Thread: Arboga mill motor rewind

I've had my Arboga mill for some years now, purchased from Futura machinery back when they had an outlet on Goodwood Road, originally 3 phase I initially mounted a single phase 1/4 hp motor on the side from an outrigger and ran a belt from it to the main motor shaft, this did the job for a year or so but eventually I found a motor winder that agreed to rewind the motor for single phase, this being my cheapest option at $150. This was partially successful, hi speed was useable but lo speed had no power at all and was unusable - this limited the mill to 4 speeds only, I learned to live with it. Now 30 yrs later VFD's are very affordable and having a better range of spindle speeds was looking achievable, provided I could get the motor rewound back to 3 phase 240v, phone calls to rewinders intialy seemed promising cost wise but as soon as I mentioned single phase to 3 phase I could detect a reluctance and the cost magically trebled, add in the cost of a VFD and I was looking at $800 - $900 minimum. Checking out Youtube videos on motor winding it did not look that hard so I thought why not, a forum member WCD had posted motor specs a few years back I already insulation from winding tube amp transformers, I only need wire, time and good luck, if I stuff it up I'll have no choice but go see a motor winder with my tail between my legs.

Doesn't take long to strip it down to the main casting that carries the stator, it'll also give me a chance to check out the insides for damage or wear, I didn't bother to note the old wiring connections, what ever happens it won't be going back to single phase. Once the casting was on the bench I see that the stator looks well glued in with varnish I decide to leave it in place, not sure if this will make the rewind harder. The windings are not easy to get out - plenty of varnish in there, a paint stripping heat gun helps to soften the varnish, took about a hour or so for all of the wire to be removed. I'll add to this post as I progress and hopefully the final outcome will be positive.

HI,

Aren't these a two speed motor?

Ben.

Yes they are originally a 2 speed motor, if this works out it will still be a 2 speed motor 3 phase 240v.

The motor winding is a single 2 pole winding that can be switched over to a 4 pole to halve the speed. Doing a bit of reading on the net I have found the extra poles are not actual physical poles but can be termed virtual or phantom poles. In a single speed setup the windings are connected such that each winding produces an opposite pole to the one next to it - moving around the circumfrence of the motor the windings will be north - south - north - south and so on. However if it is rewired so each winding produces the same pole ie north - north - north and so on a virtual south pole will be produced in the middle of each pair of north poles, effectively doubling the number of poles.

This is where the winding setup gets its name - the south pole is produced as a consequence of 2 north poles next to each other so it is a consequent pole motor thought up by a guy called Dahlander. If I retain the original 2 speed setup I won't have to run the motor too far out of its designed running frequency. I should easily be able to get 40 or 50 rpm or as high as 4000 rpm.

Hi,

Sounds interesting. I passed up a Arborga mill several years ago as it was 3 phase and I wasn't sure if it was cost effective or even possible to get it re-wired for 3 phase 240V. They are a good sized mill/drill for a home work shop.

Good luck.

I already had the wire - picked up from business at Beverly and also watched numerous motor winding videos on Youtube, I must admit I'm only 95% confident of success, I have wound quite a few transfomers I have never done this before and believe it is a completely different ball game, while I don't believe motor winding is a black art experience must count for a lot. Today it looks like one step forward and 2 steps back.

I measured the length/size of winding that I need and rig up a former on my winding ? machine which can be motorised or hand wound, I'll stick to hand wound this time- I do a dummy run using wire salvaged from a CRT TV degaussing coil - the winding looks to be too big, I make a new small former and go through the dummy run again - all looks ok.

I wind the first coil and fit it in place - goes in ok - I wind the second coil and fit that in place - not as easy as the first one, there is 123 turns and they need to be inserted into the slot 3 or 4 turns at a time, I find that the wires need to be fanned out and lowered into the slot in roughly the correct order if not done this way and they cross over they seem to want to jump back out of the slot, eventually I come to the conclusion that the coils are probably too small.

I rebuild the coil winding former a bit bigger and continue leaving the first 2 coils in place- after the 3rd and 4th coil are done I am not finding it that easy maybe I should have just left it as single phase it was after all working and useable. I'm starting to think that the wire is too thick and all 123 turns will not fit correctly into the slot with enough room for insulation as well. A quick calc shows that the motor should draw around 2.5 - 3 amps under full load, (99% of the time it will never work at full load) working on a safe current density of around 5 amp per sq mm the wire size looks right. I measure and calc the x-section of the slot and work out that the wire and insulation should take around 55-60% of the space - it should easily fit so it is must be me doing something wrong.

