1.9DG Alternator woes

[puddin]

Hi,

I've run this problem as far as I can, I have now run out of talent and need some advice.

Background
1987 1.9DG Westfalia Joker, bought it a couple of weeks ago, drove home ok.
Got home, de-greased the engine and hosed off, next time I restarted the battery light on the dash stays illuminated. My first thought was that I must have dislodged something, alternator was fine before.....

Using a meter I can confirm.
The battery seems good, I am using a charger to maintain it, it holds at 12.65V. Starts the engine OK.
+12v is present on the B+ terminal of the Alternator - Same voltage reading as battery.
Measured resistance from Alternator casing to negative terminal - around .2 ohms
When running voltage at both the battery and the alternator terminal drops to around 12.2v, less with more revs and pulls back up when the engine stops.

So far I have.....
1) Checked alternator connections,
2 x Red wires via single ring to B+
1 x Blue wire to D+
Connections a bit untidy but sound, - Didn't fix it.
2) Checked battery connections, Connections OK, - Didn't fix it.
3) Re-terminated Alternator wiring - soldered new terminal to 2 main red wires and to small blue wire - Didn't fix it.
3) Replaced regulator pack, Didn't fix it.
4) Stopped playing with Alternator to drop engine and gearbox for another issue, refitted engine and checked starter connections - Connections OK, - Didn't fix it.
5) Replaced alternator with 2nd hand - Didn't fix it.
6) Replaced with refurb unit from GSF - - Didn't fix it.

That's 3 alternators - It's possible that I have been very unlucky but I now suspect something else is causing the issue

Cheers!
Tony

[Mocki]

the thinner red wire that goes to the alternator from the starter motor may have gone rotten, allowing some power through but not much. water ingress may have made this worse.

worth replacing anyway, they are a known problem.

[puddin]

Thanks for the reply, will give that a go right away.

Cheers
Tony

[Mocki]

let us know the outcome please!

[Oldiebut goodie]

I notice that there is no mention of your checking the resistance of the power cables or the battery to earth cables.
The light is remaining lit because there is no voltage coming from the alternator which to me says that there is an earth problem. (the battery is delivering the excitation voltage but there is no earth to make the potential difference meaningful)

[Mocki]

good point ObG
BUT surely the engine must have a earth for the starter to start it???

[Oldiebut goodie]

It is baffffling - it has had different alternators, the voltage drops as the engine runs which means it is running entirely from the battery, the engine starts - which could be the starting power is bridging a corroded connection somewhere. The best thing would be to remove all earths and power connections like you said clean and remake. Interestingly my alternator has an earth added from its body to the engine block so someone before me had been down this route also.

[puddin]

OK, run a new cable from the rear of the starter using a pre-made battery lead, also renewed the other Red and Blue wires that run round the rear bulkhead to the black connection box.

So far no difference. I will run a new earth from the Alternator chassis to the body and report back.

Cheers.
Tony

[Oldiebut goodie]

What sort of resistance reading are you getting for alternator body to chassis and battery negative to chassis? As far as I can tell you haven't touched these earth tracks yet. Have you removed all the chassis earths and cleaned them up? You seem to have concentrated on the positive cabling - which will not work correctly without decent earthing routes.

[Mocki]

my next thought is to temporarily run a new signal (blue) from the alternator to the dash end, alongside the original (though not physically) to elimiate this from our enquiries, so to speak,

after you have cleaned or renewed all the earth connections ( battery earth, to bare metal) and gearbox nose

[puddin]

Installed a new 10mm pre-made battery earth cable from the Alternator chassis to the van chassis. Removed and cleaned the gearbox nose earth, battery earth, battery terminals.
Resistance from Alternator body to chassis and Alternator body to Negative post is 0.02 ohms.

Still no better.

I am out of time tonight to play further, something for me to ponder over a beer tonight.

Guys, thanks for your help today.

Cheers
Tony

[Oldiebut goodie]

Well the only thing left now is the blue wire between the D+ terminal and the dash is shorted to earth somewhere - does the battery charge light remain lit when the wire is removed from D+? If so it needs tracing to find the short or replacing - neither of which is an appealing prospect!

[ghost123uk]

Hi,
When running voltage at both the battery and the alternator terminal drops to around 12.2v, less with more revs

Aye, this one really is odd !

If the alternator is getting it's excitation voltage (and it is) then regardless of ANYTHING else there should be the usual ~13.8 volts between it's output and it's casing !(and it is securely bolted to the motor so that includes that). If the alternator is functioning correctly there has GOT TO BE

A spinning alternator with a 12v supply to the +ve terminal = ~13.8 volts (even if it is on a stationery Lister Diesel engine at a traction engine show !!)

Run a black jump lead from battery -ve to alternator bracket ?
If it doesn't produce ~13.8 volts then it has to be a case call in an exorcist !

Very very odd and watching to check out the cause...

[Oldiebut goodie]

I think that it isn't receiving the excitation it should via the blue to D+ - hence the thought that the blue wire has been accidentally grounded a some point. The battery light would remain lit if this has occurred - and it is remaining lit.

[ghost123uk]

I think that it isn't receiving the excitation it should via the blue to D+ - hence the thought that the blue wire has been accidentally grounded a some point. The battery light would remain lit if this has occurred - and it is remaining lit.

That makes sense

So, check for 12V on the blue wire, ignition on and temporarily disconnected from alternator (as this is it's "earth path" to light the charging lamp) if no 12V we are on our way to a solution