DaveEFI wrote:As a matter of interest, has the alternator done a vast mileage?
Not Really , the bearings and winding check out fine ...
as changing alternator parts has made no differance im thinking its got to be vehicle wiring thats at fault ..
Its not a complicated setup , theres a bulb in the instrument panel with a diode next to it and a single wire ( which ive replaced) going straight to the alternator less than 3 feet away ... and a postive cable going off to the battery less than 2 feet away ...
Thats it )
This is going to be one of those issues that has a simple fix but causes much head scratching I think Will be interesting to see what the cause was / is when you find it.
Range Rover 630R or otherwise known as the Money Pit
MS2 with switch MAPS for LPG
Techedge Wideband Sensor
Does the output change/become more stable when the engine is reved?
The sense part of my old alternator didn't work properly so each time I started the engine I had to rev it for it to self excite, the light would go out and would start charging properly but once self excited it would still charge at idle.
Hi all readers,
This is turning out to be a best seller ...... Sorry Bodger not for you ... the bloody thing..
Having read every answer given I think everything that could be wrong has been covered.
You mention putting a feed (pos) direct the the sense at the alternator, a good idea and may prove a point one way or another. However if you do you need to put a small wattage bulb in series with it or a 68 Ohm resistor, it does require a small load, usually your ignition light.
You mention there being a diode with the sense wire from the ignition switch. Are you sure its a diode? Not a resistor. - whatever it is ,,,,, is it open circuit?
I would like to know why a diode would be needed in a feed wire when the system is D.C. anyway. Though it could be used to make certain the current flowed in only one direction.
If it were a diode and you have removed it at some time..... you did put it back the same way??. Its very easy to do ... I done with an old battery charger once, though that was a rectifier ... same thing just bigger.
To be honest I`m clutching at straws here ... frankly I would be looking at the car wiring now. Judging by all the answers given what else could it Be???
I'm getting a bit confused about this sense wire. Some alternators - like on on my P6 3500S - did indeed have a battery sense wire in addition to the warning light circuit. It was connected near the ignition switch. I think the theory may have been to compensate for voltage drop. It's an idea which goes in and out of fashion.
My SD1 only has two connections to the alternator - output to battery, and warning lamp.
The warning light bulb also provides the excitation current needed to start the alternator charging from the off. If the bulb blows, no output. Some makers also use a resistor in parallel with the bulb so if it blows, the alternator still works.
You can test the warning light circuit by removing the wire from the alternator and grounding it. The bulb should then glow at full brightness with the ignition on.
Dave
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
SuperV8 wrote:Does the output change/become more stable when the engine is reved?
The sense part of my old alternator didn't work properly so each time I started the engine I had to rev it for it to self excite, the light would go out and would start charging properly but once self excited it would still charge at idle.
Obviously checked the alternator belt tension?
Tom.
hi Tom , yes belt tension is ok ... i havnt tested it when reving ....
The charge light goes out pretty much as soon as it fires ... but i have a volt meter in the dash running off the battery and thats needs a rev for the needle to show a charge ...but then settles down once its returns to tick over ...
Dave , this alternator has only 2 wires , one main one direct to battery and then the small one to the charge light / sense
I would recommend you start looking at your car wiring now everything else has been covered.
Dave you are correct (of course) the P6 did have a third wire to the alternator via a alternator control unit - well that is what they called it. Today we use the voltage regulator normally bolted to the back and part of the alternator so we only now need two wires.
With regards to the battery sense wire today it is now the field supply from the battery and as you stated excites the alternator until is is spinning fast enough to do the job its self.
Though I have never seen a diagram of one yet ( car manual diagrams ) there should be a resistor in parallel with the ignition lamp of 2.2 watts, the resistor at 68 Ohm only, it is shown in the Bosch automotive handbook though. The resistor keeping the system working should the ignition bulb blow the circuit would not become an open circuit and the battery would still be charged. When the ignition lamp blows most people panic instead of checking to see if a 12V supply is at the alternator field connection after checking the belt. The P6 system was a stage up from the dynamo and that big black box called a voltage regulator with 2 or 3 relays inside. I am showing my age here!!
From what answers and suggestions have been placed on the original post I can`t come up with a known fault with the alternator - it has to be the car wiring, whatever it seems like a very simple fault - the major ones being covered. Extensive checking and fault finding on the car wiring needs to be done.
The resistor to which Keith refers is in parallel with the battery lamp on the dash. It's sole purpose is to make sure the alternator still charges if the bulb blows.
First thing I'd do is check the true voltage at the battery with a decent DVM. The dash volt meter isn't going to give a 100% accurate indication of what's going on - and a poor connection to that etc could give a false reading anyway.
As regards an independent sense wire, it is/was still in use with some makes of alternators. Of course if you didn't want it, to simply linked it to the output terminal.
Dave
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
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