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Refrigerator Power Consumption / Plugging into UPS [Question] (dubvee.org)

submitted 3 weeks ago* (last edited 3 weeks ago) by [email protected] to c/[email protected]

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My power is generally pretty reliable, but when it does have issues, it often flickers violently. More than once, I thought the control board in my fridge got fried, but was luckily able to do the refrigerator equivalent to Ctrl+Alt+Delete and reset it.

I have an extra 800W UPS laying around, so I figured I'd give it a try and see if it would run it. I'm not really looking to use the UPS to keep it powered during an outage, just to deal with the power flickers/surges/brownouts that may damage it (surge protectors won't protect against brownouts). Any additional cooling time during an outage would simply be a bonus.

To my surprise, it works. Not only works, but only seems to draw between 110 and 160 watts (compressor on, door open). However, I expected it to draw power in the 700-900 watt range. Granted, the last time I worried about refrigerator wattage was years ago when I lived in the boonies, had an older fridge, and had to resource-manage when I was running from the generator on a long outage.

Is that normal for a 26 cu ft refrigerator? I'd say it's probably close to 10 years old. AFAIK, the UPS reports the wattage draw correctly (at least, the values were within expectations when I was using it with my desktop workstation). The manual for the fridge says 115v / 10 A but it doesn't seem to use anywhere close to that.

Additionally, are there any hidden risks to running a refrierator from a UPS? It's a pure sine wave UPS, so the power should be as clean as or cleaner than utility.

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[–] [email protected] 10 points 3 weeks ago (1 children)

If already cold a fridge should use very little power on an ongoing basis. The peak draw should still be high if it is running the compressor, but the peak may only be for a few seconds or even less. So an 800W fridge may peak at that full draw for just long enough to start the compressor then drop down to something similar to what you said you had for the rest of the cycle. If it were empty and warm to start I would expect a higher load for a while, but again, the big draw is starting the motor,kicking off the compression cycle, so 150W is reasonable to me.

[–] [email protected] 3 points 3 weeks ago* (last edited 3 weeks ago)

Yeah, I have no idea what the rated wattage for this is. Manual / manufacturer specs are useless. Just says like 740 KWh/yr and "115V/10A".

I've been watching it for the last ~3 hours. Fridge was already cold, but I did open the door for a minute or two so the compressor would kick in.

When the compressor's running, the draw is about 150W average (swings between 120W and about 160). I can hear it running. Haven't caught the startup wattage, but the UPS had no issues with it (would have beeped otherwise). I'm not sure if it runs harder or just longer if it needs to cool a warm fridge down (not an expert here lol).

A bit later, the compressor is not running (no hum even with my ear to it). UPS says 400W now, almost on the dot ( +/- 3 watts or so). I'm assuming this is some kind of defrost/de-ice cycle and there's a heater running or something.

After about 15 minutes, it dropped back down to almost nothing until the compressor kicked on again.

So I guess it really is that energy-efficient. lol. I guess the only remaining question is if there's anything to watch out for if I want to keep running it on a UPS.

[–] [email protected] 10 points 3 weeks ago

I'd contact your power company. I had a street feed with a similar issue that turned out to be an industrial piece of equipment on the same phase as I was. The power company switched my phase and life went back to normal.

[–] [email protected] 7 points 3 weeks ago

be aware that most fridges have a defrost heater that runs perhaps daily to melt the ice off of the coils in the freezer. You’ll need to measure the power consumption with this heater on to know the peak power draw.

under 200 W sounds correct for the compressor

[–] [email protected] 6 points 3 weeks ago

Heat pumps are very efficient when running, but require a decent amount of power to turn on. That surge is why you need the circuit sized as large as it is.

[–] [email protected] 3 points 3 weeks ago* (last edited 3 weeks ago)

Your UPS might not protect from brown outs. You would need an online double conversion or line interactive ups to protect from brown outs. Many consumer ups' are just standby.

[–] [email protected] 3 points 3 weeks ago* (last edited 3 weeks ago)

It may have a defroster heater circuit that kicks on periodically, raising the current draw.

Does it have ratings for the light fixtures? Are you using the incandescent bulbs it is likely rated for, or have you switched to LEDs?

You shouldn't have any real problems with the UPS, so long as it is rated for the 115v / 10A that the refrigerator is rated for.