Using a UPS for an Air Conditioner

UPS meaning uninterrupted power supply of course.

In my house I have an AC that will occasionally work harder and suck up some extra power for a second or two. This effects one of the rooms in my house, where, at best, the lights dim for a brief second, and at worse trips the circuit breaker.

As a temporary fix, if I plugged the AC into a UPS and plugged that into the wall, then when it wanted extra power, it would draw it from the UPS battery and not from the outlet, right?

Since it might depend on the type of UPS I’m thinking of the kind carried by the local Home Depot, such as this.

Thank you.

Actually, I guess I should have titled this “Using a UPS for an Air Conditioner”. Apologies to the mods for the title.

I doubt a small, cheap UPS like that would handle the load. You’d have to look up how many amps the UPS is capable of putting out, and try to figure out how many the AC is drawing.

The Office Depot I went to had a couple of other UPSes. The highest one is 750VA/450 Watt.

Let’s see, looking it up…I can’t find the info for the AC in the manual .

i once accidentally plugged my vacuum cleaner into the ups and whacked it completely (don’t ask me how this happened) on the other hand i have a digital clock permanently plugged into one and all is well. depends on amperage.

I’m using a 350VA for my computer…I originally just bought it for my DSL modem/router but decided, what the heck, it has three outlets for battery backup, so I plugged my computer (running on a 550 Watt power supply) and my LCD monitor as well. During the Winter we had a power outage. The UPS kept everything running until I turned it all off.

It likely won’t handle the air conditioner.

Oh well, I thought it might be worth a try. Thanks guys for helping me not waste my money.

For the cost of a UPS big enough to handle this load, you could wire a new circuit direct to the electrical box that is large enough to handle the AC load. And that will be a permanent, proper fix.

No it won’t work.

You may also have an compressor motor that’s going bad and causing this brown out. They do that before they completely fail.

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I fixed that for you.
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If this is a window air conditioner intended to cool a room, you’re probably looking at 1500VA minimum. If it’s a full-sized unit intended to air condition a full house, it most likely runs at least double that, on its own dedicated 50amp circuit.

There are battery UPS units that can handle a load that big, but they are really expensive. It’s been a long time since I bought one–I was using it for a rack full of network equipment–but I paid about $1,200.

It’s just intended to cool a room. Searching some more, I finally found the specs on it.

It’s a 10,00BTU A/C and it runs on:
Volts - 115, Watts - 1,020

I didn’t realize it took so much electricity. Yeah, it’s easy to see now that an Office Depot UPS wouldn’t work.

It’s not about just the current draw. It’s that they are not made to handle motors.

you could

source nonAC appliances on this circuit (fuse/breaker) to another circuit (fuse/breaker)

and

start the AC not in the cooling mode but fan mode (this might help if on the edge of over current)

best is put the AC on its own circuit (fuse/breaker). if it would be a permanent location then putting in a new circuit would be worth it if needed. if you install a new circuit it would be sensible to run a 3 wire cable with ground so that you could have 240V or 120V as needed.

When dad was alive he spent all his time in a chair that had a motor on it to help him get up and down. I put an expensive UPS on it so that he wouldn’t get stuck if he had an emergency.

Alas, it did no good at all. So IME it won’t likely work with A/C either.

some models of those electric lift chairs have a 9V transistor radio battery as an emergency backup.

Your A/C has a ‘RLA’ or "FLA’ rating on it that has the full load current when the appliance is running. (running load amps, or full load amps)

Starting current, however, is a lot more. (the inrush current needed to go from a dead stop to running) That is often reflected on the sticker as ‘LRA’. (locked rotor amps) This inrush LRA current is only for a second but HVACR breakers are designed to accept the momentary surge associated with start up. LRA may be 4-10 times the amount of RLA. (once again, LRA is only for a second)

If your breaker is tripping it may be that the unit is in the earliest stages of dying. (the compressor can’t start fast enough and the amount of inrush current lasts long enough to trip the breaker) If this is the case, you may add a "hard start’ to help with start up. (a defibrillator of sorts)

Or, maybe your breaker is undersized.

Or maybe its the wrong type breaker. (not rated for HVACR use)

In any event a UPS won’t even accept RLA. LRA is out of the question.

If its a window unit, it will likely be on a 20 amp breaker. It may be 110V or maybe 220V. It should be on a dedicated circuit.

ETA
Don’t put in a larger breaker without talking to a professional.

Your breaker must be, by design, the weakest link in the system. If you put in a breaker that’s too large for the wire, the wire becomes the weakest link—A Very Bad Thing.

Some of the dirtiest electricity in a house is from a UPS when in battery backup mode. UPS manufacturers (quietly) recommend no electric motors or power strip protectors on that UPS output because that electricity can be harmful.

But computers (electronics) are required to be some of the most robust devices in a house. Power destructive to small electric motors is ideal power to all computers. When selling ‘clean power’ myths to the naive, a UPS manufacturer does not like to discuss its so dirty output.

When is the UPS power cleanest? When the UPS connects appliances directly to AC mains - when not in battery backup mode.

Moving on to your AC. If lights are dimming, you have an AC wiring problem. Could be a wire daisy chained through other receptacles using the ‘back stab’ connection. Every receptacle in a circuit powering computer or AC must have wires wrapped fully around the screw. Simply remove each cover plate. Look at the side mounted screw. Are all wired connect to that screw? Is that screw tight?

Otherwise you may have a human safety problem. AC is only a symptom of a problem so serious as to threaten human life. So why would you cure symptoms using a UPS? Fix the problem.

When AC goes on, no lights anything in the house should dim or brighten. Even 1930 wiring would be that robust.

UPS is not a safe power source for ACs. Do not cure symptoms of a household wiring problem with a UPS.