UPS causing motor to slow down with a jerk - solution?


I’m running an appliance (motor) connected to my UPS. In case loadshedding happens, I want it to run smooth, without any feeling in its speed or smoothness that power has switched to UPS from wapda.

But, with current ups, there is a slight change in speed of motor, it instantly becomes a bit slow with a small jerk that you can feel, not large. And when wapda comes back, it again becomes faster with a small jerk/change in speed.

@aurangzebhaque @farhan_ds I need opinion of expert members, which ups will resolve this for sure?

Can pure sine wave ups resolve this, i.e. I feel absolutely no change in motor speed and no jerk when it switches to ups?

And if so which ups will be best for this…

when measuring power, it takes about 150 to 500 watts, depending on the set speed.
tread . mill

Slowing down can be measured. It could be due to frequency of the UPS output electricity or simply because the UPS cannot supply the required power. Without proper measurements I would go with the latter opinion.
Unless you have money to throw, I think investing in a new UPS with (probably ) bigger batteries, without taking measurements wouldn’t be a wise step.


Most likely cause is slight voltage difference between UPS output during power outage when UPS is running on batteries (probably 220 volts) and UPS output on WAPDA line voltage when power is available and UPS is not running on batteries (perhaps 230-240 volts). If your UPS voltage when running on on batteries can be adjusted physically or through software, you can match the two voltages which should solve the problem … but WAPDA voltage changes from time to time so solution may not be permanent!

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Use an online UPS.

measured power on wapda, it was well within power capacity of UPS… and it turns on + runs on UPS too … (when wapda isn’t there).

But during power outage, if it is already running, there is a slight slowness in speed, not huge… and a slight jerk… now it is dangerous as if someone running can still feel it and can fall down…

so… maybe output frequency related… or something else? like voltage as others suggested? but I don’t have anything to measure ups frequency… will it not be 50hz like wapda…

@Asad do you know of any online ups available locally ? ideally not too expensive… does online ups run the appliance directly without putting it on wapda?

i will have to check this.

edit: ups supplies 207v , lower than mains indeed.

Try it out by watching the input voltage to the treadmill. A slight pause due to switching from Wapda to UPS is unavoidable.
If you feel that there is risk of physical injury, consider using it on UPS so that there are no jerks/slowdowns due to switching over. Battery discharge can be compensated by adding an additional battery. This is likely to be a more cost effective solution. The only problem is to make a switching arrangement in case the UPS also feeds other loads.

On your frequency question the answer is yes. However it could be off by a factor of 1-3% at any particular time which would cause a jerk as you have described

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Will connecting a voltage stabilizer in front of UPS, then connecting machine to stabilizer, work in smoothing out voltage or frequency issues? Which one will be decent?

Won’t cost anything to try it out

Checked voltages… mains supply gives 221v, ups outputs 207v. Gonna try a stabilizer after UPS, connect with treadmill.

Can stabilizer connected in front of a ups act as ‘online ups’ system? as it will have fixed voltage being supplied to the machine right.

Raise the output voltage of the ups first. Easily done

can you suggest how? I don’t know too much but some pointers please.

In theory the output voltage can be varied around +/- 20 volts or so by varying a potentiometer provided in the circuit. You have to know which one before you fiddle with the machine and cause harm. Better to let a technician do it for you instead of you experimenting and causing a fu.