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I need a voltage stabilizer for my refrigerator. Can I use a UPS for this?

I own an APC Back-UPS marked "Output: 230V~, 2.6A, 50/60Hz...". The label on the fridge says "220V/50Hz". Can I use this UPS as a voltage stabilizer for the fridge?

Update: Strangely, the label behind the fridge says 85W, 220V and 1A.

Power rating

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You COULD use a UPS for this purpose, but the one you have is too small. Your fridge will have a tag that says how many amps it draws. You'd have to find that tag and provide a UPS big enough to meet that demand. –  Bob Mar 21 '13 at 12:19
Why do you think you need a voltage stabilizer? –  longneck Mar 21 '13 at 14:00
@longneck, I see everyone here in India uses a voltage stabilizer with non-trivial electrical equipment. Probably because of the quality of the power supply out here. I've heard that newer refrigerators come with built-in voltage stabilization but I don't want to take a chance. –  Agnel Kurian Mar 21 '13 at 15:14
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3 Answers

up vote 4 down vote accepted

An "online" UPS is what you need. These have circuitry that converts the line voltage (which is probably bad in your case) to DC, and then recreates the AC at its output. Without this, your UPS will often switch to battery power, allowing its batteries to discharge during use. This switching of non-online UPS will also create blips in the power output that can damage the motors in the fridge.

You also need to make sure that the UPS creates a good-quality sine wave output. Cheaper UPS will create a square wave, or a very unsmooth AC waveform. Not having a smooth sine wave output will cause damage to the motors in the fridge.

The amount of power you need is a minimum of the volts multiplied by the current of your fridge, 230 times the current that it draws. Your UPS is rated in Volt-Amps (VA), which is a slightly different quantity. It has to do with the apparent power used by your load. Modern devices will have an apparent power very close to their real power, though older devices (especially motors) will require much more apparent power than their "real power", so I'd suggest over-sizing your UPS by 20-30% for this.

In addition, motors often will have a large "in-rush" current when they first start up. This can easily be double the power required once the motor is up and running. Perhaps the 1 A already factors in this inrush current, since 90 W is less than 0.5 A at 220V.

With your UPS providing 600 VA, and your fridge needing (1.0*220)=220 W, your UPS can likely supply sufficient power. The concern are if it will damage your fridge's motors, and if the battery has enough capacity to last out the voltage swings.

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The short answer is probably No. The fridge is a fairly high current draw device, especially on motor start up. Most likely the current draw is a lot more than the 2.6 amp rating of the UPS. To calculate the current draw, either find the spec for amps or the wattage of the unit. Use a simple formula, Watts = voltage X Amps. thus, Amps = Watts/volts This will give you a good approximation of current draw, but remember when the motor first starts up, it will draw a lot more for the first second or two.

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The motor will list "locked rotor amps" or usually abbreviated as LRA. This is the current that will draw while the rotor is not turning. That happens when it is stalled (you do want the breaker to eventually disconnect in this condition) and when it is starting (the rotor is not turning, yet).

A UPS or any electronic inverter has relatively little capacity to briefly over deliver the current. One could be designed and built to do so, but it would be so additionally costly that this just isn't done.

Get a UPS that can deliver the LRA rating times voltage if you want to make sure it runs. LRA is typically 5 to 12 times the normal operation current. If the UPS cannot deliver that brief high demand of current, the motor may not get rotating.

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