Stator shows 1.3 ohms

[smokinjoefission]

Hi All,

first, I'm a long time lurker but this is my first post, greets!

I've got an '81 XS650H and am diagnosing a weak charging system. The old battery would let me ride for about 15 mins before the engine would just die. A brand new Yuasa seems to let me go for at least 1/2 hour, but a fresh charge goes from 12.5 volts to 11.9 volts during that period.

Voltage at 2500 rpm seems to be ok at around 14 volts but the battery just doesn't seem to charge from the alternator.

Going through the book and what I've read online, I've checked out/tested the brushes (14.5mm long, both), regulator/rectifier (no short circuits, no open paths), alternator coil (it magnetizes when the ignition is on) and now the stator.

Right off, it shows 1.3 ohms of resistance (brushes removed) where the manual says 5 - 7 ohms.

Soooo ... is it time for a new stator? If so, where's the best place to get it from?

Thanks in advance,

SJF

 

[xjwmx]

If you're reading 14v on the battery at 2500 rpm it should be charging, regardless of any reading anywhere else.


If the battery isn't charging then it would have to be bad. You say it's brand new; did you put it on a charger before you installed it?

 

[smokinjoefission]

OK, I'm a 'tard. I meant 'rotor', not 'stator'.

Yes, the new battery was fully charged. I measured the voltage before I started the bike, went for a ride, then measured again.

Thanks!

 

[xjwmx]

OK, I'm a 'tard. I meant 'rotor', not 'stator'.

Yes, the new battery was fully charged.

Thanks!

No, "did you put it on a charger?"

 

[xjwmx]

I ask because as soon as you put the acid in the battery and let it sit awhile it will read 12v and work to some degree. But in my experience they're funny unless you actually charge them with a charger, about 1-2 amp setting for a few hours until the charged light comes on.

 

[smokinjoefission]

I had the battery on a 1 amp charge for 12 hours before I installed it

 

[xjwmx]

After your half hour ride when you measure 11.9, is that with the engine off? What does it read at that point at 2500 rpm? 14 still? What has to happen for it to measure 14? What you're seeing might be normal. When mine reads above 14 it has to kind of work its way up there through repeated revings. Each rev gets it a bit higher. Not like a car at all, where it gets slammed to 14.6 and just sticks there.

 

[pamcopete]

smokin...,

It is a little odd that you would measure 1.3 Ohms across the slip rings of the rotor and yet still show 14 Volts at 2500 RPM, and also say that the battery does not hold a charge, so we need to verify the reading across the slip rings. If it is in fact 1.3 Ohms, then the rotor has to be replaced.

I would suggest that you go to Radio Shack and buy a couple of 10 Ohms resistors, twist them together in parallel and measure their resistance. Should be 5 Ohms. Do this to verify that your meter is OK and that you are using the correct technique.

If it is the rotor, then call Gary at Custom Rewind in Birmingham, AL @ 800 798 7282 for a rewound rotor. They are $125 plus shipping and your core. Ask him if his rotor puller tool is available on loan, otherwise you will have to buy a puller from MikesXS. Do not even think about pulling the rotor without this tool or you will damage the rotor and lose the core charge.

And, I hate to say this, but it has happened..........remove the rotor nut before pulling the rotor....

 

[smokinjoefission]

Pamcopete,

I used two separate meters: one reads 0.4 ohms across its leads, the other reads 0.3 across its leads (they're cheapie Canadian Tire units) so I subtracted those values from the reading across the slip rings.

I'm theorizing here, but as for the 14 volt reading at 2500 rpm, it may be due to a short in the stator's windings that's allowing a long enough path for enough magnetic field to be built up for it, but not enough to provide enough current to charge the battery.

MikesXS has a new rotor for $139, so after shipping is considered, would it not be better to just get that instead of a rewind?

Xjwm,

both the voltage levels of the battery were taken with the engine off.

Thanks all for the advice so far!

SJF

 

[pamcopete]

smoke....,

MikesXS doesn't ship those rotors any more. Not sure why he still has them in his catalog.

Did you mean to say rotor instead of stator? Because that is probably what is happening. Depending on where in the rotor winding the short is, it's possible for the rotor to still produce a weak magnetic field that will produce some output, but not enough to carry the load. The low resistance will potentially damage the regulator because of the additional current it draws.

So, because of the expense, I would suggest that you do the Radio Shack resistor test to verify your meter.

Be wary of cheaper new or rewound rotors on Ebay. One of the things that is not obvious is the slip ring run out, which on a cheap rotor can be very bad. Excessive runout causes the brushes to wear prematurely and also creates "valleys" in the slip rings where the brush residue collects and produces high resistance that results in a low output after just a few miles.

