VFD power calculation

rQx

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Hi,

I have a VFD from wich I cannot read the power output. However I can read the current and voltage.
Am I correct to say that this formula will give me the power consumption of my VFD? Or do I need something more?

P=√3*U*I

/Tim
 
In any case, this formula will give you the Apparent Power in VA (VoltAmper) but not the Active Power in W (Watt) which is the one that really consumes energy
 
Tim, hi. You can use V x A x 1.73 x PF / 1000 and you will get KW. However one must know the power factor. Usually it is around .8 or .9 lagging if it is a good power factor. Hope this helps.
 
saultgeorge said:
Tim, hi. You can use V x A x 1.73 x PF / 1000 and you will get KW. However one must know the power factor. Usually it is around .8 or .9 lagging if it is a good power factor. Hope this helps.
Click to expand...

.8 or .9 if working at nominal power but .1 or less if running idle without load
 
Thanks for all the help. It then seems impossible to get the power out of this drive, it has a register for power on the modbus side but it doesn't seem to work. I'll try to investigate some more about why the modbus register don't work
 
rQx said:
Thanks for all the help. It then seems impossible to get the power out of this drive, it has a register for power on the modbus side but it doesn't seem to work. I'll try to investigate some more about why the modbus register don't work
Click to expand...

What is the problem with that register, always contains zero?
 
It is a Parker AC10. It has been a while since I played with it so I don't know the exact reason why I concluded that it didn't work. I will try to test on friday what results I got, maybe they have updated the firmware also
 
Sometimes the power output is provided as a percentage of the rated motor power that you enter into the drive.

I have done what you're doing (using volts, amps and pf) with a VSD before and the results were +- 10% at best. That was with Schneider ATV61.

That calc also doesn't take into account power consumed by the drive itself.
 
I want to meassure the active power, the one I pay for. We will run a pump with a PID control at diffrent pressure and want to know how mush power it consumes at diffrent settings.
 
The register that say "read integer power value" returns zero when the motor is running. But then again I maybe dont fully understand what the register should return or mean. There is also "percentage of output torque" that also return zerio. Maybe these values are nor active when I run v/hz
 
For "read integer power value" I understand the integer part of the power, maybe in kW? maybe there is another register with the fractional part.

In your tests the motor runs with load or runs free without load?

If it turns free the active power will be very low, close to zero.
 

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