Fans Running On Ups Which Output Is Square Wave Type

[AB2005]

Dear Friends,

 

In our rejoin due to shortfall of electricity, people are installing (offline) UPSs for some lights and fans. Now many local companies are introducing their low cost UPSs. People don’t have sense to judge which UPS will be better for their applications; they just see the low cost.

I am checking a UPS of a company which output is square wave type (almost all kind of low cost UPSs are the square wave output). I was suspecting that the fans would draw high power when they run at UPS but I astonished to see that there was no difference if running the fans at utility power or at that UPS. For example,

Fan 1 On utility power 220V-75W On UPS 230V-75W.

Fan 2 On utility power 220V-160W On UPS 230V-160W.

 

Only one thing I observed that when fans run on UPS, an extra sound appears. I need help to my colleague to understand the matter. If these UPSs are ok then we will encourage people to also use them for PCs etc as people want to use those UPSs for PCs also and asks us if this is better or not? Some people used and still they faced no problem.

 

Thanks in advance.

[marke]

Hello AB2005

 

A squarewave output UPS provides a voltage waveform that has many odd order harmonics.

 

This can have an affect on the losses in iron circuits such as induction motors and transformers.

Rather than measuring the current, measure the temperature of the motor windings over a period of time.

If the motor is an induction motor, the motor may run hotter.

If the motor is an "universal motor" (has brushes) there will be little or no difference.

 

Best regards,

Mark.

[AB2005]

Hello AB2005

 

A squarewave output UPS provides a voltage waveform that has many odd order harmonics.

 

This can have an affect on the losses in iron circuits such as induction motors and transformers.

Rather than measuring the current, measure the temperature of the motor windings over a period of time.

If the motor is an induction motor, the motor may run hotter.

 

Mark.

 

Yes Mark. Fans run on that UPS became more hotter as compare with when they run on utility power. Is there any trick to reduce the losses in iron while running fans on such kind of UPSs??

 

What do you say if running the fans on "near to sine wave" UPSs?

 

If fans are become more hot means power loss but i measured the power by an anloge wattmeter and found the same power flow in both cases. This is the point of concern.

[marke]

Is there any trick to reduce the losses in iron while running fans on such kind of UPSs??

Make the waveform more sinusoidal and the losses will reduce.

 

What do you say if running the fans on "near to sine wave" UPSs?

The losses will be lower, the motors will run cooler.

 

but i measured the power by an anloge wattmeter and found the same power flow in both cases.

First, it depends on how well the watmeter handles a non sinusoidal waveform and second, if the slip is higher, the fan speed will be lower and so the shaft power will be lower.

[shartah]

Hello AB2005

 

A squarewave output UPS provides a voltage waveform that has many odd order harmonics.

 

This can have an affect on the losses in iron circuits such as induction motors and transformers.

Rather than measuring the current, measure the temperature of the motor windings over a period of time.

If the motor is an induction motor, the motor may run hotter.

If the motor is an "universal motor" (has brushes) there will be little or no difference.

 

Best regards,

Mark.

 

 

Dear Mark,

 

I have 2 questions for you.

 

1. How can u say that square wave output will be having odd hormonics?

2. If the motor is star connected, then the odd hormonics will be eliminated. Right?

 

Please excuse me if my questions are very basic.

 

sharath

[marke]

Hello sharath

 

1.Symmetrical waveforms are made of odd order harmonics. - Assymetrical Waveforms are made up of even harmonics.

This is covered in any description of harmonics. - A square wave is a symmetric waveform.

 

2. Not true. It does not matter whether the motor is in star, or in delta, the odd order harmonics still exist.

 

If you fed via a delta primary star secondary transformer, the triplen harmonics would be eliminated provided that the voltages were well balanced.

 

Best regards,

Mark.

[AB2005]

Dear Mrake,

 

I have thoroughly tested that UPS and one more which results astonished me. Please see the below pictures;

 

http://i1155.photobucket.com/albums/p553/signode/SquareWaveUPS.jpg

 

http://i1155.photobucket.com/albums/p553/signode/SignWaveUPS.jpg

 

Marke, can you explain me about the bad effects if we install that square wave UPS and run electronic equipment with it because many people installed that kind of UPSs.