Charging system problem

[farkman]

Hey guys,

It's been a while since I posted, notice a few of the older regulars aren't
here anymore.

Anyways, I have a problem with my Mk3 golf TD. I bought a new battery a few days ago (Motomaster Eliminator 875CCA), wanted a more powerful battery than stock. While hooking it up, I pulled a dumbass, and mixed-up the positive/negative. Things started cooking at the alternator. It was connected for about 5 seconds. Radio no longer works, but that isn't a big deal. Engine/lights still work normally.

I got a new voltage regulator but even still the battery light is always on.
Battery voltage with the engine off is about 14.8V. Engine on it's about 14V. At about 2200rpm the tach drops to zero and the oil light starts flashing. When I shift to a higher gear the tach works again, oil light turns off, until it hits 2200rpm and it does the same thing.

With the battery at 14V with the engine on it seems like a good sign, I think.

I've driven the car about 40km so far, and everything seems okay except for the battery and oil light.  

I did a search already but couldn't find anyone with the same problem.

Thanks for any help.

[farkman]

Anyone have an idea?

I checked the belt and tensioner and both are in good shape.

[zukgod1]

How about the fuses?

[the caveman]

14 volts actually sounds a little high . Should be more like 13.5-13.8 v. You may have cooked the regulator. It seems to work but you may have uncontrolled voltage. Do you have an ammeter to check amperage?  that will tell you if it really is working. I think the smoke you saw was 1 diode kicking the bucket.

[farkman]

Zukgod1

I just checked the fuses, under the dash and the one under the hood, they are all good.

the caveman,

Yeah it seemed way too high, maybe because it was a fresh battery, who knows. I bought a new regulator after it happened so I'm pretty sure that's okay.

I just checked the alternator and battery. Battery is at 13.2V with the engine off. Engine on, voltage measured from the alternator to battery(-) is 13.8V and was slowly creeping up.

I remember reading a post when I was searching for similar problems that it takes a little while for the brushes to wear into place in the alternator. Perhaps that is slowly happening. However the battery light is still on, although very dimly now and the oil light and tach act up above 2200rpm. I cleaned the connections around the alternator and the starter but made no difference.

[the caveman]

Since the battery is new and as you said the voltage is 13 v without it running ,it shouldn't need charging i.e. the voltage should be lower than higher. kinda really depends on how long the battery sat before installation though. The other thing you can look at is the contact for the regulator. You will have to remove it again. On the regulator there is a contact tab . Clean where it touches the inside of the alternator. Also while it's out make sure that both brushes are touching the commuter properly. Sometimes it's easy to have one go in sideways and barely touch ,if at all. Whenyou install it, try to bend the brushes/regulator away from the commuter, so that as it tightens down ,it goes straight.

[farkman]

caveman,

The battery sticker says it was manufactured Oct 2008 so it's fairly new.
I cleaned that little contact tab two days ago when I figured I should clean every contact/connection between the alternator and battery. The bottom of the brushes were nearly worn in by that time too, about 40-50km on them.

As for the commutator, it's getting worn but I'm not sure how much is acceptable. It's down about .040-.050" per side from original.

When I got home tonight I checked the battery voltage, 13.8V. I guess it's getting charged. Also on my way home, the thing it did at 2200rpm it now does at 2600rpm.

With all this said, could the battery light be on even if everything is working properly?

[the caveman]

I once had a gasser jetta with the same problem. Was charging fine, full voltage and amps , but the light stayed on, Checked all the  battery, alternator wiring , even did voltage drop tests. Checked the grounds under the hood and for the cluster. repalced the cluster with one that i knew was good. Never found the problem, but the car ran fine until it was stolen 2 years later . I suspected the regulator, but i believe she  didn't have an alternator with the removable one.

[farkman]

caveman,

I'll keep my eye on the problem but as long as the the battery stays charged, I think nearly everything is okay.

Thanks for your help.

Peter

[farkman]

No, I was wrong. Car wouldn't start today. Battery was at 14V but with the key on it dropped to 8.5V.

I'm out of ideas.

[smutts]

My guess is that you need to replace the diode pack. :cry:

[farkman]

smutts,

If by diode pack you mean the voltage regulator, I already have. Didn't make any difference though.

[the caveman]

I believe the diodes are not with the regulator. They are inside the alternator.
But now i see what you said about the battery. Even with just the key on it shouldn't drop to less than 12.v. I would get it checked out with a proper tester. Some Can tires now have the same  electronic tester at the counter that VW dealers use.  It was right 99 % of the time.

[Vincent Waldon]

Agreed...  any battery that goes from 14V to 8V immediately sounds suspicious.  With a full charge (14V) and that many CCA it should be able to grind for a long time.  Canuck Tire will be able to test it under load.

'Course part of this depends on where you are measuring from... at the posts ?

[the caveman]

Agreed...  any battery that goes from 14V to 8V immediately sounds suspicious.  With a full charge (14V) and that many CCA it should be able to grind for a long time.  Canuck Tire will be able to test it under load.

'Course part of this depends on where you are measuring from... at the posts ?

good point. do a voltage drop between the post and the connector.  Both neg and postive .As a matter of fact do voltage drop tests at every connector.