Lotus Elan

Ignition warning light

PostPost by: Robbie693 » Tue Aug 12, 2014 11:07 pm

Hello all,

Ever since I have had this Plus 2 it's had this curious trait of not extinguishing the ignition warning light after starting until I increase the revs past 1500rpm.

I was experimenting with it the other day - I start the car and it idles fine but the volt meter sits down at the 12V mark and the warning light glows. Only when I increase the revs past 1500 does the light go out, accompanied by the interior lights noticeably brightening and the voltmeter begins to climb up to it's usual 13.5V or so.

As I say the car has always done this but I'd like to find out why to see if it's connected to other charging issues.

The Alternator was replaced not long ago with a 45A type and the symptoms were exactly the same...

Any suggestions from those more adept in electrickery than myself (that would be most folks!) ?

Cheers

Robbie
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PostPost by: UAB807F » Wed Aug 13, 2014 5:48 am

I can't help you on this one Robbie, but I'd love to know the answer as I've got exactly the same thing with my Europa !

I fitted a new alternator (17ACR) and I've tried the (new) drive belt both slack and as tight as it will go but it makes no difference. If it was an old alternator I'd suspect the internal controls but this one is sparkly brand new so like you, I'm puzzled.

Start up and the light stays on with the ammeter not moving. Rev it and the light goes out, ammeter moves into charge and all is well. Interestingly enough, once it goes out it stays out when the revs drop back down.

I was wondering if the drive belt/pulley were slightly mis-matched and the start up friction wasn't enough to move it from stationary to whatever it needs to charge, but once it was moving there is enough friction to keep it going. I don't really know, electricity is just magic to me.

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PostPost by: types26/36 » Wed Aug 13, 2014 6:29 am

I had a similar problem and changed the alternator but it was the same, at a later stage I checked the connections in the alternator plug which seemed to be a little loose and dirty which I cleaned, greased and tightened.
Since doing this the light now goes out much sooner so hopefully this has fixed the problem.
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PostPost by: Plus 2 » Wed Aug 13, 2014 6:33 am

Robbie,

There are a few things that can cause this but generally they reside in Alternator condition, Battery Condition and good clean connections.

The fact you have had a new alternator and experiencing the same issue suggest you ignore that as usually I would be blaming brush/ring problems.

You also don't mention any problem starting the car after it has been left standing which sort of says there is no parasitic/aquiescent drain on the battery which I would certainly check out anyway just to confirm. I had my dipped beam relay all rotted as they are fitted upside down under the bonnet so was keeping lights on but not glowing bright. It was peculiar to work out as if I had left the switch in main beam everything was fine but if left in dip position my ignition light glowed until higher revs.

So my first check would be confirm parasitic drain you will need a multimeter with AMPS. If you need to know more detail how to do this come back.

Next I would suspect bad connections. Bad connections can cause voltage drop and you may have a weak alternator field supply. The F+ small lead at the alternator is fed from the battery actually through the ignition switch (on position) then through the filament of the red ignition light. This then creates the magnetic field which if a poor supply can take a short moment to build up. Again another quick test to do is leave the ignition on for a couple of minutes (no longer) first before starting and see if it makes any difference.

However if we are to rule out alternator and battery condition you have to go through a thorough clean up of the infamous oxydised lucar connections which includes ensuring good earths. Even the connections at the back of the ignition switch and the ignition light itself.

Worst case it could even be the ignition switch itself as these too internally can get dirty contacts which can cause issues.

I always prefer to use a test light rather than simple digital multimeters when testing line circuit as a false condition many times is interpreted when people see a 12v supply down to earth in circuit wiring tests.

The presence of a voltage reading does not indicate the supply connection will allow current flow. I show a simple test where placing a resistor in series simulating the resistance of a bad connection (generally Lucar bullits) the meter shows a reading but the current allowed past the resistance will not power the light. See pics.

The first one shows the battery voltage
Second picture the 12v battery powering the lamp.
The third two show a resistor in circuit and still getting a 12v reading (the battery was not fully charged
The last picture shows the light and resistor in series and the resistance not allowing sufficient current to power the lamp yet shows a voltage reading.

Hope this helps a little

Regards

Steve
Attachments
Battery Voltage End of Test.JPG and
battery voltage
Battery Powering Light.JPG and
Battery powering light
Battery Voltage Across Meter.JPG and
battery showing votage with resistance in circuit
Battery Volts With Resistance in Circuit.JPG and
same as above
Battery With Resistance in Circuit.JPG and
Lamp will not light due to resistance yet shows voltage
Last edited by Plus 2 on Wed Aug 13, 2014 8:38 am, edited 1 time in total.
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PostPost by: Plus 2 » Wed Aug 13, 2014 7:04 am

UAB807F wrote:I can't help you on this one Robbie, but I'd love to know the answer as I've got exactly the same thing with my Europa !

I fitted a new alternator (17ACR) and I've tried the (new) drive belt both slack and as tight as it will go but it makes no difference. If it was an old alternator I'd suspect the internal controls but this one is sparkly brand new so like you, I'm puzzled.

