Generator stator winding - Page 1
Forum section: electronics / repair

author: JohnLynn
author_rank: Newbie
timestamp: September 15, 2018, 08:04:03 pm
content: I am new to this forum, I was recommended to join by members of the Arduino forum as I have a question about stator rewinding. I will try to explain as concisely as possible.I have a 4.5Kw (Chinese made) diesel single phase 240 volt generator which has some windings of the stator coils flashed over and burnt.It cannot economically be rewound professionally so I would like to try this myself to further my knowledge and hobby. The time needed to do it is of no concern, I would feel very rewarded if I can do it.The main winding has 10 slots and coils of 0.8mm wire with a separate single coil of 0.6 wire for the AVR sensing.As it is very difficult to dismantle the coils to see how they are wound I am hoping that someone may know if there is a standard method?I have painstakingly tested the coils for continuity as far as I can but unfortunately some wiring has blown apart and it is impossible to tell where it should go.Around one half (five coil slots) of the stator wiring is intact and I can see that there are four wires bunched together which have ten turns in each coil slot before moving to the next. Along side these are another four bunched wires with only one turn in each coil. I assume but do not know that this could be the AVR comparison?Any help or advice would be much appreciated.

author: PaulAm
author_rank: Frequent Contributor
timestamp: September 15, 2018, 08:51:00 pm
content: You probably need to dig up a couple of books on rebuilding electric motors and generators. If you can find them, the copyrights are from the 50s or so. Except for large or special purpose motors rebuilding them now (except for bearings) is more or less uneconomical so you won't find anything recent on that. The controls have changed a bit, but not the basic principles.The winding geometry is pretty much determined by the output frequency, number of phases and the engine rpm. Once you get the basic principles down you should be able to make sense of what you're looking at. Single phase should make that easier.In the 60's genset I've been working on, the voltage is controlled by managing the current through the rotor and all the stator windings are used for the output.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: September 15, 2018, 09:31:31 pm
content: Welcome to the forum John. If you can find a company in your city that rewinds motors or gensets, I would simply go down and try to open a conversation with the owner to get direct advice. The problem that you are facing is that you have 2 separate issues when rewinding:First issue is the technology or design parameters/principles regarding the particular generator as in; the windings configuration and the sense circuit. There is a control PCB that is in control of this and good knowledge of the design theory of this particular generator is paramount to understand.Second issue is the actual craft of howto lay the windings and protections utilized, as in the materials used to separate windings as well as any coatings. This is done by craftsman that have done this for many years in order to master their craft. The input that you could get from the people actually doing windings in such a company would be invaluable.Also, as PaulAM suggested, find a few good books from way back when the craft was getting started, your local winding company may also offer some suggestions.Hope this helps...

author: petemate
author_rank: Regular Contributor
timestamp: September 16, 2018, 12:40:48 am
content: Hi, I recently tried rewiring my motorcycle stator and failed completely. Here is what I have learned. Keep in mind that I am an electrical engineer by trade, so while I have a lot of experience designing and spec'ing components, I have little practical assembly experience.Wiring and re-wiring magnetic components is hard work. Especially with thick-ish wire. Its literally exhausting having to do the same thing hundreds of times, while at the same time holding a large piece of metal and holding on to the already wound turns in order to make sure that they don't slip and ruin your hard work. Its easy to lose track of what turn you got to. Its also going to take a lot of copper wire.While you have shown no pictures of your stator, I would expect that your stator has a number of arms that are dipped in some sort of epoxy. Typically green or blue. Thats the green stuff you see here:https://www.eceurope.com/oc-content/uploads/128/12167.jpg. Its put on to give a bit of distance between the copper wires and the metal, to make sure the windings doesn't eat into the sharp edges and create shorts. On top of that are the windings and on top of that is some varnish. The varnish is applied to the transformer using a dipping process or a vacuum impregnation process. Vacuum impregnation is by far the best(and most expensive), since it makes sure the varnish enters every nook and cranny between the windings. This also means that the windings is one solid block that is very hard to remove. You *will* cut your hands on the sometimes razor-sharp varnish left on the wires as you unwind them. And the windings will break as you pull them off, which means that you at some point end up with nothing to grab on to. Then you got to hack away at it.When you got all the old turns removed(don't forget to count very carefully), you are down to a bare core, with lots of varnish leftovers on it. The leftovers produce a series of grooves, according to how the windings were previously placed. Its as good as impossible to place it back into those grooves, so that must be removed as well. Thats very hard to do, without removing the epoxy coating as well. So thats gotta go as well.Now you are down to the bare core. Then you need the epoxy to re-coat the stator core and varnish to re-impregnate the windings. I spent *a lot* of time getting my hands on some. It is literally impossible to get your hands on as an individual(ie non-commercial), especially for a one-time run. Thats what made me quit the operation, cause i realized that I could never get my hands on it. I tried rewinding on top of the left-over varnish grooves, but its impossible to fit the same amount of windings back onto the stator.

author: JohnLynn
author_rank: Newbie
timestamp: September 16, 2018, 07:53:30 am
content: Thank you all for your replies. I should have posted more information in my first post so here is a little more to add to the saga.There are many of these Chinese made generators on the market, usually a cheap clone of a decent machine at a fraction of the price, of course this shows in the quality of the build. Many have stickers claiming "made in the UK" or "made in Germany" written on them, they often claim to be 18 Kva not the 5 which they are in reality, even using a sticker claiming to be made by Perkins or Cummins.I have repaired a few, usually I am lucky and the problem is caused by the AVR, brushes or an easily repairable wiring problem. A common issue is a break down of insulation between the main and battery charging winding. The coils are laced tightly together with no insulation strips in between. If I did manage to rewind mine I would add some insulation.I visited a rewind shop who were very helpful, they sold me the correct wire, however they told me if they repaired it that they would have to dismantle the stator to examine how it was wound. They put it in an oven at 250C to melt the varnish first then count the windings etc. I am not sure that my wife would take kindly to having a stator baked in the oven though!I have attached a couple of pictures so you can (hopefully) see what I am talking about, one end of the stator has coils that just loop through, the other end where the problem lies has the connections. The top and bottom coils in the second picture are a battery charging coil which I do not need. Most generators have this, an unregulated 12 volt 8 amp output. the bottom coil is the AVR sensor.As said before the main output is 220 volt single phase 50 hz so the engine speed is 3000 rpm.

author: PKTKS
author_rank: Super Contributor
timestamp: September 17, 2018, 01:17:46 pm
content: I can confirm that it is almost impossible to do that manually onlyYou do need some sort of bench gig with a counter - or it will fail.Cheap alternatives exist . try ALIBABAManual Coil WinderHand Coil Counting Winding MachineVery cheap ones and some really good ones as wellCHEAPO on this folk for under 30 boxhttps://www.aliexpress.com/store/4406184?spm=a2g03.12010108.nav-home.1.43a1275b4muYaX