FLA vs input watts

[cppoly]

Looking at an exhaust fan cut sheet.

It has FLA 4.1 amps.

Then input watts at 164.

This makes no sense.

Wouldn't input watts be 115 x 4.1 = 472?

 

[Hv&Lv]

Looking at an exhaust fan cut sheet.

It has FLA 4.1 amps.

Then input watts at 164.

This makes no sense.

Wouldn't input watts be 115 x 4.1 = 472?

Can we see the cut sheet?

 

[wwhitney]

Sounds like you have a low power factor fan. Watts = Volts * Amps * Power Factor.

Cheers, Wayne

 

[cppoly]

Sure, here it is

 

[LarryFine]

Sure, here it is

* FLA (A) 4.1

** Input Watts (W) 164

*FLA is approximate and will vary slightly with the motor.

** Wattage is approximate and may vary between motors.

 

[david luchini]

Sure, here it is

A motor with 50% efficiency and 70% power factor would put FLA at about 4.1A.

 

[cppoly]

A motor with 50% efficiency and 70% power factor would put FLA at about 4.1A.

Thanks.

I think I'm having a hard time with their "input" watts.

Input watts should be on the line side of the motor, which should be FLA x Voltage = 115 x 4.1 = 472 watts

Shouldn't the "Input watts" that they're referring to as 164 really be the "output" watts. Output takes into account efficiency and power factor, right?

 

[wwhitney]

A motor with 50% efficiency and 70% power factor would put FLA at about 4.1A.

Power factor would affect "input watts", but efficiency wouldn't.

Cheers, Wayne

 

[david luchini]

Thanks.

I think I'm having a hard time with their "input" watts.

Input watts should be on the line side of the motor, which should be FLA x Voltage = 115 x 4.1 = 472 watts

Shouldn't the "Input watts" that they're referring to as 164 really be the "output" watts. Output takes into account efficiency and power factor, right?

0.22 HP x 726 = 162 watts

 

[david luchini]

Power factor would affect "input watts", but efficiency wouldn't.

Cheers, Wayne

The motor current will be affected by both efficiency and power factor.

 

[wwhitney]

0.22 HP x 726 = 162 watts

Ah, so as the spec sheet also says 0.22 HP, they have incorrectly labeled "output watts" as "input watts".

Cheers, Wayne

 

[wwhitney]

The motor current will be affected by both efficiency and power factor.

For a fixed output HP, sure. But when the motor current increases due to decreasing efficiency, that increases input watts. When the motor current increases due to decreasing power factor, that doesn't change input watts.

Cheers, Wayne

 

[cppoly]

Ah, so as the spec sheet also says 0.22 HP, they have incorrectly labeled "output watts" as "input watts".

Cheers, Wayne

Just to clarify, am I correct about the input watts being wrong in my original post? It should be output watts, correct?

 

[wwhitney]

Just to clarify, am I correct about the input watts being wrong in my original post? It should be output watts, correct?

If 0.22 HP is the correct output HP, then post #9 shows the output watts is ~160 watts. Is this motor plausibly near 100% electrically efficient?

If so, then 164W could be the input watts, and the power factor at this operating point would be 164/472 = 0.35. If not, then 164 input watts is a typo of one sort or another.

Cheers, Wayne

 

[Hv&Lv]

Ah, so as the spec sheet also says 0.22 HP, they have incorrectly labeled "output watts" as "input watts".

Cheers, Wayne

Imagine that..

 

[Eddie702]

Chances are they plotted the fan curve against the system resistance to come up with CFM static pressure and motor hP. The motor is probably oversized for the load it is driving

 

[JoeStillman]

Just to clarify, am I correct about the input watts being wrong in my original post? It should be output watts, correct?

One man's output is another man's input. Maybe they mean brake HP input to the fan, which is the output from the motor.

 

[petersonra]

Looking at an exhaust fan cut sheet.

It has FLA 4.1 amps.

Then input watts at 164.

This makes no sense.

Wouldn't input watts be 115 x 4.1 = 472?

No. The fan does not run at unity power factor.

115 x 4.1 gives you VA not Watts.