Stops charging at highway speeds

JP50515

XS650 Junkie
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Hey guys,

Got an 82' heritage special. Had a really bad battery, so I replaced it today. The bike charges the battery over 14.5V until I let on it and rev over 6 grand. I can tell when the voltage drops while riding if I burst onto the highway quick because the turn signals stop working until I sit at lower RPM's for a while.

I've seen the opposite where low revs won't charge, but I've never seen it this way.

Anyone experience this before? I've had a bad reg/rect, that would push high voltage at higher RPM's due to a bad ground, but I rode the bike 85 miles today with a brand new battery, and halfway through it was sitting at 11.99V turned off and 14.5V running and revved to 3 grand. At the end of the ride I layed into the throttle, lost turn signals, and the battery was sitting at 10.5V when off, and 11.5V running for about 2 minutes then it jumped over 12 while idling.


Any ideas?
 
When you accelerate does the headlight dim? And when you decelerate it will brighten?
 
Check the resistance of your windings.
I had a rotor that was going bad, and my symptoms were similar. I monitored my problem not with turn signals blinking or not, but with a handlebar mounted volt gauge, which everyone should have.
Anyways, my theory was that at 6000 rpm the ignition system has to produce twice as many sparks as it does at 3000 rpm, and the failing rotor just couldn't keep up with that electrical load.
The rotor completely failed (direct short -- zero resistance -- between the windings as I recall) very soon after.

BTW, the readings you are getting from your brand new battery are too low. A functioning battery should be at least about 12.2 volts, and a new battery should be about 12.7. Your low readings could be failing-rotor related. You'll never know what's really happening when you're riding without a handlebar mounted gauge.
 
Good info there guys.

I am going to pop that stator cover off tonight and pull some readings.

The headlight was dimming and getting brighter with revs with the old battery, but doesn't seem to do it with the new one.

The low voltage readings lead me to believe the system is pulling more than its replacing. It's a very clean bike, and completely unmolested (luckily) so I'm going to pull some numbers and compare against the charging guide tonight.

I'll post back with the results.

Sidebar:

If it is the rotor, anyone have any complaints about hugh's PMA? I've only ever heard good things about it.
 
Alright so a bit of an update here.

Dug into the XS tonight and found what appears to be where a mouse or some rodent chewed on the battery return from the stator (red). So I cut that part out, cleaned up the wire, and all the terminals, soldered it back together and what'ya know I got 13.5V at idle and 14.5 a 3000, never getting much higher than that as I revved higher.

Took it out for a spin to see if the problem was solved, had no issues, goosed it real hard (since that's where the problem always begins) get back and it's at 12.45 V at idle and 12.24V at 3grand....the problem persists.

What stumps me is these are about the same (a bit higher) numbers i've been getting up until I fixed that wire...it teased me with in spec readings.

I have a feeling the issue is heat related as its still charging the battery just enough after it stops fully charging to idle all night (after a quick jaunt), but if I get on the highway for a while right now, I know it will die eventually. I'm going to go out in a couple hours and see if it reads in spec again once it's cooled down...if that is the case though...it would likely be the stator windings, or the reg/rect.....right?

Any ideas? (gotta wait till the weekend before I can tear that side cover off and really find out.)
 
I'm having the same issue with a Harley... tested the rotor and it reads good. Cruised the forums and read that a bad regulator can act that way... shunt the voltage excessively as it overheats. Sometimes one has to replace the regulator first to eliminate that possibility then follow up with rotor replacement. I read that charging the battery in excess of 2 amps can damage the regulator.
 
Good ground between the battery and engine very important. Run a ground from the battery negative post to a clean bolt on the engine for a test. If things improve, clean up the ground contacts or add one.

Good 12 volts to the regulator is a must too so make sure the positive lead to the regulator is good also. Dirty key switches have been know to give issues with reduced voltage on the brown lead which is the common power source wire for lots of things.

Along with all the other check in the XS650 Tech section.
 
Monitor the voltage across the brushes during all this.
But, not directly AT the brushes, just tie-in to the rotor wires at the regulator connector.

Have something handy to do the 'slap test'.
You'll also need to monitor the battery voltage to see if/when it's charging.
So, you'll need 2 meters for this method.

Voltage across rotor, how it should work for the '80-'83:
High voltage = Current passing thru rotor, 'slap' = 'true', should be charging.
Low voltage = Little to no current passing thru rotor, 'slap' = 'false', should not be charging.

Failure synopsys:
If high voltage, 'slap' = 'false', and not charging, suspect rotor (open winding) and/or brushes.
If high voltage, 'slap' = 'weak', and not charging, suspect rotor (shorted winding).
If high voltage, 'slap' = 'true', and not charging, suspect stator and/or rectifier.
If low voltage, 'slap' = 'false', and not charging, suspect regulator (ground green to confirm), else bad power.
If low voltage, 'slap' = 'weak', and not charging, suspect wiring, power and grounds (ground green to test).

A variation on this could be done by measuring voltage between the brush green wire and ground...
 
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