3 phase 2 Speed motor wiring help?
I searched and read up on this, and did some checks with the fluke, but i'm still unclear as to how to wire this motor. from what i've read, it looks like it's what someone referred to as a center tapped motor, not 2 isolated windings.
it looks like from what i've read that i'll need to supply 3 of the phase leads (for discussion called A,B,C) and leave the other three (D,E,F) open to run in one speed. then short ABC together and supply power to DEF.
the motor is a taiwanese 2 spd ( 1750/875 rpm) 3 ph ~1-2hp 220v on a Select mill from what seems to be the 70's. the motor has 6 leads numbered 1 thru 6.
i measured resistance between leads with a fluke 87:
- 4.8 ohms between 1-2, 1-3, 2-3
- 4.6 ohms between 4-5, 4-6, 5-6
- 3.3 ohms between 4-2, 4-3
- 5.5 ohms between 4-1
this 3.3/5.5 ohm pattern repeats itself throughout
can anyone refer me to a wiring diagram of the guts of this motor? i'm having a hard time figuring out whats going on in there just from resistances. the existing wiring on the machine is not really any help, as the previous owner bypassed the contactors and just put a drum switch on the horizontal motor, and removed some switches and most of the wiring that used to run the vertical motor.
i did find this, but i need to confirm that this is the type of motor i have, and also how to identify which leads are the 3 which need to be shorted.
that's the first task to get me up and running. i was also thinking about adding a vfd to allow me to slow the spindle down as it doesn't have a back gear. the minimum speed is 250rpm in the lowest belt ratio with the motor in low speed. will a low cost V/Hz vfd allow me to slow it down to ~50-100 rpm at the spindle (~175 rpm at motor) or will i need a vector control Vfd to control at such a low speed?
Last edited by Mike RzMachine; 04-01-2009 at 11:15 AM.
Reason: added wiring link
If it's like the consequent pole motors in the hardinge
machines, draw it as a star-connected configuration, but
put a center-tap on each leg of the star. Using your
nomenclature above, the ends of the windings would be
A,B,C and the center taps would be D, E, F.
So if you leave DEF open and power ABC, the windings are
more or less in series. If you short ABC and power DEF,
then each pair of windings is then more or less in parallel.
The hardinge drum controllers are set up do this configuratation
automatically, but you can probably find one from a manufacturer
that does this. Basically it has to have enough sections
to switch each of the two pairs of three windings, plus two
more to short the three for the second configuration.
You only need two sections to short three wires.
As motor speeds are 1:2 I would think it's a Dahlander, most likely delta-double star. You should have no difficulty finding diagrams (sorry, can't post mine). Look them up in any major motor catalog. (see Jim's explanation)(I see you've found a diagram, but it doesn't show the internal motor wiring)
To find out about connections, use your Fluke while consulting diagrams. Tape labels to connections with temporary letters as you did before, just to avoid confusion.
When you think you have figured out, try with reduced voltage (maybe 20 percent) and no load! If that works, try full voltage (and be glad it's a small motor, not a large and dangerous beast).
Three contactors or a drum switch are needed for one-way operation.
Best way would be to ask an experienced electrician or motor mechanic.
I had to dismantle my drill press control box cause the drum switch (forwards/reverse, two speeds both ways) was partly broken. Those switches contain no end of little parts, but fortunately the points were marked so the connections were clear. The switch now works only one way but with two speeds which is all I need.
Good luck, and let's know how you fare. Regards, fusker
Last edited by fusker; 04-01-2009 at 12:02 PM.
Reason: Connection diagram supplied
ok, so searching for dahlander wiring i found this delta configuration as well as a wye.
from my resistance readings, it looks like i have a delta. i.e. each phase pair has pretty much the same resistance (approx r(1u-1w) = r(2u-2w)), and when i measure 1u-2u its about half, and 1u-2v is about double.
one thing i'm not clear on is why i read ~4.7 between windings when measuring across 2 coils (1v-1u, 1v-1w, 1u-1w, etc) , but more than half of 4.7 when i measured across a single coil (1v-2v, 1w-2w = 3.3). also, measured less than 1.5 x 4.7 ohms when measuring across 3 coils (1u-2v = 5.5 ohm)
just based on resistances, i think i can say that its a delta wound motor. is there any way to discern which coils need to be shorted together? it looks like i have 6 identical coils connected in series from what i can read, so it shouldn't matter. is that a valid conclusion? or are there some extra poles wound in there or something i'm not privy to just based on resistance? seems like the coils would need to be identical since they are connected in parallel for high speed operation.
also, this makes me think that i will have double the torque (due to double the number of poles) in the low speed setting, is that true?
thanks for the help,
Attached is one possible wiring diagram.
Dahlander motors, three types
According to my old K-M Schaltungsbuch there are three possible types of dahlander wiring: D/YY,Y/YY,YY/D with power ratios respectively 1/1.5-1.8, .3/1, 1/1. See if you can find the internal wiring diagrams in your K-M manual which you cited, that would be a great help to understand your meter readings. I believe the D/YY configuration is the most commeon. What is the motor labeled (Power ratings, voltage, frequency)?
When measuring, have you considered the possibility that there may be parallel current paths (if you measure a delta connection you will measure one phase winding in parallel with two phases in series). Sorry for asking, I have made many similar mistakes.
that's a great point that i completely overlooked about 2 coils being in parallel with one in series.
i forgot to mention, part of my problem is that the nameplate on the motor has been scuffed to the point where i can only read a few numbers.
i think i'm getting close to wiring it and trying one set of leads, then the other on a drum switch.