Reversing a universal motor. 4

[dunno]

I have a 1.5 HP commutator motor running on 230V AC, I need to be able to reverse the rotation, can anyone point me to some data on this type of motor, or how I can carry out this modification. It is an old Metropolitan Vickers, ( type CKS 3014. 230/450 V. )
Thanks, Will.

 

[utvol]

A universal motor, AC or DC, is reversed by changing armature polarity in relation to the field. Just swap the two brush leads. There is the possibility that it may not be designed to run in either direction.

 

[dunno]

Thanks for your reply, looks like you are right when you say that it may not be designed for reversal, I found a label inside saying that was for non-reversing applications.

 

[UKpete]

It could be that the brush holders are angled to improve the brush dynamics. If the holders are perpendicular to the commutator i.e. the brushes are radial, I can't see any reason why it can't be reversed as described by utvol.

 

[jbartos]

Suggestion to the previous posting: There may also be a need to change the cooling propeller to have the motor properly cooled.

 

[dunno]

This thing is starting to get a little involved for a non electrical guy. There are 4 brushes mounted on a moveable backplate, this can be revolved around the commutator axis by approx 40 deg. Does this change the timing? it does not change the direction of rotation.
There are 4 wires coming from inside the motor, one pair is connected to the incoming phase wire, and the other pair to neuteral.
Don't know which ones to change. Tried swapping the incoming line wires around, of course with no result.
Can anyone enlighten me, or show me some good sites with a clear description of what to do, so I can enlighten myself.
Thanks, Will.

 

[jbartos]

Suggestion: Please, post the nameplate data.
It could be a Schrage Commutator motor that has brush braces for RPM control/adjustment.
Regarding the connection and speed reversal, visit

http://www.electricmotorwarehouse.com/aosmith/C_U_CONNECT.PDF

to see what may be involved. It would be more appropriate to obtain information from the motor manufacturer.

 

[dunno]

Firstly, thanks for all the replies, sites to visit etc.
The motor is old, and I'm not sure that this company exists anymore. Nameplate reads:-
Metropolitan Vickers,
( Type CKS 3014 )
230 / 450 Volts
1450 RPM
Running on 230 V Ac, 50Hertz.
( Just realised I gave this info way back at the beginning )
The internal wiring from the junction box is all black this doesn't help at all.
The brushes are all perpendicular.
Thanks everyone,
Will.

 

[UKpete]

dunno - it isn't quite so simple as I first thought, but it should be possible with a bit of perseverance. In addition to the fan which you need to check (as per jbartos): because the brush positions can be shifted as you describe, this may mean that they are not set to the neutral position but are shifted say 10 or 20 degrees in the direction against rotation – for a motor. This is done to reduce sparking at the brushes due to an effect called armature reaction, where the magnetic field in the motor is distorted due to load current in the armature. If you reverse the direction of the machine, the brush positions will have to be shifted by the same amount the other side of the neutral.

The neutral position for the brushes coincides with the axial centre line of the main poles i.e. the stationary windings mounted on laminated poles around the bore of the motor housing. As you have 4 brush positions, you should have a 4 pole motor i.e. there are 4 main poles.

Incidentally larger DC motors (supplied with DC), particularly those meant to be reversible, usually have the brushes in the neutral position and instead have additional windings (interpoles) placed between the main poles, and possibly even compensating windings mounted in the pole face of the main poles, to reduce the sparking. I doubt very much that your universal motor will have either interpoles or compensating windings. Relying on the brush position shifting has two disadvantages:
1. the ideal position for the brushes depends on motor current - higher loads ideally require a larger shift, so some compromise may be required if the load is variable.
2. if the motor is reversed, or changes from motoring to generating, the brush position must be shifted to the opposite side of the neutral position.
Hence the technique is only used on relatively small motors. You may have to experiment with brush position to minimize sparking at the brushes.

To achieve reversal then, you should find that every other brush holder is connected together. If you shift the connections around by 90 degrees (ensuring that opposite brush holders are still connected to the same point), and if necessary move the brush positions to minimize sparking as previously described, you should be in business. You may want to experiment with on reduced voltage at first, ac or dc.

I hope this all makes sense. Metropolitan Vickers was an old UK company by the way, they disappeared nearly 40 years ago so you do have an old machine!