No load current = FLA

[electronext]

does hot rolled sheet stator lamination has something to do why no load current = full load current?

We are testing (no load) several 0.75 4Pole 220V induction motor and we are getting no load current = FLA rating.
The manufacturer told us that this was part of the design since they used hot rolled sheet for stator lamination instead of using cold rolled sheet.

Best Regards

JK

 

[davidbeach]

Amps, just by itself doesn't tell much on a motor. What is the power factor at no load, what is the power factor at full load? Watts at both?

 

[Skogsgurra]

It is also a question of actual voltage vs rated voltage. If the motors contain too little iron, saturation sets in at a certain voltage that is sometimes close to rated voltage. And that increases NLA.

Pole number also has an influence and those little machines are guzzlers anyhow.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[starkopete]

Skogsgurra is correct. I have seen some very low speed motors draw more no load current than full load current.

Thanks

 

[electronext]

the PF = 0.67 (nameplate). we also tested several 0.5Hp 3ph induction motor from the same manufacturer but the no load current was fine, around 20-30% of the FLA.
the motors were rated at 230V (+/-)5%. We measure the actual voltage around 220-222V. By the way, all motors i mentioned were 3phase, 220/380/440V 60hz induction motor.
The manufacturer are pushing that this were part of their hot rolled sheet stator lamination design.

does hot rolled sheet stator lamination has something to do why no load current = full load current?

Thanks,

JK

 

[edison123]

Hot rolled sheets have higher losses as compared to cold rolled sheets IIRR around 3 to 1. That plus poor pf (higher magnetic density) would account for such a high no-load current. 4 pole is not a low speed, so that does not account for such high no-load current. I would also rule out voltage being the cause.

Are these motors running very hot ?

Muthu

http://www.edison.co.in

 

[electronext]

recently we tested the motors using VFD, setting the voltage to its rated voltage but where still getting the same result and the motors are not running very hot.

If hot rolled sheets have higher losses, then why would they use it? I already ask the manufacturer the same question, and still waiting for their reply.

 

[edison123]

Because they are cheaper.

Muthu

http://www.edison.co.in

 

[waross]

I am concerned. If no load current is near FLC then no problem. If no load current equals rated full load current, where is the head room for the increase in current when a load is applied?
Is this a special torque motor used to keep tension on a take-up reel?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Hello Bill!

There was a discussion on induction motors a few years ago.

http://www.eng-tips.com/viewthread.cfm?qid=191338&page=204

There, the Ossanna diagram was mentioned. If your losses in the motor are high, the center of the diagram will be above the horizontal axis and the no-load vector shows that current is actually higher at no load than when load is applied. And then, for really 'bad' motors, is almost identical to FLA.

The explanation is that cos(phi) changes a lot when going from idling to loaded.

This is the reason why motor current isn't a good load indicator.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[edison123]

Bill

I have seen motors with no-load= or > FLC but on load the current does not increase and in some cases load current comes down. The PF comes into play when the motor is loaded.

Muthu

http://www.edison.co.in

 

[electricpete]

I agree for small motors there difference from no-load to full load current can be small, but it's hard to imagine equal or no-load > full load.

Is there a run cap in the motor by chance?

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[electronext]

we are going to test these motors under load and we are hoping that the current will not increase as we applied load.
i will post the result as soon as i get it.

by the way, the motor has no running capacitor. its a squirrel cage induction motor, 3Phase/220V/2.51Amp/0.67PF/1750RPM/60Hz/1.15SF