Alternator charging?

[rjbaren]

Something new to make me keep one eye on a gauge and one eye on the road.  I noticed my Amp gauge now dipping below zero and slightly into the negative.  All of a sudden it will jump back into the positive, like 15 on the scale, then work its way down close to the zero but still slightly in the positive, and then drop below zero into the negative area again.  This concerns me that I am not charging or having any alternator output.  One of the wires in the back of the alternator that connects to the regulator is rather wobbly. 

I have a diagram and instructions for a single wire alternator setup.  Is it also possible to convert to a different type pf gauge?  Any suggestions on how to test for output or a what better type gauge or alternator type to convert to?

I just don't want to find out the hard way I'm not charging.

Thanks.

[jbcollier]

Hook a voltmeter across the battery.  What does it read while the ammeter is cycling?

[Gary t]

When I repaired the wiring on my S2 I included one of those tiny digital voltmeter in the panel near the ammeter.

[rjbaren]

The volt meter reads 12 volts.  Unfortunately it is analog.  I have to look and see if I have or can borrow a digital voltmeter.

[jbcollier]

Nothing wrong with an analog gauge.  12v is too low.  Should be between 13.2v and 15.3V.  I like mid-14s myself.

[rjbaren]

I found my digital voltmeter.  Before starting the engine it was at 12.45.  Once I fired up the engine it dipped down to below 12, like 11.38.  The ammeter was in the negative.  I revved it up a bit and it and it stayed at around 12.35.  All of a sudden it went to the mid 14s and my gauge went into the positive a little above zero.  So it appears the ammeter gauge is correct showing when it is on charge and off charge.  I recently had the alternator tested and it tested good but I am not so sure any more.

[jbcollier]

It sounds like an alternator issue.  Hard to say for sure over the phone.  Make sure all the connections are clean and tight, especially grounds.

[EuropaTC]

It sounds very much like either an intermittent fault on the alternator or an external wiring issue but whatever the cause you're not fully charging the battery.  The resting charge should be more than 12.45 with no load on it,  I'd have to check for sure but IIRC a lead acid battery is around 12.7(ish) for full charge and the calcium batteries fractionally higher. 11.38 volts shows the alternator hasn't kicked in yet, mine used to do the same with the original alternator until the revs rose above tickover.

Although voltmeters are easier to fit and don't need the heavy gauge wiring that ammeters do, an ammeter is an excellent indication of what's happening to your car at any moment in time. Normally they will flick up to 10-20amps after starting for a second or so while the battery drain caused from turning the motor is replenished. Then they drop to about a needle's width over the zero, showing a very slight positive charge. If you switch on heavy loads (lights, fans, etc) then it might dip for a second until the alternator takes up the extra battery load but it will return to just above zero. 

So from what you say, I don't think there's a problem with the ammeter.

14v sounds about right and in my limited experience modern alternators either work or not. You mentioned in an earlier post about a suspect connection to the alternator, that sounds like the first port of call. Get a good solid connection and see how you go. I'd also check the drive belt tension while your there in case it's slipping under the extra load of starting up.

Brian

[rjbaren]

Thank you for the responses. 
There are a couple of tests from the shop manual to check for continuity I will try before removing the alternator to go back to the rebuilder for him to bench test again.  I was concerned about the alternator a few weeks ago when I noticed the Brown Purple wire at the back of the alternator wobbled.  It is a tight fit on the terminal but the contact which is part of the internal voltage regulator which it is  plugged into wobbles.  The rebuilder said it is OK as long as it doesn't touch ground, which it doesn't because it is a covered female connector.  The Brown Purple wire goes from Batt connection of the alternator to the solenoid which at the solenoid connects to the battery and the ammeter.

Here is another item I didn't mention since I am not sure it is related, (but I now think it is).  Every time I start the car, the radio I installed turns on immediately by itself.  I installed a new JVC AM/FM/CD/Bluetooth radio which works pretty good.  Yesterday, while driving, it turned off by itself and then a couple of minutes later it turned on again.  This happened a few times.  I thought it was my less than stellar job of installation but, I installed the same radio in two other cars this year as well.  One always turns on when I start the car like the Europa, but the other doesn't.  They are both BMWs, a 1995 and a 2000.

Now I am beginning to think the power to the radio is being interrupted, turning it off, and turning back on as the power returns, much like the signal to the Ammeter.  I haven't noticed whether they happened the same time as this whole new thing made me want to drive home before I ran out of battery in case the charging didn't come back on.  I did notice when the power to the ammeter returns it goes up to around +15 and then settles back just above the zero till it drops again into the negative and the cycle may repeat.  I recently replaced the negative battery cable and thoroughly cleaned the connection at the ground.  The ground at the Alternator is clean as well and the alternator was rebuilt before it went back on the car.  Most grounds in the car I have come in contact with I have disassembled cleaned the connections. 

[jbcollier]

Is there a good, thick, ground wire between the engine and the chassis?

[rjbaren]

Regarding the engine ground, there is a heavy braided cable connected on the engine side of the motor mount under the carbs and then to the chassis.  Both ends and clean and tight.  I did my continuity tests per the manual on the back of the alternator and the Brown Purple wire from the Batt connection of the alternator (the one that is wobbly) shows 12.35 volts.  When I wiggle it a little it drops to zero and when I wiggle it some more it goes back to 12.35.  I am pretty sure that terminal is part of the internal voltage regulator which I think is the culprit.

[EuropaTC]

Regarding the engine ground, there is a heavy braided cable connected on the engine side of the motor mount under the carbs and then to the chassis.  Both ends and clean and tight.  I did my continuity tests per the manual on the back of the alternator and the Brown Purple wire from the Batt connection of the alternator (the one that is wobbly) shows 12.35 volts.  When I wiggle it a little it drops to zero and when I wiggle it some more it goes back to 12.35.  I am pretty sure that terminal is part of the internal voltage regulator which I think is the culprit.

It sounds to me like you're on the right track, voltages shouldn't be dropping just from moving the wire around, That's going to happen with engine vibration so maybe something isn't right inside the alternator ?

Brian

ps - good detective work 

[rjbaren]

I removed the alternator and took it back to the rebuilder and he agreed the solder joint at the terminal must have come loose.  I hope to have it back tomorrow.  I hope that cures the radio cutting out too. 

[rjbaren]

The alternator is back and on the car and everything is good.  The gauge reads slightly above the zero in positive territory and the radio no longer cuts out. 
This will lead me to my next post regarding the radio.
Thank you all for your help.