Reversing rotation on a universal AC/DC motor

I have a Carter/Regent 1 hp AC/DC Universal motor with a Minarik DC drive (23001A). The drive puts out 0 to 75 VDC. The current flows thru the armature then thru the field to form a complete circuit such that the armature and the field are in series. In order to reverse this motor the armature leads have to be reversed so that current starts at the opposite brush and then procedes in series thru the armature and on thru the field. This particular drive has a polarity reversing switch. However simply reversing the polarity seems to make no difference to the motor. I runs in the same direction and has the same variable speed function regardless of polarity. I'm setting this motor up as a spindle drive and will use a contactor wired tol create the proper circuits to reverse the motor. So I have two questions. First why does it not matter what the polarity is? Second, is there any advantage or disadvantage to using one or the other polarity?

Thanks,
Rick

If you switch JUST the armature, it should reverse correctly.

Are you sure you are doing that?

Are there any other windings, interpoles, etc, that may be counteracting what you do?

JTS thats exactly what I'm doing. I can easily reverse the rotation by switching the armature wires. The contactor wiring is no big deal. The motor reverses just fine when the armature wires are switched properly. The drive can reverse the polarity from plus/minus to minus/plus. That's just the way a normal DC motor is reversed. This universal motor will run and not change rotation unless you change the wiring to the Reverse configuration. The Question is why does it run in the same direction when you change the DC polarity. The second question is which polarity is better to use. If DC current travels thru the armature then thru the windings is there any more or less resistance or impedence or other ill effect then if the DC current direction is thru the windings then thru the armature. OR is it the nature of an AC/DC universal to just run no matter how you feed it?

Sounds like this motor is series-wound.

The key with motors like this is, you reverse the current direction in *either* the
armature windings, *or* the field windings, to get them to reverse rotation.

If you change the polarity of the current driving through both of them, buy simply
feeding the series connection of field and armature with (-) instead of (+) then you've
reversed *both* of the windings, the sense is still the same and it won't rotate
in the other direction.

It doesn't matter in most cases which you reverse, field or armature. If you put
a separate reversing switch in there, don't operate it when the motor's running
as you're likely to damage the drive. Be sure it's stopped with no current
flowing before doing that.

Thanks Jim. I just had my ahah moment!

That's the reason why it will run on AC

Frank

You have rotating magnetic fields with the armature and the field. Changing the rotation of either field or armature will change motor rotation, one or the other but not both. If you change the rotation of both, nothing different will happen!

or just consider that it works OK on AC, which is always reversing...... as Froneck implied

I think he "got it" already.

To use the speed control to reverse the motor rotation, just place the series field across the + & - outputs of a bridge rectifier and the ~ leads in series with the armature.
The bridge will insure that the series field polarity stays the same even though the armature changes polarity.

Make sure the bridge rectifier is rated at a higher current than the full load armature current.

Bill