I have a 1KVA inverter/ups setup at my home, did the installation very recently. Everything works perfectly CFLs,Ceiling fans and stuff. It has stepped sine wave output (when on battery) at a max capacity of 600W. Specs are below.

UPS Specification

Battery: 150ah lead acid tubular battery.

The question I would like to ask: The pedestal fan/air cooler makes humming annoying noise when running on battery mode because of the stepped wave form. (I am located at an urban area and frequent power failure is very common and voltage fluctuation is like sea wave.)

  1. Is there any filter/smoothing device that can be used to at least reduce the noise? any links would be helpful.
  2. One of my friend (an electrician) told me that I can use an electronic regulator(the one used for ceiling fans) to filter the supply to the pedestal fan && cooler and that would do the trick. Is this true? If yes, understandable exaplanation would be helpful.


  • \$\begingroup\$ It appears that the UPS you have is having a quare wave output..It is normal to have such noisy (magnetostriction) operation with electromagnetic appliences..filer if design is quite bulky and may not be compatible with electronics of your UPS due to reactive power requirent of filter,,,vtingole \$\endgroup\$ Jun 27, 2015 at 5:47

1 Answer 1


I fear that your inverter is a square wave type which may have been marketed as a "modified sine wave" .It is feasible to filter the output .The filter components have to have meaningful reactance at 150Hz or 180Hz .This is the third harmonic of mains 50 or 60Hz .Given that you have the invertor and dont want to buy a more expensive sine wave model then you can add inductance in series with the loads that are buzzing.Speaking from experience a 40watt 4ft flouro ballast choke is good .It can handle up to about half an amp .This should turn the nasty buzz into a nice soft hum on your ceiling fan .So summing up lamp ballast chokes can be effective and should be tried if you can lay your hands on some.


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