1977 Suzuki GS750 - Honda Reg/Rec modification advice - Please

[Guest]

Hello

My bike has been destroying electrical components at an alarming rate, and I have concluded that it is due to a failing regulator. As a result I'm retro fitting a Shindengen SH678FB reg/rec unit, as originally fitted to the 2003-2005 Honda CBR1000RR Fireblade. I chose this unit as I believe it is compatible from research on this site, it has the same 5 wire configuration as my 77 GS, and above all... it was half the price of a SH775 MOSFET.


I’ve searched through the stator papers and am now suitably more confused than when I started, so I really am just after two things. The first is confirmation that my modified charging system wiring is correct. Also advice on the size of fuse I should use between the reg/rec unit and the battery. Is 30A right? I believe the unit can handle 35A.


(Don’t worry about the rest of the scribbles. The circuits are being completely redone)

Lou

question wiring.jpg

[Buffalo Bill]

I'd match the CBR fuse if the GS battery amp hours matched the CBR battery.
But you really need to diagnose what the problem is.

[LoobyLou]

Hi Bill

I'm sure the problem is a faulty regulator. Though not tested its original 40 year old kit, and nothing else could cause the symptoms of blown bulbs and friend electronic ignition units after long hard runs. The bike was extensively rebuilt with the exception of the wiring circuit. Rectifiers check out ok. Stator was ok. Some signs of overheating in one leg of the rectifier. Severe corrosion across the loom.

The bike is getting a Dyna S system to replace the Boyer Branson unit that it has fried twice. It has new coils. Will get the new reg/rec that is on order. I always intended to rewire anyways as the circuit design is old, whilst a more modern design with multiple fused subcircuits and relays has numerous advantages. I guess once all that is done, then the only thing that can be failing would be the stator, but I don't see how that could cause an excess current in the loom.

I'm no electronic person, just trying to understand.

Thanks for the advice on the battery. That makes perfect sense to me. The standard GS is a 14Ah 12V unit, the CBR1000RR is a 7 - 10Ah unit, so I guess if I match a fuse for the Honda, I should be OK

question wiring2.jpg

[posplayr]

The short circuit current has something to do with the amp-hr rating but not what you think. It has to do with battery internal resistance. As a first approximation multiply the amp-hr rating times 10 to get short circuit current .
14 amp-hr implies 140 amps short circuit.
10 amp-hr imples 100 amps short circuit. You don't want to set the fuse size based on this. Fuse is sized to the wire size not the amp hours or the lowest peak current your expect.

In the case of GS charging it also depends on how you wire the R/R. The lowest shoudl be 15 amps when R/R is wired to the "T".

It is hard to saw what was wrong before; a volt meter would have been helpful.

I don't know if the Shindengen SH678FB is a series R/R although that is what is indicated by the SH family prefix.

BTW, there is no information in the schematic about what you are doing except the specific R/R part number.

[LoobyLou]

In the case of GS charging it also depends on how you wire the R/R. The lowest shoudl be 15 amps when R/R is wired to the "T".

What's the T? Sorry... don't understand.

It is hard to saw what was wrong before; a volt meter would have been helpful.

Two fried electronic ignition units, numerous blown bulbs, and some rather toastie looking connections.
Rectifier tested OK. New coils. New battrey. Cleaned ignition switch gear. Stator a little cooked from memory. Charges good. Always blows a device after a long multi hour ride cruising at 80mph +

GS750 with 850 bore and 70+bhp at the back wheel

BTW, there is no information in the schematic about what you are doing except the specific R/R part number.

Sorry, it shows that I plan to cut out the routing of one arm of the stator through the lighting switch, linking the all three arms of the stator directly to the reg/rec unit. Also shows the modified wiring connectingreg/rec directly to battery via a 30A inline fuse.

Not shown is the power and control circuits will come from the battery through + busbar to blade type fusebox to controls, and also via relays for horn, lighting, ignition.

Jo

[Nessism]

Stator direct into R/R, bypassing stock harness.

+ output from R/R should be T configuration: one leg of T feeding main harness and the other going to battery (with fuse in-line.) The line going to the battery can be through your fuse box or a separate fuse. Doesn't matter.

- from R/R can go direct to battery or better yet, T configuration with one leg tying into the harness ground configuration (black/white wire w/ring lug attached to frame) and the other going to the battery.

Regarding all the problems you have had, did you ever measure output voltage at the battery? That's how you can tell the function of the system. There should be about 14.5 VDC across the battery at 5000 rpm. More than that indicates a bad regulator.

[Gorminrider]

BTW, there is no information in the schematic about what you are doing except the specific R/R part number.

exactly. These don't show up on the interweb easily so a picture of yours would help so we can see how many wires it has at a minimum. Your diagram is confusing because it shows Recitifier and Regulator as separate components. Not impossible, but generally, nowadays an "R/R" combines Rectification and Regulation in the same component.

did you ever measure output voltage at the battery? That's how you can tell the function of the system. There should be about 14.5 VDC across the battery at 5000 rpm. More than that indicates a bad regulator.

exactly. That's the first thing to do. If it's low or non-existant, check all connections especially ground and then check the stator's AC output when disconnected from the R/R.

If it's overcharging (which points to blowing stuff up) R/R is bad OR perhaps there's an extra wire-a voltage- sense wire on this R/R you have not connected correctly.

[Steve]

Regarding the "T":

In the stock configuration, power comes from the battery, through the MAIN fuse, toward the ignition switch. Between the fuse box and the ignition switch, there is a junction where the regulator output meets. THAT is "the T".

Unless you do some major re-wiring that you have not yet described, you would be better off routing the output of your R/R to the "T" location, not to the battery.

Why all the relays? If it is to correct a low-voltage problem, take a good look at the voltage on the orange wire after the ignition switch first. If that is low, why not fix the overall supply problem, rather than apply what is essentially a bunch of Band-Aids? It would make more sense to use the ignition switch to control ONE relay that supplies good power to everything.

.

[posplayr]

The "T" is shown in the first schematic. If you think about it the "T" and the SPG are distributing and collecting currents respectively.

https://www.thegsresources.com/_forum/showthread.php?152769-GS-Charging-System-Health&p=1138531#post1138531