Difference in FLA at 50Hz & 60Hz 2

[Reg Varney]

Scenario:

A single phase Bluffton/Franklin motor, 2.25kW with start capacitor on the motor (no run capacitor) designed for 50/60Hz running:
[ul]
[li]FLA of 12.4 amps at 230v, 60Hz,[/li]
[li]FLA of ???? amps at 230v, 50Hz?[/li]
[/ul]

The same single phase scenario with no load bench test is as follows:
[ul]
[li]230v 60Hz NLA = Expected 6.0 - 8.0 amps[/li]
[li]230v 50Hz NLA = Expected ??? amps[/li]
[/ul]

Can anybody advise me what I should expect for the above missing data?

Thanks for your time

 

[itsmoked]

Suggest you give this a read:

faq237-1224

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Reg Varney]

Thanks Keith,

I did find that article but couldn't get the information that I'm looking for from it.
Is it that I can't interpret the information in it, and apply it to my question?
In fact, that post was what led me to create my own for the very specific question that I have.

 

[LionelHutz]

It would be name plated with both ratings or there would be a datasheet with both ratings if it could be used on both frequencies.

I expect the current will be higher. No way to know how much though.

 

[petronila]

Reg Varney

Whenever you plan a frequency change, my suggestion is to pay special attention to the load. Just note when changing the frequency from 50 to 60 Hz the operational speed increases and the load in the motor also increases. Fan and pump loads vary by the cube of the speed.

Best Regards

Petronila

 

[waross]

FLA of ???? amps at 230v, 50Hz?

Maybe this should be:
FLA of 12.4 Amp at ???? Volts, 50 Hz.
Motor maximum rated current is based on the I²R heating of the windings.
It is basically the same regardless of the frequency.
Voltage: When a motor supply is changed from 60 Hz to 50 Hz there is a danger of magnetic saturation.
When the frequency is changed from 60 Hz to 50 Hz, the voltage is lowered in the ratio of 50Hz/60Hz.
So your chart becomes:
FLA of 12.4 amps at 230v, 60Hz,
FLA of 12.4 amps at 192v, 50Hz?
Note: The HP drops in the same ratio.
What is wrong with this statement?
Heating; The skin effect is greater at 60 Hz and the effective AC resistance will be higher, hence higher heating at 60 Hz.
Cooling; The fan is running slower at 50 Hz and so the cooling is less at 50 Hz.
Both these effects are slight and are offsetting.
I can't remember seeing a dual frequency motor with a different current rating at 50 Hz vs 60 Hz.
What does the difference mean?
A few months taken off a possible 20 years lifetime of the motor,
IF
The motor is operated at Max rated HP in max rated ambient.
Other opinions may differ.
No load current: This is mostly magnetizing current, limited by the impedance of the motor winding.
The impedance of the winding is dominated by the inductive reactance. At lower frequencies, the inductive reactance is less which would imply greater current.
However at lower frequencies the current will be less.
These effects are offsetting in the same ratio.
With some motor designs there may be a noticeable increase in the no load current at 50 Hz, vs 60 Hz.
With some motor designs the difference may be so slight as to be hard to measure.
Opinions may vary.

BUT
Many single phase 60 Hz motors are not suitable for use on 50 Hz due to the setting of the centrifugal switch.
If the name plate does not give 50 Hz ratings on a single phase capacitor start motor, be vary of 50 Hz operation.
If a 60 Hz single phase capacitor motor must be operated on 50 Hz either check the centrifugal switch for reliable operation or used an external electronic starting switch rated for 50 Hz.
Opinions may vary.

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