Spot the connection

Just dismantled the 2.2kW 3 phase motor from my lathe as the first step in re-commisioning it. Rather than just snip away I wondered if anyone out there could hazard a guess as to where best to start to locate the star point.

The lacing looks like a waxed cotton thread to me - similar to carpet thread, and I happen to have a small amount - do you think that is suitable when it comes to lacing it up again (assuming I get that far of course). 

The photo in my album appears much larger than it seems to in this post.

Edited By Steve Pavey on 04/10/2015 20:58:03

Just carefully cut the strapping away and it will tease away from the windings and pull out

then tease the wires out and you should easily see the star point

cut and solder on new wires and then use your strapping or small tie wraps to tidy up

Is the Star point located to the left the termination box? I see some Grey wires......

hi steve, before you hack into the windings, how many wires are there in the connector box on the motor? if there are six, you don't need to touch the wihdings

phil

That blob at 6 o'clock, could it be that? My theory says that it should be close to the first set of coils (not where the lead out wire are). this is based on the first wire goes around coil #1, then coil #4. . . the second wire goes to coil #2, then coil #5. . . wire number three goes to coil #3, then coil #6. So the ends of the wire must at the last coil, the last but one and the last but two. This should be close to coil #1, or where we came in.

Try picking out one lead out with a sharpi type marker, perhaps you can identify the start or ends of the sets of coils. A colour code would help, black, red and green or blue could be used for the input wires, then any sleeved long wire must go to aq coil or the star point.

If you consider the service of the motor, hot with vibrations, the leads must be supported really well, I am not confident that stripping away all the lacing then trying to replace it all would add to the reliability of the motor, so minimum modifications must be the way to go. Just remembered of some incidents at work, because of the internal temperature rise, the actual coils change shape and move about, just something else to fret about.

Frank

Oh how I wish there were six. Unfortunately not

John - The grey seems to be something like a piece of tape, rather than wires or sheathing. There does seem to be a couple of likely looking bits of sleeving at the 5 to 7 o'clock position - I didn't say so in the original post because I didn't want to colour anyone's thinking and I wasn't at all confident anyway.

I'm definitely all in favour of creating minimal disturbance Frank - it's a Brook Crompton motor, and everything looks so neatly laced I want to keep as much as possible intact.

I have some shrink sleeving at the ready to make the three new connections once I locate the star point - presumably soft solder is ok?

hi steve, ok its not a problem, and this may sound obvious, but you are looking for the biggest lump in the windings, find where the tails that go to the connector block are solered to the windings, and look at the same place on the other side of the windings, and also at the other end of the motor, you cen cut the string binding and remove the taping, but keep bending of the wires to a minimum. when you find the star point, unsolder the connections, solder on some tails of similar size or larger, and route them into the connector box, then tape up the connections and tie them back to the windings with cotton string, and varnish them up to stop them moving , job done!

phil

Steve,

Why do you want to find the star point? Do you now want it to be connected in a delta?

james

Star point connection splitting to convert for delta = 240 volt inverter operation (usually).

I have converted 3 so far (a tiddler that was easy as its star point was really obvious with tails soldered on, a 3/4 hp which was less easy and a 1.5 hp which was a pig!). If you look at the tails they used you might be able to identify it by elimination - if you are lucky they used colour coded tails so you want something that is NOT connected to the termination tails and NOT one of the repeated field winding connections. That is a poor description but I cant think of a better way to explain it. If you are really lucky you might have one sleeve with three different colour wires in it - that would be a result!

Mark

Edited By Mark C on 04/10/2015 23:04:37

PS. Don't forget the big green and yellow wire - I reckon after a spot of DIY electrickery in a motor, that becomes very important indeed.....

Edited By Mark C on 04/10/2015 23:07:05

When I split the star points on the motors of my mill, an elderly friend, who'd spent his working life in this area, warned me to eschew soldering the new wires in favour of using mechanical crimps. He reckoned that the temperatures reached in the windings would cause soldered joints to deteriorate. He also advised against using plastic insulation, for the same reason.

I don't know if its true, but I heeded his advice anyway.

Crimps done well cold weld and are the most reliable way of joining wires.

Neil

Just to clarify, as I have an abandoned conversion, is the star point always at the same end as the existing connections?

Must have another look at mine. When I mentioned my difficulty I got the response that 'it easy', ' I've done loads' etc.

