Using a DC motor to provide load on another motor? 2

[trygw]

Im a new test engineer and I've been assigned the task of creating a small motor test stand. I've been told to use a DC motor with varible drive to provide a controlable load to the motors we want to test. Has anyone ever heard of this? What happens if you force a DC motor to spin the opposite direction that the voltage source is trying to make it spin? I assume the motor will start to heat up and potentially burn out if run like this for too long. I am really not an expert on motors at all and any info about using a DC motor in this way would be very helpful.

Tryg Waterhouse
Hypro Corporation
New Brighton, MN

 

[Skogsgurra]

Hi trygw,

This is done all the time. Test stands for car and truck motors do it. And all kind of dynamometers use that technique.

The motor (brake) simply feeds the power back to the grid (you may even get paid by the utility, if you are lucky).

The thyristor rectifier works against its nature, so to speak, and outputs a negative voltage while the current flows in the normal direction. The normal mode of operation is to let the motor (the tested one) determine speed and have the brake run current controlled.

Google for "four quadrant" and "test stand" it should give you lots of information.

I need to add that modern test stands do not use DC motors and thyristor rectifiers anymore. The vector controlled frequency inverters are so good today that they have taken over the test stand market almost 100 percent. They also work "against their nature" and convert energy from the brake back to DC (in the DC link) and then (via a four quadrant mains rectifier, IGBT or thyristor) back to 50 or 60 Hz that is delivered to the grid. It is very efficient and convenient. And you do not need to burn power in big resistor banks.