Uninterruptable Power Supply (UPS) and Motor start current

Thread Starter


Joined Apr 3, 2011
Dear Community,

I need to acquire a UPS to supply a small motor. The motor is a vacuum pump that must not be interrupted (during say a short power outage). I am concerned about how to deal with the high in-rush current normally associated with motor starting and how this may effect the operation of a UPS and especially how to specify the power rating of such a UPS.

The motor sige is 0.12Kw however the in-rush start current could normally be expected to be about 5 to 7 times the run-current for a short period.

Can any experienced person in these matters suggest how I should specify the rated power of such a UPS. Do I need to take any other factors into account - such as some some sort of UPS with a soft start facility or UPS especially associated with motor start in-rush currents. ?

Thanks in advance for any assistance.


Joined Nov 25, 2009
Is the UPS supposed to start the engine if needed, or it only needs to support it while it's running in case of a black-out?


Joined Jun 7, 2009
are you starting under load? I envision that you'd have atmospheric at start up, then loading up as you draw up the vacuum? I wouldn't be overly concerned with high inrush in that case. If your starting with an established vacuum, then your loading/inrush will be much higher, depending on the load.


Joined Nov 30, 2010
The compressors I work with pull about 12x the running current, and they are started with the pressures equalized, as in, "no load". This suggests that the reality is the worst you can imagine, like a killowatt+ UPS to start an eighth of a killowatt motor.

Thread Starter


Joined Apr 3, 2011
Thanks to all who replied,

The motor would be starting using the UPS and would be drawing upon full atmospher to start.

I am concerned about any special requirement for wave-form or form-factor running (and starting) a motor from a UPS. Any suggestions as to anything to be on the look-out for in terms of wave-form generated by the UPS.