I ran a couple of examples of rotors on my lathe

Here is a video of a bad slip ring run out on a new rotor:

Video of a Bad New Rotor

and here is a video of a Custom Rewind rotor:

Video of a Custom Rewind Rotor


The slip rings on the bad new rotor had to be cleaned about every 100 miles due to low voltage at the battery.

The bad new rotor in the video was actually more expensive than the Custom Rewind rotor. There are also cheaper rotors out there as well, so you can go high and you can go low, but you can't beat Custom Rewind.

 

[retiredgentleman]

Great videos Pete!

 

[pamcopete]

RG,

Yea...as long as nobody asks me how I know so much about bad new rotors that cost more than Custom Rewind!! (Don't ask....)

 

[xjwmx]

Pamcopete,

I'm theorizing here, but as for the 14 volt reading at 2500 rpm, it may be due to a short in the stator's windings that's allowing a long enough path for enough magnetic field to be built up for it, but not enough to provide enough current to charge the battery.

SJF

No, there's no thing as not enough current to charge the battery, if the voltage is staying at 14. If it couldn't supply all the current the battery is capable of drawing, the voltage would drop according to I= V/R.

That's why I said if you see 14 the battery should be charging, regardless of any other measurement . If the rotor wasn't even there but you somehow read 14, the battery should be charging

 

[pamcopete]

xjwmx,

Well, of course. If there is 14 volts available and if the battery needed to be charged, then current would flow and charge the battery, but there is some contradiction in what smoke says about all that:

"I've got an '81 XS650H and am diagnosing a weak charging system. The old battery would let me ride for about 15 mins before the engine would just die. A brand new Yuasa seems to let me go for at least 1/2 hour, but a fresh charge goes from 12.5 volts to 11.9 volts during that period.

Voltage at 2500 rpm seems to be ok at around 14 volts but the battery just doesn't seem to charge from the alternator

 

[xjwmx]

I do realize it doesn't make sense. Maybe he mis-measured the rotor and everything is ok really. Gripped both probes with sweaty fingers and read both resistances or something.

 

[pamcopete]

xjwmx,

Yes, something doesn't add up, so I would use the corollary to yours and say that if the rotor is confirmed to have 1.3 Ohms across the slip rings, then it has to be replaced.

I don't know if he has a stock setup with the safety relay to turn on the headlight. Perhaps the 14 Volts happens when the headlight is off, but if he has a way of turning it on, then that would definitely drop the available voltage / current to charge the battery when he is underway.

 

[smokinjoefission]

I phoned a local Yamaha dealer on a lark just to see if 1) they had a replacement rotor and 2) how much. I knew I was in for a giggle, but not this much of one: 1) no but if they did it would have been 2) $850

Looks like I'll be sending it out for a rewind.

 

[xjwmx]

xjwmx,
I don't know if he has a stock setup with the safety relay to turn on the headlight. Perhaps the 14 Volts happens when the headlight is off, but if he has a way of turning it on, then that would definitely drop the available voltage / current to charge the battery when he is underway.

Pete, I'm curious about something. Is the starter circuit cutoff relay energized whenever the bike is running? I know you can't use the starter then, but is that why? I can't find a diagram that shows its internals well enough.

 

[pamcopete]

xjwmx,

The safety relay removes +12 from the starter solenoid so you cannot operate the starter motor after the engine has started. It also helps to disengage the #4 gear because it operates faster that you can release the start button.

The safety relay also turns on the headlight. In fact, with '80 to '83 models, there is no headlight switch and you are completely Dependant on the safety relay to turn on the headlight. But, the safety relay in later models has an additional latching relay that keeps the headlight on should the alternator quit, which just leaves one problem.....if your alternator quits and you shut off the engine, the headlight will not come on when you restart...bummer...especially at night.

I think all of this complexity was a case of lawyers trying to be engineers. They don't want you to ride home at night if your alternator is not working. God knows what the hell they expect you to do under those circumstances. Any thing, I suppose, as long as it doesn't involve liability for Yamaha.

I got around this stupidity by installing a relay on the neutral switch that turns the headlight off when in neutral. I also installed a diode to illuminate the headlight white light if the alternator is not producing, so I will be warned but able to ride home, or to some other safe location.

 

[xjwmx]

Thanks. My reason for asking was I replaced a broken clutch switch with a jumper, so I could still start it in gear without the switch. The clutch switch is wired to the starter circuit cutoff relay. I guess the line from the alternator is or'ed with the clutch switch so that the relay would be energized when the engine was running anyhow. The diagrams all just present the relay as a functional block so I don't know what goes where internally.