Elise electrical question

[caterhamnut]

Mate has a standard Mk1 Elise. Few weeks ago the alternator light came on, so we took the alt out (a damn sight easier in a Caterham - blimey!) and got it tested - its fine. So, start car, charging light stays on - a few blips, and light goes out, but sometimes it doesn't, sometimes it flickers etc etc. When this happend before, the car did break down.

So I guess it is a short somewhere - but anyone know where in an Elise - or at least where to start looking!!

cheers

angus

 

 

www.mycaterham.com

here

91,000 miles -1st 1.6k Supersport, '95 Motor Show car

[Chris W]

Angus

 

If the charging light goes out over about 1200-1500 rpm approx it suggests that there may be a fault in the circuit that connects the alternator to the charging light. There is often a resistor wired in parallel with the charging light which supplies the initial current (of around an amp) to magnetise the field coils on the alternator in order to kick it into life as it starts turning.

 

Without this initial current, the alternator will only kick into life above some moderate revs as residual magnetism allows the alternator to kick start itself. Once kick-started the alternator produces its own field current by tapping off some of its own output.

 

It could be that the resistor has failed or, more likely, the wiring is suspect. It would normally be about a 10 ohm, 10 watt resistor probably about 2 x 0.5 x 0.5 cm in size.

 

The charging light is basically telling you that there is a different voltage on either end of it - hence it lights. ie: when you switch on the ignition, the light has 12v from the battery on one side of it and nothing on the other as it is connected to the not yet functional alternator. The alternator's field coils simply act as a path to ground and hence the light comes on.

 

Once the alternator is working, there is about 14v on both sides of the light so it goes out. If there exists a small voltage difference, the light glows, as in this case. A slipping alternator belt could cause the same problem and effects.

 

Hope this may help

 

Chris

 

2003 1.8K SV 140hp see it here