Alternaor

[bendyone]

I have been having problems with the alterator on the Nanni. It is (was) a 60A fully insulated unit. However I decided to replace it with a car type. An Astra one fitted OK but it only has 2 terminal B+ and D+ also a - ground stud. I fitted it yesterday with the B+ going to the battery and the - sutd to the engine earth. The wire from the inst panel to the D terminal at no stage showed any voltage so I left it disconnected. ( I think the charging light circuit, a diode/resistor is broken)
On running the engine the alternator charged the battery shown by 15Volt on the battery. I therefore assume that the alternator is self exciting.
Rather than replace the control panel should I just connect a small bulb from the starter switch to the D terminal on the alternator? If so what rating should the bulb be?

 

[VicS]

If the alternator does not require the current from the warning light to provide the initial excitation then the smallest wattage 12v bulb that you can find and expect to see when illuminated will do. Normally to provide that excitation one would expect to see 1.2 w perhaps. Consider a 12volt led, or an "ordinary" led with a series resistance. (I assume you have actually tried the existing one)

The 15 volts is worrying though. It really should not be that high. 14.4 absolute max I would say. Assuming you don't have some smart regulator that was the reason for it.

 

[Anonymous]

[ QUOTE ]
The 15 volts is worrying though. It really should not be that high. 14.4 absolute max I would say. Assuming you don't have some smart regulator that was the reason for it.

[/ QUOTE ]I agree but would add that if you look at the full spec of some of these alternators, they have a wide voltage tolerance e.g. 14.2V - 14.8V I've never seen a spec up to 15V, though, something is clearly wrong there, unless there is an alternator booster (e.g. Adverc/Sterling) in the circuit, as you say.

 

[William_H]

I have not heard of a "self exciting alternator" howeer it is possible that the alternator can self excite however this is likely to be unreliable ie does not always self excite.
So yes connect a small bulb between battery and the D+ to provide some initial current to excite the alternator.
I don't think an LED would provide enough current. Well it may do.
Anyway you would want to connect the lamp through a switch so when the engine is stopped the lamp and excier do not discharge the battery. Which brings you back to the control panel circuitry.

good luck olewill

 

[VicS]

[ QUOTE ]
I have not heard of a "self exciting alternator"

[/ QUOTE ] Nor have I but I was not prepared to stick my neck out on that point.
[ QUOTE ]
I don't think an LED would provide enough current

[/ QUOTE ] A 12volt led (an led with a resistor in series) and a shut resistor would do it wouldn't it?
[ QUOTE ]
Anyway you would want to connect the lamp through a switch

[/ QUOTE ] He did say from the starter switch to the D terminal!

 

[halcyon]

Some cars run at 15 volt, so may be right, may also be wrong. Also alternators on some cars are controlled by the car's ECU, this regulates to cover voltage, load, tepreature. So self exciting need not be a no no, these days you need to be a lot more careful with the scrap yard and modern cars.
If you have a positive diode gone it can give a back feed to the feild diode/s thus being self exciting.

Probably best bet is to get LSUK or simliar to check out the alternator, and advise on terminals, then you know were you stand.

Brian

 

[ex-Gladys]

I've had recent experience of two vehicles where the alternator self excited. FIrst was the Landy where the crap over the alternator plug block stopped the warning light coming on. If you had the interior light on, and revved the egine fairly hard, you could see the charge start from the brightening of the light. The Octavia estate that has replaced it had the control connection plug drop out, and the same thing was possible. 3000 RPM and it'd charge to about 14V

 

[michael_w]

My old boat had a Prestolite self exciting alternator.

 

[bendyone]

Thanks for the comments, when I said 15V this was right after the engine had started after the battery had sat for about 3 months without use. It was a quick look at the voltmeter on the inst panel ( cant say how right it was maybe 14.5 volt) but it had moved from 12v upwards so I assumed that I had a charge going in. Should have done it before lunch /forums/images/graemlins/wink.gif