dc electric motor test

[trygw]

I want to test some small (.06-.75 HP) DC motors. I need to test torque, rpm, voltage and current. Can I use another DC motor and a torque cell as a dyno to test the motors I want. If so, what requirements are there of the "load" motor. Should it have more HP than the test motor or less? Does anyone know the specifics of testing a motor this way. Any information I could get would be helpful.

Tryg Waterhouse
Hypro Corporation
tryg.waterhouse@hypropumps.com

 

[MikeHalloran]

Most of the complexity and cost of a torque cell is associated with getting a strain gage signal off of a rotating sensor to a stationary observer.

Using a torque cell is a silly way to test a motor, unless you've already got one on hand. Using another motor as a generator and feeding the generated electricity into a resistor is nearly as silly, even if you have all the parts lying around already, 'free'.

All you need to make a basic dynamometer is a controllable brake, and a means of measuring the torque required to prevent the brake from spinning, e.g. a stationary torque sensor, or a beam and a force sensor.

If your time is worth anything at all, you're better off calling Magtrol, Buffalo NY. They can sell you a nice magnetic particle brake, or a whole dynamometer, already set up to test small motors.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[aolalde]

trygw:

For the size of your motors (0.06 to .75 HP), you can manufacture a very cheap dynamometer with a commercial single groove pulley, a spring scale and a rope.

You need the motor bolted on a base, the pulley is secured in the shaft with a proper key, and the pitch diameter must be measured. The scale hangs aligned with the vertical line of the rope (attached to the scale hook) tangential to the pulley. Then two or three turns of rope (3/8” dia.) are wound loose around the pulley. The rotation should be selected such that the friction force reaction pulls the rope.
The loose end of the rope is tightening gradually until the full load torque is developed.
The motor power is dissipated as heat in the pulley and rope so the test is limited to a few minutes especially for the ¾ HP motors.
The motor torque is the product of the scale force (weight) and the pulley pitch radius.

As an example a 0.75 HP, 1750 rpm motor will develop:
Tfl = 5252*0.75/ 1750 = 2.25 Lb*Ft

With a 6” pitch dia pulley (3” rad = 0.25 Ft) the tension in the rope is:
F = 2.25/.25 = 9 Lbf

 

[blacksea]

You may design load simulation systems by regulated brake (Huco)and torquemeter (Futek, Himmelstein).
The thermal model based method of motor SOA testing maybe suggested also. This method was designed by R.H.Welch Jr., well known motor designed and expert. You may contact him directly: (rhwelch@stthomas.edu).