Electrical Short

[dleemiller]

Well, I just tested the leads to my battery...165k ohms. My battery is discharging over a 2-3 hour period and it appears I have a slight short somewhere. Anybody encountered this?

[starwalt]

How did you test the leads to your battery?

The negative lead (black) is much longer than the positive (red).

A little more detail please.

Did you remove them and check them or disconnect both ends and check them?

[beRto]

You can test for the presence of an electrical short by measuring current leakage (instead of the resitance measurement you quoted before):



You can find a full-sized version here:
http://i216.photobucket.com/albums/cc179/gs_beRto/currentleakagetest.jpg

[sledge]

Hmmm unusual prognosis........ Owing to what at this stage we assume to be a very low resistance to ground I would advise the patient undergoes a precautionary disconnection of the Reg/Rect with hourly monitoring of the battery condition as a follow up. This will determine the overall condition of the Reg/Rect and if it has been having an adverse effect on the battery. Dont worry...it will live..... but in the worse case scenario it may need a Reg/Rect transplant. However this is a routine procedure, there are plenty of donors about and the side effects will be minimal.

Do you concurr DrStarwalt?

[dleemiller]

good call on the current leakage, i'll try that next. i found 2 open wires in the headlight that the previous owner must have ghetto rigged together. i taped them off but i dont think that was the problem. what i did to check was disconnected the terminals from the battery and tested the resistance across them. if the battery is leaking current, the circuit must have some finite resistance across the terminals.



i did some further sleuthing and found a 1.2M ohm resistance across the leads going to the rectifier...i think that's enough to leak the battery out of juice, so if it discharges again it has to be either the rectifier or something else down the line from it.

[sledge]

Seriously though......if its flattening a battery in 3 hours there will be some big-amps flowing somewhere.....see if any cables are getting warm and put your hand on the reg/rect, it should be stone cold if the bike hasnt run for a while.

[SIKDMAX]

The 2 empty wires in the headlight are normal - spare power lead from the factory.

[dleemiller]

Seriously though......if its flattening a battery in 3 hours there will be some big-amps flowing somewhere.....see if any cables are getting warm and put your hand on the reg/rect, it should be stone cold if the bike hasnt run for a while.

that's true, but you can only get big amps with a low enough resistance.   I = V/R  so at 12V/1.2M ohms we're talking 1x10^-5 amps. (.01 milliamps)

so that says to me that maybe the battery isn't getting charged very much in the first place...the battery is only a few months old, so i'm pretty sure it's not the problem.

this is helping.... discussion is so productive sometimes. lol

The 2 empty wires in the headlight are normal - spare power lead from the factory.

thanks, that's def helpful to know.

[sledge]

My "big-amp" guess was based around the original figure of 165K. Tried load testing the battery?

[dleemiller]

ok, i think we can rule out the current leakage now. i tested for current directly from the battery after running it a while and didn't get a reading.

what i'm thinking now is that the rectifier is bad. there's a little plastic plug that goes to it and it has 2 wires. 1 wire is red and 1 is black with a white stripe. i unplugged that because i think it supplies the voltage to recharge the battery. when i ran the bike with it unplugged, it sounded better and i only measured .71 V across the plug...i'm thinking that should read 12 V. anyone know what plug i'm talking about and can verify this?

[dleemiller]

just found this online:

http://www.bbburma.net/Documents/JohnBates_ChargingCircuitTests3.pdf

in case anyone else thinks they might have a bad RR or stator, this has some good tests to try. i'm going to give it a go tomorrow and see if anything turns up.

[beRto]

I think sledge is on the money. If you don't have a current leak and your battery won't hold a charge, your battery is probably dead. As with all electrical testing... start with the battery! I would suggest you take the battery to a shop for a proper load test (which is often free). Also confirm that the cells are full of liquid.

[dleemiller]

the battery is 2 months old. i seriously doubt the battery is cached.

[starwalt]

... what i did to check was disconnected the terminals from the battery and tested the resistance across them. if the battery is leaking current, the circuit must have some finite resistance across the terminals.

An interesting though uncoventional test but valid if you are popping your 20A fuse instantly with keyswitch ON. 165K ohms may or may not be normal depending on the condition of switches for the turn signals, horn, etc.  I think you have worked your way through this enough to see that your problem may be somewhere else.

One thing to be careful of is to use the diode scale on the meter when testing semiconductors - rather than just the resistance scale. For DVMs this is very important as you could/will be misled of the circuit conditions. If using an old analog VOM (the kind with a needle movement) this is usually not an issue -- IF the battery of the VOM is good.

... i did some further sleuthing and found a 1.2M ohm resistance across the leads going to the rectifier...i think that's enough to leak the battery out of juice, so if it discharges again it has to be either the rectifier or something else down the line from it.

You have already found other resources for testing the R/R I see. Of course with the battery connected and RPM above 3k (or 5k which is above 3K) you should see more voltage at the battery than when the battery at rest. This is a quick indication of the R/R health.

Sledge - Good to hear from you!