Dc Motor Wiring Question

[richardm6994]

The DC motor I'm wiring up on the milling machine power feed has 2 pairs of +/- DC feeds going into it. One pair is to feed the motor's magnetic field and the other pair is to feed the motor's commutator.

 

My plan is;

 

To alter the motor's direction, reverse the polarity on the field circuit (but keep voltage constant).

To alter the motor's RPM, vary the voltage on the commutator (but keep the polarity constant)

 

Is this the right way around? or should I be varying the voltage on the field and reversing the polarity on the commutator instead? or does it not matter which way around?

[IanS]

Does not matter which you switch for direction, just dont switch both.

Reducing field too low with commutator at full bore is a recipe for disaster as now no back EMF to limit commutator current.

So if you only want to vary one it has to be the commutator.

[sj-bradley]

As above. The field is designed to run at full voltage and the commutator is the one you put the varying voltage onto.

 

If you reverse polarity on both windings, the motor will run in the same direction as before. Only reverse one of the windings (either is fine).

 

Simon.

[fry61]

Have you got a DC supply for this motor Richard? because with field windings & a wound armature with commutator it can be run on AC -- its known as a universal AC/DC motor.

 

Bringing the field & comm lines out will allow you to wire a change-over switch -- easy reversal of feed direction.

 

Can also be wired in series & an external speed controller governs rpm

 

Simon will be able to tell you the latest gubbins to control speed at constant torque.

Edited May 8, 2016 by florin metal works

[richardm6994]

Unfortunate I've not got it working yet and am banging my head now....

 

Here is what I've tried so far..

 

 

 

This was the ac voltage reg used...

http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=162023997886&category=42899&pm=1&ds=0&t=1462738376064

 

And this is the DC motor speed controller....

 

http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=161975055276&category=42899&pm=1&ds=0&t=1462738587397

 

And this is the transformer which I think I've now bust....

 

 

It has different output voltages which I've tried using the lower voltages for this to work.

 

My main problem is that I can't get he motor to run slow enough (except when I did circuit 3 but this bust the transformer).

 

I've worked out that the speed I need is somewhere between 25 and 35 volts DC, but can't quite get that straight from the transformer on the different outputs.

[richardm6994]

For ease, I've omitted the motor reverse switching and smoothing capacitors from the drawings.

Edited May 9, 2016 by steamer

[fry61]

What does the motor rating plates say? & are the 2 controllers (from Bang-good?) a new addition to old circuit wiring ?

[richardm6994]

The motor plate says 100vdc, 4.8amp.

 

The story goes.....I bought the machine knowing there was a problem with the power feed. On testing, the motors worked perfectly fine and the problem was the internal machine powerfeed control box had blown (it looks like at some point in its life coolant got into the cabinet and blew the controller).

 

So the motors work perfectly fine, I just need to get a new source of DC voltage to them.

 

The 2 controllers I've tried so far are new additions.

[fry61]

Has your company or a mate got a 240/110 volt portable tool transformer? If so wire this direct to your motor controls, by-passing the suspect transformer.

 

Would still try motor wired in series ( field & comm ) which will then allow it to run on AC & even,maybe 230 volt. Should then only need one controller for speed, but as said before may not give a constant torque at lower speeds.

[fry61]

Just looked at your 2nd electronic gubbuns & it appears (to me ) that its max output is 50 volt -- your motor needs 100 ??

[richardm6994]

Cheers Bob,

 

100V is to run the motor at top speed (which I don't need).

 

For machining speeds, I think I need between 25-35 volts.

 

The transformer I've been using has multiple outlets at different voltages. for this, I used the 50VDC outlet but even at 50V the motor span too fast and needed turn down further.

 

The transformer also had a 24VDC outlet, but this just wasn't enough power......which is why I think I need between 25 and 35 volts to run at machining speeds

[fry61]

As said try running in series Richard, can't do any harm as you will be increasing the resistance & therefore lowering the voltage.