Re: 78 GS 1000 charging problems
I recently had that same problem with my 1150. To determine if it is the stator or the regulator/rectifier at fault, you can do an easy test. The stator is a three phase unit and each leg should output 80 volts AC at 5000 rpm.
The stator has three output wires. They will usually be yellow, but on some models they are different colors. The color does not matter. All legs are the same. The R/R should have 5 wires, 3 yellow AC input wires, and two DC output wires, usually red and black. Sometimes there will be a 6 th wire that is green and it is an additional ground wire on the DC side.
Disconnect the stator output wires from the regulator/rectifier. Set your multimeter to 200V AC. Start the bike, let it warm up and make all AC voltage measurements with the bike running at 5000 rpm. If we call the leads from the stator A, B, & C, then you want to put the meter test leads between A and B for one leg, A and C for the 2nd leg and B and C for the final leg. If all show 80 volts, then the stator is fine. My stator did output 80 volts @ 5000 rpm and I assumed it was the R/R that was faulty. I replaced the R/R with an electrex and charging is normal now.
The red + and black - DC output wires from my regulator/rectifier are connected directly to battery terminals. If connected this way, an additional casing ground wire on the R/R is not needed.
When someone is having electrical problems causing the bike to run poorly, my first suggestion is to check wiring connections for corrosion, but for a charging problem, I dont think that applies. The charging circuit is immune to excessive resistance and corrosion in the rest of the bike's wiring harness because electricity will always take the path of least resistance.
The charging circuit consists of the stator, regulator/rectifier and battery.
If the R/R's DC red+ and black- wires are connected directly to the battery terminals, that will always be the path of least resistance and the R/R will only be concerned with battery voltage (electrical pressure) Even a direct short in the bike's lighting system will not alter the maximum possible charging voltage from the R/R as it is limited to a max of 14.9 regardless of the draw (if working correctly). In the instance of a short, you would still have an output from the R/R of 14.5 +, (due to brands and individual units, max output can vary) but there would be no wattage (flow) left to charge the battery. The charging system would function normally.
To verify this, you can disconnect the red and black wires between your R/R and the bike's battery and connect those wires to a spare battery on your bench. Leave the original battery in the bike hooked up. This isolates the charging system from the bike. Start the bike and do the same tests of R/R output. If the voltage level of the spare battery (electrical pressure) is the same as the voltage level of the battery in the bike, then the charge rate will be unchanged. The R/R adjusts to draw to maintain a constant voltage, so electrical draw from the bike will not change the R/R output. Charging voltage will be the same regardles of whether the headlight is on, off, on high or low or only the ignition running.
This was quite a bit longer than I had intended, but I thought that an explanation of why and what would make it easier to trouble shoot the problem than just a list of values to check. If you know what is happening and why youre doing something, its always much easier to fix it.
Earl
craigmech said:
I recently bought a 78 gs 1000, runs good but I think the carbs need to be rebuilt. Anyway, the charging system works well, 13.5 volts at 3000 rpms. But as soon as I turn the headlamps on it drops to 12.5 and keeps going down from there, if i turn the headlamps off it slowly rises back to 13.5 volts. It has a Vetter windjammer fareing on it, could this be part of the problem? or just the stator,rectifier or regulator.
Thanks for any info.
Craig
