Charging system problems

[tomm]

Due to the terrible inadequacy of my Hanes manual I need help identifying parts. On my 78 GS750EC there are two finned items that look very similar and both are attached to the battery box. Is the finned item that is attached to the bottom of the battery box the heat sink? And is the R/R unit the finned item under the left side cover bolted to the side of the battery box? If the later is the R/R unit it appears there is a single bolt through the center of the unit which attaches it to the battery box with a black & white wire also attached to this bolt. Is this the ground wire mentioned above that I have highlighted in red? If so, in addition to the wire that is already there under this bolt could'nt I add an additional length of wire under this bolt and run it to the (-) terminal on my battery?

On your model, the part under the left side cover with the bolt through it attaching it to the battery box is the Rectifier. The part under the battery box is the Regulator.
As BassCliff suggested, you will be better off getting a replacement unit that integrates both the Rectifier and the Regulator into a single assembly.
It is a much more robust design. (Contact Duanage.)
If you stick with the current components, the problem is the regulator. It has a single lead which connects to one of the stator outputs. The ground is through the battery box, which is very unreliable. So just running a ground from that bolt through the rectifier to the battery negative takes care of your rectifier ground, but not necessarily your regulator ground. Any there is no ground wire coming off the regulator that you can run directly to battery negative.
If the regulator ground fails, then there is no place to sink any excess stator output. Result is a boiling battery and a failed stator.
The integrated replacement unit regulates the total rectifier output. There is one ground which you can run directly to battery negative. In the old design, one stator output is regulated, one is unregulated and the third is unregulated but only active when the headlight is on.

[GS750GUY]

On your model, the part under the left side cover with the bolt through it attaching it to the battery box is the Rectifier. The part under the battery box is the Regulator.
As BassCliff suggested, you will be better off getting a replacement unit that integrates both the Rectifier and the Regulator into a single assembly.
It is a much more robust design. (Contact Duanage.)
If you stick with the current components, the problem is the regulator. It has a single lead which connects to one of the stator outputs. The ground is through the battery box, which is very unreliable. So just running a ground from that bolt through the rectifier to the battery negative takes care of your rectifier ground, but not necessarily your regulator ground. Any there is no ground wire coming off the regulator that you can run directly to battery negative.
If the regulator ground fails, then there is no place to sink any excess stator output. Result is a boiling battery and a failed stator.
The integrated replacement unit regulates the total rectifier output. There is one ground which you can run directly to battery negative. In the old design, one stator output is regulated, one is unregulated and the third is unregulated but only active when the headlight is on.

Thanks for the terrific information regarding my bike. Problem is I have not been able to find an original manual for my bike so with the exception of what I can gleen from the Hanes manual I'm kind of in the dark on a lot of things.
I wonder if Suzuki felt at the time that a seperate regulator and rectifier would be an improvement in some ways. Here is a thought regarding the regulator........I wonder if the two bolts connecting the regulator to the bottom of the battery box is considered the ground?? Would it work to connect a wire to one of the regulator mounting bolts and run it to the negative terminal on the battery?

Thanks again!
GS750GUY

[spyug]

Individual regulators and rectifiers were fitted to most bikes prior to the late 70s and early 80's. Common to most all Japanese bikes. Earlier model regulators were mechanical in nature ( a set of switching points) and not as reliable as the solid state devices of today. You can still get seperate regulators and rectifiers and one company I know of http://www.oregonmotorcycleparts.com/index.html makes several types. I'm not sure if suzuki models are covered but have a look or e-mail Tony. I just got a regulator for my XS650 to replace the mechanical one and it works perfectly.

Today the combo R/Rs are fitted to bikes and the favourite conversion already mentioned is the R/R from a later Honda and Duanage is the go to guy.

In most applications, I believe, the regulator is ungrounded so fitting a lead would have no practical value. The ground lead we all mention is from the rectifier (black/white) ground directly to the negative post of the battery.

Hope this helps.

Good luck and keep us informed.

Cheers,
Spyug.

[tomm]

In most applications, I believe, the regulator is ungrounded so fitting a lead would have no practical value. The ground lead we all mention is from the rectifier (black/white) ground directly to the negative post of the battery.

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.

[tomm]

Problem is I have not been able to find an original manual for my bike so with the exception of what I can gleen from the Hanes manual I'm kind of in the dark on a lot of things.

The Clymer manual, while not great, is definitely better than the Haynes manual. Also, I copied my original owner's manual for the 78 750 in pdf format and it is available on BassCliff's website.

[GS750GUY]

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.

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

[tomm]

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.

[GS750GUY]

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

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

[spyug]

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

[tomm]

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

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. \\/\\/

[GS750GUY]

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

[GS750GUY]

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.

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