New alternator - low volts?

[Oldiebut goodie]

led or bulb? Surely you haven't both fitted? (which of you is Shirley? )
As I said - some are self exciting - is yours an original alternator or a replacement?

[ghost123uk]

I will be removing my LPG lambda monitor / test lights tomorrow so whilst I am "in there" I will fire it up with no blue wire and see what happens. I don't know of course if my alternator is OE of course. It looks like a standard one, but will likely have been replaced (like for like) at some time.

[Yozza]

Crikey, there has been a lot of activity on this thread.

It seems we're all on the edge of our seats, will the bulb or blue wire determine if the battery charges?...

My missus is off to aqua zumba (whatever the hell that is) so when she's back I'll get the spanners and voltmeter out for some further investigations later tonight.

As soon as I have a conclusion I'll be back on here with the findings

[Yozza]

Just returned from the garage

Here is what I found...

I didn't have 12v on the end of the blue wire (at the alternator), I checked the LED and this was fine I checked for 12v on the flexi circuit and had it everywhere that was exposed but not on the blue wire (terminal 11 of the white connector) that goes to the alternator. At first I thought it was a break in the flexicircuit just before it enters the connector. I prised open the white 14 way connector and took out terminal 11 (attached to the blue wire) and discovered it was my old enemy - oxidisation - doh! Scraped this off and replaced the terminal and connector. I flicked the switch and the LED finally glowed back at me checked the battery voltage ~14v

It would seem that the alternator I now have (GSF - Delco - re-manufactured) does need to be externally 'excited' - saying that - dont' we all

What have I learnt? Well I broke my own rule and didn't diagnose the fault before trying to implement a 'solution' - never ASSUME. I was too quick to get the wallet out rather than the manual!

Thanks again for all the replies and pointers - great forum!

Yozza

[Oldiebut goodie]

Now change your username 'Mr. Two Alternators Yozza'
The manual most probably wouldn't have helped if you don't know that you need exciting, you would likely as not just think that the charge light is a tell-tale rather than a vital component of the charging system.
At least you have a spare for when the bearings start to fail on the old alternator!

[ghost123uk]

Good stuff Yozza

Looks like I stand corrected in this case !

Was that charge indicator an LED or a filament bulb ?

[Yozza]

Alternators are bought on an exchange basis so I'm a one alternator man.

It's a standard LED rather than a bulb.

The manual helped as it told me which terminal the 12v should be leaving the dash, but the actual procedure should of been, forum - manual - diagnose (properly) - fix!

Thanks folks

[Oldiebut goodie]

I am surprised that an led gives enough current to excite it, I wonder if there is a larger diode in parallel?
A lot of places do alternators without exchange at the same price somehow. Just bought a new one for my boat - same price as an exchange one and I get to refurbish the old one at my leisure.

[ghost123uk]

I am surprised that an led gives enough current to excite it,

I have had a read around and I think it might. Apparently it is a cascade type event. A very small magnetic field is generated and this produces a very small voltage, which is fed back to the field coils by the regulator, this in turn produces a higher voltage, the process continues for milliseconds until a status quo of ~14 volts is obtained. The warning lamp then goes out because the voltages on both sides of it are the same (the blue wire terminal on the alternator now producing ~14 volts) so no current flows through the lamp. This solves a puzzle I had whereby I could not understand how the blue wire, being fed with voltage through the lamp, still had enough current to fire a split charge relay. Of course it doesn't, the current to fire the relay only appears when the alternator is up to speed and comes from the blue wire terminal on the alternator, not the other way around.

Sorry if you all knew all of this