Alternator Oddities

[flamodamo]

Hi,

I am having trouble with an intermittently charging alternator.

An auto electrician diagnosed the old one as faulty. I replaced it and at first the battery was charging, although the warnign light remained on. The next day, I started the engine again but this time the alternator was NOT charging. I took the risk, drove for two hour and hey presto it was working again. The same thing happened the next day.

I have checked the earthing, this is fine. The charge OUT of the alternator is 12 volts, as expected.


The charge into the alternator, along the exciter wire, is just 5 volts. Could this be the problem?

Or could I have bought the wrong alternator?

Any other ideas please? By the way, my old alternator broke after just one year's use, and this is my third or fourth alternator in about 4 years.

All suggestions welcome! My van is a 1989 T190, 2.5 Litre, Di. It's an old ambulance, SWB, (I think that makes it a bus chassy?)

Many thanks

Damian

[Altransit]

So far as I can remember, the exciter wire should carry battery voltage, so this could be the problem
12v output is not enough for charging, as it should be around 14 volts to charge a 12v battery

[Keef]

If you've got through an alternator a year for the past 4 years, there's something wrong. Are they new or used alternators?

What made you think the alternator was charging if the warning light was on?

[flamodamo]

The alternators are reconditioned, I think, at a cost of about £100 normally.

The reason I felt it was charging was because, after two hours driving, I pulled up, got out my volt meter, and the battery was reading well over the 14v mark (as opposed to about 12.4 at the start of the journey).

With the exciter wire, in order to test this theory could I disconnect it and run a temporary exciter wire directly from the battery into the alternator?

By the way, I should mention that I also have a relay switch (for my leisure battery which I have temporarily disconnected in order to eliminate that end of things). I might try bypassing that for now - good idea?

Thanks all for your help

Damian

[flamodamo]

Here is a picture of the beauty, on the Isle of Harris earlier this year.

[Keef]

The later part of this link explains it quite well and will give you a few things to check with your meter

https://www.woodmizer.com/us/portals/1/ ... e77ef1.pdf

I would definitely isolate your split charger until you've found the problem, the split charge relay may even be the problem.

It almost sounds like the alternator is wired up wrong to me.

[flamodamo]

Thanks Keef,

That guide looks really handy. Big pictures and not too many words - exactly how I like it!

Your guide implies that the exciter wire should carry 12v to get the alternator going, and it is only carrying about 4. So I think it may well be corroded somewhere along the line.

Hopefully I will find out later tonight and post the end result.

Thanks

Damian

[MinorMatt]

Has it had a 3 bolt alternator fitted at some point or is it still the 3 spade type?

I'm just wondering if its been converted and the exciter wire is wired to the tacho output?

[flamodamo]

As of last night, I have managed to get the alternator charging again, but I do not think that I have solved the whole problem.

I tried wiring a new exciter wire directly from the battery to the alternator, this made no difference. So I put it back to how it was and then removed the Relay. I started the engine and the alternator started charging again, hooray! I tested it again this morning and it is still working.

Only thing is, the battery warning light remains on.

I may be imagining this, but you know when you have to give it a good throttle in order to get the alternator working? Well the alternator now seems to require an extra large amount of throttle to get it going.

I will look into the wiring as suggested. There may well be a problem there as I had to customise the back of the alternator to suit my older wiring set-up (The alternator I bought had the wiring sockets in a slightly different position as to what I was used to)

Thanks all!

Damian

[flamodamo]

MinorMatt, I am not sure what you mean by a 3 bolt alternator. I am using 3 x spade connectors. At some point I had a plug in the back, which melted whilst on holiday and the mechanic just wired the wires directly in using spade connectors.....

[RileyJames]

Hi,

I am having trouble with an intermittently charging alternator.

An auto electrician diagnosed the old one as faulty. I replaced it and at first the battery was charging, although the warnign light remained on. The next day, I started the engine again but this time the alternator was NOT charging. I took the risk, drove for two hour and hey presto it was working again. The same thing happened the next day.

I have checked the earthing, this is fine. The charge OUT of the alternator is 12 volts, as expected.


The charge into the alternator, along the exciter wire, is just 5 volts. Could this be the problem?

Or could I have bought the wrong alternator?

Any other ideas please? By the way, my old alternator broke after just one year's use, and this is my third or fourth alternator in about 4 years.

All suggestions welcome! My van is a 1989 T190, 2.5 Litre, Di. It's an old ambulance, SWB, (I think that makes it a bus chassy?)

Many thanks

Damian

The low voltage on the exciter wire (5V) could be the problem—most alternators need around 12V to work. Check the wiring, connections, and battery health. If alternators keep failing, there might be a deeper electrical issue. Hope you fix it soon!