Cooked BP motor- rewind or replace?

[Pete O]

The 1.5hp 3-phase motor on my frankenmill BP J-head has died a smoky death. Partly through my own 'messing with things you don't understand' habits; I was using the mill when it gave a few loud cracks and then blew the circuit breaker, upon pulling the cover off the motor I discovered that the old rubber insulation on the connection wires had perished and the wiring had shorted out to the motor frame. With little to lose, I dismantled the motor and attempted to re-tap the stator with fresh wire tails. This of course meant picking at the varnish to get at the joins where the wire tails connect to the ends of the windings; in doing so it seems that I have broken the insulation across the windings. I hooked it back up and it ran but made unpleasant noises and started smoking like an Indonesian schoolboy. Stripping it down again reveals that one section of the armature is now burnt.
Very frustrating as the Frankenmill is not long ago completed and I would much prefer to be using it to work on other things rather than start working on it again. :~

The motor plate shows it to be of 1962 vintage (like myself). It has a long shaft to run the step pulley and an odd flange mount. Seems unlikely that I'll find a direct replacement for a reasonable price. I'm wondering if it might be worth getting it rewound rather than having to modify something else to fit. How much should I expect to pay to get the armature rewound? Can anyone recommend a motor rewinder on the east side of Melbourne or in Gippsland? Also open to other suggestions of course, although I'm not interested in a single-phase conversion or a treadmill motor setup as I have a perfectly good RPC to run things.

[China]

Just as a guide I had a Armature from a 2 hp 3ph rewound about 9 months ago, I just dropped it off , they dissembled cleaned checked, rewound the Armature reassembled
it cost $720.00, same situation new motor would have required lots of mods and stuffing about, and in the long run probably would not have been much less expensive

[BaronJ]

Hi Guys,

Having a stator rewound should be a fair bit less costly than trying to get a new one, particularly if you are stripping it out of the carcass.

[Pete O]

Just as a guide I had a Armature from a 2 hp 3ph rewound about 9 months ago, I just dropped it off , they dissembled cleaned checked, rewound the Armature reassembled
it cost $720.00, same situation new motor would have required lots of mods and stuffing about, and in the long run probably would not have been much less expensive


Wow that's about what the whole conversion cost me, from getting the j-head here from WA to getting the overhaul bits, paint etc. Perhaps I can find a rewinder who'll do it for less if I do the lackie work, strip it down etc as Baron J says. Any leads on such a person would be great.

[QC Inspector]

I searched for "electric motor rewinders Melbourne" and found 11 places on the first page there that deal with motors. Five or six for Gippsland so there seem to be lots to look into.

A number of years ago I had a 2 speed carbide grinder with a dead motor and they said it would be at least $400 to rewind. The local rewinder said it wasn't economical to rewind any motor under 60 hp unless it was special and can't be replaced with a stock motor. Your J-head is pretty much in that category.

Pete

[Karl Robbers]

Can you adapt a common stock motor to do the job?
Perhaps a BP motor sourced out of the US may be an option. Voltage could be an issue, but there do seem to be a few suppliers of BP parts in the US.

[Neil317]

I've had two rewinds done here:


http://www.eastlandelectricmotors.com.au

As I recall, not particularly cheap but well done.

[malb]

Wow that's about what the whole conversion cost me, from getting the j-head here from WA to getting the overhaul bits, paint etc. Perhaps I can find a rewinder who'll do it for less if I do the lackie work, strip it down etc as Baron J says. Any leads on such a person would be great.

Have only ever had a 5KW 3ph motor rewound by a guy who was down the road from our factory in Heidelberg. This was about 15 years ago and the cost was about $500 then from memory.

I doubt that a reputable rewinder would accept individual parts from a dismantled motor for rewinding, they would be concerned about defects in other components of the motor that you may not have noted, and your ability to reassemble the motor correctly. From that perspective, it would be better to give them a complete motor, and let them strip it, repair it, reassemble it and warranty their work. Because the do it everyday, then can probably strip and reassemble a motor rather quickly without causing further problems that need to be repaired later.

If the notion of $700+ for a complete rebuild concerns you, just think about how you would feel if you did all the lackie work, and had it rewound for say $450, but nicked a winding reassembling it and had to strip it and get it rewound again. I have heard of it happening before. You only need to damage the insulation on two adjacent wires in a winding to create a shorted turn and blue smoke, that's not a very large scratch.

[Pete O]

One of the effects of the passing years is that everything is more expensive than you think it's going to be. There's no way I can justify throwing $700 at a repair on a hobby machine but the flip side is I can't leave it defunct after spending a similar amount on it over the past 12 months. A BP motor off the shelf appears to be somewhere over $900 so even further out of the question.

Most likely path at this stage I think will be to find a generic flange-mount motor, extend the shaft and make an adaptor to mount it. Which of course will be a pain without the mill working, but I guess I built the frankenmill without a functioning frankenmill so, where there's a will...

[BaronJ]

Hi Pete,

I agree with you, its a lot of money to spend in addition to the amount that you have spent already !

I would still get some competitive quotes just to get a more general idea. Anyway good luck which ever way you decide.

