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2 Speed 3ph motor rewind - assistance needed.

2 Speed 3ph motor rewind - assistance needed.

(OP)
Some time back I asked a question on motor winding layout and connections and received helpful replies and assistance, the plan was to return a small milling machine 2 speed (Dahlander) 3ph motor that had been rewound for 240v single phase back to 3 phase. Back when the single phase winding had been done VFD's were were almost as costly as the mill, now however the Chinese have fixed this issue and it would be nice to have the mill opertaing with more than the 4 speeds the gearbox provides. It's now 4 yrs since I posted and my question and I'm only just starting this project, to date I've removed the old windings (past the point of no return) cleaned up the stator and started to insert the new windings into the motor slots but find that as I read and watch youtube videos on motor winding I'm starting to second guess myself so would appreciate a knowlegable person confirming that the winding layout and connections I have will result in a successful job.
Pic 1: https://postimg.org/image/5a0sg9jhh/
Pic 2: https://postimg.org/image/r6n0e0rlx/

Pic 1 is the layout and basic delta connection diagram - 6 leads will be bought out of the motor L1,L2,L3 and T1,T2,T3 - for lo speed (Delta-4 poles) connect 3phase power to L1,L2, and L3 - T1,T2,T3 are left unconnected.
Pic 2 for Hi speed (Double Y 2 poles) L1,L2,L3 are bridged and 3 phase power is connected to T1,T2 and T3.

The stator has 24 slots with 12 coils - all windings consist of 2 coils connected in series, the first or "A" winding coils span slot 1 and 6 and 2 and 8. The next winding "B" has coils that span 5 and 11 and 6 and 12 and the third winding "C" has coils that span 9 and 15 and 10 and 16. This layout repeats again with the second "A" winding starting at slots 13 and 14 - the last two coils of the second "C" winding fit into slot 3 and 4. In the pic the dot denotes the start of the series connected coil pair. I have a copy of and have read Rosenberg's book and the layout in the pic looks right for a Dahlander or consequent pole motor. Having fitted a 3ph motor and VFD to my lathe I feel that running a motor too far outside of its designed frequency and speed range may not be good thing so would like to retain the two speed winding setup and use the VFD to make small adjustments above or below max and min speeds.

Lastly a question about the actual coils, I notice in youtube videos that placing the coils in the slots stating from slot 1 they lie over and under each other - once they get back to the start I would have to remove one side of the "A" coils from slot 1 and 2 to fit the last pair of "C' coils and then refit the "A" coils back into slot 1 and 2 - is this purely for appearance and neatness or is there a physical/electrical reason the last 2 "C" coils need to lie underneath the first two "A" coils. Having already placed come of the coils into slots I find it is not as easy as it looks on youtube, if I fan out the wires and place then in order they almost "fall" in - if I get some crossed over it makes the rest of them a chore to fit in and they seem to want to spring out.

Sorry for the long post I hope someone takes the time to read it. I should mention I have never done this sort of thing before - I approached a number of motor winders and as soon as I mention single phase to 3 phase the price seems to treble to a point where it is out of my budget.

RE: 2 Speed 3ph motor rewind - assistance needed.

And here I've been sitting with the reverse of your dilemma. I have a 3 phase 380V 2-speed Bench drill that I want to run on 220V single phase. Have been reading about all sorts of cowboy hacks with capacitors, static and rotary phase convertors but seemingly the only cost efecetive solution lies with a step up transformer to get 380V from the 220V supply and a VSD to generate the 3 phases.

This sketch from a hobbyist machining website put the connections into perspective for me.


RE: 2 Speed 3ph motor rewind - assistance needed.

(OP)
Andiri

sounds like you have a similar machine - mine is an Arboga made in Sweeden. My machine was originally 415v 3 phase 2 speed and the most cost effective way for me to get it running was to have the motor rewound for single phase with 2 speeds - it was partially successful. Hi speed was fine and useable but lo speed was was no good lacking power, I could stop the chuck by grabbing it - this limited me to hi speed only. In addition there was the issue with energising the start winding to get the motor up to speed, single phase motors need to have a start winding enegergised to get them up to speed, this is usually done with a centrifugal switch being 3 phase my motor like yours has no centrifugal switch so I had to devise a hack which consisted of an an extra switch mounted on the back of the start switch. Press start to go - and then pressing a bit further activated the start winding - hold start button until up to speed and then let go, the button would drop back slightly as it latched releasing the start winding switch - not much movement here and I had to use a microswitch. Having been through the process I would recommend you either purchase a 240 to 415v VFD Direct Drives in the UK have them (not cheap though) or you find a motor winder to rewind the motor as a 2 speed 3 phase but for reduced voltage of 220v and then run it from a VFD - 220V single to 3 phase VFD's are quite cheap now.

RE: 2 Speed 3ph motor rewind - assistance needed.

You have picked a pretty good battle.

