and cause a short cycle on the compressor. A relay on the compressor feed may just as good.

Here is one, there 100's of different ones. This one is adjustable. This one might work.

http://www.ebay.com/itm/DAYTON-6C055-120V-Relay-Current-Sensing-NEW-Series-A-/151155783587?pt=LH_DefaultDomain_0&hash=item23319637a3

beachdreamer

Re: Appliance Toggle Switch to reduce peak power

Thanks for the ideas. A relay sounds like a good approach but will have to see how that works with the defrost cycle.

Good point about the duration of the peak power. The meter may have seen that peak for a short enough time that the inverter can handle it. Maybe when both were in defrost mode or one in defrost and the other turning on. I may need a better power meter and I do need to determine what is driving that peak power number.