dc motor speed control

Hey Guys,

This might be a dumb question but I am in need of controlling a dc motor that draws 50 amps at 36 volt max. Does anyone know of a controller I might build. It need to be as cheap as possible.
Thanks much
Jim Cav

Jim,
That depends on your definition of as cheap as possible. You can probably buy a cheap DC drive for the cost of parts and labor to build the thing. Check into the Woods brand, possibly even do a Google search on DC controls and see what pops up. There are many out there with varying degrees of sophistication that obviously affect the price.

i did that there does not seen to be a standard type that can handle the current

Jim

You didn't say what input voltage you had available. There are PWM controllers available which operate from a 36 volt battery supply. Golf cart or battery powered fork lift controllers are this type.

If you need it to operate from AC, you probably won't find a single phase input drive which has a 50 Amp capacity. My suggestion would be to buy a 3 phase, 50 Amp DC drive that has the capability to have separate power and control inputs. If you were to run the power section at line voltage the DC output would have a very poor form factor. Adding an inductor to the output will help but a better solution is to put in a 3 phase step down transformer to give you about 40 volts input to the power section of the drive. This transformer must not have any phase shift between the primary and secondary. The Armature Feedback Voltage to the drive should also be re-scaled because of the low motor voltage. If you are not experienced doing this type of conversions, you should get a drives integrator to do it. It will not be cheap. A cheaper solution would be to by a new DC motor that can run from a standard drive.

You leave an awful lot of unknowns.
What is load?
How much speed control do you want
What is power source
DO you need to reverse
what kind motor series shunt compound (short vs long?)

At simplest 3 good size automotive batteries may work wih just a relay. Gonna be light show at start of course.

Next use relays so to start at 12 VDC then 24 VDC then 36 VDC. IF shunt or compound a reheostat for field control.

Look into the electric vehicle pages and forklift spare parts outfit in your town for parts.

Dan Bentler