Drag on Universal Motor.

[Andre]

I am taking a break from my lathe build, and am making a endmill end touch up grinder and slitting saw sharpener. I am currently using a Hamilton beach universal motor. But universal motors require drag for safe operation. It is a double ended motor, one side has a grinding wheel, and the other will be used to impart drag.
Does anybody know of a way to impart drag on the spindle? I was thinking of a hamster wheel fan, but I thought I'd ask here first.

Thank you!

 

[Hawkeye]

Brush motors usually only need a continuous load if they are series-connected. Without a load, these will "accelerate to destruction".

Series-connected means that the field coils is in series with the armature. Shunt-connected will have the field in parallel with the armature.

 

[David S]

Andre what was the ham beach motor out of?

David

 

[John Hasler]

Brush motors usually only need a continuous load if they are series-connected. Without a load, these will "accelerate to destruction".

Series-connected means that the field coils is in series with the armature. Shunt-connected will have the field in parallel with the armature.

"Universal" motors are series wound. That's why they can run on either AC or DC and are, therefor, "universal". However, the high windage and friction losses in small ones limit their speed. A fan is still a good idea, though. While the motor probably won't blow up run no load it was designed to always have a load.

 

[Andre]

"Universal" motors are series wound. That's why they can run on either AC or DC and are, therefor, "universal". However, the high windage and friction losses in small ones limit their speed. A fan is still a good idea, though. While the motor probably won't blow up run no load it was designed to always have a load.

Yes....it will blow up. With no load (after rebuilding) I let it go running. It didn't stop accelerating in 50 seconds, reaching near 5-10k RPM (No tach, but that's where it seems it was running) , I don't want to push it further.

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Andre what was the ham beach motor out of?

David

No clue, most likely a fan but why would it have two shaft ends? They made motors for a lot of things, this one could've been from a watchmakers lathe as a lot of people use them for little watchmakers tools.

I got it with a bunch of small motors from a friend, so it's a mystery from where it was from.

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Brush motors usually only need a continuous load if they are series-connected. Without a load, these will "accelerate to destruction".

Series-connected means that the field coils is in series with the armature. Shunt-connected will have the field in parallel with the armature.

Well, there is no continuous load with a grinding wheel. Not grinding when checking endmill grind or flipping the endmill over.

I tested the thing yesterday, worked very well, but was way too fast so I had to kinda hold the other end of the shaft to keep it from accelerating more. Thing has a little torque.

 

[kd4gij]

Add a speed control and you won't need to put a load on it. A foot pedale from an old sewing machine would work great for your app.

 

[Andre]

Add a speed control and you won't need to put a load on it. A foot pedale from an old sewing machine would work great for your app.

Universal motors need a load no matter what voltage.

 

[David S]

Universal motors need a load no matter what voltage.

I am not quite sure where you received this information. As a motor designer for Black & Decker for years I certainly am not aware of that. Most motors at least have and internal fan of sorts. Consider for example a router or a die grinder with no gears to act as a load. These are examples of universal motors and can run no-load all day around 20,000 to 30,000 rpm depending on model.

I can run the universal motor on my Unimate lathe with no belts connected.

I would however think that your motor may be way too fast for a grinding wheel of decent size, and if you slow it down via a speed control it may not have much torque. All this without know exactly the type of motor you have. Does it have a nameplate?

David

 

[Andre]

I am not quite sure where you received this information. As a motor designer for Black & Decker for years I certainly am not aware of that. Most motors at least have and internal fan of sorts. Consider for example a router or a die grinder with no gears to act as a load. These are examples of universal motors and can run no-load all day around 20,000 to 30,000 rpm depending on model.

I can run the universal motor on my Unimate lathe with no belts connected.

I would however think that your motor may be way too fast for a grinding wheel of decent size, and if you slow it down via a speed control it may not have much torque. All this without know exactly the type of motor you have. Does it have a nameplate?

David

That's true.

I started a thread on...well....another forum. *couch*
They told me it needs a load to run safely, as does Wikipedia.

The grinding wheel is a 2" diamater wheel with a max RPM of 6k rpm I believe.

The nameplate just says Hamilton Beach, model number, and voltage.

Sorry I do not have it with me, visiting somebody in home right now but ill get the info to you ASAP.

 

[kd4gij]

I have a universal motor with small cone shaped felt polishing wheels on bouth ends It has a speed control on off switch. It runs with no load untill you are polishing something somthing.It is over 20 years old and hasn't blown up yet. It sounds like your motor is going to be way to high of RPM for that wheel.