AC to DC

I used to own a Dremel speed control box. It was for the old Dremel tools which didn't have speed control on them. This thing would speed-control any little motor. I used it on my 11,000 rpm 4" grinder to slow it down to 5,000 rpm to use a big cup stone on it, for example.

It won't take very long to try it! :-)

Grant Erw> Several days ago I bought a Bodine gearmotor on Ebay to use for a power feed on

Brush type and PM do *not* make an AC motor. Brush type plus a field coil makes a universal motor (since the polarity of the field will swap with the polarity of the feed through the brushes) -- which can run on AC or DC. Are you *sure* that it has a permanent magnet field? If it does, it can't run from AC (unless a bridge rectifier has been included in the housing).

If it is brush type and field coil, it might work on the DC controller, if it is a shunt wound motor. If it is series wound, I think that the controller could get very confused. :-)

If it is an induction motor (AC only, no brushes), the Variac will only reduce the torque, not the speed, which will be locked to the power line frequency until it develops so little torque that it stalls.

I think that a shunt wound universal is more likely for a gearmotor, but I could be wrong.

So -- a bit more detail from re-examination of the motor would help.

Good Luck, DoN.

And it won't take very long to smoke it either...

If it's a universal AC motor, it will work. Induction motors require a VFD.

OP sez brushes and magnets, so it's probably safe to run on DC.

Tim

-- "That's for the courts to decide." - Homer Simpson Website @

Good point, DoN- it was described as a PM motor but then was also described as a DC motor. I'm not a motor expert but I get your point.Another thing is that this motor has an oil-filled running capiacitor which may get some sort of digestive upset on DC? If I got a Dremel tool controller (as has been suggested) does it have the feedback detection mechanism that tells the controller that it isn't running at the speed that the dial position indicates? Engineman1

Brush type plus PM = DC motor. If it has those it is not an AC motor. You might need to take off an end and look inside.

Tell us what you see.

Ted

The oil-filled capacitor suggests that it is a capacitor-run motor, which is *purely* AC. Possibly even a hysteresis-synchronous motor, which is noted for having very *stable* speed, and it would fight you all the way as you tried to vary the speed.

In any case, it would just let out the magic smoke if you tried to run it on DC. :-)

I would suggest that as a single-phase motor, it is singularly unsuited for speed control. If it were a three-phase motor, you could control it with a VFD, and there have been some nice new Mitsubishi units on eBay for 1/8 HP motors -- which sound about the range that you have. But yours are *not* three-phase (as evidenced by the run capacitor), so it is highly unlikely that you can control the speed.

But if it has a run capacitor -- why does it have brushes?

I suspect not -- unless it is a more complex Dremel speed controller than those which I have seen.

Can you take the motor's part number and go onto the web to find Bodine's web site, and see whether you can find the specs for the motor? A quick check with nslookup shows that

exists, and it might have the information. you need. Since you have the motors, and thus presumably the model numbers, I'll let you dig through their site to see if it is covered. :-)

You may be better off seeing if you can return the motors to the surplus place, as being incorrectly described. (They might even just opt to let you keep them, and refund your money, if the price was low enough.

Good Luck, DoN.

Not very much speed control, unless it is also three phase.

He also says (later in the thread) that it has an oil-filled capacitor connected to it, which suggests that it is a capacitor-run induction motor, not a universal. (But if so -- why the brushes, if they

*really* are there.

Enjoy, DoN.

Add in the oil-filled capacitor mentioned in a later part of the thread, and you have total confusion. :-)

Amen!

Enjoy, DoN.

Is it possible that someone, manufacturer or other, wanted some filtering on the incoming DC? Stranger things have happened.

Really, it needs looking inside.

Ted

Centrifugal start switch?

I assumed from the description that it was a brush type PM motor but looking at it closer I see it has a wound field. There are no brushes so it must be an induction motor.It has an oil filled capacitor with a pressure sensor which shuts the motor off if the oil gets too hot. The cap must function as a current limiting device in case the motor is stalled. 3 wires go into it. I contacted the vendor and he admitted his mistake and said he'd send me a DC motor, also I can keep the one I have now. Anybody want it? Engineman1

ME :-)

Naturally

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Why go to the extra expense of an oil-filled capacitor unless it is in the circuit full time?

Enjoy, DoN.