[familyguy]

Have you given the idea of a diy rewind any thought, it really is not that hard, there are some techniques used to get the coils into the slots but these can be learned as you go. A few years back I rewound my Arboga mill motor for 2 speed 3 phase 240v, ( link here https://metalworkforums.com/f65/t200978-arboga-mill-motor-rewind) the allup cost was less than $100 - $70 of that was for a 5kg spool of wire. If your motor is cooked anyway you don't have a lot to lose. I know it sounds daunting but motor winders are not special people that have been trained in a black art they are just ordinary people like you and me, there is a good link to a diy rewind in this post https://metalworkforums.com/f309/t201410-diy-3-phase-motor-rewind - it is well worth a look.

[Pete O]

Have you given the idea of a diy rewind any thought, it really is not that hard, there are some techniques used to get the coils into the slots but these can be learned as you go. A few years back I rewound my Arboga mill motor for 2 speed 3 phase 240v, ( link here https://metalworkforums.com/f65/t200978-arboga-mill-motor-rewind) the allup cost was less than $100 - $70 of that was for a 5kg spool of wire. If your motor is cooked anyway you don't have a lot to lose. I know it sounds daunting but motor winders are not special people that have been trained in a black art they are just ordinary people like you and me, there is a good link to a diy rewind in this post https://metalworkforums.com/f309/t201410-diy-3-phase-motor-rewind - it is well worth a look.


Yes I've been looking into rewinding it myself and that looks like a reasonable pathway. I've been looking at several videos on youtube but the only ones I've found that detail the calculations and layouts are in Hindi. I'll have a look at those links, thanks. Might have some questions for you.

[BaronJ]

Hi Pete,

If you go down the rewind it yourself route, remove one turn at a time, counting them and measuring the longest turn length. Measure the wire diameter so you know the gauge.

The idea of removing and counting turns is so you know the turn length and how many turns you need for each coil. The total weight will give you a guide as to how much wire you will need. In a three phase motor all the coils should be the same size.

Modern enamelled wire has a much more tough insulation layer than the older stuff, which is somewhat more delicate.

Make up a wood former with a removable side so you can get your new coil off the former. I've used my lathe in the past to wind coils this way. Its not difficult, but can be very time consuming.

The tedious part is fitting all the coils into the carcass, hopefully the slot insulation can be left in place and reused, if not then you will need to get some new stuff.

Hope this helps, its an interesting exercise but not a job that I would want to do too often. :U

[familyguy]

I found the same thing with youtube videos on motor rewinding, while they are of some use sadly most seem to be produced in Hindi or Indian. As Baron states it should not be too difficult to note the coil turns count, span and wire size it is just the coil connections that you'll have to dig down into the motor to find out. My situation was a bit different as I was going from single phase and back to 3 phase - however the forum called Eng-tips has some very helpful members that guided me through the coil connections. A bonus was that I had enough wire left over for a magnetiser/demagnetiser that I'm planning on making - I'm getting sick of swarfe sticking to everything.

[BaronJ]

Hi FamilyGuy,

A couple of pictures of my tool demag coil.
380954 380955
Its just a single phase washing machine pump motor with all the bits stripped away. To use it just pass your tool through the jaws or drag it across the top. You can use it hand held to demag much larger objects.
However you only have a minute in which to use it because it gets hot quite quickly. It will demag almost anything in just a few seconds though.

[Pete O]

I can bring this thread to a happy, if slightly embarrassing, conclusion. Rather than shorting the windings when I replaced the internal connection wires, I had simply mixed them up. I went inside the motor again looking at the windings in preparation for stripping the thing out, and it occurred to me that I may not have correctly identified what went where. The little identifying tags on the old wires were completely illegible- I could just make out 'A2' on one of them but nothing at all on the others- and in my ignorance I had not labelled them when dismantling the motor. I had replaced the wiring with cores from some 3-phase flex, same colour wire across each phase with red heat shrink one end and white the other, to identify pairs and groups. Turns out I had one phase reversed, which became apparent when I looked more carefully at the furrows in the lacquer where I had dug the old wires out. I partially reassembled it and did a test run, it ran quietly with no smoke so I re-labelled the connectors and reassembled. Runs like a charm. I couldn't believe it wasn't cooked after the amount of smoke that came out of it with one phase reversed, but all the pairs had the same ohm reading and no shorts to ground so i seem to have dodged a bullet. So I'm as happy as a pig in mud, after quotes of '$450 minimum' and $600 from rewinders and several hours of daunting research on a DIY job. Thanks to those who have replied with helpful advice. If nothing else, I have learned a lesson about dismantling motors without making sure the wires are labelled.

[BobL]

Good to hear its working but if you've already let some smoke out I would at consider having a Megger (insulation) test done on it otherwise it could go anytime.

[Ropetangler]

I think that BobL has a point here, but if you speak with a motor rewinder, they may be able to just clean and revarnish the windings to basically make it like new again, worth asking about it anyway IMO. In any case I wish you good fortune with it whatever you decide.

[familyguy]

That's excellent news, good to hear you have dodged a bullet, while a diy rewind might have turned out a bit of an adventure - it's an adventure that is best avoided.