Alternator help please

[ric355]

I'm having some trouble with my alternator. It isn't generating any output. I found a helpful book extract on the web (for boats but prob doesn't matter) here and I've followed the various suggestions, but so far have not been able to understand what is wrong (other than it's probably broken!)

 

As suggested on that link, I've:

- checked the output from the diodes with the ignition off (0v)

- checked the output from the diodes with the ignition on but engine not running (1.6v approx)

- checked continuity from the alternator body to the engine block and block to battery negative.

- checked continuity from the alternator output to battery positive. With everything off I get 12v at the alternator output. With engine running, same reading (i.e. no output).

 

At one point I noticed the warning lamp wasn't coming on with the ignition. Fiddled with the wires behind and it came on. However I note from that link that some brands of alternator won't work if the light auxiliary output circuit isn't completed with a suitable load. Now that is fixed I still have no output.

 

I suppose it might have just gone pop but here's the thing - it's brand new and was a replacement for another brand new one which was rather noisy after half a day of track use.

 

Just after I installed it, there was no output but it did kick in after a few seconds of running.

 

Can anyone offer any suggestions or does it just sound like it's bust?

[Normans_Ghost]

Is it wired correctly. You should have a live wire, a warning lamp wire and one or two heavier brown wires (the output to battery).

 

Also is it earthed? You haven't said what engine this is on so it's difficult to advise on the wiring in any other than a general manner.

 

^{Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here}

You and your seven toThe French Blatting Company

[ric355]

Sorry it's on a K series. There are only two connections - thick brown wire to battery, and what I think is the warning lamp wire. I believe it's earthed via the body - block connection.

 

Alternator is labelled B+ (thick brown) D+ (thinner brown) and W (not connected - I understand this is supposed to be tacho pulse?).

[Bob_Rich]

The alternator warning light supplies a small current to the control circuit ( inside the alternator body) and when the alternator kicks in the voltage at the control terminal rises and so with something like 12V on either side of the bulb when running it goes out. U say you waggled the light and it came on but still no output when engine ran but is the connection intermittent? so after the waggle it reverted to an open circuit so bulb dont light and alternator thus wont start producing output.

 

U said U had +12V at the alternator main terminal with the engine off or running I think, so to eliminate the possibility of the control circuit not being powered via the ignition bulb run a separate circuit.

 

Take a lead direct from battery +ve to one terminal of a side or tail light bulb then from the other terminal of the bulb take a lead to the alternator control terminal removing the existing lead on that terminal. Bulb should light, start engine, bulb should go out if not it looks like alternator control is playing up.

 

TO ensure the alternator is grouded well to the body measure the alternator output terminal voltate to the alternator body it should be the same as to the engine block or chassis

 

Best of luck

 

Bob

[ric355]

Bob - after waggling, light came on and stayed on even with the engine running.

 

I was running the car at Keevil yesterday and didn't realize until early afternoon that there was no output from the alternator since I didn't know the lamp wasn't working (I did test it after initially installing it last week though). As a result, the battery is pretty flat and so I'm using a booster pack to start the engine. Lamp stays on even with the booster pack connected while engine is running.

[Bob_Rich]

Does look like the alternator is not energising then.

R U sure that the Connection U called W is not the one for control? I have not heard of a tacho output on an alternator B4. Certainly the larger terminal is the main current output but from the description not clear about which of the the other two may be the control.

 

best of luck

 

Bob

[ric355]

I'm not at all sure to be honest Bob. If it is, then I've no idea how to connect it up.

 

The original alternator had only two terminals. There was a hole where the third terminal is on the new one - so I connected the wires up in the same positions and remember I did get over 14v at the battery when it was first installed.

 

Minor interest but apparently alternators have a tacho output

 

 

[rj]

If....

 

you have changed your warning lamp to an LED you need a resistor in parallel to ensure enough power for the alternator; use a 68 ohm / 5W resistor or better still two 150 ohm / 5W in parallel. The led will also need a series resistor depending on which type led, probably 470 to 560 ohm. Use 1W here.

 

 

/regin

[Bob_Rich]

Well I have learned something but it has not helped U!!

Assuming all the wiring is OK it looks like an alternator fault. other longer shots could be

(1)If there was a short after the ignition bulb then the alternator control would have no input so no output

(2) if you run the car with the boost charger on does the alternator think the battery volts are fully up and so does not charge--bit of a long shot and easily tested I guess

(3)The only other thing I have known is that just occasionally the ignition light bulb is not enough current to kick off the alternator regulator -- direct connection with a slightly bigger bulb perhaps say a 6W tail as described earlier might be worth a try. this would also eliminate a possible short after the ignition warning light.

 

That me thought out!!

B interested what U find!

 

Best of luck

 

Bob

[ric355]

Plan to try your tail light suggestion tomorrow Bob - thanks for your input - will revert in due course.

 

Regin - bulb is just the original one, not replaced with a LED.

 

 

[ric355]

I have now bench tested the alternator and it doesn't seem to be generating an output. My test bench consists of a tail lamp bulb, 12v car battery, appropriate wiring, and an electric drill & socket to drive the pulley nut.

 

I've verified that the test works with an old alternator which I know to have been working when it was taken off the car. Output is around 13.5v at the speed I'm managing to spin it at.

 

With the faulty alternator on the same test I'm getting only battery voltage at the output as I was on the car. I've read that with ignition on, the voltage at the control terminal should be 1-2v. It's about 1.56v with the working alternator, but over 3v with the faulty one. This apparently is an indication of diode failure.

 

I can always just put the old alternator back on to get it going, but I don't know if the output is strong enough. The new one is higher capacity after an engine upgrade (160bhp). Opinions on using the old Rover one?

[Bob_Rich]

I test alternator with the arrangement U described and it always seems to be a test that sorts out the good from the duff. In electrical terms the old alternator should supply more then enough current to run the engine. I dont think the ecu, ignitions system and fuel pump are that high a current demand compared to say engine fan, screen wipers and all lights sides and main beam if they were all on together If you rev it higher with the modified engine perhaps that maybe a risk

 

anyway glad U have found the problem

 

regards

 

Bob Richardson

[ric355]

Fitted the old one this afternoon Bob - seems ok so far. Will send the other one back for replacement or repair. Rev limiter is set at 7100 at the moment so hopefully it'll be fine.