Charging issues on ‘79 G5

[guzzisteve]

Did you get the Ohm readings cause yes it does matter.

[ritratto]

Ok... so I finally found time to check everything and have basically nothing above .8 on the three circuits and only reading about 3 volts at 3500 rpms. Open stator?

[blackcat]

I made an easy test diagram when I was having problems with mine. It's a bare minimum on how it all works, but should hopefully help you isolate the issue



Good luck

Not to sidetrack from the original problem but I have a question. My 81 CX charging system works whether the dash light is working or not working, I’m not complaining but I thought the system had to have a working light.

[wirespokes]

There are basically five parts to the system - rotor, stator, diode board, regulator and the wiring. It's got to be one of those. Since you've already replaced the diode board and regulator, hopefully we can check them off the list.

The most common failure in this system is the rotor opens up. It may check out fine at rest, but when spinning can go open circuit. When I go on trips I carry a spare along with the second most common failure point - the diode board. Haven't needed either, but a friend did need the rotor once.

When checking the stator, was the meter set on AC? One of the leads touching a good ground?

At this point it's most likely the rotor. When removing it after pulling the stator (carefully - and be careful installing it - if it get's cocked going in it'll break) Have a big box padded with shop towels in front of it so when it pops off it doesn't fly onto the floor damaging the slip rings. They don't always fly off, but it's a good possibility.

[blackcat]

My guess...
My CX charging system will NOT work without a working dash light (I also have a volt meter gauge) and as far as I can tell the wiring on mine conforms to the diagrams...stock.

Yours may be modified??

It has been re-wired with a new Lemans I harness from Greg Bender.

[blackcat]

Ah!
That's probably the answer.

I've had my ('81 CX) charging system go down twice and the volt meter saved me from grief and both times I made it to the barn.

I figure that some clever owner can figure a way to bypass the problem w/out too much pain.

Volt meter works for me.

:-)

My original dash is long gone, but I did like the voltmeter.  I just changed the dash from the 1000S clock holders to the standard LM I dash, but the bulb holders are an issue, so I have no idiot lights at the moment.

Anyway, just throwing this out there to the original post. I chased a charging problem on My CX for almost a year, and I finally found the problem. There was a hairline crack in one of the bush holders that kept it from making good contact.  Once replaced, everything worked fine.

[guzzisteve]

If you had 3 ohm at rotor slip rings then it's the stater. .3 ohms at 2 of 3 phase output wires (3 prong plug) is what stater should be with all wires unplugged and cardboard under brushes.

[wirespokes]

"If you had 3 ohm at rotor slip rings then it's the stater."

................... ................... ................... ..............
Not necessarily, Steve. There is a possibility resistance goes infinite once the rotor starts spinning.

I don't know how to test for that one.

The test for the regulator is to bypass it. If the system now works (but voltage keeps going up the higher the revs) you know it's the regulator.

Stators - a good resistance check should be good enough.

If you don't have a spare rotor, it's a good idea getting one. Hard acceleration and deceleration are the killers - big changes in inertia loosen the windings leading to broken connections. That's probably a reason for Ducati going to the permanent magnet system.

[chuck peterson]

everyone step back I can fix this without looking from 2000 miles away.....

Check the length of the brushes. A friend w LM V had on off charging light issues. It always looked like the brushes were seated firmly on the rotor. He is a great mechanic, but Fooled Again, they were just floating close to the rotor and not firmly seated. Worn, short was the problem. The springs had bottomed out on the fixture and not pushing the brushes fully seated onto the rotor anymore. Rotated the brushes so they weren't at 12 o'clock, too...

Fixed. See, amazing uh?..... howz it running now?

It's really funky to see how hidden this is. It'll look all good but it's in the last .01 w the spring bottomed.

Good luck, all the best. I have run a second ground wire off the diode to the engine case...it helped and found another 1/4 to 1/2 voltage....using the adjustable voltage regulator?

[Perazzimx14]

When reassembling my T3 from a frame powdercoat i chased a charging problem for several weekends. It ended up being two wires on the wrong terminals on the stator. I had checked the wiring 20 times. I Ohm'ed the rotor, I phased the rotor, I changed the rotor, with a known working one, I changed the diode board and still no charging. Then when stepping back in frustration then came back with a clear head and really compared the pre-disassembly photos with the way the stator was connected.  I had 2 wires switched. Some of this old wiring its hard to determine what color they truly are and its easy to confuse dark blue for black or some greens for blue.

 

[Chuck in Indiana]

When reassembling my T3 from a frame powdercoat i chased a charging problem for several weekends. It ended up being two wires on the wrong terminals on the stator. I had checked the wiring 20 times. I Ohm'ed the rotor, I phased the rotor, I changed the rotor, with a known working one, I changed the diode board and still no charging. Then when stepping back in frustration then came back with a clear head and really compared the pre-disassembly photos with the way the stator was connected.  I had 2 wires switched. Some of this old wiring its hard to determine what color they truly are and its easy to confuse dark blue for black or some greens for blue.

Yep. A guy called me to look at one after he was totally frustrated. He'd changed rotors, stators, diode boards, regulators, and it still wouldn't charge. He had the +on the wrong terminal. <shrug>

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everyone step back I can fix this without looking from 2000 miles away..... :popcorn:

that's a fact..

[Frenchfrog]

I recently made the exact same mistake...took me a good while to realise as the cable colors were wrong!