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xJAyx (Electrical) (OP)
16 Aug 04 20:30
Does anyone have any tips for sizing a UPS when it is driving a motor load? My applicaiton requires the motor to start while under UPS power. My main concern is how to include the inrush current when calculating the load and run time?
RonShap (Electrical)
16 Aug 04 21:15
Depends on the type of UPS and type of motor/application.  If the starting power factor will be very low, and considering the inrush, you will need to share that with the UPS Vendor to determine how much it needs to be derated.  The UPS is generally rated at .8PF
rbulsara (Electrical)
17 Aug 04 13:43
You need to check with UPS mfr.

UPSs have limited capacity to deliver short circuit current or starting current for loads such as motors.

Most UPS will transfer to it's static bypass source in 10 seconds if the load is more than 125% its rating.

Make sure this is acceptable for your application. Check against your motor's starting current and its duration (acceleration time) vs. UPS overload characteristics.

Using solid-state starters or VFD's should help.
controlnovice (Electrical)
17 Aug 04 15:43
Is your UPS battery driven or does it use a fly-wheel?
jraef (Electrical)
19 Aug 04 2:42
You may be able to help the UPS by using a soft starter on the motor as well. I recently did some A/C compressor motors that needed to be run on a UPS and adding soft starters allowed us to use a 25kVA instead of the next size up, a 50kVA. The soft starters kept the motor starting current below the peak rating of the UPS.

"Venditori de oleum-vipera non vigere excordis populi"


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