Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Battery warning light

Don't bother with the multimeter, get a battery test meter they are only about £30 itl test the battery and charging circuit

https://www.amazon.co.uk/dp/B071NS7...BVDQC9GYW421ZES?_encoding=UTF8&psc=1

Bart your problem is unlikely to be the ECU as a car of that age will likely have a machine sensing voltage regulator within the alternator. If the voltages seen were on the cars own battery voltmeter they do indicate a problem but don't pay too much attention to the actual values as these instruments are notoriously innaccurate. Its the variations you saw that are relevant. With engine running above idle you should be seeing over 14 volts at the battery or alternator main output (thick cable from B terminal) unless the battery is well discharged but you will need to measure this accurately yourself with a multimeter.

Having checked for obvious stuff like loose drive belt, bad connections etc. and if problem remains, I would remove alternator and take it to an auto electrical engineer who should be able to test it fully in short order. If you want to have a go yourself, bear in mind a diode down would reduce output current by a third (each can be checked with multimeter) and might explain the low output volts, poor condition brushes could cause intermittent output and a regulator failure usually means no output.

So will the DC voltage function on a £20 multi meter!

Arwyn

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Get a multimeter. A far more useful bit of kit. I have 2. One stays in the car for emergency use to check power supply to whatever fails. Petrol pump suspect? Step1, is there power to it? Fuse ok? The cheap, basic car one cost about £10 from somewhere.The garage one about £30 I think and does many function checks. Bought from Maplin a few years ago when they were open.
Get a smart charger to maintain the battery.

Agreed, but better still one of these.



I seem to have acquired three

Does it do audible continuity? That's by far the most frequently-used function on my multimeter.

Picked mine up from LIDL about 12 years ago for 15 quid, its been dropped, crushed, run over, drowned and had mains voltage shorted through it but still functions!

Arwyn

No but it has this magic pointer that leaps across a huge scale and in so doing tends to grab your attention
I'm deaf anyway

Hi all,
Many thanks for all the information .
Over the next weekend I will check and do some tests suggested in the text above.
Thanks for the quick replies.
For DaveW you speak about a separate diode circuit, where should I find this?
The battery is still OK , put it regular on a C-Tek charger, the LUCAS alternator is only about 3 years old , but will test the unit by a company the next days.
Best regards,
Bart

If it helps Bart this is a typical but simplified alternator circuit diagram as the regulator in the field circuit is not shown.



The extra set of diodes you queried are to the right and provide half wave rectification of the three phase output to maintain the field circuit, as explained in earlier post. Sometimes referred to as the diode trio, virtually all automotive alternators have such although of lower current rating than the three main pairs of diodes shown top and bottom which provide full wave rectification of the same three phase output, to charge and maintain battery loads.

Some alternators have a pulse terminal labelled W, taken from one of the phases and which can drive a tachometer calibrated to alternator drive ratio.