Help diagnosing alternator fault please

[Oldiebut goodie]

That is certainly at variance to my experience - I am not doubting what you have observed there. There must be a common fault on a lot of alternators that prevent self excitation when the excitation wire is removed though. The Valeo that was on my van certainly wouldn't work without excitation. I will check the Lucas one that is on there now when I get a chance.
I am wondering if they will self excite if there is no residual magnetism to generate a self starting voltage. I doubt it.

[itchyfeet]

That is certainly at variance to my experience - I am not doubting what you have observed there. There must be a common fault on a lot of alternators that prevent self excitation when the excitation wire is removed though. The Valeo that was on my van certainly wouldn't work without excitation. I will check the Lucas one that is on there now when I get a chance.
I am wondering if they will self excite if there is no residual magnetism to generate a self starting voltage. I doubt it.

I will check my lucas one too before fitting the 90a bosch at the wend and checking that too
most have a bosch on their t25 and thats what the op has and bigherb has tested
bigherb is that an early or late bosch and what amps?

[bigherb]

I am wondering if they will self excite if there is no residual magnetism to generate a self starting voltage. I doubt it.

No it can't if there is no residual magnetism.

bigherb is that an early or late bosch and what amps?

Original 45A air cooled alternator.

[ghost123uk]

I would love to "put this one to bed". Are the usual alternators fitted to our vans "self exciting" or not.

What have I / we started At least at the end of this it will be "put to bed"

[123-jn]

terribly exciting though eeh!!!!

I have learnt alot as I did not know that my alternator needed to be excited to work? Do you think it will work with the missus?

[badgerfax]

Just to finish, the I ordered a new brush pack from M.U.R.E
http://www.ebay.co.uk/itm/171194815358? ... EBIDX%3AIT" onclick="window.open(this.href);return false;

Delivered in less than 24 hours from Northern island to Kent







All fixed

Just want to say thanks to all of you who helped me understand how this part of the van operates and where its connected to.
Special thanks to Itchyfeet who kindly sent me a brushpack to try. This will be in the post to you today.

[Oldiebut goodie]

I would expect that the voltage would be higher than that with a 14.7v regulator - it looks like you have lost approx half a volt between alternator and battery. What was the alternator voltage output?

[badgerfax]

I would expect that the voltage would be higher than that with a 14.7v regulator - it looks like you have lost approx half a volt between alternator and battery. What was the alternator voltage output?

Hi Oldie, I have just taken a reading off the main alternator terminal and I'm getting 14.6v so you're correct. Did not check yesterday at source.
The ring connector has 2 cables going into it. Its not in fantastic condition. I have not got that size of connector/tool at the mo.

Both cables are red with white stripe. Can you give me an idea where they go. Battery connection is plain red although I seem to remember a red/white used in the westy bbb charger

[Oldiebut goodie]

You would be better waiting for someone with the knowledge of the setup that you have but a quick look at a wiring diagram shows that the 2 R/W go to a join (I don't know where - possibly in black box on bulkhead?) then comes from that in one thicker R cable to the starter solenoid thence to the battery. Several joints there that need looking at / repairing / cleaning.

[badgerfax]

Thanks Oldie, Will investigate further

[bigherb]

Water cooled engines alternators are wired two different ways
Two wires to the post in the box in the engine bay then one heavier wire to the starter motor.


Or one heavy wire direct to the starter motor and a smaller one to the post in the box

[itchyfeet]

That is certainly at variance to my experience - I am not doubting what you have observed there. There must be a common fault on a lot of alternators that prevent self excitation when the excitation wire is removed though. The Valeo that was on my van certainly wouldn't work without excitation. I will check the Lucas one that is on there now when I get a chance.
I am wondering if they will self excite if there is no residual magnetism to generate a self starting voltage. I doubt it.

I will check my lucas one too before fitting the 90a bosch at the wend and checking that too
most have a bosch on their t25 and thats what the op has and bigherb has tested
bigherb is that an early or late bosch and what amps?

Ok just checked the lucas currently in the van and it does the same as bigherb says, no power until you rev it a bit for say 20 seconds then it starts producing power, let the revs die down and it continues producing power.

[dave friday]

With my old alternator I had to take the revs to 1200 before the charge light went out,with the new one the charge light goes out as soon as the engine starts at 750rpm.

[itchyfeet]

With my old alternator I had to take the revs to 1200 before the charge light went out,with the new one the charge light goes out as soon as the engine starts at 750rpm.

Sorry should have explained more, we were discussing if the alternator will self excite (produce power) with the charge light connection (blue thin wire) removed, it appears it will but only after reving

if this is happening to you then the alternator is probably fine its probably the small blue wire thats at fault, im sure many people have wasted money on a new alternator because this connection was bad, you may never have noticed because when fitting the new alternator you inevitably remake that connection and all is well again

i think we have finally 'put this to bed'

[bigherb]

Ok just checked the lucas currently in the van and it does the same as bigherb says, no power until you rev it a bit for say 20 seconds then it starts producing power, let the revs die down and it continues producing power.

It is not actually time, it is RPM dependant, you can rev all day but unless you reach the RPM threshold around 3000 RPM alternator shaft speed 1500-2000 RPM crank speed it won't self excite.