Lotus Elan

Alternator / charging issues on an early plus 2

PostPost by: gibbon » Tue May 12, 2015 8:29 pm

Hello there,

I would very much appreciate the wisdom of the forum, as I am new to the marque.

I have a charging issue with my '68 plus 2.

Symptoms -
* Ignition light does not come on at all, at any point in of the key turn or with engine on or off, nothing
* Battery taken out and charged, shows 12.61v when disconnected, shows the same when connected and ignition off, so I assume no parasitic losses
* Voltage drops to 12.28 - 12.31 when engine running irrelevant of revs
* Car works fine for a couple of weeks light use, then battery died, push started easily, ran fine from then on, but after a long drive battery still dead

Car information (apologies, as its new to me i shall try my best) -
* Is 1968 model, with positive earth 'RVI 2402/04' tachometer, which works, but I think is reading high and a little jumpy
* Speedometer pretty accurate but 'bounces slightly' (not sure if relevant)
* Appears to me that the battery is wired up as a -ve earth (the metallic looking cable connection is connected to the -ve terminal, big thick black cable to +ve terminal
* Has an alternator conversion, looks new to me, or at least fairly new
* I believe has an electronic ignition
* Has a battery kill switch in the boot
* Still has the original Ammeter, no Voltmeter, appears to swing slightly to the right, -ve when car running

I have read a little around this using the forums, which has helped a little, hence the above tests.

I tried to check whether the alternator was producing a charge but very much struggled to get to the wires (one red, one black) on the alternator, and struggled to make contact with the insulated connections on the alternator, I was also not sure where i should be attempting to earth the negative probe of my multimeter. Is there a trick to this that doesn't involve Mr Tickle arms?

I believe it is critical that the ignition bulb is functioning in the tachometer, could someone please explain how to test this, please adopt a manner assuming that i have basic knowledge at best, in reality please assume I am a complete idiot.

Could someone else, again, adopting the idiot tone, please explain the best way i can remove or access the tachometer in order to change the bulb.


I very much appreciate the help, I feel a touch out of my depth with this but am keen to learn and attempt a resolution before I give up and hand over to an auto electrician!

Cheers

A. Primate.
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PostPost by: TroonSprint » Tue May 12, 2015 9:18 pm

Hello Gibbon. If your car has been converted to use an alternator it must be wired with negative earthing.

The "ignition" light is nothing to do with the ignition. It is a charge warning light. Uniquely among car bulbs it is wired with one side directly to the battery and the other side to the small wire that comes out the alternator. No part of the bulb's contacts must be earthed. When you switch on, battery voltage is fed to the bulb and it earths through the alternator field windings, so the bulb lights.

When you start the engine, the voltage produced from the alternator balances the battery voltage and so there is no potential across the bulb and it is extinguished. A decent alternator will generally produce between 13.5 and 14.5 volts at anything above 1000 rpm. This can be measured simply across the battery terminals as the alternator is directly connected to the battery positive. Or you can measure from any live terminal to earth. The readings you have given are low and are probably why your battery goes flat.

If your light doesn't ever come on, the bulb is probably blown. I'm not familiar with the Plus 2 as I own a 2-seater, but generally the bulb simply pulls out of the back of the instrument, assuming you can get your hand up behind the dashboard. The bulb is an essential part of the charge circuit because alternators need a small load to kick-start them, and the resistance of the bulb does that. So first off, change the bulb and take the voltage readings again. Without the bulb, an alternator might not begin to charge properly until you rev above 2000 rpm.

The speedo is entirely mechanical and will not be affected by any electrical maladies. I hope this helps. No doubt others will have more info for you.

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PostPost by: gus » Tue May 12, 2015 11:48 pm

has the car ever charged in your ownership?

Positive ground alternators are rare to say the least.
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PostPost by: billwill » Wed May 13, 2015 12:00 am

As Mike says, you can simply pull the bulb-holder out of the speedo, you may need to remove the knee trim to be able to get at it with your hands.

When the bulb-holder is hanging down you should be able to get the bulb out of the holder. It may be baynot type or it may be a small screw type or even, I think, some may simply be two-prong type.

It is a 12v bulb, so you should be able to test it by connecting it between a convenient 12v point and any grounded metal, chassis or engine. Or you can test it by setting a multimeter to the lowest OHMS setting. If you haven't got a multimeter buy one; they are dead cheap nowadays.

Without a working bulb, the alternator might not work at all as startup then relies on residual magnetism in the rotor and that might be negligible. We discussed this here last year and I think it is supposed to be a 2 watt bulb.

If the bulb is OK, and the connections to the alternator are ok, then alas the internal electronics of the alternator may be dead.

