SE6a alternator/ ignition light

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andy99
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SE6a alternator/ ignition light

Post by andy99 » Sun Sep 20, 2020 8:58 pm

I went down to the New Forrest today and about 15 miles into the journey the alternator light came on, only faintly but worrying all the same. I decided to push on as it may break down on the way back if I turned round, or if it stopped on the way I could get recovered. Anyway there was no sign of anything else wrong, and I noticed that the volt meter was showing a healthy 13v. when I got off the duel carriageway the light went out but came on intermittently.
I am thinking that the fan belt needs replacing, and true it is a little worn. So my question is does anybody know of anything else it could be?



5eon
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SE6a alternator/ ignition light

Post by 5eon » Sun Sep 20, 2020 11:19 pm

I wouldn't trust the car volt gauge to be accurate, I'd start by doing an alternator test, lots of 'how to'" videos on Youtube. This is how mine acted at first then the light was on all the time, new alternator fitted and problem solved. I upgraded to a 65 Amp and ran an extra brown cable to be on the safe side as I didn't trust the extra amperage on the old cables.



se6b
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SE6a alternator/ ignition light

Post by se6b » Mon Sep 21, 2020 12:34 am

What does the voltmeter gauge actually measure...is it the alternator output, for example if using a multimeter, it shows around 14.2V with engine running, should the gauge indicate that exactly?



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philhoward
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SE6a alternator/ ignition light

Post by philhoward » Mon Sep 21, 2020 6:01 am

It measures system voltage and in a nutshell anything over 13 means the battery is charging. Anything over 15 and the alternator is overcharging and anything below about 12.5 and the battery is discharging (or pretty flat anyway) - all with the engine running.


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nuclear_jimbo
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SE6a alternator/ ignition light

Post by nuclear_jimbo » Mon Sep 21, 2020 12:35 pm

The Smiths voltmeters use a bimetal strip with heater and I've found them not to be especially accurate. Mine is a brand new one from Caerbont and reads 13v but my DMM reads 13.8v across the voltmeter terminals.



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Old and Slow
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SE6a alternator/ ignition light

Post by Old and Slow » Mon Sep 21, 2020 1:31 pm

nuclear_jimbo wrote:
Mon Sep 21, 2020 12:35 pm
reads 13v but my DMM reads 13.8v
I reckon that's not far away from +/- 5%, which isn't bad for an automotive instrument. I don't think the Smiths gauges were specified better than +/- 10%


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SE6a alternator/ ignition light

Post by philhoward » Mon Sep 21, 2020 2:21 pm

“Indication only” as an instrumentation engineer would say :mrgreen:

To be honest after a while you know where the gauges should sit and look for differences from the norm.

Reminds me of a story about when the V12 Jags came out which was happy running at 100 degrees - owners taking them back to the dealers citing “overheating”. Jaguar answer was to change the gauge to a “C N H” one..


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andy99
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SE6a alternator/ ignition light

Post by andy99 » Mon Sep 21, 2020 7:10 pm

I phones QRG today and have ordered a new fan belt and a new alternator, they are not expensive and I would rather have the peace of mind as I am going away this weekend, lockdown permitting, and don't want to break down.
I would say though that I got from Reading to Beaulieu and back and the battery was still fine so I am guessing that the alternator is working. The volt meter went right down when I was at a standstill on the M3 but then the fan had kicked in and it went back up when it was off.



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adamwilkes
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SE6a alternator/ ignition light

Post by adamwilkes » Mon Sep 21, 2020 7:50 pm

Before fitting the new alternator, check & clean the connections. A flickering light can easily be a dirty 'little' plug-in wire that switches the alternator on & off.


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Dennis Nicholas
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SE6a alternator/ ignition light

Post by Dennis Nicholas » Mon Sep 21, 2020 11:49 pm

I am sure I remember opening up an alternator and there is 1 or 2 small brushes inside that can be renewed quite easily. Yes just looked in the workshop manual; "Field current is supplied via two small brushes to face type slip rings which are carried on a small moulded drum attached to the rotor shaft."
If brushes are worn or slip rings dirty field current may be erratic in supply and hence output to battery would be erratic and ignition light also erratic. I changed my brushes once many years ago.
Brush length1/2 inch - renew when worn to 5/16 inch.
I am sure the regulator module can be changed also without too much difficulty. Changing the diodes is a bit more tricky.
Workshop manual actually gives a good description of testing and repairing (the 17ACR)

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SE6a alternator/ ignition light

Post by scimjim » Tue Sep 22, 2020 7:42 am

LRA100 is the repair kit for the ACR alternators (like this) if you fancy having a go.

I like the A127 type alternator, which has a replaceable module containing brushes and regulator.
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SE6a alternator/ ignition light

Post by AJL Electronics » Tue Sep 22, 2020 2:45 pm

The whole point of analogue instruments is that you don't actually READ them. They are arranged so that a quick glance will see everything pointing around the vertical and so all is well.


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andy99
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SE6a alternator/ ignition light

Post by andy99 » Mon Sep 28, 2020 6:54 pm

Thanks for all the advice, I changed the alternator as I was going away last weekend and didn't want to risk the repair mot working. The light went out and we had a great long weekend around the New Forrest, the Scimitar performed well, not a hitch. Anyway I will have a look at the old one, rebuild and put it on the shelf as a spare.



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