Alternator earth

[nelmo]

My voltmeter gauge has been slowly dropping over the last few months - used to show 14v when revving but now down to 13.3v.

I'm thinking possibly the problem is that the alternator bracket to engine interface maybe has some corrosion/rust and the earth is worse than it was?

Before I take that all apart, I was thinking of testing it by just putting a temporary earth wire from the alternator body to the engine block.

Does anyone know if that will need to be a chunky/braided earth wire or will any bit of old wire do?

I know there's always a lot of current with alternators but I'm not good enough with electrics to be sure...

[IanS]

Before I did anything else I would check the actual voltage at the battery terminals.

There are so many possible points of high resistance that could cause this of which the alternator earth is only one.

If the voltage is good at the battery then the problem is in the wiring to the voltmeter. (including its earth)

If the voltage is low at the battery then the charging circuit is suspect.

If charging is at fault then measure voltage from alternator body to Battery -ve which should be below 100mV if not check voltage alternator body to engine block.

Be methodical in running voltage checks before fitting random wires.

[nelmo]

Ok, good idea... Will try those... thanks...

[nelmo]

17 hours ago, IanS said:

If charging is at fault then measure voltage from alternator body to Battery -ve which should be below 100mV if not check voltage alternator body to engine block.

Is that done with the engine/ignition on? 

[IanS]

Needs to be done with the engine running so that the alternator is producing electricity.

[traci15Ren]

this is useful information

Edited April 14, 2022 by traci15Ren