Red warning light on intermittently

[Blue_SV]

Hi

The red warning light in the tacho has started to come on when the engine it hot. It first started at the Anglesey Sprint when we had to spend ~1hr waiting in line with the engine idling but would clear if the engine was rev'd. Since then, it has started to come one when driving, particularly when traveling at modest speed (in town, stuck behind other cars at 40-50mph). It does clear when driving a little more enthusiastically (rev's pick up). However, even that is not working now.. 

I did check the voltage at the battery when idling & it was ~14.5V so alternator seems to be doing its stuff. 

Any thoughts?

Cheers

Jon

[SM25T]

Have you checked the tension of the alternator belt ? Should only be 1-2mm deflection mid span.

[Jonathan Kay]

This is the charging warning light: normally off at rest and constantly on while the engine is running? (Mine's not in the tachometer.)

Any suggestion of it not charging properly?

First things to check:

• Alternator belt tension and condition
• Alternator bolts and fixing
• The wire that runs from the alternator to the light: general condition and quality of connection at the alternator.

Jonathan

 

[Nigel Riches]

Check the resistance of the wire from the alternator to the battery, this should be very low, lower the better, also check the crimped terminals for corrosion, either of these may well show 14.5v,but there would be less current flow, and a lack of charging. 

Nigel 

[Steve Sheldon]

Change your alternator - it is starting to fail. Classic sign is intermittent warning light.

[Paul Deslandes]

sounds like a secondary rectifier failing, which is part of the regulator.  Take it to a local auto electrics man who will overhaul it for less than half the cost of a new one.

[Jonathan Kay]

Paul: How much would you check while it's on the car before taking it off? Voltage on the warning light terminal when the fault occurs?

Thanks

Jonathan

[Paul Deslandes]

Not much really, although if the battery voltage remains high at slow idle it would suggest that the regulator isn't controlling the output voltage and you could boil the battery if not fixed.  Loss of the secondary rectifiers stops the regulator working correctly and, in turn, brings on the red light as the voltage that they generate doesn't match the charging battery voltage, the potential difference between them powering the lamp. 

They will often fail if the load is suddenly removed from the alternator, such as if you have a cutout switch without the load resistor, or the battery is disconnected with the engine running.  The transient blows the diodes.  I blew mine on a boat when I switched off the electrics before stopping the engine with the decompressor.  I did it twice before I realised what was going on but fortunately mine could be replaced with nice fat diodes from Maplin rather than needing a complete regulator.

Paul

[Jonathan Kay]

Thanks

Jonathan

[Blue_SV]

Thanks all.

A bit of an update - I had the car remapped by the two Steves this week (fantastic service) and so could see the voltage while the car was running for an extended period. For 10+minutes on the rolling road, the voltage was consistent at ~13.7. There was then a clear spike coinciding with the red light coming on but then the voltage remained constant after that for the rest of the remap (few hours) but at ~13.4. Occasionally the light would go out at the upper end of the power runs (>5-6k), stay off for a short while but then return whilst running in mid revs. 

Sadly, I suspect this all points to something beyond DIY and will need to find a local auto-electrics person. Anyone know such a person in the Market Harborough/Corby/Leicester/Peterborough area?

Cheers

Jon

[Paul Deslandes]

Sounds like a dicky internal connection or component in the alternator.  In the absence of any recommendations try 'auto electrics' search in yell.co.uk for your area.

[revilla]

Hi Jon,

If your car is EU3 K Series, I've got a good spare alternator, I'm not so far away (Loughborough) and more than happy to pop over tomorrow afternoon if you're around to help you sort it out if you want.

Andrew

[Paul Deslandes]

http://www.pd-motors.co.uk/car-electrics.html

from google

[Blue_SV]

Paul

Thanks for the advice - I will give them a call and look around a little further.

Jon

[revilla]

I spent some time at Jon's today looking at this; it's not as simple as it first seemed.

