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Charging system problems

  • Thread starter Thread starter GS750GUY
  • Start date Start date
tomm said:
Although I've never opened one up, I would be very surprised if the regulator on the 78 750 is mechanical and even if it was, it would still need a ground connection, there being only a single wire between it and the rectifier. In any case, the wiring diagram shows an SCR-type circuit along with a ground connection which can only be through the case.

A ground wire directly from the regulator to the battery along with a ground wire from the rectifier to the battery should help as long as the components themselves are good and all the connections are clean. But if the connections have been poor for some time, damage may have already been done and the last thing you want is for something to fail completely out on the road someplace. You're hearing a general consensus to replace it with the integrated unit. Not that expensive and a much more robust design.
Click to expand...

Thanks Tomm. You have been very helpful. I am definitely going to take everyone's advice and go with the integrated unit. Please see what I have highlighted in red above. You mention "a ground connection which can only be through the case". Just curious, does this mean then the regulator unit is grounded through its mounting bolts and the battery box?
Gs750GUY
 
Yep . . . that's what it means. Nothing really wrong with the electrical design, however not ideal either. But the mechanical implementation doesn't hold up really well after 30 years.
Depending on which grounds deteriorate first, the ones between the components (regulator and rectifier) and the battery box or the one between the battery box and battery negative, or any of the connections determines which kind of problem you'll see. But problems include burned connections, low or no output, high output, boiling battery, and burned out components.

Bottom line is that the 78 750 charging system is capable of 14 amps at 14 volts at 8000 RPM. That's 196 watts and a lot of heat if everything is not connected perfectly.

I've attached a couple of images from the Clymer manual that may help. Image on the left is a schematic of the charging system. Note the separate rectifier and regulator and the connection between them. Both need to be well-grounded. The image on the right shows the rectifier attached to the battery box and regulator (black rectangle) underneath it.

78_750_charging.jpg
 
GS750GUY said:
Thanks Tomm. You have been very helpful. I am definitely going to take everyone's advice and go with the integrated unit. Please see what I have highlighted in red above. You mention "a ground connection which can only be through the case". Just curious, does this mean then the regulator unit is grounded through its mounting bolts and the battery box?
Gs750GUY
Click to expand...

I did some testing and wire work last night and found the following:
The regualtor on the bottom of the battery box actually does have two wires coming from the unit. A yellow that connects to one of the stator wires and a black & white ground that connects to one of the regulator mounting screws.
I removed and replaced the 30 year old battery ground wire. It looked pretty crusty. Just for laughs I cut the black plastic outer insulator off the old ground wire to see what a 30 year old ground looks like. The full lenth of the wire had green corosion between each individual strand and led me to believe I may have discovered a huge portion of my charging problem since both the regulator and rectifier checked out o.k.
I went ahead and replaced the battery ground wire and ran an additional ground from the ground connections on both the rectifier and regulator and made sure all connections were clean, sealed, and tight.
I'm still going to take everyone's advice and replace these with an integrated unit but thought I would make these minor improvements so I could ride while waiting for the unit to arrive. I will also wire my lights around the switch so I can eliminate that leg of the circuit.
Thanks again for everyones help regarding this.
Gs750Guy
 
I wrote that I didn't think the regulator would be grounded and couldn't see the need for it. I must have had too many brown pops:shock:

I was thinking of the new regulator I got for the XS and in terms of the need for adding a ground from the module to the negative battery pole which of course I do not need since the device has a ground running from it to the bike's harness. What a major brain fart.

Also, I did not mean to infer the GS regulator was mechanical in nature just making a comment about earlier models.

Sorry if I added confusion to the thread. I'll go stand in the corner now:(

Cheers all,
Spyug
 
spyug said:
I wrote that I didn't think the regulator would be grounded and couldn't see the need for it. I must have had too many brown pops

I was thinking of the new regulator I got for the XS and in terms of the need for adding a ground from the module to the negative battery pole which of course I do not need since the device has a ground running from it to the bike's harness. What a major brain fart.

Also, I did not mean to infer the GS regulator was mechanical in nature just making a comment about earlier models.

Sorry if I added confusion to the thread. I'll go stand in the corner now

Cheers all,
Spyug
Click to expand...

Apparently my brain must have had a vacuum leak as well. Could've sworn that when I replaced my stock regulator a couple of years ago, it only had one wire. Probably should've kept all my old parts as I replaced them, just for reference purposes. Don't like giving out bad information. The give and take is good. Keeps us all honest and and there's always more to learn. :)

Anyway, what's important is that GS750GUY would appear to be back on the road and another classic GS is breathing the summer air again. \\:D/\\:D/
 
Thanks Spyug and Tomm!

Tom, I think I understood your last message just as you intended. You have been a great help through all of this.
You are right Spyug, after two years of hard work and a lot of help from my GS friends it does appear another GS was resurected from the junk heap and restored to life once again. My GS is going to be seeing a lot more of the road now that I officially after approximately 30 years have my bike license again.
This morning my brother and I rode to the local DOT office so I could take the riding skills test and renew my license. When we arrived there were approximately 20 guys and a few gals standing in a group waiting to test as well. The two years of knuckle busting was all well worth it with the reception we recieved. There were lots of oooo's and aaaa's and everyone wanted to know the story behind this once graveyard specemin of a GS. And it was a fun story to tell. And I owe most of it to the people that make up this great site GS Resources.
GS750GUY
 
flyingace said:
You first need to verify battery will hold a charge. Put it on a trickle charger or a 2 amp charger (less time of course). You should be able to obtain and HOLD at least 12.72volts. If you can't, buy a new battery.

You don't really need to be fancy about charging system testing. I shine my headlight on the wall and rev the engine. The light should brighten slightly when you do this. If it doesn't, you probably have a dead stator or R/R. I check my charging status every time I leave the garage. Of course, it's possible the charging is marginal, but this occurs a lot less than just plain zero.
Click to expand...

Thanks flyingace for your above tip that I highlighted in red. I tried this on my last trip out. I shined my headlight on the garage door and gave the throttle a slight rev and did see the headlight brighten a bit.
This will be a standard part of my pre-run check from now on.
Thanks!
Gs750guy
 
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