I have a pure sine wave inverter 12v to 220v AC, its continues output power is 600VA and the surge power is 1130VA, I want to running my 200W fridge, but unfortunately my fridge surge power is a bit more than inverter surge power, its need to about 1300VA for a few seconds so when i run the fridge the inverter shut down.

I'm wondering if i can decrease the surge power of my fridge by using for example a dimmer(motor speed controller) just for the starting, or any other solutions for this problem?

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    \$\begingroup\$ NTC comes to mind, but compressors are tricky. How much work are you willing to put into it to make it work? \$\endgroup\$
    – winny
    Sep 17, 2018 at 18:12
  • \$\begingroup\$ I don't try any solution until this time because i worry about the compressor maybe damaged if i use the wrong solution, the only thing that i do PFC by adding a capacitor because the PF was 0.6 and now it is 0.95 \$\endgroup\$
    – M.A.K
    Sep 17, 2018 at 18:21
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    \$\begingroup\$ extending start times with 3x power disspation in motor can increase winding temps considerably. The start motor cap is supposed to improve PFC so check that one. But if it cuts out and doesn't by changes, its a reliability tradeoff \$\endgroup\$ Sep 17, 2018 at 18:26
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    \$\begingroup\$ Sure, you will enter a territory outside of what it’s made for. If you are not comfortable with that, you need to get a (much) larger inverter. \$\endgroup\$
    – winny
    Sep 17, 2018 at 18:39
  • \$\begingroup\$ Looks like if you limit the current to less than 4A with an NTC surge suppressor that it may work. Look at this Anatherm NTC: ametherm.com/datasheetspdf/MS3250006.pdf Remember that the NTC will run very hot after the start surge, so you need it in a well aired box. \$\endgroup\$ Sep 17, 2018 at 19:10

1 Answer 1


You can try series resistors up until the voltage drop is too much, as an isolation from the inductive loading. But the inverter may burn up in a years time like mine did. Mine was an APC 1300 VA and it seemed to have ample power, but in 6 months its step-up converter burned up.

I talked with an APC tech who seemed annoyed, as if he had this issue all the time. This issue turned out to be the way AC motors and especially AC motors with start capacitors not only hit the UPS with a reactive load, the capacitor causes a phase shift in the waveform based on uneven current loading, in spite of the UPS attempts to maintain a sine-wave.

Even though the UPS was rated 3 times the refrigerators maximum load, it was not a balanced load. The typical UPS, sine-wave or not, is meant to drive wall-wart transformers and switch mode power supplies which have dynamic resistance, but little reactance.

I thought something was wrong when I noticed the UPS seemed to be constantly charging, especially after a power failure then the power comes back on. Yet the refrigerator was no more of a load than my stereo with the volume cranked up. The APC tech warned me that big audio amplifiers have a big transformer that can cause stress on a UPS.

The ends result is I run the refrigerator and stereo directly off the AC outlet. My only option was to buy an expensive generator which ignores asymmetrical loads.


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