Faulty Charging System - Regulator/Rectifier?

Hello again,

Last week I found that my battery in my '79 KZ 650 was completely dead. I pulled the battery and found that there was almost no acid in the battery (!). Bought a new battery and had it charged. The bike ran fine with the new battery. I took if for an hour and half ride yesterday and the battery was dead by the end of the ride. Clearly the charging system is faulty.

I've currently got the battery out of the bike on a trickle charger. I opened up my Hayes service manual for a 1980 KZ650 (no difference I assume?) and started looking into the charging system. Once the battery is charged I can do running engine checks on the alternator and battery. I was able to find what I though was the silicon rectifier and checked the resitances between all the wires as the manual suggested.

In reality, the bike has a combined regulator/rectifier. My understanding is that the single rectifier essentially acts as a diode (only allowing current one direction) and allows the positive portion of the alternator's current to charge the DC battery. So, if the rectifier has equal resistance going both directions for a given set of wires it is faulty. Based on my resistance tests, at least two sets of wires were experiencing similar resistances in either direction, therefore the unit is faulty.

However, the testing procedure in the manual is for the rectifier, not the combo unit. My question is: does this testing procedure hold true for the combo regulator/rectifier? And should I attempt to clean all of the connections in my charging system before buying a new regulator/rectifier? Also, are there any tips for checking the alternator, or any other aspect of the charging system?

I did some searching on this forum and was able to find some relative info, but couldn't quite seem to find the answer I was looking for. I have attached a photo of what my regulator/rectifier looks like (photo not of my part).

Sorry for the long post, any info provided would be a great help.

Would assure integrity of ground connection where negative battery cable attaches to rear of engine.

Then measure voltage across battery terminals at idle and again at 4000 rpm.

Look for 12~13 volts at idle an 14~15 volts at 4000 rpm.

The following applies to the large fours, but guessing also applicable to other displacements.



Good Fortune!

Thanks for the help Patton. To test the voltage with all of the lights and accesories turned off should I entirely disconnect my headlight and taillight? On the later models you cannot entirely turn off the headlight.

I checked the voltage across the battery while it was out of the bike (fully charged and new battery, it passed). Taking a voltage reading across the battery while the bike was running at both idle and 4k rpm I measured about 13V. This is below the desired 14v-15v. This reading was taken with the 9-pin connector behind the headlight unhooked (so all lights/gauges/switches unhooked).

I unplugged the regulator/rectifier from the system, this lowered the voltage drop across the battery for both idle and 4k rpm readings. The drop was only about half a volt. I am about to check the resistances in the alternator leads as suggested by my Haynes service manual.