Speed VS load

[pheel]

Hi everyone,

Were testing a small system at our shop. We had a small powerflex4 drive with a 1.5 HP SEW motor and a gearbox (but no real load).

I didn't really understand but we had 4A at 60HZ, 5A at 30HZ and 4A at 10HZ.

The drive was set to constant torque.

Can someone explain that to me ?

thanks

pheel

 

[jraef]

How are you taking these current measurements, on the VFD display or with a clamp-on ammeter?

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[Marke]

Hello pheel

What voltage is the motor rated at?
Where and how was the current measured?

If you run a motor with constant flux in the gap, you will have constant magnetising current when run at zero load. On small motors, this can easily be over 50% of the rated current of the motor. If the voltage applied on the motor terminals is high, the magnetizing current will be much higher.
You need to be careful with metering as many of the electronic meters will read high on the output of inverters due to the switching current spikes. You need to use a true RMS meter to give you the correct answers.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[jraef]

Well Marke, I was going to get there when he answered me

 

[Skogsgurra]

You both spoiled my fun ;-)


Gunnar Englund

http://www.gke.org

 

[pheel]

sorry i guess I could have written more information.

I was reading the amp on the drive display. This was a 230V motor, DC bus was about 280V.

The motor is rated 5.75A. Is it correct to think without a load, most of the current is reactive and by putting a load, this current will then be an active current ? So if I put a load, then value of current won't change a lot ?

My main concern was the fact the current increased while decreasing the HZ from 60 to 30 but re-increasing while approaching 10HZ.

thanks

pheel