Start up and the light stays on with the ammeter not moving. Rev it and the light goes out, ammeter moves into charge and all is well. Interestingly enough, once it goes out it stays out when the revs drop back down.

I was wondering if the drive belt/pulley were slightly mis-matched and the start up friction wasn't enough to move it from stationary to whatever it needs to charge, but once it was moving there is enough friction to keep it going. I don't really know, electricity is just magic to me.

Brian


Brian I have forgotten now from my TC Europas as they had the additional drive from the cam.

For sure if the belt driving the alternator is like the Elans it is best not to have them too tight as it loads up the waterpump bearing and reduces life.

The thought on the mis match start up friction does not add up. Alternator pulley diameter can have a small influence but generally if the alternator is receiving a good stator field it should be quick to click over and regulate the output supply.

Your problem really does read as a F+ field supply poor connection. An alternator does not use permanent magnets and relies on the Field supply voltage/current when ignition is turned on to magnetise to create the magnetic field which is part of the function of creating electricity. Seems like yours is being a bit slow to build up and then when built up OK.

Brian Types26/36 pretty much pointed it out about the connection quality being the major factor too.......that is if the alternator has been eliminated by renewal.

Regards

Steve
Last edited by Plus 2 on Wed Aug 13, 2014 8:36 am, edited 1 time in total.
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PostPost by: TroonSprint » Wed Aug 13, 2014 7:37 am

There is an amazingly useful web site written by MGB enthusiast Paul Hunt and when I have questions like this I always look there. After all the ?lan is a sixties British car and as such is very similar to any other in many ways. Here is what Paul says about the alternator and the warning light.

By contrast an alternator system takes much less explanation - unless you get into the theory of semiconductors! In an alternator the warning light (brown/yellow connection) is connected to the field windings, which because they are relatively low resistance and connected to earth, offers an earth-path to the bulb to light it when the ignition is turned on. So it is the warning light current through the bulb and the field windings which generates the initial excitation for the output windings. This generates an initial output voltage, which is fed back to the fields as well as the output terminal by a set of diodes, to give the full excitation voltage and hence the full output voltage. It is at this point that the bulb has full system voltage on both sides and therefore extinguishes, which is usually at about 900rpm. With the alternator charging, as the engine is slowed the alternator output voltage drops, and hence the field excitation current, until at about 600rpm charging suddenly stops and the warning light will glow.

From this it can be seen that the ignition warning light is necessary to give the alternator its initial excitation, and some schematics do show a resistor wired across the warning light to ensure that this initial excitation current is available even if the bulb has blown or is removed. However, I have never known of this resistor being provided in practice, and also in practice a used alternator has a little residual magnetism that is usually enough to 'kick-start' it into charging, although the engine may have to be revved to 2000 or 3000 rpm before this starts happening. Once it has started charging, it will charge normally i.e. down to about 600rpm as before, but then need to be revved to 2k or 3k again to start charging again. A new alternator just out of the box may not have this residual magnetism and so may not be able to kick-start itself, in which case the ignition warning light circuit is essential. ON NO ACCOUNT should you try to generate this magnetism by 'flashing' the alternator connections across the battery like you would polarise a dynamo, you may well blow the diodes or other electronics.

The web sit is called www.mgb-stuff.org.uk

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PostPost by: UAB807F » Wed Aug 13, 2014 7:48 am

Hi Steve,

Thanks for the explanation of how the internals work and whilst reading your first post it made a lot of sense sense about the smaller terminal and the magnetic field theory. I soldered the new connection at the alternator but everything else is the old loom so there could easily be a problem hidden away in the circuit.

First job this morning is to switch on and leave it a few seconds before starting up to see if it makes a difference. If not then it's easy enough to follow the wiring back and look for dodgy connections.

Thanks for chipping in.

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PostPost by: Robbie693 » Wed Aug 13, 2014 8:22 am

Great tips everyone, thanks very much. And so early in the morning too :)

I've checked for parasitic drain before but it was so long ago I can't remember the results :oops: will have to do it again. I'll also recheck all the connections but I've cleaned these often with no improvement, even the spade terminals on the ignition switch (this doesn't rule out the internals though).

I like the test lamp suggestion - will have to dig mine out.

Brian, yes mine is exactly the same - once started the ignition light stays out. Even yesterday when I had almost everything electrical switched on in the pelting rain, the voltmeter was down to about 12V and still the ignition light stayed off.
Like you, my first check will be leaving the ignition on for a short while before starting.

Could the fault lie in the ignition warning light bulb? Perhaps the wrong rating or dirty connections?

Cheers

Robbie
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PostPost by: RichC » Wed Aug 13, 2014 5:25 pm

check earth to speedo ?
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PostPost by: Plus 2 » Wed Aug 13, 2014 7:55 pm

Robbie,

Any oxydisation on terminals or lamp connections can result in a weak current flow, typical examples are lamps that go dim due to corroded lucar bullit connectors..