See topic:
lotus-electrical-f38/alternator-problem-t33730.html?hilit=alternator
Which contains this diagram:
Image
Does it help?
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PostPost by: gibbon » Wed May 13, 2015 6:56 am

Thank you chaps.

I do indeed have a multimeter.

I think the first port of call is to remove and check the bulb, it sounds like this should be achievable without removing the dash. I thought it was likely the alternator was providing a charge as with a dead battery the car still ran fine once running, so I guess it must be producing something? That wiring diagram kindly provided to my untrained eyes seems to confirm this as the charging circuit to the battery would be broken with a blown bulb.

I shall check the bulb and report back.


Many thanks all.
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PostPost by: PeterK » Wed May 13, 2015 7:11 am

Whereabouts are you in the UK ?

The best question so far is indeed 'has it ever worked /charged'. Do we know that the alternator conversion Is correct and complete?

Assuming that it has worked previously, then one way to easily test the bulb and associated wiring is to remove the large plug from the back of the alternator. Then use a short wire to connect the thin (normally brown with a yellow trace line) to earth. Be very careful to not Earth the large wire(s) !. Switch the ignition on and the bulb should illuminate.

If the bulb doesn't light, then as mentioned, you need to put your hand up behind the dashboard to remove the bulb - not easy, but doable. Also, as mentioned, there maybe a trim piece under the dash / above your knees that you need to remove (just a few screws).

The power feed for the warning light (at least on later cars) comes from the power feed to the voltage regulator. Does the fuel gauge work OK ?

To avoid damaging the alternator, never try to start or run the car with the alternator plug disconnected and do not turn the battery isolator off when the engine is running.
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PostPost by: gibbon » Wed May 13, 2015 7:22 am

I am based in central east London.

I am unaware if the charging system has ever worked, but I suspect not, however, in one of the photos sent from the vendor I can see the 'ignition' red light is on, so I shall check this first and go from there, hopefully it will be as simple as a blown bulb.

Yes the fuel gauge works.

Silly I know, I meant to check the charge across the battery terminals when I bought it, but left my muiltimeter at home. :(
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PostPost by: gibbon » Sun May 17, 2015 5:25 pm

Ok, so i have pulled the bulb, and it does work.

Could anyone explain now, once again, assume you are talking to a small child, how I can go about testing the circuit to the bulb? As previously mentioned, i have a multimeter.

Thinking about it, the indicator light also not come on, so in actual fact non of the speedo or rev counter lights appear to work.

Does this sound like a half baked alternator conversion?

Once again, many, many thanks.
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PostPost by: billwill » Sun May 17, 2015 6:24 pm

Speedo & rev counter panel lights are not relevant, that a separate problem.
~~~~~~~~~~~~

OK, you need to be systematic about checking things.

You say the bulb works. Did you test it by letting it light up or just with the ohm-meter? I think it is supposed to be a 12v 2 watt bulb but I'm not sure. Try to read its markings with a magnifying glass. If it is indeed 12 volts, check to see it it lights up when connected across the battery. This will be a fiddly job, generally with wires connected by croc clips to the batter, take extreme care that you do not short such wires together; there is a lot of ooomph in a car battery and simple thin test may melt explosively.

Next lets find out if battery voltage is reaching the charging bulb when the ignition is on.

Assuming that you can get your multimeter probe into the charging light bulb holder.

1. set multimeter to voltage range greater than 12 volts, usually 20 volt range.
2. check that multimeter works by prodding across the battery in the boot it should read somewhere just over 12 volts.
3. Fiddling around under the panel wedge negative probe onto an earthed point (often done using a crocodile clip).
4. probe with the positive probe both of the contacts in the bulb holder, with ignition off and then with ignition switch on.

In the ignition on position, one of those contacts should read very nearly the same as the battery voltage (step 2). If it doesn't you need to find out why. Could be a fuse blown somewhere or the wire is not properly connected to the ignition circuit.
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PostPost by: gibbon » Sun May 17, 2015 6:40 pm

Thats great Bill, thank you, i will do this and report back.

I tested the bulb both with multimeter ohm setting, and with a regular small battery and wire, which faintly lit it up.

A silly question, but what would you suggest i use as an earthing point?

I don't think there will be an issue getting the multimeter probe into the bulb holder.

ps the panel lights work fine, as in the instrument back lights, but the indicator light etc in the speedo/rev counter, as with the ignition light doesn't. The handbrake light is also fine.

Cheers
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PostPost by: billwill » Sun May 17, 2015 7:23 pm

The metal fastening studs of any of the instruments for which panel lights work, should be a good earth point. There should be a black wire joining all the metalwork of them and going to a chassis earth point. It must be intact or the panel lights wouldn't light-up.

The failure of the flashing indicator light is still a separate problem, solve that later.
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