Mark C is right - I want to run the motor from the single phase 240 v supply using a vfd. I don't know how much of the existing electrical control gear currently fitted to the lathe I will be able to incorporate (for example it has a fwd/off/rev switch on the front panel - I'm guessing that it can be wired back to a suitable vfd). Anyway, the initial aim is to convert the motor from star to delta. I have yet to even look at the coolant pump, except to note that it has 3 red wires attached to it so is obviously another candidate for conversion.

I'll try to take some more photos this afternoon when I get the scalpel and plastic 'spudger' out.

Re the crimps vs soldered joints - I would think that if the solder was going to be affected by heat then the motor will have other, more major problems, so while I agree that crimp connections are excellent i'm not sure they are absolutely necessary. They are also fairly bulky compared to a soldered and shrink-sleeved connection, which might make it tricky to lace everything back together neatly. The heat shrink sleeve I have is rated up to 125°C and again, if the motor runs correctly after my surgery, it won't get anywhere near that temperature.

Bazyle,

It is easy but some are less so. It requires patience and a steady hand along with a bit of thought as to what you are doing. If you are ham fisted it is probably not a good idea to try but for anyone used to fixing stuff it should be straight forward. Hardest part is finding the connection in the first place- which is what started this thread!

Mark

Steve,

You might find your luck is in with the coolant pump - they tend to be dual voltage from my experience. You will need another inverter for the coolant pump or the motors will be very un-matched and both will vary speed together - which might be good for matching flow to rpm but I will bet the pump rate will not be linear with rpm! This might be a good time to investigate capacitor running of a synthetic phase.

The switch gear should be capable of re-wiring but it might take a bit of working out (I am assuming it is a "standard" rotary switch with multiple poles). You will then only need an emergency stop switch (assuming you want to wire one) which will shut the thing down if the rotary switch fails or some other disaster ensues. You will probably want to wire for "two wire" control and should be able to find a diagram that works for your inverter along with the correct programming parameters. All that you need then is a pot for speed control - check the value for your inverter as they are not all the same (some 5K others 10 and I have one that needs 4K7).

Mark

Heres a series of pics I did to illustrate an article on how to change from star to delta

its a brook motor so very similar to yours

Edited By Ian Parkin on 05/10/2015 11:08:38

Then after checking continuity heat shrink the connections twice and wrap or tie wrap all the wires back into place

colour code or mark each pair and bring the wires out to the connection box and reconnect as delta

Ian

Regarding soldered connection, and over heating, if we had any reservations we used to silver solder them. I have used crimp connectors as there usually space some where to fit them in. Not so neat as a soldered one. I'm out of tough, but know doubt sister flex is still available, from the local re winders, but heat shrink is good and air drying varnish is also available via the net. Ian says he did an article on converting from Star to Delta using a Brook motor, has the article been published and if so where. Perhaps he could send a PM or publish here for more to see. John

When I wound motors in our winding shop we used oxy-acetylene to fuse the two wires into a small ball. To lace the windings we used flat cotton tape about 10mm wide and a piece of lewmex wire as a needle to thread it through the windings, systoflex heat resistant glass fibre based sleeving was used to sleeve joints.

Mike

Edited By Michael Poole on 05/10/2015 13:26:00

A scalpel and some blunt softwood wedges later, and I have this - (1) undoing the lacing, (2) separating the wires with softwood wedges, and (3) opening up the sleeve to reveal what is hopefully the star point:

There is only one other place where three wires come together, but two of them are clearly the original wires leading out to the connection box, so this is the one I chose to dissect. I'm fairly happy that the 3 wire connection in the last photo is the star point, but if anyone knows different I would think now is a good time to shout!

I have some glass fibre type heat resistant sleeving but I'm waiting for some coloured heat shrink sleeving and numbered collars to arrive courtesy of eBay (hopefully tomorrow). I think there is enough room for crimp connections if I want to use them.

All the information above has been really helpful, especially Ian's photos and the info on the coolant pump motor etc from Mark - I think John Mills (Doubleboost on Youtube) converted his coolant pump to single phase with a capacitor so I need to have a dig through his videos and find some info on capacitor sizes.

Have yet to choose and buy a suitable vfd - presumably they all cater for wiring in external control switches (???). I'm not sure what you mean by '2 wire control' Mark, but perhaps that will become clear when it comes to wiring up the vfd.