Low stator output; bad rotor?

[evanwilliams]

Hello,

I have an 85 Honda Shadow VT700C that can't hold a charge. I've replaced the stator (it was shorting to ground) and I thought that was the only problem, but the bike still wouldn't charge. My battery was old so I replaced it, still no luck. After finding the info mentioned by TechBMW (on the "charging problems" topic below) and completing the tests, I'm pretty sure my reg/rec is fine, and my stator is still good (2 wires read 2.3 resistance on the ohmmeter and one reads .6, all within the range TechBMW mentioned--none of them read anything to ground).

Now for my question, I read that you can test the AC volts between any 2 of the 3 stator wires and they should read anywhere from 20-50V depending on RPM; mine reads 0.8-1.5V--RPMs don't affect output. Since my stator passed both the resistance and ground test, does this mean my rotor is weak/bad? Does anyone have any recommendations for where to get a replacement, are used ones ok?

Thanks for any help anyone may have,
-Evan

[evanwilliams]

After giving it some more thought, the resistance readings (in ohms) between each of the three stator wires is 2.3, 2.3, and 0.6. Touching the probes of my ohmmeter together gives a reading of 0.4. Subtracting this from the reading I have above, I think that one coil is out of spec and is likely to be the problem. I'll remove my stator and take it to the shop to be checked out.

Does anyone have any experience with chronic stator failure? Any ideas why my OEM stator lasted the bike for 45k miles while the last 2 have lasted about 16k miles total? I'm thinking (hoping!) the rebuilt units I got were subpar.

-Evan

[Gummiente]

Was there any damage to the inside of the stator? Any of the varnish on the wires rubbed away? Could be that the rotor is grinding away at it and eventually shorting out the stator in one spot. Check the bearing and shaft of the rotor for excessive freeplay.

[evanwilliams]

I just removed the stator. It doesn't look like the rotor has rubbed it at all, and the rotor still seems magnetized. What I did find though was some burnt flecks around some parts of the stator, especially where the 3 main feed wires left the core/winding.

My bike appears to be killing stators; the first (OEM) lasted for about 45k miles then shorted to ground, I replaced that 2 years ago and last summer (after about 15k miles) it failed again by shorting to ground. Just 2 weeks ago I decided to get my bike running because of gas prices and replaced the stator again (with the current one that I'm posting about) and now it appears to have burnt/opened and increased resistance. WTF?

From what I understand, charging systems like mine--85 Honda Shadow VT700C--have the stator pruduce full output at all times and then just shunt the excess/not needed voltage to ground. So even if there was a short somewhere in the bike causing excess drain, I wouldn't think the stator would be affected as it would be producing electricity at full blast no matter what. Maybe the voltage reg would be in trouble if I had a short but mine passed all the tests and when the stator was working I was getting about 14.5 volts to the battery.

I got both replacement stators from a local shop--the were rebuilt ones. Has anyone had any experience with ElectroSport products? Any ideas?

-Evan

[Gummiente]

From what I understand, charging systems like mine--85 Honda Shadow VT700C--have the stator pruduce full output at all times and then just shunt the excess/not needed voltage to ground. So even if there was a short somewhere in the bike causing excess drain, I wouldn't think the stator would be affected as it would be producing electricity at full blast no matter what.

With a permanent magnet rotor, power output varies with engine speed. The regulator/rectifier controls how much current flows through the system and makes sure the battery is charged as well; if you're getting 14.5VDC at idle that sounds about right, but what does it read when you twist the throttle? It should stay at 14.5VDC, any more than that indicates a faulty reg/rect and usually results in a burnt out stator.

[Gummiente]

From what I understand, charging systems like mine--85 Honda Shadow VT700C--have the stator pruduce full output at all times and then just shunt the excess/not needed voltage to ground. So even if there was a short somewhere in the bike causing excess drain, I wouldn't think the stator would be affected as it would be producing electricity at full blast no matter what.

With a permanent magnet rotor, power output from the stator varies with engine speed. The regulator/rectifier controls how much current flows through the system (and makes sure the battery is charged as well). If you're getting 14.5VDC at idle that sounds about right, but what does it read when you twist the throttle? It should stay at 14.5VDC, any more than that indicates a faulty reg/rect and usually results in a burnt out stator.

[evanwilliams]

Gummiente,

My voltage between posts is 11-12V when the bike is running, that's the problem. I know my charging system is busted, and I'm quite certain it's the stator, in my earlier posts I mentioned how a continuity test with an ohmmeter gives me 2.3, 2.3, 0.6 between when testing between the 3 wires running from my stator. None of them are shorted to ground.

What my real problem is now is finding out why I've lost 3 stators in this bike in the last 2 years. 1 OEM, 2 rebuilts. I thought it may be a short somewhere on the bike is drawing enough juice to burn out the stator, but after reading a good bit about this on the net, I don't think that's the case as a stator (not my damanged ones, obviously) is always giving out full power when the bike is running, RPMs affect output but the stator is always generating as much juice as possible at any given RPM; which the voltage reg then limits. My rec passed all the diode tests I can throw at it, and when my stator WAS working, my reg gave about 14-15V to my battery... which means that's good too.

I'm beginning to think I've been getting screwed by my local bike shop with badly rewound stators (the last 2 I got were from the same shop). Unless someone can explain how my bike could cause the stator to meltdown.

Thanks for your reply--it's lonely out here when you're looking for electrical help.

-Evan

[TechTMW]

Hi Evan, sorry I didn't see this sooner...

When you dynamic tested the stator (Bike running, stator unplugged from the regulator, voltmeter leads on the stator wires) you were only getting .8 - 1.5 volt??

I think that you are getting bad stators. Your first (OEM) stator lasted a decent amount of time. Maybe you should buy a new stator instead of rebuilt? Unless you take it to the shop (W/ your reciept) and they give you a new one for nothing.

[evanwilliams]

Hi TechBMW,

I was thinking the same thing; I'm prolly going to get an Electrex stator instead of another rebuilt. I just assumed wires were wires, but I guess I was wrong. What has me concerned is what (if anything) on my bike would cause the stator to fail. Read my last post in this thread, second paragraph, does that makes sense when I think there really isn't anything on my bike that could cause the stator to burn out?... since it's always going at full blast independent of demand from the bike.

Unfortunately for me, I don't think the shop will take back the old stator, as the receipt says ABSOLUTELY NO RETURNS ON ELECTRICAL PARTS and the guy there is kinda a d*ck... which is another reason I won't be buying another part from that shop.

Thanks for the reply,
-Evan

[TechTMW]

Evan, you've got it a bit wrong Gummi's right on this one - a stator's output is dependant on RPM. Typically a stator will put out ~18Vac - 20Vac per 1krpm ... so at 10,000rpm, a stator should be putting out 200 volts ac. It is sufficient to perform your dynamic test at idle, however!!

Like I said, I think you got bad stators. You should let the guy know that both stators you bought from him went bad and you won't be buying from him again.

When a stator goes bad and you get continuity to ground, this is called an Insulation breakdown. This usually results from time or a crappy rebuild. Your third stator hasn't got resistance between one of the coils, therefore I think it was probably a bad winding job.

In sum, I think your stators were bad, but the fault is not wth the bike, since the stators failed for different reasons. If you buy a factory stator (or OEM quality) and IT goes bad, then you might want to look at the bike. But right off the top of my head I can't think of anything (except loose bits of metal or something rolling around the stator housing) that would cause a stator to fail.