Electric Gremlins

[Varget22]

 First the background. Last summer I had a charging problem with my 86 and finally spent a small fortune at a dealership to get it fixed. It turned out to be a bad regulator and a faulty Stator. I picked up a used alternator that had a good Stator and had to eat the price of a new Yamaha regulator. They put it all together and everything worked just fine until last night. I pulled the battery and charged it last night and checked the voltage this morning, it showed 12.94V. I put the battery back in and started the bike and at idle it shows 12.46v across the battery. I rev the motor to 4k to 5k rpms and there is no change in voltage. From what I understand if there was a problem with the regulator it would show a very high voltage, like 15Vish or higher. I pulled off the cover to the alternator and checked the wiring. On one of the wires to the rectifier the solder joint had broken and I figure its an easy fix. I solder it back, retest and no change as to the output. Next! I pull the alternator and do some measurments. The stator coil shows 0.8ohms sounds good. Field coil measured 4.7ohms sounds good. Next I checked the rectfier. I set my meter to diode setting and followed the manual. I have the factory Yamaha manual not the Clymers or Haynes so I think the test data is correct. D1,D2 and D3 all show a reading of 505 in one direction and open in the other direction. D4,D5, and D6 all show open in both dorections. So I'm concluding that the latter bank of diodes are toast. Does this sound correct? I'm thinking that the break in the solder joint was enabling the field in the alternator to build a charge above what is normal, due to the fact there was no were for it to go and intermittently dump the over charge into the poor diodes and fry them. Sound reasonable? Anyhow, now I'm in need of a rectifier. Does anyone have one laying around they would be willing to part with? A new one from Yamaha is about enough to make me want to get rid of the ! bike. I've seen some aftermarket ones that are much cheaper but I don' t know much about them. Any thoughts or Ideas? I love the bike but these alternator issues are starting to make me think I should have painted it yellow.

Chris R
Sierra Vista AZ
86 FJ1200

[Dan Filetti]

How old is the battery?  Not sure in your case, but I've seen some strange behavior from a dying or week battery. 

My $0.02, (which it may well be all it's worth.) 

Sounds like you have a good methodology.

Good luck,

Dan

[andyb]

Troubleshooting logic sounded good in the first post, assuming that things were disconnected when you stuck a meter on them.

Throw an R/R at it and you'll probably be in good shape.  Now is a good time to relocate it for better cooling, and improve the wires (think about how old that wiring is....).

[xt550]

do you have alternating current out of the generator?
If the diods are not rectifying the generator it should be alternating not be dead.
Are u sure theres no other "glitch" there?
try ohm meter + - and ground from/on the generator if you still have it disassembled.

[Varget22]

do you have alternating current out of the generator?
If the diods are not rectifying the generator it should be alternating not be dead.
Are u sure theres no other "glitch" there?
try ohm meter + - and ground from/on the generator if you still have it disassembled.

Not quite sure what you mean by trying ohm meter+- and ground on the generator? If you mean stator resistance I did measure it at approx 0.8 ohms on all three legs. It's a little bit high but I feel its still within tollerance. When I tested the rectfier it showed the diodes as a open circuit (no continuity). If they showed as a short(continuity) I could see how they would pass ac current. I do have to entertain the possibility that the regulator may also be fubar but without the rectifier opprating nothing else is going to look right.

Chris R
Sierra Vista AZ
86 FJ1200

[RichBaker]

You've got it right, Chris.... open diodes will NOT pass any current, so you're only getting half what you'd normally have.

[Varget22]

I've got a line on a used alternator for a good price and hopefully the rectifier is good. If not I'll have to do some calculations on how many solar panels I'll need to supply about 14.5 volts and build a trailer. Red-neck style.

[xt550]

Sorry my bad english.

if your handy you may rebuild it with "blue berry's"
http://www.startmotor.se/ItemInfo?itemId=77758477&itemName=Diod+6A+400V+Universal

about 2.5US$ pcs