Test motors under load
Test motors under load
(OP)
In our rewind shop we want to test repaired motors (up to 60 HP) under load.
It seems that such dynamo-meters from various manufacturers are extremely expensive and we would try to do something ourselves using brakes or generator or motor etc...
Is there any idea how to do it?
Probably, someone has already done it.
Any help will be valuable.
It seems that such dynamo-meters from various manufacturers are extremely expensive and we would try to do something ourselves using brakes or generator or motor etc...
Is there any idea how to do it?
Probably, someone has already done it.
Any help will be valuable.





RE: Test motors under load
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Test motors under load
I'm not familiar enough with the VFD, can you explain in more detail?
RE: Test motors under load
You should google for VFD.
There is an elite version of VFDs that can return energy to the power supply from an over driven motor. You can use one of these and a motor to load another motor for testing.
After you have looked up VFDs and educated yourself on them a bit come back and check these threads relating to using VFDs for test setups. Don't bother looking at them until you understand VFDs a little better though.
thread237-344979: 3-Phase Motor Drive, Induction Generator, Controlling Torque?
thread237-173814: VFD control method for back to back loading
thread237-137071: invertter motor load test stand
thread237-261800: Dynamometer in thinking stage- VFD or DC drive
thread237-169558: dynamometric testing for AC& DC electric motors
Keith Cress
kcress - http://www.flaminsystems.com
RE: Test motors under load
We used to use a 25hp motor to load a 10hp motor for testing. We basically use one of our soft-starters with the SCR connections reconfigured to create a current controlled rectifier.
We have since switched to using VFD's to load the motor since we now have larger test motors. I was hoping that the VFD would create a load capable of acting at a constant torque but that never worked well. So, I set them up so the VFD is energized at 60Hz once the motor is running and then a pot lowers the VFD operating frequency which puts a load the other motor.
RE: Test motors under load
Thanks for your suggestion.
That was my first thought because it seems to me, that's the simplest.
I have some experiance in use of DC current for braking of AC motors.
Can you say something about the calibration ie. how to determine braking torque/power knowing the voltage and current of the DC supply?
RE: Test motors under load
I suppose if you instrumented it then you might be able to correlate the DC current to a torque but once you setup the instrumentation you might as well just keep using it.
RE: Test motors under load
RE: Test motors under load
www.KilroyWasHere<dot>com
RE: Test motors under load
How do the prices of basic VFDs compare with Regen VFDs?
Either way, if you are going to do many hours of testing, the energy savings will add up in your favor.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Test motors under load
We did a couple high performance 200KW vfd's with high speed fiber optic link between for A Nasa shuttle project once; we could sync down to the PWM pulses between the two drives. The motor was actually a redundant motor being proposed for the hydraulics pump on the shuttle; pancake style: 180 degrees was one complete motor, other 180 degrees the 2nd one for backup. we could use one as a motor, other as generator load to fully test the whole capabilities. We even synced the PWM pulses to not have any extra shaking or eddy current losses or anything. These same drives are only about 30% more expensive than generic ones, so the moral is buy good like Waross suggested.
Keeping in mind that the motor under test will be taking MORE power than the generator puts back on the DC link, there is no need for regen drive - just a normal old DB circuit - in only one of the 2 drives - for stopping fast.
www.KilroyWasHere<dot>com
RE: Test motors under load
Keith Cress
kcress - http://www.flaminsystems.com
RE: Test motors under load
The question is do you want to be locked to running the motor under test on a VFD or not? We setup our regen drives as loads so we can apply a load to whatever is being tested.
RE: Test motors under load
Best way by far is the regen VFD.
For it to be accurate you MUST perform the autotuning function, otherwised you will not be able to trust the torque and power values.
The poor man's way, but still very accurate:
Build a pony brake. (Search "pony brake dynometer" on google, and look at the images.)
Long arm style, use ~ 20" flat or multiple grooved pulley with an assortment of tapper lock bushings.
Oil soaked maple blocks for the friction parts.
Use a digital scale / load sensor.
Use a prox sensor on the shaft or pulley for speed pulse.
Get data aquisition hardware for your laptop from DATAQ.com so you can trend rpm, amperage, and the scale output all at the same time.
Viola - You have a very accurate dynometer for about 10% of the cost of a 60hp regenative VFD. The only caveot is that you have to manually tighten the screws.
RE: Test motors under load