charging system problem

help!!!
1979 ks650
installed new dyna-s coils with electronic ignition,
also did the rewire for more power to coils using the schematic provided by wired george, (thanks for that, goood spark now). but with the engine at anything under 2500 rpm's the battery voltage is below 12 volts and continually dropping. go over 2500 and it will go up to about 12.4, 12.6 max at 4500. only change i made was to take the wire going to the starter relay terminal, put it on the pos battery terminal. was easier. should not make a difference, should it?
so, am i doing something wrong,or is the "alternator" just not holding up?

thanks, jim

Can you measure the voltage at the regulator/rectifier output wire (white, I think)?

Also, check for lost ground connections on the reg/rec.

Were you having any charging problems before installing the Dyna components and doing the coil repowering upgrade? If you can't say for sure, most likely one or more of three issues may be the problem.

First, is to check connections. The connection to the reg/rec is vital as it carries AC to the reg/rec. The ground will be a black/yellow wire and you likely have a brown wire which provides voltage feedback to the reg/rec. Last, will be a white and/or white/red wire going to both the battery and main fuse. All these connections must be right and tight in order to get good DC voltages. Recheck voltages at the battery again... if still bad:

Next thing to check would be the stator. If your bike has a three wire stator, three wires will connect into the reg/rec. These will likely be pink, blue, yellow OR all yellow. Get the bike running. Take a multimeter set to VAC scale and put a probe on one of these AC wires and the other on another of the AC wires. If you have a manual, it will tell you exactly what voltage to expect at a given rpm. This will tell you if you have a problem in your stator.

Of course, the reg/rec will be the last piece that could be bad. If you have gone through the first two operations (wiring check and stator check), the reg/rec would very likely be the culprit.

Thanks for the suggestions. Will check them out, but, the voltage regulator went out this summer, and was replaced. It was with a used one, so, it's certaonly possible that it's gone bad again, but, it the bike was charging fine until I installed the Dyna S ignition, Dyna Green coils, and did the WiredGeorge wiring mod. I think it's more likely the problem is there.

Will see after checking out items suggested.

Could it be a failing battery? Or perhaps a faulty ground connection from negative battery terminal to engine/frame?

Good luck!

It's possible, but, the battery was bought new in July. I'll definitely have it load tested as part of the chasing-down process, but, I'd think it's unlikely the batter is bad.

I'll recheck the ground again.

JC, No offense, but the battery may well have issues. Depends on how it was initially charged. If you charge a bike battery too quickly, using a car charger, it can KILL cells... this is a good point I didn't think of as the battery must always be the first thing that is verified when trying to troubleshoot a charging issue.

Get you down to a auto parts store and buy a SMALL hydrometer. It looks like an eyedropper with colored balls in the clear part and should cost under $3.

You put a small piece of hose on the eyedropper part and suck in some fluid from each cell, one at a time. The balls in the clear part will either NOT FLOAT, SOME FLOAT or ALL FLOAT. If all float, the cell is OK. If some float, the cell is partly sulfated/bad and if none float, it is fully sulfated and won't hold a charge.

The specific gravity of the sulfuric acid solution changes when the plates sulfate and that is why some or all the balls won't float. This is a cheap way to check a bike battery and actually works decently.

If the battery checks OK, then go through the other steps I noted.

thanks for all the info. not sure what i did. but charging problem is resolved. put new connectors on the rectifier. and had the battery on slow charge overnight. checked yesterday and again this morning. both times it is charging at 12.2 to 12.3 at 1000. rpm. goes up to 12.9+ as soon as give a little gas.

wasn't looking at the max voltage, but i did see it get into the mid 14's.

thanks again for the assist.
jim

Post edited by: jccwall, at: 2007/11/16 10:34

It really needs to go up to about 14.5v when revved to about 3,000 RPM.

Back again. Thought problem was resolved, but, it is not. Bike is not charging enough to keep the batter up.

Went through the testing procedure laid out in Clymer manual:

Ac voltage test from generator: should be 75 volts a/c @ 4000 rpm. Tested 65 -71 volts.

Resistance test through stator: Clymer calls for less than 0.4 ohms. Tested 0.5 -0.7 ohms.

This leads me to believe the stator may be bad. What puzzles me is that 4 months ago, it was putting out too much juice. Blew out every bulb on the bike. Had to replace the regulator/rectifier. The bike has gone less than 300 miles since then. Seems odd that this comes up so soon.

Wanted to try the stator from my '81 model, but, it has three wires, thie one on this '79 model only has 2 wires.

Is there something else to look for?

If it is the stator, what is a good source for one? Is rebuilt ok?

One way a regulator fails is to drop the voltage at higher RPMs. You mentioned you saw 14v on the battery at some point. Do a careful voltage check while slowly revving the bike up in RPMs. By the time you hit 2000 or 3000 it should be a solid 14.3v or higher. If it starts dropping below 14v as you rev higher, then the regulator is bad. The regulators go bad very gradually in this manner. Initial symptoms are that the voltage will only drop a little. As it gets worse, the voltage will drop below 13 as the revs go up. However, at lower RPMs (like 2000), the battery usually hits 14v so people stop the test there. This leads them to believe the reg/rec is good. This type of failure is the most common failure I've seen, and it's one of the harder faults to detect.

Post edited by: loudhvx, at: 2007/11/29 14:51

was watching voltage. 11.5 to 11.8 at idle. gradually increases to about 12.6 at 4k.

jim