How do I condition power between a generator that does not produce a clean sine wave and a UPS to such a standard that the UPS will accept the power? I have tried running through a power conditioner, but I believe the problem is that the power conditioner does not stabilize or control the frequency of the power coming in which is probably all over the place. I believe the generator is also unlikely to put out a good frequency until it is under load and until the UPS accepts the power from the generator, no load is put on the generator. Is there a cheap way to do this other than buying a new generator?

All that needs to run on the generator is 1 desktop computer, 1 server, 1 router, 1 switch, 1 printer, and a few other small things. All told the load is under 500 watts as long as the server is not under a heavy processing load (which it almost never is). The UPS I am currently using is an APC Back-UPS. The generator puts out 800 watts, 900 peak.

2 Answers 2


Use a SmartUPS. The UPS use the power from the line to charge the battery while the output from the UPS is from the battery. APC call that way True Online. The line stay more isolated than like a backups where it's a on/off to go on battery in case of a powerloss.

Edited: The input range must be between 50 & 60hz, else it will fall on battery

  • 1
    Would you happen to know offhand how wide a range of power frequencies a SmartUPS will take in? Jan 30, 2015 at 1:48
  • I know it can "trim" or "boost" the input, but like 5% or 10% of it (up and down).
    – yagmoth555
    Jan 30, 2015 at 1:51
  • Is that for frequency or voltage or both? I think my voltage should be trim-able via the power conditioner, I'm most worried about frequency fluctuations. Jan 30, 2015 at 1:52
  • Let’s consider a scenario. Suppose the upper transfer point of a SUA1000XL is set to 127V and the lower transfer point is set to 106V. At the beginning let input voltage be 120V, hence the output voltage of SUA1000XL being 120V as well. Then the input voltage begins to decrease. The output voltage decreases along with the input voltage until it hits the lower threshold of 106VAC. At this point the Automatic Voltage Regulator (AVR) kicks in and boosts the output voltage by a certain extent, which is 15% in the case of SUA1000XL..... check in example
    – yagmoth555
    Jan 30, 2015 at 1:53
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    Just ordered an inverter generator I found on sale that produces a pure sine wave and should take care of the problem. I will mark your answer as correct if you modify it to mention that the range must be within 50-60 Hz as you stated in your comment. Thanks! Jan 30, 2015 at 3:03

Rather than adding a conditioner, get a generator that is meant for office/home loads. I'm guessing the generator you have now is meant for building sites & power tools with a specific type of electrical motor in them.

A domestic type generator will also be more quiet and efficient. And you can move it & use it for your fridge/freezer when needed.

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    Definitely correct. I wanted to know how to condition the power, but did end up buying a clean sine wave generator as it appears to be the cheapest way to go. Was thinking about using a battery charger, battery, and clean sine wave inverter but the generator was cheaper. Will up vote once I get the reputation points! Jan 30, 2015 at 15:53

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