After placing the 7th coil with much difficulty I'm thinking that the coils are still too small and I'm asking my self who had the dumb idea to rewind the motor.

Before packing up for the day I pull all of the coils out so I can start again, I can see the sharp edges of the stator slots have made nicks in some of the varnish coating I decide to not use them just in case, they weigh around 150grams each so I 've used around 1.1kg of my 5kg spool - plenty left for a complete set of new coils (or more stuff ups). I'll redo the coil former and have another go tomorrow.

VFD arrived today so won't have to wait to do any testing once the job is done.
4. dummy test coil for size.jpg4.1 Making a start.jpg5. size looks ok.jpg6. first coil started.jpg

Hi dude,

I reckon I have a "can attitude" when it comes to stuff like this, I think nothing of converting a motor from star to delta but I must confess, I probably would never attempt a motor rewind. Hat goes off to you for having a crack! I have already learnt a bit about motors in this thread. I'll be watching with much interest. I wish you every success.

Simon

If you look at your second photo in post one, you should have some insulating material protecting the coils from the laminations.

Michael

Well done for having a go, my son-in-law is a motor rewinder, so I defer all rewinding work to him.

But I can point you towards the "bible" for rewinding, see if you can get a copy of Robert Rosenberg's "Electric Motor Repair"

It's not a cheap book, but it covers everything you need to know. You might be able to borrow a copy through your local library?

I assume you are dispensing with the two speed Dahlander winding?

Just wiring for single speed 240 volt delta?

Ray

PS. Just check the current price, and outch. It's over $200, maybe I could scan a few relevant pages for you.

Thanks for the encoragement after today's set back it won't go astray.

Michael - I will insulate all of the slots, was intending to do each one as I went I figured it may be a way of keep track of slot 1 which is after all abitrary, it just happens to be the slot you start from, I have a sheet/roll of stuff I picked up from O H O'Brien for transformer insulation it has a sort of parchment like look and feel to it - not sure what it is.

Ray - I do have a copy of Rosenberg's book was lucky enough to download it in PDF and even went to the trouble of printing them, 2 volumes text in one and illustrations in the other, after reading it a few times I feel it is ok but not great, in the section on polyphase motors Rosenberg states he won't be dealing with single layer windings which is what I have. Some of the youtube videos are good - the ones posted by guys from India, however some are in Hindi so I can't understand what they are saying.

I plan to keep the 2 speed Dahlander setup initially so I won't have to run the motor too far out of its designed running frequency, I should be able to get any speed from 40rpm to 4000rpm. I have just a few weeks ago finished fitting a 3 phase motor and VFD to my lathe and I notice that there is a wierd vibration at certain revs/frequency which is not what I expected, nothing serious but it can be felt, I don't think it is the motor as this is brand new. I googled this and found it is quite common with VFD's which is why they have a few skip frequency settings. I've done a few tests and think the vibration is at 36 Hz and 24Hz. I called the motor seller and explained the issue and he says that it does happen and claimed that Hyanyang VFD are not particulary good quality - he no longer sells then for this reason and has gone to a different brand, not sure if there is anything to his claim.

My biggest concern WAS getting the coil layout and connections but I found a forum called Eng-Tips and some helpful guys there guided me through it, good on you for having a relative that can do the job for you I wish I was in your situation, I did find a motor winder though that offered to test it for me rather than risk damaging my new VFD just in case I screwed something up.

You may find it a lot easier to place and hold the new coils if you push the stator out of the casting!
There are one or two grub screws in the casting holding the stator in position.
Once they are out, it takes a good bump to get the stator moving, but then it easy. It's only tight in the first and last 15mm or so, the rest of the casting is relieved.
Just measure and note down the distance from one end and mark the orientation so the grub screws line up again.

Sent from my InFocus M808 using Tapatalk

I don't doubt it would be a lot easier, I did try but not that hard to remove the stator from the casting I backed off the grub screws and and using a piece of round timber gave it a some good hits with a hammer but it did not budge, it looks like the guy that wound the motor over to single phase poured varnish all over the inside of the casting from both ends probably would need to take my map gas torch to it to burn off the varnish, I'll have another go today at placing the coils and if I still have problems I make a better effort at removing the stator.

