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UPS for motor load 1

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thekman

Electrical
Sep 3, 2009
90
2HP hyd pump motor 230v 1phase. FLA 10A, reported inrush 53-63A. Customer wants a UPS on it - I found a 4kVA inverter rated for 12kVA surge for 20s. The ~14kVA inrush lasts only a second or so. I've been going back and forth with the mfr about it, he thinks it will burn out 'prematurely' and (obviously) wants me to get next larger UPS but it's 2X cost. I don't know exactly what 'prematurely' means here, a month or 14 years instead of 15. Am I wrong in thinking that the 12kVA/20s surge rated can handle 14kVA for 1s? 5%? My feeling is that its life may be reduced but insignificantly. I do not have the option of adding a VFD or a softstarter. I haven't looked at a SS contactor, but wouldn't that reduce the inrush a little?
 
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Just sounds like a bad idea all round to be honest. Motors and UPS are never happy bedfellows. Out of interest, what were the reasons why the VFD isn't an option? A 1.5kW motor and matching VFD isn't all that expensive, and would be a lot friendlier to the UPS.
 
Mashup = UPS + DOL motor I take it.
Worst part is they are 1ph motors, so they basically need new units.
Luckily they're just around the corner...where the Atlantic ocean and Africa are the corner.... in the middle east.
 
ScottyUK, my first response was to put VFDs in, all I heard was 'they don't want to'. I don't think they have much of a choice.
 
contrast the price of a larger UPS with the price of a VFD and 3 ph motor and generally less problems.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
ScottyUK is right, it is generally just a bad idea.

Assuming that it does have the surge capability, and can operate such that it can provide that amount of current, there's also whatever inbuilt protection might be present to detect some sort of fault in connected equipment and might shut down the output. As you've found, the way to get around it is to oversize it, but that's obviously expensive.

There's also the consideration that provision of a UPS is generally done because the load needs to keep running in arduous circumstances, not really that useful when the UPS itself won't allow the motor to start, or keeps shutting down on fault conditions. The risk to the UPS really is the capability of the switching stages to be able to handle the heat generated from the much higher current, and for smaller UPS units in this case, the resultant life is probably more of a guess than anything.



EDMS Australia
 
In addition, single phase motors are usually going to have capacitor starting which, when the capacitor is on line from the UPS, will look like a short circuit to the UPS output monitoring circuit, shutting it down on do/dt (delta time /delta current, s steep rise in current in a short time). Surge or no surge capacity, the UPS output is most likely transistor based and will have di/dt protection to avoid blowing the transistors.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
 
I haven't seen AC motors put on UPS.
On the other hand, essential duty drives are DC, put on DC UPS in power plants.

Rompicherla Raghunath
 
Itsmoked said:

Meaning the cheap ones just let the transistors act like fuses?! I had a cheap little UPS for my PC, my daughter plugged in a table fan (because there was a free outlet, not because she wanted the UPS), the transistors popped like little firecrackers.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
 
I did see an uninterruptible power supply for a motor.
Two large rooms full of batteries cells.
The motor was a 10,000 HP motor driving the feed water pump for a nuclear reactor.
The UPS had enough power to keep the motor running long enough for the backup generators to start and come online.
Maybe not applicable in this application. grin


Bill
--------------------
"Why not the best?"
Jimmy Carter
 
Yeah, there are similar inverters for the gas circulators on the AGR family of nuclear plants. Probably overkill for this application. :)
 
Offer then the choice of the larger UPS (with a soft starter) or the current size plus a VFD.
The UPS+VFD will be the much more reliable package.
We had a bunch of small motors on UPS+VFD and it worked very well.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
 
If it were a 3 phase motor and VFD, there’s no need for the UPS, you can just put a battery system on the DC bus of the VFD. Done all the time that way, there are commercial off the shelf battery backups for them.

The problem here is that he has a single phase motor and although there are VFDs for single phase motors, they cannot be used on ones with capacitor starting, which is the vast majority of them.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
 
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