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help building a dc motor controller Answered

I am trying to build a simple dc motor controller.  The motor is from a treadmill rated at 90v dc, 21 amps.  I have a PWM (rated at a 90 v dc, capable of controlling 0.01-1000w max 15a)  and a bridge rectifier model mp3510s (35 amp single phase).  I can get the dc out of the rectifier at 106 volts.  How can I drop this to 90v  safely to make it work?  I have just enough electrical knowledge to be dangerous, and I know this!  any suggestions?     The end result will be to power a 12 inch metal lathe


Don't worry about it. You'll find that the duty cycle on the controller won't go to 100%, and the number you're reading off the recifier isn't the true RMS value of the voltage.

Just to see if I could regulate the output from the rectifier with the PWM I placed my meter across the PWM output. When I plugged it up the 250v 15 amp fuse blew. I was able to run it with the 12 volt charger from my Paslode nail gun. I have a small transformer that will put out 44 volts. I was going to run this through the rectifier just to see what I had, but the fuse on the PWM blew first.

I have even thought of rewinding my own transformer to near 90v.

NO !
NEVER short a supply with an Ammeter !!!! You've probably ruined at least the meter.

You are talking 12 inch bed not 12 inch chuck?

No it is an older Atlas 12 swing with a 48 inch bed metal lathe. I have seen many people run these lathes on the same type motor I have. They are using controllers from the treadmill or an aftermarket. I am trying to do this on the cheap and trying to learn a little along the way.

If the motor is a 21A motor it will try to draw 21A if you try to feed it 90VDC. If the PWM outputs at 106VDC max it can be turned down to the 90VDC you need but it won't support the amperage. It would be way too easy to burn out the motor with what you have. If you still have the treadmill then get the controller from it or buy a controller rated for that motor.

I think that motor would be better suited for a wood lathe not metal. I don't think it has the horse power to turn metal.

Actually there are many people who use these motors to run these lathes. I just don't want to spend $200 for a controller if I don't have to. The controller for this treadmill was integrated into a large board and I could not make sense of it. I only paid $25 for the treadmill since the walking board was broken. Original price $700-800

No, it will only draw 21A, if its loaded that much that it NEEDS 21A.

His 106V is on unloaded rectifier which is likely to be distorted by the meter.