Hi guys.
I have motorbike that has a 3 phase anternatoor coil connected in delta. It failed and I decided to rewind it by hand. I used the same 1.12mm wire as it had before. It failed again in 4000 klms. I will clean it again in a couple days to check what may causes the damage and I hope the cause was something I did wrong.

the OEM stator though is not so reliable so me rewinding it the same way maybe makes it not so reliable again?

Can I change something to make it tougher?

Currently it has 6 coils of 50windings each making it 300 windings on each phase.

Could I use a little thicker wire, like 1.15 to make it tougher or do less windings or anything?

Thanks in advance for any help

 

How does it fail?
Sounds like the load may be too great.
A bad regulator could to that.

 

It fries on one of the coils and shortcircuits to ground. The regulator constantly keeps the voltage at 14.1v. I have inspected with a multimeter by diode testing it and it seems fine. I have read somewhere that on my model the magnets on the flyeheel are a little too powerful and cause the coil to overheat and thats why the OEM stator is not so reliable.

 

I have read somewhere that on my model the magnets on the flyeheel are a little too powerful and cause the coil to overheat and thats why the OEM stator is not so reliable.

If that's the case you might try fewer turns to reduce the voltage.
But without knowing the open circuit voltage of the alternator it's a guess as to how many to remove.

You could try rewinding it with the original number of turns and then measure the stator open circuit AC voltage.
It should be around 15-25Vrms at idle.
That will increase as the engine speed increases.
If it's significantly above that voltage then you could try removing some turns.
Removing 1 turn from each winding will reduce the voltage by a factor of about 1/300 or 0.33%.

 

Thicker wire means better current output, i would rewind both the stator and rotor, it could be one of the bridge diodes thats failing causing burnout.

 

I remember measuring ac voltage between phases with the stator disconnected from the rectifier and wqs getting around 20volts at idle. I have a voltgauge installed on my bike and see that even on idle the voltage is 14.1. I can see it drop only when the radiator fan turns on. You think by reducing the turns I could make it run a little cooler?
And if so, how many turns should I remove? Each phase has 300 turns as I said earlier divided into 6 coils of 50.

What do you mean stator and rotor?
My system has e permanent magnet flywheel that revolves around the stator that carries the coil.
I have tested all the diodes on my regulator and they seem ok.

 

I remember measuring ac voltage between phases with the stator disconnected from the rectifier and wqs getting around 20volts at idle.

If you are getting 20Vac at idle then you probably don't want to reduce the turns much.
You might try going to one wire gauge size larger and use that to wind as near to the originals number of turns as possible on all the coils.
That would reduce the heat generated by the current in the winding resistance, which is what causes the failure.

The rotor is the part that rotates and the stator has the coils.

 

Cool. I will try the 1.15mm then. Lets hope it fits cause the 1.12 was tight enough!

 

Cool. I will try the 1.15mm then. Lets hope it fits cause the 1.12 was tight enough!

Just wind as many turns as you can.

 

The calculation is linear? For example if I wind 1 turn less on each coil which makes a total of 6 out of 300 this means I lose 6/300 voltage? which means 2% voltage loss overall? Like 0.3v at idle?

 

It's a honda cbr1000rr 2005 model. And it is known to have this issue with the OEM stator :-(

 

I just found out this announcement

"American Honda has determined that riding a 2004-2005 CBR1000RR motorcycle in the low rpm range for an
extended period of time may cause the ACG to overheat, which causes a short circuit of the stator windings,
resulting in insufficient battery charging."

How is that possible that low rpms overheats the coil but high rpms don't???

 

How is that possible that low rpms overheats the coil but high rpms don't???

That's a puzzle to me also, since the alternator puts out more current at higher RPMs.

 

Yeah I have already read about that but I think I am outside of warranty. The bike has changed 4 owners, I am the 5th and I think the warranty was up to 6 years? Also I still have a lot of 1.12mm from my first rewind and 1.15mm wire cause I have rewind a friends ZX10 2009 model which also fried the stator...
So I will try rewinding it again with 1.15mm wire and some fewer turns. If it fails again I will probably look into getting an electrosport stator. I hope I won't have to spend money on this though.

 

Well I have already done couple of rewinds. Also I have a volt gauge installed on my bike so I am all the time aware of my charging system. The good thing was that the stator shorted managed to produce enough voltage to get me back home
I was seeing 12.5v at idle and 13.0 volts around 6-7k rpm. Lets hope the next rewind holds. Else I will go with the electrosport one.

 

Is it possable that the stator was wound with the wrong temperature rated wire? the original lasted a lot longer than your rewind, did you use the correct grade of wire?

From here, https://en.wikipedia.org/wiki/Magnet_wire
Although described as "enameled", enameled wire is not, in fact, coated with either a layer of enamel paint nor with vitreous enamel made of fused glass powder. Modern magnet wire typically uses one to four layers (in the case of quad-film type wire) of polymer film insulation, often of two different compositions, to provide a tough, continuous insulating layer. Magnet wire insulating films use (in order of increasing temperature range) polyvinyl formal (Formvar), polyurethane, polyamide, polyester, polyester-polyimide, polyamide-polyimide (or amide-imide), and polyimide.[3] Polyimide insulated magnet wire is capable of operation at up to 250 °C. The insulation of thicker square or rectangular magnet wire is often augmented by wrapping it with a high-temperature polyimide or fiberglass tape, and completed windings are often vacuum impregnated with an insulating varnish to improve insulation strength and long-term reliability of the winding

 

Yeah the wire I got is rated up to 250C with double insulation. I don't think the wire is the problem.
On the arm that got damaged the first time, the epoxy insulation was damaged too. And I coated it with teflon. I want to see if the damage is on the same arm again and if the issue was that the teflon didn't hold. If so I will repair the arm with epoxy this time.

 

Ok
So I unwound the stator today. The problem was on exactly the same spot it shorted the previous time. So the insulation I did with the teflon tape didn't hold. I think that the vibrations caused the metal (which was very sharp) to tear the teflon tape (it was just wound around it) and short the wire. I have rounded the metal a little bit and I will coat any exposed area with a high temperature epoxy and try again with the 1.12mm wire.

 

I have rounded the metal a little bit

Good idea. Not only are the windings subjected to vehicle vibration, but because they pass AC adjacent turns attract/repel each other at the AC frequency causing high frequency vibration unless they are glued together.

 

Good idea. Not only are the windings subjected to vehicle vibration, but because they pass AC adjacent turns attract/repel each other at the AC frequency causing high frequency vibration unless they are glued together.

Yeah
I hope that with the epoxy it will last. It is rated to 180c temperature
And I have already used it on a friends ZX10 stator which still works fine after 4-5k kilometers