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What is the expected voltage from an alternator??

The ignition light goes out on my car and the voltmeter on the dash slowly creeps up to just over 13, checked with a digital meter on the battery terminals and depending on revs the meter only goes up to 13.5 ish volts?

kc

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Your alternator is probably faulty - we had a similar problem discussed on here a few months back.  The specification is for between 13.6 and 14.4 volts at 3000 engine revs if this is a Lucas ACR type alternator. It is usual to actually have at least 14volts -  so it is possible the regulator has died or perhaps some of the rectifier diodes. 

The other possibility is a bad connection in the alternator wiring so it's worth checking that first. 

Lucas fault finding document here, which might help - or might not !  https://www.gomog.com/allmorgan/LucasFault.pdf

Are you having problems keeping the battery fully charged?

Edited by RobH
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2 hours ago, RobH said:

Your alternator is probably faulty - we had a similar problem discussed on here a few months back.  The specification is for between 13.6 and 14.4 volts at 3000 engine revs if this is a Lucas ACR type alternator. It is usual to actually have at least 14volts -  so it is possible the regulator has died or perhaps some of the rectifier diodes. 

The other possibility is a bad connection in the alternator wiring so it's worth checking that first. 

Lucas fault finding document here, which might help - or might not !  https://www.gomog.com/allmorgan/LucasFault.pdf

Are you having problems keeping the battery fully charged?

Hi RobH!

Thanks for that Document, it looks very useful?

Bruce.

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Yes thanks for the link to the Lucas doc, excellent electrics bible

I replaced the battery about two months ago as it was 7 years old although I now think the alternator may have been the culprit the whole time. Will test it using the document for reference

Is it better to replace with the same or a higher output model???

kc

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3 minutes ago, kcsun said:

Is it better to replace with the same or a higher output model???

It depends what you have now. If your accessories draw more current than the existing alternator can supply or if you intend adding more loads to the system, then upgrade.   There's really no point in having a larger alternator than the maximum demanded load, but there's no harm in doing so either except paying for something you do not need. 

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12 minutes ago, kcsun said:

Is it better to replace with the same or a higher output model???

 

I had my original Lucas rebuilt maybe 20 years ago with the output increased to 45 amps, at the time the auto electrician said it would cost no more than the original. From memory the Lucas could have gone above 45 amps  what was in issue to me was putting more current through the original wiring after a long cold start ,PI priming, cranking episode.

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On 10/16/2020 at 7:09 PM, Mike C said:

I had my original Lucas rebuilt maybe 20 years ago with the output increased to 45 amps, at the time the auto electrician said it would cost no more than the original. From memory the Lucas could have gone above 45 amps  what was in issue to me was putting more current through the original wiring after a long cold start ,PI priming, cranking episode.

My 17ACR failed during the warranty period and I went to the local Lucas main agent. Quote: We only fit the 18ACR ( 45 amps ) on all Triumph PI cars because of the  current draw in slow moving  or stopped traffic. I certainly did notice the difference when I had the indicators on and the heater blower and the PI pump played a different tune!

Bruce.

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