Motors Connected to UPS

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FaradayFF

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Hi,

Is there a good technical resource out there that explains how the motor loads affect the performance of UPS? I've been told that motors drain the batteries rather quickly.
If the UPS unit is UL924 listed, doesn't it mean that the batteries must be sized adequately to maintain UPS rating over a 90 minute interval if the UPS is listed for emergency duty?

Thanks,
EE
 
Doesn't matter whether the VA draw is from a light bulb or a motor. The only reason I can think of a motor drawing down a UPS more quickly than expected is if it has a low PF. Most UPSs have a bit of motor loads, but they're usually small fans, not a 10 ton refrigeration compressor or 10k CFM fan (more likely they're on the generator, if there is one).

Is this for Art. 700 Emergency loads? NFPA 110 and others will play in, too.
 
There is a phenomenon called the "Peukart effect" in battery use wherein the rapid discharge of high current can cause a marked decrease in the total Amp-Hour capacity of the battery. So if starting an AC motor across-the-line, the starting current of the motor will rob a significant chuck of the total capacity of your UPS battery run time. To try to help prevent this, some UPS designs will artificially limit the current peaks, but that can sometimes result in larger AC motors not being able to start at all. I had a project to run a refrigeration unit with a 10HP 3PH motor from a UPS for 30 minutes, it required a 25kVA UPS to allow the motor inrush and needed 2 huge battery banks attached to it to overcome the effects of starting that motor on the battery capacity.
 
Jraef said:
There is a phenomenon called the "Peukart effect" in battery use wherein the rapid discharge of high current can cause a marked decrease in the total Amp-Hour capacity of the battery. So if starting an AC motor across-the-line, the starting current of the motor will rob a significant chuck of the total capacity of your UPS battery run time. To try to help prevent this, some UPS designs will artificially limit the current peaks, but that can sometimes result in larger AC motors not being able to start at all. I had a project to run a refrigeration unit with a 10HP 3PH motor from a UPS for 30 minutes, it required a 25kVA UPS to allow the motor inrush and needed 2 huge battery banks attached to it to overcome the effects of starting that motor on the battery capacity.
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At what point does a generator make more sense? That seems like a HUGE UPS and battery bank ($$$$$) to run a refer compressor. Could the process really not tolerate the downtime necessary to allow a genny to start? This seems like a special circumstance; I'm curious. I've seen several UPS systems this large in the Entertainment industry, usually to seamlessly back up large stage automation effects that have to be able to fail safe (usually gags with performers on them, or near audience members).


SceneryDriver
 
Usually the surge of startup will throw most UPS’s into alarm (unless they are very large) I have had several different customers that would have issues when drink machines would be plugged into the wrong receptacles. Some types of printers will also play havoc, they have a heater that keeps the ink warm, and they draw 10-15 amps for a few seconds.
 
SceneryDriver said:
At what point does a generator make more sense? That seems like a HUGE UPS and battery bank ($$$$$) to run a refer compressor. Could the process really not tolerate the downtime necessary to allow a genny to start? This seems like a special circumstance; I'm curious. I've seen several UPS systems this large in the Entertainment industry, usually to seamlessly back up large stage automation effects that have to be able to fail safe (usually gags with performers on them, or near audience members).


SceneryDriver
Click to expand...
This was a military application for a portable battlefield related system that was generator powered, the 30 minutes was to give them time to find and bring in another generator if the first one was destroyed.
 
If a seamless transition is needed, perhaps a flywheel type would work. Did that on a state computer room where they were upgrading the ups, but didn’t trust the existing genset. Hooked up a portable as backup. The flywheel would keep power up long enough for the transition. Payroll for the whole state went through that computer system, so they didn’t want to chance it going down.
 
Jraef said:
This was a military application for a portable battlefield related system that was generator powered, the 30 minutes was to give them time to find and bring in another generator if the first one was destroyed.
Click to expand...

Certainly sounds like a special circumstance to me! :)

My projects rarely have to account for incoming enemy fire, though the average stagehand is almost as rough on gear.


SceneryDriver
 
zbang said:
We get back to the question of how big/many motors and whether they need to be UPS protected or can restart from a generator (which wasn't mentioned by the OP).
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Yo see right through my logic ;). I don't think using UPS would be a good idea in my application. I've got two 5 HP motors, VFD driven, in addition to emergency lighting that needs to be powered from a listed emergenc power source. Emergency generator is probably the better way to go.
 
The VFDs add another dimension since they won't have the starting surge but could have an interaction from UPS inverter to VFD rectifier; probably not but worth thinking about for a minute. (A pure bridge rectifier shouldn't be a problem; Jreaf can tell us for sure.)
 
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