It just needs an approach to systematically go through and clean all the connections and earths in the circuit.

It is little understood and quite incredible that a simple blown lamp on the ignition lamp can leave you soon stranded by the roadside. I have only had this twice on helping friends in over 45 years but the alternator needs the lamp filament to pass the current through to the field windings.

There is a 'fix' that can place a diode resistor in parallel with the lamp that will always mean you will get home.

It is not a 'given' the alternator will self excite at certain revolutions but if recently undergone stop/starts then residual magnetism may be present.

The field can be excited, and I have used a small 6v alarm battery to do this with a diode in circuit. Indeed on the last friends roadside failure (20 years ago) when he had left his car at the airport while on holiday and managed to travel around 40 miles before the battery was too low to feed a spark, I actually flashed across from his 12v trakker battery, he then drove home safely (with a warning not to turn the engine off) with all lights available full power and the alternator taking over and charging the battery.

As an MGB owner I frequent Paul Hunt's MGB site and concur it has excellent everyday information that does cut across many marques. Ineed the electric architecture during 60's to 80's in the UK automotive industry was very Lucas/Smiths dominated so whether looking at MGB's MGA's, Triumphs, Rolls Royce, Jaguar's and indeed Aston Martins there is a lot in common.

Picture shows the culprit, one of my relays which sat under the bonnet and was the cause of both parasitic drain and my ignition warning light staying on longer. As I rarely drive my classic cars at night I had not realised my dip beams were not working because the contact had rotted but there was damp and corrosion inside the relay which was causing a partial bleed current to the lights circuit.

Regards

Steve
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PostPost by: TroonSprint » Wed Aug 13, 2014 9:17 pm

Interestingly, the new small alternator I have bought for my Sprint has three terminals. One is the main power feed to the battery, one is the brown/yellow wire to the ignition lamp, and the third is to be connected directly to an ignition key controlled source and is for the sole purpose of exciting the alternator so it will charge from the moment the engine starts. I've never seen this before.

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PostPost by: prezoom » Thu Aug 14, 2014 1:59 am

Like Mike, I have a Denso 55 amp alternator from a Suzuki with the three wire connection. The lead from the ignition excites the alternator to start the charging function. No more glowing warning lights from a too small generator while at idle.

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PostPost by: Plus 2 » Thu Aug 14, 2014 4:48 am

Hi,

Certainly the 3 wire alternator system is a far superior update if wired in correctly onto an earlier car. There are variations of wiring depending on the alternator model
3 Wire Alternator.jpg
3 Wire Alternator.jpg (18.53 KiB) Viewed 1964 times

imagesCA7YNY4C.jpg
imagesCA7YNY4C.jpg (29.98 KiB) Viewed 1955 times


The hand sketch below shows how very simply the circuit on a standard alternator is for the ignition light and field windings.
Simple Alt Wiring.jpg and


Point A is the terminal F+ (field positive supply) the small wire at the back of the alternator. Point B is within the alternator at 0(zero) potential until the alternator starts to turn and as then produces a voltage supply at which point B will then receive a voltage from the alternator through the internal regulator. The alternator field windings are then also supplied direct by the power from the alternator itself.

The reason the ignition light then goes out is because both sides of the light have a 12v* 'potential', one side from the battery + and the other, while the engine is turning, from the alternator which means no current will now flow through the lamp filament. For current to flow in a circuit there has to be a 'Potential Difference' Voltage difference.

If the battery is small, poor condition or a bad cell, remembering just starting the car will have taken its toll, the ignition lamp may appear to stay on dimly for a moment as the alternator is then producing a higher voltage than the battery until the battery receives some charge back from the alternator to then equalise the voltage either side of the ignition lamp and then the lamp will go out

* Whilst we refer to 12v actual voltage may be somewhere between 12.8 and 13.8.
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PostPost by: billwill » Thu Aug 14, 2014 11:02 am

Alternators have been extensively discussed before:
Here is one of the topics:
lotus-electrical-f38/new-alternator-not-charging-batt-light-stays-t28734.html?hilit=alternator%20circuit

The usual circuit of an alternator is:
Image

Without the link shown from F to IND, it is the 3 wire configuration (plus Earth), with it in place it is the two wore config (plus Earth)
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PostPost by: Plus 2 » Thu Aug 14, 2014 3:12 pm

Not sure the link Bill is that relevant to the OP's problem or the circuit diagram, but an interesting thread that equally seems to have gone off what the OP's question was. I have tried to send you a PM but it appears to stay in my outbox.......maybe I have not reached the status level yet to send PM's. :?:

Reading through all old threads that come up on a search hoping to find a solution to a particular problem can be quite time consuming as they wander off topic and as can be seen thankfully still plenty of people willing to simply and quickly construct a direct response to anyones issue.

The OP appears a well experienced forum member understanding searches, maybe if not electrics.

I actually read through the link and found nothing on the point the ignition light delays going out relative to RPM. :roll:
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