Stator Woes

[Arfdog]

Hi all,
My bike kept crapping out last week, because my battery just got flatter and flatter till it was dead. It was getting no charge, so I spent some time going through the http://www.thegsresources.com/garage/gs_statorfault.htm STATOR PAGES yesterday.

I found that resistance readings between the three stator windings were equal and about 1.3 ohms, meaning the coils were continuous and in good shape. There was infinite resistance between the windings and the chassis ground, meaning the coils were still well insulated. No problem there. Then I discovered that at 2500 rpm, I was only finding roughly 7 volts AC between the three winding phases - at this point the windings were not connected to anything else.

So, my question is this: What the hell can possibly be wrong with a stator thats windings and insulation is intact? It makes no sense at all! Only thing I can think is that the magnets have demagnetised themselves, but thats not it, is it...

[tfb]

Hmm, well *if* you've followed through the flow-chart in the hallowed Stator Papers, and it says your stator is dodgy, then dodgy it is.

But, your battery is going flat, hmm? Have you considered that it might be a faulty reg/rect. unit? If the diodes in that thing get cooked, then the juice from the battery will run straight to earth when the engine isn't running, I believe. So check that out, too.

Can the magnets lose their oompfh? Well after 25 years or so, they will be losing a bit of strength... but it's debatable how much they have lost, and whether we'll see another 25 years out of the beasties.

The viabilities of re-magnetising... ... who knows.

I saw a GS somewhere on the web, where the owner had rigged up a chain drive from the crankshaft end, to an alternator he'd mounted on one of the frame downtubes, behind the front wheel. We could always pull that stunt if we happen to outlive the original stators. :-D

[SPARKSS]

Hello there "Arf". Your description of symptoms and testing is indeed puzzling and makes me wonder: Was it working correctly, as-is, just previous to this occurring? Was the stator or stator side cover removed prior to this happening? With this apparent failure just cropping up on a previously working system, after double-checking my measurements and/or measuring instrument (meter), I'd want to pull the side cover and examine, in particular, the harness for a melt-together (giving you the cross-conductor low resistance but not necessarily a short-to-ground). Examine the rotor magnets for disintegration and also for strength (this is a crude test.......for even a fair amount of attraction should cause fair output with a good stator). Make sure the rotor is still turning with the crank even. Although it sounds like you know what you're doing, I recently worked with a skilled fellow who got mixed up with his fancy auto-ranging meter while checking an ABS system.......auto-ranging = big chance for bad ju ju!

Although I see measuring coil resistance often quoted as criteria for passing-failing, bear in mind that MANY meters with low range scales have errors of .1 to .4 ohms that may or may not be compensated with the probes........Take 18 gauge copper wire for an example and see what that error amounts to at a resistance of 6.5 ohms per 1000 ft at 25C and you'll see that a single phase consisting of anywheres from 15 to 25 feet of wire would require a lot of precision (you're measuring 2 of these in series when checking a WYE wind and 2 in series, IN PARALLEL with 1 when looking at a DELTA wind!)

Bottom line......AC OUTPUT line-line AND ANY AC VOLTAGE between any LINE-GROUND (to doublecheck your resistance measurements!). Magnetic field has to be there to cut the windings (inducing voltage).....the field must be strong relative to the cutting and in the very odd case that a different stator or rotor was somehow put into the bike, it's possible that either the pole number is incompatible with the rotor OR that the air gap between the stator poles and rotor is large (small diameter stator somehow butchered in there).

All I can think of over a cup of mud here this morning

[lurch12_2000]

Just sharing my experience with my stator and r/r failure on my GS110G:

I had readings of 8v,9v,and 14v off the 3 stator wire pairings at 4k rpm and replaced the stator and new one read 56v with all pairings at 4k rpm.
Stator was now fine so no issue with magnets, resistance, etc...

Then I was able to check the R/R and found that was not reading proper output and replaced that with Honda R/R from GSR user Duaneage.

Needless to say by this time my battery was no good(dry cell and then wouldn't hold a charge) from overcharging(r/r failure) and then not charging (stator failure).

You'll have to do your own proper troubleshooting but I would get the stator voltage readings at 4k rpm, not 2500 rpm, and if not above 50-60v on all 3 pairings, accept the fact you'll have to replace($110).

More important is now with a good stator check the R/R for failure and replace($40) if faulty before possibly damaging the new stator and battery($35 if that had to be replaced) before you put any miles on it.

Again, I was very pleased with R/R replacement from Duaneage and he sent the appropriate connectors and directions.

Now if had checked the R/R when I first got the bike...maybe I would have saved $145:shock:.

[gsgeezer]

Years ago, when I read the stator papers, I just got the electrex stuff, problem solved before it started.

[Redman]

Arf,

Sounds like you know what you are doing, you did state volt reading of "7 volt AC", but whats the chance that meter was selected to DC instead of AC?

[Arfdog]

Thanks for the replies, guys.

My meter was definitely set to AC. I'm going to re-measure this evening with my other multimeter just to make sure it's not playing tricks on me.

I've got a second GS450 donor bike, and I removed the stator the other night. Unfortunately one of the wires was broken where it attaches to the single core coil wire, but I think I have fixed it and it'll hold. Just need to get hold of a new gasket before removing the faulty one, but still hoping that my multimeter was just faulty as I'm not really keen on getting all oily...

I'm in the UK, but will see what I can find on the Electrex reg, or even try cook my own one up.

[Steve]

I remember reading a problem similar to yours. Check the magnets in the rotor. What you are looking for is, I believe, three magnets attached to the inside of the rotor. A previous poster had found that one of the magnets broke and/or slipped to a different location. This causes the magnetism to hit the windings at the wrong times, which would lead to low output, even though the stator readings appeared to be OK.

Just a thought, but that's what you are looking for right now.


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