Today I modified the coil former so it is a bit larger and wind the new larger coils - 1 goes in easy, the 2nd 3rd 4th 5th and 6th coils go in quite a bit easier this time I'm feeling a bit more optimistic though I'm only half way to fitting the coils, I decide that if I stuff it up I,ll just redo it again and persevere until it works. Perhaps the bit of experience with the discarded coils has helped.

I use a toy compass and 9v battery to check the polarity of the coils is correct as I go. All goes well until I get to the last 2 coils (12 in total) I realise I need to lift the coils out of the first 2 slots (first ones that went in) to be able to get the last two coils in - being a basket wound motor 7. Half way through.jpg8. Checking coil polarity halfway through.jpg8.1 three quarters there.jpg9. all done.jpggetting there.jpgthe coils go in over and under each other so when viewed from the top it looks like a basket, not sure if this is done for neatness or if it will affect the way the motor runs but to be safe I decide to follow convention and pull the coils out of the first 2 slots. They can't be removed completely as there are 2 coils inserted over the top of them so I tie them out of the way as best I can to make room to get the last 2 coils in, once tied back the neat wound coil look has gone and they look like a bowl of spaghetti, knowing how important it is that the wires go into the slots in order neatly I begin to have more doubts. I walk away a few times to take a break - the internal diam of the stator is only 70mm this does not leave much room for the two coils I have pulled from the slots and tied out of the way, my hands and also the last of the coils being inserted. Finally all done, I push the wires into the slot with a stick that I have cut into a sliver just wide enough to fit into the top of the slots, much easier to get this into the motor than my hands. I've labelled all of the coils as I went and I use the toy compass again to check the direction of the coils, this goes as expected - just need to connect up all of the coils now and give it a go with the new VFD.

The windings look ok but certainly not as neat as real motor winder would have done - counting the dummy run this is effectively the 3rd attempt and I think that if I had another go I could do a much better job, perhaps in hindsight I should have removed the stator from the casting like Joe suggested but I was bit concerned about damaging it. I connect up all of the coils and power wires (6 in all) and do the best I can lacing the windings with cotton tape (bias binding from the sewing shop) I put the rotor back in and but can't test it as no 1 son has dropped in for a visit and I'm called in to entertain him, will have to wait until tomorrow - darn.

Got out to the workshop this morning to try the motor, overnight I thought I should test the insulation with my megger, so I hooked it up and no issues at 1Kv, wired up the VFD a quick check of the basic settings and ------ it works !!! video link here https://youtu.be/8aMBLB2Hgzk

I tested both speeds and they seem to work as expected hard to tell with out a tach though. A fair amount of work, for me I estimate a difficulty level of around 7 out of 10 at the beginning of the job and falling to 4 or 5 by the end, all up cost around $80 for the wire and I still have some left - I already had a sheet of insulation to cut up, I did think of using cardboard from filing cabinet suspension files, I have used this in transformers before it is heat resistant and has good insulation properties. Only time will tell if the the quality of my work is any good hopefully the windings don't fail, they don't seem stressed I ran it for around 30min, the VFD says current draw is 1.2 amps with no load I could not feel any temperature rise in windings after the 30 min run. Any failure should it occur would almost certainly be due to poor workmanship on my part. Now I need to varnish the windings and once dry reassemble the mill checking all bearings etc. Then do the electrics - I'll keep the 2 speed setup and see how it works I might find that I don't need a 2 speed motor any more and if so I'll permanently connect to it the speed that suits me best, I'm not keen on the original speed switch as it has a centre off position I would prefer a straight 1-2 switch. I've spent some time looking on the net and can't find a reasonably priced replacement I think I need a double throw 6 pole switch, the original is I think a 3 position double throw 6 pole (18 terminals) with centre off. Other option is with contactors which means a 24v transformer and it starts to get like a lot of work as I'll also need an enclosure to house the contactors - for now I'll just stick to the original switch.

Still have a lot of work to do mounting the VFD, I want to keep the mill self contained so if it ever needs to be moved it can be just picked up with out disconnecting wiring - so I need to put a bit of thought into the mounting position of the VFD and controls
insulation test.jpg

Nice work, congratulations on making it all the way through. Must have been a great feeling to see it running!

I'm not sure if it's just me, but I couldn't see the YT video, it said "This video is private"

It seems to work now, very nice and neat!