One for you electrical BOFFINS

chrisk

chrisk

Hero member
Location
Brisbane, Australia
My battery is going flat, with ignition off.
With battery + connected, I get a 12 volts between neg on battery and the earth lead. Short, clearly. Put the metre on and it reads a few mA.
If I disconnect the wire from the charge output at the alternator I get no voltage across earth, and no mA.

If I put my meter across the output terminal on the alternator and wire to the battery I get 12.28V.
Then if I put my meter across earth and the wire to the battery I get 12.37V.

Where the hell are my volts missing volts going?

Bear in mind, I ground one of the mounts off on the alternator, could there be a little amount of aluminium dust shorting out something inside the alternator?
If that were the case, why is it that when the output wire to the battery is disconnected, I don't get an ohm reading between output terminal and earth?
 
mauricejota7604 said:
Hey Chris in your wiring circuit do you have anything from +battery that is not going through the switch that maybe drawing current,
Voltage regulator maybe??
Click to expand...

Maurice, there is a regulator within the alternator.
 
Owners of old Jaguars know all about this Chris...They develop leaks to earth very easily.
have you anything like an ampmeter in the circuit ? Any aftermarket electrical gauges ?
 
No Greg, purely power to ign switch, which while finding/looking for the short is 'off', the only other item off the wire is a cigarette lighter socket.
I have tested the disconnected alternator for ohm's (teminal to earth) with both positive and negatives of the meter, but get nothing.

Reconnect the wire and I get 12V if I measure between the battery and negative lead. I can light a small LED light from the current (between the earth cable and the neg battery terminal), but not a globe.

I'll do a check at the cigarette lighter socket, just in case ..........
 
chrisk said:
I'm starting to think the diodes in the regulator section are cactus.
Click to expand...
me too
If using a digital multi meter to measure then you will get discrepancies just part and parcel i am afraid.
Tend to use a proper ammeter when nailing down an issue but dmm's in most parts work ok.

See how George checks his diodes hope this helps
 
Chris, Brett has a point with using an analog meter for ease of use, but if you hook it up backwards the tons get mixed up and pegs the meter in the wrong direction. If you use the digital in the current mode put it in series between the battery and the battery lead. It doesn't matter which you use, positive or negative, just reads + one way and - the other. If you have current flow with the switch off and you think its the alternator disconnect it and if the current flow stops you nailed it. If it's still showing current flow with the alternator disconnected then look for a leak at the switch. Metal filings in the alternator, or a shorted diode, will reek havoc on the system!

Clay
 
Um, what is a buffin. Is it a bread muffin or something hipster like that?
 
'71 SF said:
Chris, Brett has a point with using an analog meter for ease of use, but if you hook it up backwards the tons get mixed up and pegs the meter in the wrong direction. If you use the digital in the current mode put it in series between the battery and the battery lead. It doesn't matter which you use, positive or negative, just reads + one way and - the other. If you have current flow with the switch off and you think its the alternator disconnect it and if the current flow stops you nailed it. If it's still showing current flow with the alternator disconnected then look for a leak at the switch. Metal filings in the alternator, or a shorted diode, will reek havoc on the system!

Clay
Click to expand...

Thanks Clay, I'll look into it. Bloody thing is driving me to drink..... There's an idea!
 
You need to measure the resistance with a digital ohmmeter. Disconnect the + cable from the battery, and connect the meter between this disconnected cable and the negative terminal on the battery. (If you want to be extra safe, disconnect both terminals and connect the meter to the + and - wires). With the ignition switched off, I would expect a reading upwards of 1 meg-ohm, less if the bike has an electric clock.
 
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