Alternator problems

Batteries, Alternator, Wiring, Lighting, etc. (Please discuss ignition problems in the Engine category)
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Alternator problems

#1 Post by M5driver » Thu May 09, 2019 3:33 pm

How many of you have had an alternator surge in current. Fortunately on a MK1 you have an ammeter. You will observe the needle go up to the end stop of charge. This problem started in the latter part of last year, it made the head lights go very bright and the pi pump speed up at bit. Then all would settle down a few moments later.
I have dismantled the alternator (not original AC type that blew up years ago). In the photo you will see the regulator wires have split! :oops: so this is out for replacement. I have read if left unnoticed there is a possibility of overloading the loom, then a fire starting. Would of thought you could damage the battery.
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Re: Alternator problems

#2 Post by johnnydog » Thu May 09, 2019 4:55 pm

Whilst at the last Northumberland National in my 'J' reg. Valencia 2000, the alternator began to overcharge. It only did it intermittantly on the way there, and the first thing I noticed was the voltmeter was right at the top end of the reading. It would then drop down to its usual 13 /14 volts. It then started having a constant high voltage reading, and the battery was very hot to the touch. As it had a very early 15 (I think from memory.....) ACR alternator on it with the early style plug from the loom, I couldnt find a replacement whilst there, other than the the standard type with the L shaped plug.
I avoided using it for the majority of the National week which was a shame, but on the way home I travelled with the headlights on, heater blower on high (not that it blew me off my seat mind you...), interior light and radio on (there was nothing else left to switch on!) to have as higher drain as possible. Unfortunately it doesn't have a heated rear window, which would have been a great help at the time.
I got home ok, but the battery died shortly afterwards - probably 'cooked'.
I got the original early alternator repaired and totally overhauled for £40 - the regulator I believe had died. Looked superb when I got it back - like a 'new old stock' item, but not new 'out of the box'.
I could have quite easily had wiring overheating issues which could have resulted in more serious consequences.
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Re: Alternator problems

#3 Post by Firewatcher » Thu May 09, 2019 9:32 pm

I had the same problem about 2 years ago on my Mk2, first noticed the headlamps would brighten for a while - voltage increased to over 15V. Ran it for a few months ( and I use it most days) before I got round to swapping the regulator with one I found in an alternator which needs a full service. Didn't notice any other problems, but have no sensitive electronics on my motor so maybe just lucky.
General point - JCR Supplies is good for alternator parts, brushes and rectifier pack for mine was only about £15 including postage.

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Re: Alternator problems

#4 Post by Calorian » Fri May 10, 2019 7:16 pm

Had this same issue last week. I've a digital voltmeter that goes in the 12v plug and it has been reading up to 18.8v!
Even with all electrics on (halogens, blower, rear demister etc) it held at 16.4v. Got a new regulator and so far so good.
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Re: Alternator problems

#5 Post by Dave B » Fri May 10, 2019 9:24 pm

Calorian wrote:
Fri May 10, 2019 7:16 pm
Had this same issue last week. I've a digital voltmeter that goes in the 12v plug and it has been reading up to 18.8v!
Even with all electrics on (halogens, blower, rear demister etc) it held at 16.4v. Got a new regulator and so far so good.
Cautionary tale on this one. A few years ago my digital multimeter was reading high (16-17v). After trying on another car and getting a similar reading I eventually traced it back to a nearly exhausted 9v battery in the meter! There was nothing wrong with alternator.
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