Firstly, the alternator warning light was off when first starting the car but tended to come on at idle as the car warmed up. It also tended to come on with anything else that caused the revs to drop, such as the fan coming on. Initially once on it would go off with a blip of the throttle but after a while it came on solidly and stayed on. Battery voltage check confirmed that when the light came on, the battery was not charging (12.5V), when the light went out it was charging strongly (14.2V).

Belt tension was fine. Engine cranked strongly so we know the connections from battery to earth and at least as far as the junction on the back of the starter motor were good. Connection from the starter to the alternator seemed sound (no sign of damage, securely attached).

So seemed on the face of it like a simple case of a failing alternator. Luckily I had taken three spare alternators with me ...

Not one of the spare alternators showed any sign of charging at all on Jon's car. I knew that at least one was good as it was on my engine until a few weeks ago. Since returning home I've put the other two on my spare engine and run them up and they charged absolutely fine, so I think we can rule out internal alternator problems as being the cause. In every case, on Jon's car the alternator warning light remained solidly lit and the battery voltage sat at 12.5V. In the end we refitted Jon's original alternator and the original behaviour was restored; intermittent charging.

I'm confident we connected the other alternators correctly.

The only explanation that I can think of was that the current feed through the warning light was not sufficient to provide excitation of the alternator windings, and that Jon's alternator was a little more tolerant than mine so that it worked at least intermittently.

I didn't have all the wiring diagrams with me at the time so I didn't play around with testing the current feed from the warning light / exciter connection, but when I got home I tested my own car to get a reference figure which was surprisingly low; with the ignition on, two-pin plug off the alternator and an ammeter connected from the brown/yellow wire to ground I was only reading 4.3mA which must just be the current draw of the LED indicator in the tacho.

My understanding was that the alternator would expect considerably more than this and that it was not normally possible to use an LED indicator alone reliably; I understood that if replacing a bulb-type alternator indicator with an LED it was normally required to add parallel resistance to ensure that enough current was passed to excite the alternator. Typically a 2W indicator bulb would be passing around 160mA.

Can anyone confirm what current would be normal here?

Jon, in the meantime could you repeat my test on your car please? With the ignition on but the engine not running (don't run the engine with the alternator disconnected), remove the two-pin plug from the back of the alternator and with your multimeter set to read milliamps / current (not voltage), connect it between the pin with the brown/yellow wire and the battery negative and let me know how much current it passes? I'd just like to know if yours is substantially different to mine.

The only other connection to the alternator is the Digital Field Monitor. My understanding is that this allows the ECU to read the load on the alternator and allows it to preempt changes in idle speed caused by electrical load variation. If this is true, it does not in any way control the alternator, simply allows it to be monitored. Can anybody confirm that this is correct?

The battery (Powervamp) had been on trickle charge and seemed fairly healthy. Cranking was strong.

Anybody got any ideas?

[Paul Deslandes]

My boat Hitachi alternator uses a 3.4W bulb so stalled rotor current would be about 300mA, somewhat more than an LED will deliver without burning your eyeballs.  I'm sure your analysis is right Andrew and the LED current is very marginal although I thought that once the alternator was producing current, the bulb current was irrelevant as it self excites, but clearly not in this case.  The Emerald doesn't have one of these clever circuits for race cars that disables the alternator at full chat to reduce the load on the engine, and this is contributing to the intermittent nature of the problem?  I think I'd try with a 3W panel bulb across the LED (+ its resistor if it's external) and see what happens - it won't hurt.

[Jonathan Kay]

What Paul says, but from a position of greater ignorance.

If all 3 thought-to-be-good alternators show the same problem then what is the common factor? It's either the warning light system or the rest of the electrics including the car battery.

It's quicker and easier to assemble a new warning light system than a safe load for the alternator that is independent of the rest of the electrics so try that first. (Although the latter isn't too hard with some thick cables and another battery.)

Jonathan 

PS: Exemplary generosity, Andrew.

