Not charging like she used to..

[nhmaf]

Tillie the Teutonic Twin needs some maintenance now - the GEN light bulb will glow ever-so-very-dimly (only noticeable when riding after sunset really) and I've checked the voltage at the battery (which is a 2-year old AGM sealed battery that is kept on a battery tender, so I think it is fine).   At idle the battery terminal voltage is 12V, and even at 5000 RPM it doesn't rise above 12.9V (and I'm sure my multimeter is good).  So, time to check the alternator, brushes/slip rings, voltage regulator, and diode board/wiring.   I'll take pics and do some sort of write up for the wiki if needed as I get into it.

[Bob_Roller]

My '81 started to have a faintly glowing 'GEN" light, at about 50,000 miles (82,000 km), worn brushes were at fault .

I cut two small pieces of plastic, and placed them between the brushes, and the 'snail' spring .

Worked great, until the new brushes showed up, from Motorrad Elektrik .

[nhmaf]

Hmm, I'll keep that in mind if I need a temporary fix (and it turns out to be brushes) - good roadside repair tip, too.

[Patrick_Krivacka]

I noticed that my gen light blinks a little when starting it up in the morning and then some while the bike warms up. this morning it was more pronounced and even did it briefly after I got under way. I continued to glance at it during my commute and saw no blinking. Is this something to be concerned with?

[nhmaf]

The GEN light should glow brightly when you first turn on the ignition key but before you push the start button.   While the bike is starting it may flicker - doesn't matter what it does while cranking.   When the engine speed is below 1500 RPM or so it may glow dimly/go on and off, up to about 2500-3000 RPM where it should be fully, completely "OFF"/dark with no flickering or blinking.   It is just telling you that there is a voltage difference across it, and if the charging system is working properly then above 3000-3500 RPM there should be essentially "0" (or very small - too small to even light the bulb) voltage drop across it.   If it illuminates at all above these speeds then your charging system isn't working properly, and the fun starts.

The best/easiest way to test is to get a multimeter (cheap one will suffice) and check the voltage AT the BATTERY terminals.  With a good battery and charging system, you will typically measure:
Key off, nothing turned on:   12.8V - 13.4V
Engine on, idling (RPM <1500):   12V (approx, maybe 11.8 - 12.0)
Engine on RPM > 3000: 13.4V to 14.2V
  
If you get a multimeter with a diode test function on it, then you can even test and diagnose/repair the diode board, if the problem turns out to be there.  One can test diodes with just a multimeter and a small battery, resistor and test clips, but it is more complicated.

[Patrick_Krivacka]

thanks mike. your description makes me think I'm good to go. the flicker/blinking only occurs when the bike is stumbling while warming up, and the blinking this morning when I was taking off happened with some stumbling of the engine as well. If I'm reading you right, then it would be normal for it to do so. I'll give it a look over with the multimeter as well.

[Ed Miller]

I replaced my brushes the other day.  I used a tip that Joel Rapport (sp?) posted to the Airlist last year.  He doesn't solder the brush leads to the holder, he attaches a crimp ring terminal (1/4") sized to fit the little studs that hold the male spade connectors to the brush holder.  You don't have to remove anything, just pull the spring out of the way, pull out the old brush, put the new  brush in, and attach the lead to the stud.  My only problem is that I couldn't see what I was doing, but my 20 years younger friend did the actual brush swapping very quickly.  I need new eyeballs.

The email I saved from Joel was confusing me, as he said he removed the rotor and stator.  This week, after doing the job without removing them, I emailed him and asked him why he said to do that.  It was just because he dropped something in there the first time, he doesn't normally do that.  

[nhmaf]

I am hoping it is something simple and cheap like brushes, or maybe one bad (open) small diode on the diode board.   I rechecked the battery voltage today: 12.6V @rest (I didn't put it back on the tender last night), 11.9V @ idle and I could manage to sometimes get it barely above 13V at 5500 RPM, so it does partially work, but not well enough.  I can't take the front cover off etc. until this evening but I did pull the tank off and cleaned all the connectors, voltage regulator terminals and relay terminals under the tank with electrical contact cleaner and did get a fair bit of oxidation and crud out.

[Edit - 10:00 PM  EDT]
I *think* I found the problem - or at least A problem that could contribute to this reduced-charging behavior.  I found that the wire that connects from the center "Y" (or WYE ) of the stator to the left side of the diode board was basically broken off at the crimp connector which plugs onto the diode board.  The heatsrhink tubing kept everything "appearing" OK visually, but when I tried to pull the connectors off the diode board I felt that the wire inside the heatshrink wasn't connected to the terminal, and just sort of "wobbled around" while inside the heatsrhink tubing.  It easily pulled/broke off when I tried to pull on it.

All the diodes tested OK, though one has a marginal solder joint and the conformal coating is starting to peel off the board and the mounting points (the other points where the diode board can get a ground) were corroded.  I've measured the rotor resistance (3.5 Ohms) and each phase of the stator (0.5 Ohms) and the brushes ( < 1 Ohm) and cleaned the slip rings and all connectors.  I'll fix up the wire, clean the board and touch up the solder joint and see how it all goes this weekend.   I may still order a new diode board from Motorrad Elektrik so I at least have a backup/spare and I may also get a higher voltage regulator from them too, as these AGM batteries like a bit higher charging voltage than the old wet cells.