Electrical Rewinding old 3-phase stator: Non-symmetrical layout

[Tom.G]

I checked my notes and reviewed the photos once more.
It for sure sums sup to something very non-symmetrical like this:

Phase A has 5 coils With 160 turns total
Phase B has 5 coils With 180 turns total.
Phase C has *4 coils With 160 turns total.

Our discrepency seems to be the B phase coil at the 2 o'clock position. The photo is unclear there and it could be labeled either '20' or '40' turns. My assumption of 20 turns was based on three observations and an assumption.

Observations:

• In the photo, the count label seemed closer to '20' than to '40'
• Phase A clearly has two 20-turn windings
• The photo may show that the coil in question has more of the bobbin end-piece showing than the 40-turn coils (this is highly questionable though)

Assumption:

• For load balancing, all phase voltages should be identical; a reason for equal turns

Perhaps @jim hardy, the local power guru, can come up with some 3-phase waveforms showing the two different interpretations. This would require accounting for the field rotor passing both the non-symmetrical physical layout and the differing turns counts. (Sorry Jim)

It may turn out that everything evens out in one of the implementations.

(Wow. A couple good posts while this was being written. Lots of various ideas.)

 

[Baluncore]

Phase A clearly has two 20-turn windings

That may be true of the faulty example, but it is not the case with all advertised replacement stators.

 

[jim hardy]

Perhaps @jim hardy, the local power guru, can come up with some 3-phase waveforms showing the two different interpretations.

My alleged brain hasn't been able to work this one mentally.
I was struggling to come up with something like baluncore wrote .

Until it's verified the regulator rectifiers are intact we have the unresolved question "Did the battery run down backwards through the winding and wreck it?" That happens a lot .

Shorting the windings doesn't hurt anything because only enough armature current flows to cancel the permanent magnet's field , that's how they regulate voltage.
However in normal operation those those armature amps flow through all 40 turns on a coil.
Should a single turn on one coil short, current in that turn will be many fold higher so will overheat that turn and damage adjacent turns on same pole. .Your photo suggests that , but it does not explain why the other phases open circuited too.
That's why i keep beating the "Look at the rectifiers" drum. It's a single point failure that can affect all 3 phases through a neutral tie.

Sorry @Tom.G , google is still rebelling and only serves me advertising.

old jim

 

[jim hardy]

I've been more distracted by the 30 degree magnets vs 20 degree coils. Sounds like "Fractional Pitch" and 2/3 pitch reduces harmonic content.
https://www.ntnu.no/c/document_libr...205-cb04-4928-9ba1-c3eed0b1f62e&groupId=27629

Anyhow - it's an experiment. My advice is build a trial with balanced windings that'll be easy to take back to original if it turns out necessary.

We don't know what goes on in the ignition coils magnetic circuit . Amp-turns in adjacent charging coils can put the squeeze on flux over there.

Nice observations by all here.

old jim

 

[Baluncore]

Here is a plot of three phases, two with peak amplitude ±1.0, one with amplitude ±0.9, plotted relative to the star common = zero.
Once the floating three phase star is perfectly rectified and referenced to zero, the output voltage varies between 1.4 and 1.7321 = √3.
Notice the minima of the rectified signal has a slight phase shift as expected.
When the phases are balanced, all with amplitude ±1.0 then the perfectly rectified output varies between 1.500 and 1.7321

 

[Baluncore]

We don't know what goes on in the ignition coils magnetic circuit . Amp-turns in adjacent charging coils can put the squeeze on flux over there.

Maybe halving the number of turns on the 3PH end coils, on either side of the HT, is a window function designed to better isolate the power from the HT.

 

[Tom.G]

Here is a plot of three phases, two with peak amplitude ±1.0, one with amplitude ±0.9, plotted relative to the star common = zero.

Nice!
What turns count distribution did you use? Since you have come up with a way to simulate the darn thing, could you make a run with the 15 coils and the turns distribution as speculated in post 19?

 

[Kjell Amundsen]

First comment I have here is that there will be a reason for this. With mass-produced Motor vehicles (and the old RD350 was a popular machine in its time), the manufacturers have spent a lot of time getting it right, so stick to the original scheme, no matter how much it doesn't make sense to you or me.

Secondly, If the Yamaha is the same as My HONDA VFR800 the three-phase AC is fed directly into a rectifier and becomes DC, so any imbalance can only have an effect of the actual windings that you are repairing.

A Question, DO you know what fried the stator windings? Was it a failure somewhere else, and you have found and repaired it, OR was it just a time thing?. My experience is that the regulator rectifier and the stator windings go hand in hand, if one fails you should be examining the other to be sure it is ok before starting it all back up again.

