Identifying Winding Pairs

[Baluncore]

In this case DC current and a magnetic compass are not needed, because the connections of these Dahlander motors is internal, so relative polarity of the coils cannot be reversed. When you look at a row or a column in the resistance table, the two lowest resistance wires identify the ends of the two closest coils. So for example, #7 is between #8 and #16. That process continues to fully identify the ring of six coils.

Since the two rings of six coils show no connection, we know that there could be at most, one wire shorted to the motor frame. You should check the insulation is good, from the motor frame to one wire on each of the two windings. Remember to protect the coil insulation, by earthing the motor frame.

The experiment comes when you connect power to the motor. You need a fast breaker in case there is something unexpected. Three filament lamps rated to the line voltage will limit fault currents if there is a problem. Equal lamp dimness will tell you if things are balanced. Then you can apply the full supply, without the lamps.

 

[gah]

If it’s any help, it looks like your two Dahlanders are:

1. 3600-1800 switching 2 to 4-pole
2. 1200-600 switching 6 to 12-pole.

I’ve also seen someone using a DC power supply to inject controlled current into winding ends, watching the behaviour of a compass needle to check the phasing is correct.

OK, that is almost what I just figured out.

But it is 3, 6, 12, and 24 pole. Being used to thinking about single phase motors, which need an even number of poles, but not for 3-phase.

So, the 12 and 24 pole version will use all pairs of consecutive poles.

And the 3 and 6 use groups of 8 poles. I was trying to figure out before why 16 and 8 are not divisible by 3, (or 6), but it works if you do it that way.

The effect is of 24, 12, 6, or 3 poles, and 600, 1200, 1800, and 3600 RPM.

If you follow the previous suggestion of a small DC current, and a compass, you should be able to figure out the pole polarity, with different windings.

 

[Guineafowl]

I’m not sure what you’re driving at there ^. Are you trying to equate the number of stator slots with pole number?

For three phase motors, the number of poles is given per phase, so a 2-pole version will have 6 poles overall. For the synchronous speed, you use the per phase (P) figure in this equation:
$$N_s = \frac {120f} {P}$$
Hence, the field of a 2-pole (per phase) 60 Hz three phase motor will spin at 3600 rpm.

As far as I know, there are no 3-pole induction motors. It has to be an even number.

 

[Guineafowl]

I’ve just re-read the thread. Sorry, Baluncore, I missed that you’d already mentioned the compass trick. I take your point about this not being useful when each of the 6 windings aren’t separate.

Each set of 6 wires comes from a series delta, and each wire is from two winding ends either at a vertex or a mid-point. The vertices are the ones commoned in the double-star mode.

- Can we assume that the lowest-numbered wire is a vertex, and that increasing numbers count round the delta in a direction that’s consistent between the two Dahlanders?

- if we muddle the vertices with mid-points, does it matter?

- For the OP, does the lathe have a reversing switch before the speed selector? This would be a useful feature for threadcutting.

 

[Grubbs1960]

I wired the lathe today and it seems to be running as expected, although I have not yet attempted any actual turning.

 

[Grubbs1960]

I’ve just re-read the thread. Sorry, Baluncore, I missed that you’d already mentioned the compass trick. I take your point about this not being useful when each of the 6 windings aren’t separate.

Each set of 6 wires comes from a series delta, and each wire is from two winding ends either at a vertex or a mid-point. The vertices are the ones commoned in the double-star mode.

- Can we assume that the lowest-numbered wire is a vertex, and that increasing numbers count round the delta in a direction that’s consistent between the two Dahlanders?

- if we muddle the vertices with mid-points, does it matter?

- For the OP, does the lathe have a reversing switch before the speed selector? This would be a useful feature for threadcutting.

No reversing switch. This is a wood lathe, so there is little likelihood of threadcutting.