Alternator Issues

[85AW20v]

Last raceday the overcharging warning came up on my shiftlight so did the last race with the alternator disconnected as I didn't want to wreck the battery. Took it out and to the autosparky who tested it on his test bench and it was only putting out 14.2v so he said there didn't seem to be anything wrong with it. Put it back in and overvoltage warning came up again and the battery is getting 15.3v.

Any thoughts? It's a Nippondenso with 3 pin oval plug if that helps anyone.

[matt dunn]

need to check the power to the 3 wires in the oval plug.

With the key one and the plug disconnected you should get 12V on all 3 with a voltmeter,

or bright power on two and not quite so bright power on the other 1 with a test light with a 4w bulb.

If not there is a wiring problem.

If there is no sensing power it will overcharge.

[85AW20v]

Thanks Matt.

Test results are as follows:
battery voltage - 12.33v
S terminal - 12.25v
Ign terminal - 12.25v
L terminal - 11.40v

So could it be a problem with the module in the alternator?

[matt dunn]

Yeah my guess would be faulty regulator,
or internal in the rotor but that is not that common.

[85AW20v]

Brilliant.

Thanks Matt, I'll get one ordered from the local guy who tested it.

[rollaholic]

sounds like you needa find a new sparky?

actually speaking of alternators matt, have you done much with modern stuff whose charging rate is ECU controlled? is it difficult to test?

[matt dunn]

:? sounds like you needa find a new sparky?

actually speaking of alternators matt, have you done much with modern stuff whose charging rate is ECU controlled? is it difficult to test?

Depends on what you mean by difficult.

We have electronic simulators for most of the ECU controlled alternators at work,
so you just plug them and and run the alt to see if it is working or not,
and can test the alt output like a normal alternator.

Other than that they can be a bit of a PITA to diagnose if it is not the alt itself,
but usually it is the alt or occasionally the engine ECU.

[85AW20v]

OK. Put the new regulator in and still got 15.3 charging volts. It did drop very slowly to about 14.9 after about 10 minutes and battery is up to 12.96v. Any other thoughts?

Should have asked this before too - how do you test the rotor for internal issues?

[rollaholic]

i guess thats what i mean by difficult - working out if its the alt or ecu. like you say though its typically the alt.

last time i saw an alternator being bench tested it was on one of those big machines the size of a wardrobe that spun it up on a belt. was just wondering how things had moved along

[matt dunn]

last time i saw an alternator being bench tested it was on one of those big machines the size of a wardrobe that spun it up on a belt. was just wondering how things had moved along

Um, that machine would be ultra modern compared to what we use at work.

[rollaholic]

south island etc

[85AW20v]

OK. Put the new regulator in and still got 15.3 charging volts. It did drop very slowly to about 14.9 after about 10 minutes and battery is up to 12.96v. Any other thoughts?

Should have asked this before too - how do you test the rotor for internal issues?

What do you think Matt?

[matt dunn]

Should have asked this before too - how do you test the rotor for internal issues? What do you think Matt?

Not easy to test, usually by elimination, if everything else is ok and a new alt fixes it, then it is probably the rotor.
Or can hook up to check rotor current on the test bench,
but even then they wont show up sometimes till on the car again.

My suggestion, try a whole new alternator.
Do you run a 16V or a 20V alt,
and is the plug round or 3 pins in a row with rounded plastic.

I have a few good alternators here and may be able to help.

[Rob]

I didn't read all the posts on this but My commod had similar beef and it turned out to be a faulty connection on the battery to the warning light.

Was charging at 15V as well

[85AW20v]

What should happen if I pull the 5A Charge and the 10A Engine fuses? At the moment with both pulled I'm still getting 15.2v at the battery and the dash voltmeter is reading high.

With the alt plug out, the dash voltmeter drops to battery voltage of about 12.5v and not surprisingly, 12.5v at the battery.

So what now?

[matt dunn]

What should happen if I pull the 5A Charge and the 10A Engine fuses? At the moment with both pulled I'm still getting 15.2v at the battery and the dash voltmeter is reading high.

With the alt plug out, the dash voltmeter drops to battery voltage of about 12.5v and not surprisingly, 12.5v at the battery.

So what now?

the charge fuse is between the alt and the light,
so only really affects the light circuit.

Not sure if the engine fuse controls the other feeds or not?

If you unplug the 3 pin plug and it drops voltage then it is in the alternator.
Soinds like you need a better auto sparky.
Have struck them with a faulty rectifier will overcharge,
but any 1/2 decent auto sparky should be able to test that,
as the rectifiers are easy to get out and test,
and if it's run in a test bench you would hear it growl.

[85AW20v]

Thanks Matt - I'll have another "chat" to him tomorrow.

[85AW20v]

OK. Have now tried another alternator and still get the same result 15.3v at the battery. Connected a spare battery, left it running for 15 minutes and same thing - 15.3v at the battery.

Dash gauge shows about the same voltage and drops slowly when running the radiator fan and wipers as does the reading on my meter connected directly to the battery.

Any other thoughts?

[sergei]

stab in the dark: voltage sensing wire is not hooked directly to the battery.

[matt dunn]

faulty voltmeter?

just seems weird.