Alternator/Charging issues

[redcar]

Ok, I will post pictures of my setup when I'm near my car on the weekend.

Thank you for the help

[Brianmoooore]

Ok, I will post pictures of my setup when I'm near my car on the weekend.

Thank you for the help

One medium sized red wire looks very much like another medium sized red wire, so while pics. may help, you'll still need to double check which battery wire the fusebox feed is connected to.

[redcar]

Thank you for the help Brian and Dan.

Just looked at a photo I had of my engine bay and I do indeed have the e30 fusebox and starter motor/alternator connected to the thick wire.
Then the engine loom is connected to the little wire.



Is this correct?
If so, what could be the problem as to why my battery light is dim?

[redcar]

Hello, any other ideas as to what the problem could be please?

[DanThe]

Have you removed all earth/power cables cleaned the contacts and greased them?
If you have 14v with the engine running I wouldnt worry too much tbh

[redcar]

Have you removed all earth/power cables cleaned the contacts and greased them?
If you have 14v with the engine running I wouldnt worry too much tbh

will do this meticulously on the weekend and see how it goes.
Hopefully it'll be alright as like you said I'm getting 14v at the battery.

[redcar]

So I've cleaned all the battery connection and checked the earth straps they're all fine.
Battery light is still dimly lit. I have no idea why. Are there any other things to test/do?

[Brianmoooore]

Try connecting all the 'battery +' wires at the front to the large cable from the rear, leaving nothing connected to the smaller one.
Battery light is glowing because there's a small difference between the apparent battery voltage that the warning light is seeing and the voltage being generated by the alternator.
This could be under or overcharging, but seeing as how your battery goes flat, we have to assume it's undercharging.

[redcar]

Connecting all the wires to the large cable made no difference.

Battery hasn't gone flat yet and have driven/started it good few times.

Any other suggestions as to what the problem could be?

Thanks for all the help.

It's strange that this problem has only occurred as the first alternator stopped working/putting out anything over 12v.
We have been doing some welding to bits on the car, could that have broken something?

[Brianmoooore]

The voltage that is lighting the warning lamp is coming from somewhere!
Measure the voltage on the blue wire on the alternator and a green wire from the ignition switch, then measure the voltage between them, noting which is more positive than the other.
Both these wires are accessible at the accessories socket is it's exposed. Blue on pin 'C', and green on pin 'B'.

[redcar]

The voltage that is lighting the warning lamp is coming from somewhere!
Measure the voltage on the blue wire on the alternator and a green wire from the ignition switch, then measure the voltage between them, noting which is more positive than the other.
Both these wires are accessible at the accessories socket is it's exposed. Blue on pin 'C', and green on pin 'B'.

ok will do this.
I don't understand exactly what you mean but do I measure voltage between blue wire and earth, then green wire and earth, and then use the multimeter with one wire connected to blue and one wire connected to green?
And do I do it with the engine running?
Thank you.

[Brianmoooore]

All as you say, and note whether your meter gives a negative or positive reading for the third test, also noting whether your red probe is on the green wire or blue wire.
You will be effectively measuring the voltage across the warning lamp.

[redcar]

16v on c
14v on b
2v when measured between them with red on c and black on b

What could the problem/solution be now that we know a bit more info.

[Brianmoooore]

One more measurement. Measure between the green wire on pin B and the red/yellow on pin Z. It should be a very small voltage, if detectable at all. Engine should be running as before.

[redcar]

Hi Brian sorry for the late reply. Been so busy.


Between B and Z there is 0.05V with red on Z

[redcar]

Bump, help please.

[Contours]

The only time I saw this battery light on mine was when the alternator brushes were worn down. Maybe though you have looked at this.

[redcar]

Hello, the alternator has been replaced with a working item.

Any help with this please?
Brian?

[Brianmoooore]

16v on c
14v on b
2v when measured between them with red on c and black on b

What could the problem/solution be now that we know a bit more info.

