Topic: Charging question...

[SClay115]

Ok, I think I may be putting my foot in my mouth here as I don't know too much about motorcycle charging systems. But here goes, little back story first.

As you may or may not know, just recently got my Cafe up and running, and rode it around all day yesterday, ran great, go to ride it today and it dies on my about 50 feet from my house. Hm ok. So turns out the voltage on the battery is around 6v. I have bridged the charging fields so they are both on at all times, since the headlight is on 100%. But it appears it's not helping. So questions.

Put the battery on the charger, ok, reading a hair over 12v. So here is what I do, turn the ignition on, that is including headlight, take note of the reading, somewhere along the lines of 11.89v. Start the bike, reading doesn't change. Obviously, it's not charging. So, where do I start? I checked the rectifier, and the regulator. Both check out ok. So, what I really need to know is if I should be seeing 12v out of the alternator itself. If so, then that's the issue. But as I am understanding it, I shouldn't be, but I could be wrong. More to the story:

Took it for a ride around the block, came back, checked the voltage across the battery again, 11.7. So I KNOW it's feeding off the battery. I guess what I really need to know is how should I check the alternator itself? I checked the manual, and it passes all those tests, but it's still not working, so I don't know what that's about...

I just need some input, what would you guys do/check next?

Steve

[Bodi]

What bike?
I figure it's a 450 or similar, since you mention bridging 2 charging coils.
This type of alternator has a permanent magnet rotor and 2 stator output coils, using one coil for "day" and both for "night". It's a single phase system with a 4 terminal rectifier having two AC "~" terminals connecting to the alternator coil(s)  and the "+" and "-" terminals connecting to the battery.
Usually the stator has 3 wires, a common and 2 coil outputs. Whenever the rotor is turning, you get AC voltage from the coils. Therefore you should get DC voltage from the rectifier DC terminals when the bike is running. It will be considerably more than 12V if all is well, with the battery disconnected. You can test this by touching a 12V bulb to the frame and touching the rectifier + wire to the lamp base terminal... it should light up plenty bright, flickering quite noticably at idle.
(don't just disconnect the battery - disconnect the rectifier "+" DC terminal leaving the battry connected to the bike. Once you get the system working, running without the battery could give an abnormally high voltage and burn out your lighting quickly... plus the bike won't run with the battery disconnected and a bad alternator)
First suspect is the rectifier. It's easy to check with a multimeter, use the diode function if you have one or the resistance function if not. First put the red lead on a AC terminal. Touch the black meter lead to "+", you should get a high or low reading. Touch the black lead to the "-" terminal and you should get the opposite reading. Put the red lead on the other AC terminal and repeat. The readings should be identical - whatever they were with the other AC terminal. Now repeat with the black lead on the AC terminals. The readings should be again identical for both AC terminals but reversed from before (if you had a high reading to + with red on AC, it should be low with black on AC). Any devuiation from this pattern says "bum rectifier". Good news though, simple bridge rectifiers can be found at Radio Shack for less than $10.00, look for about 25 amps and 100V.
Measuring the coil wires with them disconnected is a fair test of the stator. You should get something well over 12VAC between the common and each output coil wire with motor running
It's possible to connect the wires wrong, mixing a coil wire with the common, that way you will only be getting charging power from one coil. Check the colours carefully against the original wiring diagram. You can identify them easily with the coils disconnected, check resistance between pairs of wires. Calling the wires A,B, and C you will have a resistance for A-B, A-C, and B-C. One resistance reading will be higher than the other two: that wire pair is the coil outputs and the other wire is the common.