Direct connect fan motor overload ratings?
Direct connect fan motor overload ratings?
(OP)
Is there a Code or Standard that allows motors that move air across itself to be overloaded more than the service factor? An example is a fin/fan motor that is rated at 3.2 amps full load (575Vac)operating at 3.8amps. This is an ~19% increase.
Thanks in advance for your comments/references.
Thanks in advance for your comments/references.





RE: Direct connect fan motor overload ratings?
That's a substantial overload.
It all comes down to the motor temperature. If it is somehow below the maximum allowed you will be OK. This could be by the motor running in a cold environment or thru massive air flow. Or thru an overbuilt or lucky build.
If you can measure the temperature and find it acceptable then you're good to go.
If it is over temperature then you are rapidly carving running hours off.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Direct connect fan motor overload ratings?
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: Direct connect fan motor overload ratings?
Are the Temp Rise numbers printed on the nameplate referring to some random unspecified internal location or the case temperature? Seems since the rest of the plate info seems to be for the guy wrenching the motor into its location that putting a rise number on that cannot be measured nor even guessed about, would be pretty useless to me.
I expected them to refer to the motor's external case after thermal equilibrium is reached and excluding non normal conditions like having high velocity air blown on the case.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Direct connect fan motor overload ratings?
RE: Direct connect fan motor overload ratings?
Motor temperature information link
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Direct connect fan motor overload ratings?
Thanks for the article Jeff. Interesting read. I may try that sometime since I have an ohmmeter that reads way low.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Direct connect fan motor overload ratings?
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Direct connect fan motor overload ratings?
When I was testing motors "rise by resistance" was always used. Even when we had implanted T/C's in the windings.
It is pretty tricky though. The motor has to sit in the same, well know, temperature (25C) for at least a day, preferable more. Cold esistance is taken. Then the motor is run at load until it is stable (usually a few hrs). Then disconnected. And then hot resistance taken immediately, with a millohmeter, using Kelvin leads.
Immediately, means, right now! Gotta be quick, as the resistance will start changing the instant power & load is removed. And invalidate your measurements.
Ed
RE: Direct connect fan motor overload ratings?
Noted how? External case temp?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Direct connect fan motor overload ratings?
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Direct connect fan motor overload ratings?
We attached T/C's to the end turns and on the frame, Both PE and OP ends. they in turn ran into a chart recorder. Stable was defined as flat lined for 1 hr.
there was also a T/C hanging loose, in free air, to track the ambient and make sure that it hadn't effected the heat run.
Ed
RE: Direct connect fan motor overload ratings?
Can you comment on any number you saw as the Tdiff between your generally calculated winding temp verse the outer case temps?
A typical difference? It would be nice to have some rough idea for someone stuck out in the trenches trying to make a call.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Direct connect fan motor overload ratings?
I'ts been waaay too long since I've seen any numbers. I'm not really sure there is any.
There's too many varibles involved. Hp., Frame size, Frame materials, TENV, TEFC, and .......
Ed
RE: Direct connect fan motor overload ratings?
I know this is not answering the original question but if the motor is pulling too much current then you should protect it, whether it is getting too hot or not.
or have I missed something somehwere?
RE: Direct connect fan motor overload ratings?