How to Brake Single Phase Motor


Thread Starter


My application is a single phase 5HP motor on a 1947 DeWalt, model GE, 16" radial arm saw - this info for any tool guys :).

The motor spins freely for 2.5 minutes after removal of power. For convenience only, I'd like to stop it in 5-10 sec.

I have tried DC injection, using up to 24V @ 20A (the limit of my available DC power) with limited effectiveness. It works quite well when the RPM is very low, but it takes a while to get down from 3450.

I apologize if I missed this topic in my search of posts. It seems I scanned several thousand but could not find anything specific. There's lots of info for doing this with 3Ph and VFDs, but alas, I have neither. If someone wouldn't mind directing me to a thread, I'd be most appreciative.
ET12K... Use Control.Com's "Search The Site" Box.

For example, type in +Motor +Brake , and you will find over 200 threads, including several on DeWalt!

Phil Corso

Curt Wuollet

Many of these schemes for single phase motors charge a large capacitor when running and dump it into the motor (after disconnecting the power) to stop. That way you have the type of current that it takes to brake the large inertia. You can dump in quite a bit because it's for a short time. The braking gets less effective as the speed gets lower. You don't want to stop too fast or the blade will unscrew the blade nut, unless it's a diamond arbor or some such.

I would expect most of these are designed empirically as there are a lot of variables. Some playing around with a bridge rectifier, resistors to limit the charge and discharge current and a fairly large capacitor would probably get you what you want. Make sure your switching can handle it. I work in a place with a lot of saws, I can check what they are doing, these are mostly fairly recent and they stop pretty fast per OSHA.

Thank you Mr. Wuollet.

I really like the concept of using caps. My basic problem is not knowing how to determine component 'sizes'. If I had a large supply of different caps, I'd test to determine. For me though, I'd have to buy the first cap, and when that didn't work, order another one, and so on. I could get lucky or it could get expensive quickly.

Guessing, I would say I could compute the energy input during no load conditions, then determine a cap with equal energy plus some overhead. I haven't a clue for figuring a current-limiting resistor as I have no idea how much current it will take.

Though an engineer, I am not of the electrical type, and I know enough to do a lot of things in a brute force manner. However, I am always in search of the elegant solution!
Thank you Mr. Corso.

Actually started that way. Scanned a very large number of posts on this forum. Took your suggestion and did it again. I did find some additional information which was very helpful and insightful, but still not quite enough for my very limited electrical design background.

Thank you very much for the kind offer to render assistance. I shall contact you as suggested.