Lucas A127 only charging at 14.1 volts?

S

SlowlyButSurely

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My Lucas A127 alternator which usually charges at 14.4 volts has recently dropped to 14.1 volts. The ignition light is also taking a long time to go out. Revving the engine makes no difference. It's a cheap one off Ebay and has done about 400 hours. Any ideas why this is happening?
 
Is it internally sensed or does it have an external regulator?

Sounds like a check of cabling and connections is worth a look the ignition light should go out if it receives voltage back from the alternator sense
 
SlowlyButSurely said:
My Lucas A127 alternator which usually charges at 14.4 volts has recently dropped to 14.1 volts. The ignition light is also taking a long time to go out. Revving the engine makes no difference. It's a cheap one off Ebay and has done about 400 hours. Any ideas why this is happening?
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Check brushes and if com rings are clean.

Remember the alternator regulator only limits max voltage, so 14.1 volts you see is set by the battery, the regulator only stops it going above 14.4 volt. So you may have a duff battery that has a cell starting to fail, so check batteries also.

Brian
 
Bear in mind that the voltage indicated by your meter may be affected by the waveform and/or noise, there are various ways of measuring voltage and different meters may indicate different voltages depending on method and waveform. The fact that the ignition light is reluctant to extinguish is suspicious. Check cables and connections.
 
SlowlyButSurely said:
My Lucas A127 alternator which usually charges at 14.4 volts has recently dropped to 14.1 volts. The ignition light is also taking a long time to go out. Revving the engine makes no difference. It's a cheap one off Ebay and has done about 400 hours. Any ideas why this is happening?
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Classic symptoms of brushes starting to go.
S
 
SlowlyButSurely said:
Stu,
Is this the typical life of one of these cheap alternators. It came from http://www.startermotor-alternator.co.uk/ so presumably made in China or somewhere?
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Before making an assumption find the fault, is it running at high current @ 14.1 volt ? that will drop the voltage, as said before a faulty battery will, how old are they ? Many faults can give the problem, but remember it is the battery that sets the voltage.

Brian
 
halcyon said:
? Many faults can give the problem, but remember it is the battery that sets the voltage.

Brian
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A faulty regulator could give the symptoms described couldn't it ?

I'd check brushes and slip rings first as you suggest.

I am wondering why the warning light is taking so long to go out. Brushes, slip rings or regulator .... or simply a bad connection somewhere ?
 
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halcyon said:
Before making an assumption find the fault, is it running at high current @ 14.1 volt ? that will drop the voltage, as said before a faulty battery will, how old are they ? Many faults can give the problem, but remember it is the battery that sets the voltage.

Brian
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Just to confirm what was said and give an example. I have one starter battery and 2 domestic split with a 1-2-both switch. I went down to the boat yesterday I wanted to give the batteries a bit of a charge. The starter battery was good and when the engine started it was showing 14.3v when I switched to the domestic bank there was a slight noticeable drop in the revs and the readings dropped to 14v After about 30 mins running it was up to 14.1v. I switched back to the starter batt and it was still showing 14.3v so I assumed my domestic bank must have been well down. I had suspicions end of last year one of the domestics may be on the way out. Further investigations needed I think.
 
Thanks for the replies. I have now done a few more checks.
The batteries are 8 months old; they are sealed lead acid. The magic eye on both is showing green. After charging with the battery charger they both show 12.8 volts. There is no voltage drop on any of the cables connected to the alternator and all connections are clean and look OK. The alternator itself looks as clean and shiny as when I fitted it about 18 months ago and it has done 400 hours. The belt is in good condition and properly tensioned.
I tried running the batteries down to 12.5 volts and then starting the engine. The voltage was showing 14.1 volts as before. I tried switching off each battery in turn and the voltmeter showed the same 14.1 volts when charging either battery independently of the other.
Are there any other checks I can do to diagnose the problem or is it time to fit the spare alternator?
 
SlowlyButSurely said:
Thanks for the replies. I have now done a few more checks.
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Are there any other checks I can do to diagnose the problem or is it time to fit the spare alternator?
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Well fitting the spare alternator would at least, if it works normally, confirm that the other one is at fault rather than something obscure wrong elsewhere. I'd missed the fact that you had a spare available!

With the dodgy one off , and its not clear if this is a genuine Lucas A127 or a cheap far Eastern made copy, you can inspect it . My money would be on a defective regulator if the brushes and slip rings are OK.

New regulator c/w brushes available for around £13

Complete overhaul kit for £33
 
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