Ignition light

[rcourtney]

Morning,

Happy Sunday.

Whilst driving the Elan, in heavy rain, last week the ignition light came on. The light stays on but gets brighter when the car is rev'd - is hardly visible at turn over and at full brightness from about 3k rpm onward.

Initially I thought it could be an electrical gremlin due to the rain, sadly not that stright forward; the problem persists despite drying out.

I have checked the alternator - it's turning with no slippage, the connections seem fine. I can't locate any wayward wires and the instrument grounds seem in order.

I assume it's a lamp / connection issue as the car doesn't appear to be draining power from the battery.

Any thoughts ? Any suggestions much appreciated.
Ralph

[TroonSprint]

The "ignition" light is a kind of balance between the battery and the alternator. If the alternator is not charging there is a voltage difference between the battery and the alt, and the light is on. If the alt is charging properly the battery and the alt are at the same voltage so the light is off.

You have the light on with the engine running, and it gets brighter when you rev the engine. Therefore there is a voltage difference between the battery and the alt, and to me it seems likely that the alt is over-charging, that is to say it is producing too many volts. You need to put a meter on the battery terminals with the engine running. It should read between 13.5 and 14.2 volts, and no higher.

If that is the case the regulator in the alt is faulty and you risk damaging the battery. Check it out.

Mike

[billwill]

I regret to say it but, those symptoms often indicate that either a diode or the voltage controller inside the alternator has blown.

[Europatc]

Mike can I just say what an excellent reply. Concise and easy to follow.
well done
Stuart

[StressCraxx]

Could the cause of the ignition light remaining on be a lack of fan belt tension?

That happened to me, very early on in my Lotus ownership, when I was trying to get the water pump to live just a little longer.....

[TroonSprint]

If the belt is loose and the alt isn't being driven at normal speed, then the battery voltage may be higher than the alt voltage, and that would indeed put the light on, the brightness of the bulb being a function of the number of volts difference between alt and battery. But speeding up the engine ought to make the alt run faster, even if the belt is slipping, and that would tend to even out the voltages. Don't forget that, unlike a DC generator, an alternator can produce 12v at quite low rpm.

Ralph says that the belt isn't slipping and that the light gets brighter as he revs the engine, with it being at full brightness from about 3000 rpm. For the bulb to be at full brightness it needs to see a difference in the voltages of around 12 volts. If we assume the battery is at 12v, the alt must be producing around 20+ volts to achieve this. This will overheat the battery and could cause it to boil and/or warp the plates.

Thanks for your kind comments Stuart. I'm no expert, just an enthusiastic amateur with nearly 50 years of mucking about with cars under my belt.

Mike

[Galwaylotus]

If the belt is loose and the alt isn't being driven at normal speed, then the battery voltage may be higher than the alt voltage, and that would indeed put the light on, the brightness of the bulb being a function of the number of volts difference between alt and battery. But speeding up the engine ought to make the alt run faster, even if the belt is slipping, and that would tend to even out the voltages. Don't forget that, unlike a DC generator, an alternator can produce 12v at quite low rpm.

Ralph says that the belt isn't slipping and that the light gets brighter as he revs the engine, with it being at full brightness from about 3000 rpm. For the bulb to be at full brightness it needs to see a difference in the voltages of around 12 volts. If we assume the battery is at 12v, the alt must be producing around 20+ volts to achieve this. This will overheat the battery and could cause it to boil and/or warp the plates.

Thanks for your kind comments Stuart. I'm no expert, just an enthusiastic amateur with nearly 50 years of mucking about with cars under my belt.

Mike

That's assuming there is 12v on the battery side of the ignition bulb. If there is a bad connection somewhere there could be a significant voltage drop from battery to bulb and hence alternator voltage on the other side of the bulb could cause the lamp to glow brighter. As you rightly point out, the voltage across the bulb must be close to 12v for the bulb to glow brightly; however, the direction of the current doesn't matter. It's probably worth taking a voltage meter reading between alternator output and a good earth (ideally straight back to battery(-)) to confirm the regulator is working correctly. If that is the case then the fault must be too large a voltage drop on the (+) side of the bulb. Either way, the reading should isolate the fault to one side or the other (of the ignition lamp).

[rcourtney]

Thank you all so much for your replies - I am planning on having a good look at what's going on this week, but your replies give me something to go on

Ralph

[rcourtney]

Morning,

I have decided to change the Alternator and see if that sorts it.

I am replacing with -
Make Lucas
Type 18 ACR
AMPS 45A
Supplier bbclassics.co.uk
Price 39.99 GBp

Ralph

[rcourtney]

New Alternator fitted .. all sorted

40 GBp from BBclassics.co.uk (Highly recommended) for a Lucas 45Amp ACR (new - non exchange. Slotted stright in). This should be everyones first port of call when having issues .. change the Battery and Alternator all in less than 100 GBp and off you go. If that doesnt work then consider the alternative. Sometimes too much information can cause unnessacary concern! For a moment i thought i was going to be going over the car with a volt meter, getting the dash out etc etc .. phew - what a relief.

Thanks again for everyones posts / advise

[billwill]

Ahem ....

I regret to say it but, those symptoms often indicate that either a diode or the voltage controller inside the alternator has blown.

But you really should get a multimeter and learn to use it too. They can be dead cheap nowadays. And you wouldn't need to get the dashboard out until after you had eliminated a lot of other possibilities by prodding around in easier places such as the fusebox.