alternator overcharging

[cyrus]

Hi geoberni well I am puzzled by the 3 wires you mention as I only have 2 that colour, the other 2 are brown.....and these are the colours on the wiring diagram in the Haynes manual I have for the later saloons. They would have originally gone to A1 and A on the RB106. Not sure what is going on there. Anyway the good news is that all these weird voltage readings do seem to have been caused by the lack of suppression on the ignition. I wired up the meter on very long leads this morning and not until I got the meter about a yard away from the passenger side wing did I get steady readings .... 13-14.5 volts with an occasional excursion to 15. So that was the problem. I shall await the arrival of the used RB106 I have ordered and wire it all up tidily to that. I think it would be a good idea to double up on the supply wire from the alternator as they have used the original dynamo wire and of course the alternator provides more amps. And there is a spare common terminal that can be used for that. As for the old battery maybe it died from old age after all, who knows. I will try and charge it up and see if it will hold a charge off the vehicle as a test. I think it's had it though.
Many thanks for all the help, everyone, I was on the point of going back to a dynamo........

[geoberni]

Well, that's really odd.
I've never heard of a Meter being affected by a lack of suppression on the HT, but then I suppose if they can cause a pulse 'click' on a radio they can affect an unshielded meter.

As to wiring Colours, I owe you an apology.
The Diagram I found that comes with a typical Conversion Kit is wrong.
On closer examination of the BMC Diagram, using a pdf copy and enlarging it, I can see that it is actually 2x Brown (N on A) and 2 x Brown/Blue (NU on A1).

Dynamo Diag.JPG (99.11 KiB) Viewed 595 times

But I really don't get why that thick Brown/Yellow goes where it does.
The only output connections should be to the Battery, via the Solenoid terminal.

The Output cable of the Alternator should be either 1 heavy cable or 2 medium cables in parallel, hence why the Alternator has 2 Output tags to allow a double cable run.

If you only have a single output cable, connected to the car circuitry via that one 'Chocolate Block' connector....
I'm surprised it hasn't started to melt.....


So the bottom line is that it might just be a faulty battery and you've been chasing red herrings due to HT pulse on the Multimeter...
So you now have a spare Alternator.

[cyrus]

Well, that's really odd.
I've never heard of a Meter being affected by a lack of suppression on the HT, but then I suppose if they can cause a pulse 'click' on a radio they can affect an unshielded meter.

It's a really old DMM from 1994 but quite good quality.....but maybe more subject to interference than a modern unit?



But I really don't get why that thick Brown/Yellow goes where it does.
The only output connections should be to the Battery, via the Solenoid terminal.

I will check that again......

The Output cable of the Alternator should be either 1 heavy cable or 2 medium cables in parallel, hence why the Alternator has 2 Output tags to allow a double cable run.

If you only have a single output cable, connected to the car circuitry via that one 'Chocolate Block' connector....
I'm surprised it hasn't started to melt.....

Yes I'm going to run another cable. Probably got away with it as I hardly drive at night and try not to use classic vehicles when it's raining! So not much load