[Blue_SV]

Andrew (& others)

I finally got a chance to check the current tonight and had a rather surprising result. Following your instructions, the current between the alternator plug pin (cream/brown) was 15.5 A! I had to double check but the fact that the test leads became instantly hot was the clue.. I had checked with the multimeter on low current readings but nothing registered until I went to the highest setting. Unless there is a fault with the meter I am no wondering whether there are some wider (and more serious) electrical issues. It all seems a little perplexing because the car actually runs well (as you saw) and the 2 Steves successfully remapped the ECU with the light flicking on after about 10 mins.

Is the high current reading simply reflecting a straight loop from battery to alternator plug, and then back to battery via multimeter?

Jon

[revilla]

Jon,

 

15 AMPS!?

 

My first though was that you must be mistaken but if the multimeter test leads were getting hot that does sound like a hefty current flowing. I wouldn't recommend repeating the test either as that kind of current will damage something.

 

I'm really not sure what to make of that. It just doesn't make sense. It sort of suggests that there's a short circuit in the warning light circuit and that the warning light wire is straight off the battery through a very low resistance, however the LED looked to be lit normally and there's no way an LED is going to pass even a fraction of that current without going pop in a very tiny fraction of a second.

 

Forgive me if this is a silly question but ... you did test this with the plug disconnected from the alternator didn't you?

 

This isn't making a lot of sense to me. I will have a think. Anyone else got any bright ideas?

 

Andrew

[Jonathan Kay]

How about rigging a new warning light system for testing? (And disconnecting all of the old one.)

Jonathan

[Richard Price]

Jon,

You say "the current between the alternator plug pin (cream/brown)"

exactly where did you have the multimeter connected?

Have you disconnected the cream/brown wire from the alternator, and put one meter lead on the alternator connector, and the other lead on the cream/brown?

Or, have you put the meter lead onto the cream/brown cable connector, and the other meter lead somewhere else?

[sjmmarsh]

15A sounds like the meter was connected incorrectly!

If swapping alternators has the same problem, then attention moves to the wring - particularly connectors. Try waggling the wires while someone else watches the LED. 

Ste e

[Blue_SV]

I disconnected the plug from the alternator. The plug is 'D-shaped' and the cream/brown lead enters the back of the plug adjacent to the flat end of the D. My test leads have 'pin probes'  and I inserted a (red) probe into the front of plug pressing it against the metal connector. I then placed the other (black) probe onto the negative battery terminal.

Could the wires to the alternator plug be switched? Could the other (brown) wire be the warning circuit but that would mean the digital field monitor had high current... I did not test that lead for fear of causing short/etc.

It is rather confusing since the red warning light went off as I removed the connector from the alternator, but then relit as soon as the plug was reconnected. It cannot be passing 15A since both the warning light continued to work and the wires to the alternator plug were not hot! 

I was doing the testing using head-torch and workshop light so perhaps I will have another look in daylight.

I could try the alternative warning light option but would much appreciate some advice on how - I presume it would be a temporary swap by disconnecting the original circuit and replacing with a short test circuit within the engine bay?

I much appreciate everyone's help here

Jon

[SM25T]

Is an FIA type switch fitted. Could there be a fault with the ballast resistor or a wiring/switch fault that is drawing a heavy load ?

[Richard Price]

Jon,

I suspect the cream/brown lead is effectively connected directly to the positive side of the battery. When your multimeter is set to a current range, there is negligible resistance between the leads. Therefore, you've created close to a dead short between the battery positive and negative. Thus the high current and warm leads.......

The magnitude of current that will normally flow is very low. When the alternator is not producing voltage,  the cream/brown will have battery voltage on it, and there is a path to ground(negative) through the alternator, so the light illuminates. When the alternator is producing voltage, that voltage will be on the cream/brown and also on the battery. As they are at the same potential, no current flows, so the light is not illuminated.

We're Andrew's other alternators identical to yours?

'Still sound like a duff alternator to me.