Some background on the Regulator-Rectifier . (R/R)
I took a quick look at an RD350 Forum and it appears that the Regulator rectifier works on the same principle as used by a lot of other motorcycles. The Field poles are permanent magnets so there is no control over the output voltage. It changes with engine RPM. In order to get useable output at low RPM the Magnets must be specified to give at least 13 to 15 Volts at idle, and as the Engine RPM Increases the voltage will increase above this, and can get to a couple of hundred volts at Max RPM if the R/R is removed.
To keep the votage down to the correct level the R/R will start shorting the output of the windings through its semiconductors, to "Pull the volts down" . This is why there is a substantial heat sink on the R/R .
If the R/R is turning on incorrectly or Failed short, this could be the reason for the fried windings.
Just a thought.
I notice, like on other motorcycles, Third parties have started marketing phase controlled Rectifiers to remove this seemingly senseless "Shorting", in a bid to make life a little easier for the stator windings.

Forgive me if I have gone a little Off Topic.Tom

You are right about the R/R part.
I have read descriptions of poor and corroded connectors and groundings as the main enemy of charging systems like these.
That is - when the battery is charged and the bike is running with low load (no main lights on), the poor connections will thus have the potential to prevent the needed current draw to "pull the volts downs" just like you described.

This supposedly can cause the voltage to rise to unwanted levels - causing overcharging to battery and and hurt other things as well.
In my case however I do not know what went wrong and started it all.

But I remembered I did charge the batteries a couple of times while the battery was hooked up to the system + ignition on while doing some other testing.
Could that be the cause of a reveres current of some sort? Must check wiring diagram for that theory.
But I am sure there was something wrong before I started charging so often, otherwise I wouldn't be needing to in the first place. So there maybe the coils were partially dead already.
I will also check the R/R itself and post the results when done.

Regards
Kjell

 

[jim hardy]

Could that be the cause of a reveres current of some sort? Must check wiring diagram for that theory.

Correcting a mistake i posted yesterday evening (thanks @Tom.G )

When a battery gets hooked up backward and the sparks fly
observe that all six rectifiers are forward biased, if ever so briefly.
One or more if them will likely fail to a short circuit during that "oops " moment. Might fail open soon afterward if the battery is stout enough to melt the internal wire.

Two shorted as shown will let the battery, when reconnected properly, run down backward through the coils and fry them. Path is in orange.

Just one shorted will interfere with normal alternator operation but I've not enough hands-on experience to tell you what symptom to expect.
Open rectifiers will give low alternator output.
If you have access to a similar machine, measure both the DC and AC across the batteries with engines at same RPM.

Image courtesy of a pretty good article at
http://www.electrosport.com/technical-resources/technical-articles/how-motorcycle-charging-system-works

 

[Baluncore]

What turns count distribution did you use? Since you have come up with a way to simulate the darn thing, could you make a run with the 15 coils and the turns distribution as speculated in post 19?

In your post #19, you propose 14 coils giving 160t : 160t : 160t. Output will vary between 3/2 and √3. Ripple will be symmetrical.

The graph I posted had phase amplitudes of 1.00 : 1.00 : 0.90, which is the equivalent of 200t : 200t : 180t. That is very close to the partially compensated 180t : 180t : 160t, with amplitudes of 1.00 : 1.00 : 0.889

I wanted to see the effect of a minor phase imbalance on the rectified output when there is no neutral connected to the centre of the star. All I have done is simulate the 3 phasors, with normalised relative amplitudes and 120 degree separation. I then perfectly rectify the 3PH by picking the difference between the highest and lowest voltage phases, which gives the output voltage plot with ripple. Such a trivial model ignores diode voltages, RPM, flux, pole position, harmonic content and reality.

 

[Tom.G]

Such a trivial model ignores diode voltages, RPM, flux, pole position, harmonic content and reality.

Ahh, I see. Perfect for what you were after. I was a hoping there was something with more detail involved. (A case of 'If wishes were horses, beggars would ride.")

 

[jim hardy]

Such a trivial model ignores diode voltages, RPM, flux, pole position, harmonic content and reality.

But it sure gives one's thinking a jumpsart...

 

[Kjell Amundsen]

Hi all.
I thought I'd add some updates after finishing my diy rewind of the stator in question. I decided to go simple, and estimated roughly 40 windings for each core. Doing it by hand is not ideal as it was hard to keep the wires as tight as a machine would. I compensated with generous amount of transformer grade varnish to finish off and secure any slack. Anyway after testing and installing, the charging system produced around 12.9 Vdc at idle and 14.5Vdc at 4-5000 rpm with the headlights lit and measured at the battery terminals. 14.5V is at the high end of what is normally required and is slightly above factory spec. Probably due to a few more total windings and or less resistance in the copper wire (uncertainty when measuring old wire gauge due to varnish). I have not bothered to measure ac phase voltages so far. I think I will just leave it with that. Thanks for interesting inputs along the way on here.

 

[anorlunda]

Moved to our new DIY forum. This thread is a perfect fit for that.