Help: diagnosing overcharging.

Well sure I realize that now. Wasent really aware of the reputation of mikes until it was too late. I thought they were the guys to go for in relation to all things xs. I'm realizing now how many other and better sources there are. But sure, you live and you learn.

I sent a used rotor to destroyasaur, It tested good and the varnish looked good yet. Since this is the second maybe third rotor to die in short order on this bike I suspect something on else in the electrical is causing the charging system (rotor) to overheat. IMHO a few hundred hard miles even in 100F ambient should not cook the rotor.
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Restomod a 79 with an eletrex rotor and stock mechanical regulator had "just" a color changing LED voltmeter. It had tended to show a bit of overcharging at speed the last couple of years but was showing good numbers this year. While doing some looking at idle voltage with various headlights I put a digital voltmeter on and was getting low voltage at idle (an H4 automotive 55/60 bulb, the stock sealed beam is 40/55ish). But that got me looking a bit further. I shore charged the battery and it would only top out at a rather low voltage, pulled the battery and found it was basically dry, yet the bike was still starting, running, "just fine". Battery was installed 2012 (I date mark all my batteries), even refilled with distilled water she was boiling and not going all the way to the "green charged LED" on the smart charger. I decided I had got my money's worth out of THAT battery and bought new.
Will be doing some more voltage at various RPM testing when some H4 LEDs get here. But today's project is a magneto rebuild on the Farmall. It's always something.

Totally agree gggGary. High speed and hot days/hot motors (I am all up in the oil temp thread) aren't his problem.
I also suspect his battery. From looking at it on the web it is a small unit without much room for water. IME a battery will boil dry on these, especially if the charge voltage is running 14+ volts. IME a unit that tops out at 13.8 volts keeps the battery fully charged. But hey they are all different animals and I don't know shit from shinola.

If he has a bad battery that keeps the charging system below the regulator's set point, the regulator will keep full current flow to the rotor windings.
Normally the rotor will have 2 to 2.2 amps for the first 10 to 20 minutes of a ride to recharge the battery. Once the battery is fully recharged, the regulator reduces the rotor current to around 1 amp.

If he was trying to charge a bad battery, the rotor current would never reduce, but stay at the 2 amps.
Power (watts) = current squared X resistance
For a fully charged battery: 1 squared X 5 = 5 watts
For a battery that is bad and does not charge: 2 squared X 5 or 4 X 5 = 20 watts

So, his rotor may have produced 20 watts of heat for the entire trip, which is 4 times the normal 5 watts.
Double the current = 4 times the amount of heat

What type of battery does DESTROY have and how old is it?
DESTROY should charge his battery with a bench charger for say 10 hours, and see if it ever reaches a full charge voltage, and then have it load tested.

jussumguy said:

I'm running a yuasa ytx5L.

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The physical size is less than 5x5x3 IIRC. A wet cell maintenance free unit. So no way to check the water level?
No math or blackboards involved but my experience is once the battery is low on water it wants to charge all the time. With a VOM it will show a charge but doesn't hold up to a load test. Once the water is re-filled it will recover IF it is still a good battery.

Another way to monitor charging system health would be to connect one of those budget digital voltmeters to the "regulated" brush terminal, or the more convenient regulator terminal. Measure between green (regulated) and ground.

Could also add a switch to an existing voltmeter, and switch between battery/brush voltage.

For the 70-79 charging system, a higher voltage would indicate higher rotor current, and higher alternator output.

For the 80-up charging system, a lower voltage would indicate higher rotor current, and higher alternator output.

For those running the 70-79 charging system with the original mechanical regulator, to prevent possible voltmeter damage, stabilize the readings, and avoid negative readings, it would be best to add a protection diode:

http://www.xs650.com/threads/alternator-rotor-inductive-kickback.42605/

Interesting about jussumguy, but I'd like to hear from DESTROYASAUR.

retiredgentleman said:

Interesting about jussumguy, but I'd like to hear from DESTROYASAUR.

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Ooops yes my bad. Zero'ed in on the battery size and didn't look at the poster.

So here's where we stand. That battery am using is an AGM 2113-0031. It's the battery that was in the bike when it came to me about 2 months ago. It tested good then, it tested good a few weeks, and it tested good last Wednesday (two days before my trip that where the rotor failed) I checked voltage on it when the bike left me stranded and it was all the way down to 7 volts. I've had it on a trickle charger since Friday. I noticed that it only went to 12.8 Volts DC even with the charger plugged In. I just brought it to oreiley and now it's testing bad. My figuring is that the battery was borderline, good enough to test as a good battery but barely. I've got a rotor coming from Custom Rewind, and I'll get a new battery. Hopefully those things together plus some spacers on my alternator cover will keep me In buisness. Just in case I'm getting a bar mounted voltmeter as well.

Just a side note, remember how one of my brushes was damaged? I went ahead and ground it down but in doing that it tended to just crumble. I got it as flat as possible but it's still not making contact on about half the brush. Could that have had an influence on frying the rotor?

It sure appears that you had a bad battery. You can't charge a bad battery, even though the regulator tries and over heats the rotor as a result.
Two failed rotors (Chinese maybe?) show that 20 watts of rotor heat, on a 100 F day, for 100 miles produces the required amount of heat to cook the rotor winding. Maybe it melts the insulation on the wire.

Brushes are inexpensive......................buy a new set.

They were both stock rotors, the mikes one was a lemon and bad from the factory. But I do think you're right, the battery sounds like somethin that checks all the boxes and has a workable solution.

What's your guys favorite source for brushes?

I like originals. N.L.A. from Yamaha but widely available on eBay for pretty much the same price as repops. Why use anything else?

Fair enough. I'll see what I can dredge up. Thank you very much RG!

DESTROYASAUR said:

It tested good then, it tested good a few weeks, and it tested good last Wednesday

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How was it tested?

DESTROYASAUR said:

...What's your guys favorite source for brushes?

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Whatever you get, examine them closely.

http://www.xs650.com/threads/another-failed-mikesxs-part.3146/page-4#post-51347

http://www.xs650.com/threads/mikes-alternator-brushes-product-warning.47536/

I had it it on the trickle charged while the bike was sitting. The actual testing was done at oriely auto parts or auto zone with their battery check machines. Always with the battery fully charged and just off the trickle charger.

I went ahead and got some brushes off eBay. They seem perfectly fine. But we'll have to see when they get here.

Rehash.....Man, you just gotta get all of those components good and working together. At every try you've had one or more bad components in the mix. Replacing everything doesn't usually have to be done either, but, your next try will probably be hindered by those reg/recs. The automotive type reg would be so much easier on your system.