Charging issue

[jrdrag2562]

Hello. New to the forum. I have searched the threads but can't find the information I'm needing. My e30 won't charge the battery. It's a 1989 325i. I have the alternator checked at autozone and it tested good. I have a fully charged battery and it doesn't have anywhere near 13 volts at 1500 rpms. My battery light inside on the dash lights up but how much voltage should I have at the d+ terminal. I currently have about 1.6v. I just took it on a 500 trip to north Carolina and had a coolant line blow. I'm not sure if that could help in the diagnostic aid or not. Is the cable only from the alternator to the starter, like 2 feet maybe? And after that it should go straight to the battery if I'm not mistaken. I was thinking of ohming the alternator to starter wire but I'm not sure what good that will do if my excited circuit isn't working.

[tH16]

Where in NC are you located? There is a huge community here in NC that can provide some on site help depending on where you are.

[jrdrag2562]

I am now in ohio. I'm here for school

[Liquidity]

The D+ should be at 12V+ when the car is running. That D+ terminal is what "excites" the alternator - basically turns it on. Pretty sure that wire comes directly from the ignition.

[Liquidity]

ok NO, that wire doesn't come directly from the ignition. I just checked mine and the D+ terminal was low with the key on but engine off, it doesn't go high until the engine is running. I'm not exactly sure where it comes from.

[jrdrag2562]

Yea it has 1.6v running. I guess I could run 12v to it and see if it excites the circuit or do you think it might hurt a component?

[Liquidity]

Seeing as it doesn't come right on with the ignition and has some complicated circuitry behind it, I can only assume that's because the alternator can be damaged if the D+ terminal sees 12v when it's not spinning. I'm also pretty certain that terminal only needs 12v for a second to excite the windings, after that, the alternator can maintain itself, so maybe a push-button switch wired to it would be best.

But before you start messing with all of this, go double check all your fuses first.

[TurboJake]

No. There is no complicated circuitry. the D+ comes straight from the cluster to excite the field coil. If 12v isn't being charged, the battery light comes on. It's very simple. voltage is supplied until start, once started 12v comes from the alternator back into the D+ and neutralizes the circuit so the light no longer comes on as there is no current flow.



Run the 12v ignition jumper wire to the alternator and report back what happens. It will not damage it. You can do this by disconnecting the C1, or the cluster itself and providing 12v at pin 1 on the C101.

A lot of times, it boils down to a bad ground. But there is the chance that internal voltage regulator and field coil is bad, causing the no charge condition.

[Liquidity]

The cluster isn't complicated circuitry? Come again?

[e30rida]

Double check the engine ground that goes from the pan to the frame, I've seen those break or come loose. Also make sure everything on the alternator is bolted on tight or that neither of the wires is missing, one may have broke off or come loose before you had it checked.

[jswest69]

Had a similar problem with my car. turned out to be the wrong bulb in the dash for the battery light. That bulb is apparently what excites the alternator. Good luck.