Winding repair shops have access to computer programs to help in figuring out complex winding jobs.
When those don't work, they have the resources of the Electrical Apparatus Service Association and its members.
Most all of the EASA material available to its membership is proprietary and unavailable to the general public.

Your request is bordering outside the scope of what an Internet forum can provide for you.

I've pulled an old paperback winding book off my bookshelf, Googled the author and have found it is on the Internet.

The book is nearly 2 inches thick consisting of 766 pages including the index.

Here is the URL to the Internet version: https://babel.hathitrust.org/cgi/pt?id=mdp.3901502...

You may find the dated material useful in what you're trying to do.

I'd say "Good luck", but that's a tall order in this case.

John






RE: 2 Speed 3ph motor rewind - assistance needed.

(OP)
Thanks for the advice - however I don't believe this is a complex winding job and I also don't believe Electrical Trade Associations are operated as secret societies keeping knowledge away from the uninitiated. I did ask a similar question a few years back when I first decided to go down this path and was helped out by some knowledgeable and helpful forum members, circumstances intervened as they do and I am only now doing the job. I did in the intervening period read a lot and also watched many how-to youtube videos which may have been unwise as I eventually began to second guess my data. In any case I have passed the point of no return and am 3/4 way through placing the coils in their slots, I'll keep going I'm sure there will always be someone that will help whether on this forum or others after all that is what forums are about.

RE: 2 Speed 3ph motor rewind - assistance needed.

Within the electric motor repair field; the number of turns of magnet wire, the size of the wire, the number of “wires in hand”,
the span of the wound coil, the number of stator slots, the dimensional size of the slots, the diameter of the stator bore,
the power supply, the way the coils are connected, and a whole host of other necessary informational gathered notes… is known as “Winding Data”.

It is absolutely essential to retrieve, (save the extracted winding connection in some instances) and record this data in some manner for use at a later date during the rewinding process.

To state in your own words:

“…It's now 4 yrs since I posted and my question and I'm only just starting this project, to date I've removed the old windings (past the point of no return)…” reveals your project is not
suitable for discussion here. Unless you want to start a new subject called,

[Developing a New Winding Using an Existing Bare Stator Core].

Veteran motor winders who have decades of winding electric motors under their experience have
memorized certain connections because they have seen them over and over again throughout their career.
Someone among the crowd here may step up and give you their best guess as to what to do with your winding
project but they also know it’s a “crap shoot” as to whether it will work because they did not record the data
as it was originally extracted from the motor stator.

What complicates your project is this statement:
“…return a small milling machine 2 speed (Dahlander) 3ph motor that had been rewound for 240v single phase back to 3 phase.”

I’m trying to think of an optimistic way of giving you encouragement with your rewinding project, and I'm pulling at an air gap.

This is what I suggest… if you want to continue the discussion.

Post some photos of the motor. Take a picture of the nameplate.
Show the rotor and what, if anything was altered during its change from a three phase motor to a single
phase machine.

You may, ( might) get further replies from the crowd.

Let's see!

John

RE: 2 Speed 3ph motor rewind - assistance needed.

Hi, retailer,
This 4/2 pole , single-layer winding ( 12 coils) is really simple but it is far away from best option.
See an attached similar diagram (concentric instead of lap winding) and correct your description:

Quote (retailer)

"A" winding coils span slot 1 and 6 and 2 and 8
.
Should be 1-7, 2-8.
Regards
AC Windings

RE: 2 Speed 3ph motor rewind - assistance needed.

(OP)
Yes Zlatkodo I can see the error it is though a typo as one of the "B" winding coils occupies slot 6, thank you for the winding layout and connections I appreciate you taking the time. The motor winder that rewound the motor for single phase did give me the original winding layout and connections but it has been over 20 yrs and they have been lost.

RE: 2 Speed 3ph motor rewind - assistance needed.

(OP)
Hello Zlatkodo

I have finished the rewind, it looks OK but not as neat as a real motor winder would have done, I did have to stop and pull out the coils part way through as I could see that the coils were a bit on the small side, it was also compounded by the fact that the motor is small (rotor is 70mm diam) and I don't have a press so could not get the stator out of the casting that forms part of the machine - I had to discard these 6 coils. The second attempt went much better until I got to the last 2 coils and realised that I needed to lift the first 2 coils that I had inserted to get the last 2 coils in, the lack of room made it hard going but in the end it was done. I labelled the start and end of each coil as I went and at this stage I checked polarity/direction each coil with a 9v battery and a child's toy compass placed in the middle of the stator, it all went as expected. Once the coils had been connected and secured with tape I installed the rotor and hooked up the VFD - it works !! I tried both 2 and 4 pole connections both work as expected although it hard to judge the rotor speed, I don't have tachometer, I ran it for around 30mins continuously the VFD tells me it is drawing 1.2 amps with no load, windings did not feel at all warm to the touch after this . I'm now waiting for the varnish to dry before I reassemble the machine, hopefully my work is good enough to get another 20yrs trouble free, thank once again you for your assistance.

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