Rectifier question - causing dead battery?

[KnuckleBuster]

Okay, I'm starting my journey into R/R and Stator hell. Since buying my 1978 GS1000 several years ago, I have needed to put a new battery in it every single, stinking year.

I know, I should have figured it out befor enow, but I'm lazy.

Anyway. I'm tired of buying batteries, so I figured I'd dive in with my multimeter and figure out where the problem lies. Just out of pure curiosity, I put the leads of my ohm meter on the battery cables - it showed a closed circuit - there was continuity...not much, but it's there!

Now, this is key off, no battery.

I started tracing wires and came up with the rectifier (my bike has separate reg./rec. units). I did the diode tests per the Clymer manual and the diodes all checked out good. As soon as I unplugged the rectifier, I no longer had a closed circuit. If I touch one lead to the black/white ground wire of the rectifier and the other lead to the red wire on the rectifier, I get a reading of 27 ohms which is exactly what I get with everything plugged in and measuring from the battery terminals.

So, the question is: the rectifier is junk, right? All of the electrical connectors look like new except the ones for the rectifer - they have a copper plating that doesn't belong there and the rubber sleeves that surround them look like toasted marshmallows. At the rectifier itself, the red wire has a little green corrosion showing where it connects to the rectifier.


I haven't gotten into checking the alternator yet because I don't want to fry another battery, but the last time around, I got a voltage reading of less than 12 volts at idle and when you rev the bike it drops down near 6 or 7 volts.

Thanks, folks - one of these days I'll get this thing right.
Jay

 

[Steve]

Sounds like it's long past time to replace your rectifier and your regulator with a combination r/r unit. You can choose to go with a used one from eBay or get a new Electrex unit from Bike Bandit or Z1 Enterprises.

Either way, that sounds like that's all you need. But, just to be sure, remove the three wires from the input to the rectifier (they come from the stator). Arbitrarily label them A, B, C. Put your multimeter in AC volts mode, and make sure it is in a range where it can read about 80 volts, if it is not an auto-ranging meter. Run the engine about 4-5,000 rpm, measure the voltage between A&B, then B&C, then C&A. You should get over 70 volts from every pair, and the three readings should be about the same. If you don't have the right output here, you won't be able to trust anything else you read downstream.


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[KnuckleBuster]

Okay, at 5,000 RPM the voltage is 70 VAC on all 3 pairs - starts out low voltage at idle, then tops out at 70 volts at 5,000 RPM. You mentioned "at least" 70 between 4,000 - 5000 RPM - does this point to a bad stator, or am I doing alright? Maybe I can get away with just buying a new r/r?

Thanks for the help,
Jay

 

[Steve]

70 volts should suffice. I just looked in the book for my 850 and it specifys 75 volts, but your bike might be a bit different. Besides, it's going to get rectified and regulated down to 12 volts DC, so it appears that there is plenty to start with.


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[tconroy]

It may take a little longer to go to 75 ohms on your bike or you might have a cheaper meter,either way that should do .I would replace the r/r and clean all connections and dont use the plastic P.O.S. to connect them. Wire them direct with soder and shrink tube for better connnections and you should be ok. Ijust replaced my battery after 2 years and the r/r connection was starting to melt cause of the plastic plug in connections.