This 2V is what's lighting up the warning lamp. Pin C is the D+ warning light wire from the alternator and pin B is ignition switched power from the ignition switch. The warning lamp is connected across these two wires.
Pin Z is direct from the battery + terminal, via the thick battery cable from the boot, the medium sized wire to the fusebox, and a fuse in the fusebox.
A red wire goes on from the fusebox to the ignition switch and then back, on a green wire, to pin B
I was hoping that most of the 2V would appear between B and Z, indicating something resistive in that loop (most likely the ignition switch itself), but it appears that is not the case.

The voltage on both output terminals of the alternator should be near enough the same. They are generated by the same windings in the alternator, although they are rectified to DC by two separate diode arrays. The B+ output from the alternator is connected to the battery +, of course.
Can you measure the voltages on the B+ (small wire) and D+ (large wire) terminals directly at the alternator, with the engine running? You should be able to get at them with the air filter swung up out of the way a bit.

[redcar]

Brian thank you for the help.
I've measured the voltages directly at the alternator terminals with the engine running -
There is 16v on the small wire and 14v on the large wire. Would this suggest that the alternator needs replacing?

[Brianmoooore]

One last check. Polish up a small area on the side of the alternator body and use your voltmeter to check if there's any voltage between the alternator body and a good body earth, such as the LH bonnet rear catch.
If there's nothing there, I can't think what the problem can be other than the alternator.
14 volts on the large terminal is about right, but 16 on the other seems too high.

[redcar]

Hi Brian, no voltage between alternator body and a good body earth, as tested before...
Can you think of anything else to check or should I go ahead and try another alternator?

Thanks a lot for the help.

[Brianmoooore]

Can't think of anything else left! It's a fairly basic charging system, with the alternator main output going directly to the battery, and a 12 volt ignition switched feed supplying the field windings through the warning light before the alternator gets up to speed, which is then replaced by a rectified supply from the main windings, controlled by the voltage regulator pack. Either the regulator pack is faulty, or is being upset by a faulty diode.

[redcar]

When you say faulty diode would this be a diode in the alternator?
If the diode is in the car electronics how would I test this?

[Brianmoooore]

Yes - there are nine in total, six which full wave rectify the three phase output from the stator windings to charge the battery, and three which half wave rectify the stator output for the field windings in the rotor.
I'm not sure which sort I think is faulty. I can come up with a theory that it's a main diode, and can come up with an equally valid one that it's one of the field ones, but it's making my brain hurt trying to decide which is right.

[redcar]

Yes - there are nine in total, six which full wave rectify the three phase output from the stator windings to charge the battery, and three which half wave rectify the stator output for the field windings in the rotor.
I'm not sure which sort I think is faulty. I can come up with a theory that it's a main diode, and can come up with an equally valid one that it's one of the field ones, but it's making my brain hurt trying to decide which is right.

ok, so worth just changing the alternator? I haven't been able to find any documentation of a problem like this...So I'm assuming it's more likely that it'll be fixed by changing the alternator. Especially as the warning light has only come on since changing the alternator.

Unless there's something related to the old alternator failing, and the reason why the warning light it on now, despite a replacement alternator.

[Brianmoooore]

If you have an old alternator lying around, with an identical regulator pack on the back, try swapping that around (five minute job), and if that doesn't give a cure, fit the pack from your current alternator to the old one, and fit that.

[redcar]

OK will fit the regulator pack from the old alternator.
Don't understand how fitting this regulator pack from new alternator to the old one will help as the old alternator completely failed and wasn't even charging.

Will get back once I've tried this out.
Thanks again for all the help.

[Brianmoooore]

Check the condition of the brushes on the regulator before you fit it. If one or both are short with signs of arcing on the end, give them a gentle pull to straighten out the copper braid that retains them.

[redcar]

Fit a replacement alternator an no problems at all.
No battery light at all. Glad that problems finally fixed.

Also fit a new Odyssey pc680 battery as the last one had been drained flat so many times over the winter and wasn't holding charge.

Thanks for all the help