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Old 10th January 2019, 20:13   #1
RPWC
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Default Charging system

My brother in law called me today to ask about a battery problem. I popped round with a voltmeter after he had charged the battery and taken the car for a good run. The reading was 12.83, after starting the engine it went to 13.88, but when the revs were increased the reading remained static, instead of inreasing to 14.3. Does this mean the alternator is not charging?. I tested my own vehicle and once the engine was started and revs increased it went sraight to 14.3v.
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Old 10th January 2019, 21:02   #2
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Rich,

With my own cars I have noticed some variation in the charging voltage. 13.88 volts is fine.

Simon
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Old 11th January 2019, 09:25   #3
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13.8 will be ok Rich, but it depends how many on board systems the car has, obviously 14+ would be better.

It may be the first sign that the alternator is wearing out.
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Old 11th January 2019, 20:12   #4
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Andy is spot on 13.8 can soon drop when on idle with lights/heating/stereo/and wipers running, I would suggest turning on all the accessories and then measuring it at idle.
I too would rather see 14+ at idle
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Old 11th January 2019, 20:30   #5
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Quote:
Originally Posted by RPWC View Post
My brother in law called me today to ask about a battery problem. I popped round with a voltmeter after he had charged the battery and taken the car for a good run. The reading was 12.83, after starting the engine it went to 13.88, but when the revs were increased the reading remained static, instead of inreasing to 14.3. Does this mean the alternator is not charging?. I tested my own vehicle and once the engine was started and revs increased it went sraight to 14.3v.
Interesting that he found the need to go for a good run.--


The lower voltage could indicate the battery was nearly fully charged. The internal resistance of the battery INCREASES as it charges. Could be making that multi-meter voltage drop slightly.

Also the voltage regulator could be the limiting factor due to a slight change in which its internal components are working.

However 13..88 volts will keep the battery charged in normal use of the car.---

Don't forget that you will only get an accurate voltage reading from the battery several hours after it has come off charge. Immediate readings are never accurate.---
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Old 13th January 2019, 20:47   #6
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Richard.


How did you get on with that problem you asked a question about ???
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