Stock 78e low charging behavior

TimeMachine

TimeMachine

SeventyEighte
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Hello all. Today is still progress regarding my long time 78e electrical issues. I have disconnected an ugly rear brake switch. Other than that the electrical is back to completely stock. This is a 10k mileage bike. Today I resurfaced one of the brushes with a fine stone lap. That brush was clearly not making good contact. Today the bike starts very easily. Runs very good. Light Switches all working better than ever. Here are the current charging symptoms I know. Battery is at 12.28v with the bike off. At idle voltage drops to 11.71 approx. And at 3thou rpm voltage reaches 12.15 approx. And It will go even higher. I believe by watching response in rpm changes that the charging system ie: rotor, rectifier, voltage reg. Are all working, just not well. Though the fuse use to blow, it is not now. The voltage regulator was also proven as my best of 3 on my last 78e project. Again all electrical components including starter are seemingly fine. I really am anxious to ride this long term project 78e but am hitting a wall on the electrical. Any quick check I could look for to add info to my symptoms ? Thx, -RT
 
Lunch break thinking. Is it reasonable at this point to suspect the brushes ? The surfaces looked less than good and the wires soldered to the brushes are a little frayed . ?
 

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You're barking up the wrong tree. I don't think the resistance of the brush is going to change significantly with the amount of area making contact.

I would suggest this. First check each and every component involved, out of the circuit. How to do that is well-documented. Then I would check them in-circuit and include the connections on both sides of the test. If a connection consists of wire 1, female connector, male connector, wire 2, component under test; then you have to test the component from wire 1 because there are two crimps in play that could be bad, and they often are. People tell you shine up the contact surfaces but the crimp is as likely or more so to be the problem. Last, look carefully for p.o. weirdness. A p.o. changed my fuse box and when I started removing tape and looking at the connections they really darkened bad twisted connections. An afternoon fixing that mess and previously addressing a bad crimp fixed my persistent charging problem.

Having said all that, I wish what I had done was just buy a new replacement stock harness and avoid the headache. The way the connectors are it's virtually impossible to plug it up wrong, because every connector is different :) Good luck.
 
Thx, xjwmx, here is the only PO weirdness . I dont like it but it seems connected ok . Im digging around now of course .. ugh
 

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What is that TM?

Some sort of defeat for the reserve lighting thingamajig?
 
Have you ever tried a voltage regulator adjustment? Apparently, it's something that needs doing occasionally. The 650 manual doesn't mention this but the XS750 triple (uses same regulator) manual does. It says you should check/adjust the unit every 8K miles. If that does turn out to be the issue, do the VR115 upgrade, you won't be sorry. And you may extend the life of some of the other key components (stator, rotor). Even when adjusted for proper output, that old mechanical regulator is very erratic. It's output bounces all around, probably due to vibration. That works the stator and rotor harder than need be.

A little side note - your brush wires are routed incorrectly. They should run to the outsides and pass through those little notches in the holder. Here's a pic of mine. The right (inner) brush wire is correct, the left (outer) brush wire is not. I have since corrected it .....

BzlvmLV.jpg
 
Nice, 5twins . Im going to look the brushes over in a few. The VR was adjusted on my previous XSe and that was actually fun. Im pretty confident there for now. I do have plans for the VR115 and chinese rectifier when I get there.. I am so simple , I dont have online hahaa jeez
 
You might try cleaning the slip rings, it may help some. I've fixed non-charging systems in the past by just doing that.
 
It's probably been installed wrong like that for so long, it's taken a "set" like that. It probably won't hurt anything to leave it. Mine was wrong for God only knows how many years, lol.
 
Personally, I like originals. If you shop eBay, you can find them new and for not much more, if any, than the repops. I think they're made and wear better. I have 32K on mine which I'm pretty sure are the originals, and they show barely any wear from new. Outer measures 12.5mm, inner still at the new spec of 14.5mm, or at least that's how they were at the last check about 3K miles ago.
 
That brush life is amazing to me 5T.

Back in the ‘70s I had an XS650B and I chewed my way through alternator brushes in 6-10,000 miles like clockwork.

As I recall it, a set of brushes cost me $6 CDN at Ian’s Yamaha Cycle in Kingston, ON, and of course they were all OEM parts back then because nobody know how rare and valuable an XS650B would eventually become and so there were no re-pops of anything. Maybe my slips rings were rough - hmmmmm.
 
Well in the end of a Sunday, whether it will charge or not, In the neighborhood it blew the fuse again ! Double Dog Dang again this bike which I like so much is just a biach and is more puzzling than the others.... I may need professional help, me & the XS
20171022_152210.jpg
 
DB , tho I can do many mechanical things, me measuring a rectifier is just not reliable. I have poor electrical meters, poor electrical knowledge, and on top of that being a "Redhead" as MaxPete knows.. I have no patience either. Im more likely to speak German than successfully diagnose that rectifier ! I need one I'll just betcha -RT
 

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Ha! Fair enough.

It is possible for a bad rectifier to allow backward current to travel to and through the alternator via the yellow wire shorting to ground through the starter safety relay. I had ridden to meet Pete for lunch and on my way back blew the main fuse for the first time. I'm sure you recall my saga.

The actual measuring of the rectifier is not hard at all, but you do need a decent meter to measure such low readings accurately.
 

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