Machine refurbishment.

[Farmer Giles]

If his motor states just 400v on the tag doesn't always mean that it is not dual voltage. I took an old motor to a winders and he pulled some wires from the windings altered them to make it dual.

I've did this on the Tom Senior milling machine as the motor on it was a modern motor, single phase but was 2800rpm not 1450rpm as it should be, fortunately the original 3 phase motor was with the job lot I bought. Below shows the original motor on the left and the motor that it was using on the right.

The problem was that it was fixed voltage, 400v, i.e. star wound. If you look at the diagram below, all it means is that the star point is soldered together in the windings, not brought out to a patch panel where you can arrange the windings in star or delta.

What you need to do is find the star point in the windings, cut it and solder on extension back to the other winding connections, you can then configure it as a delta or star wound motor. A good place to look is where the external connections come into the windings, you can see them on the right.

Here's the star point in the motor I was working on, it took a bit of time to trace it out and I had to cut some of the lacing.

I then cut the star point, extended the wires to outside the motor and used some heat shrink to cover the soldered joints.

I then tested each phase to make sure I had continuity and no shorts between phases then wired it delta using the original terminals. Modern motors have six terminals so you can wire in either configuration by just moving a couple of metal straps.

I could then run it off the ubiquitous single phase 240v to three phase 240v VFDs, but first get rid of that horrible hammerite and paint it properly, then bench test it. It worked fine but I thought the little white plastic box for stop/start and speed was incongruous, I liked the original on/off switch on the left.

So I painted it up and moved the gubbins from the plastic box to the original metal box. Not sure why the power feed selector box is on the left, I may have painted it at the same time.

I didn't like the speed control knob on the box above so I bought a chicken head knob for the speed control. Here it is in place on the side of the milling machine, much better

Cheers
Andy

 

[wallace]

Where have you seen vfd's for £20? At that price it would make a re-wind at the motor factors well worthwhile.

What I meant was it cost me £20 for my motor winder guy to do what the clever farmer just showed us, then I was able to buy the cheaper vfd for £200 instead of needing a one that has to change the voltage and phase for maybe £450