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PostPosted: Mon Oct 22, 2018 12:54 pm 
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Dear Uhm members

Before setting off this morning I took a voltage reading (12.3V) across the battery with a multimeter - car turned off. After a 50 minute commute at almost motorway cruising the reading was 13.2V.
When the engine is running at idling speed the voltage across the battery reads about 14.6 - 15.2V, so the alternator is still doing its job.

My thoughts are that the battery is on the way out.
The reason for taking these readings is that every 5-7 seconds there is a slight dip/reduction in the strength of the front lights beam. This is evident also when the car is idling and the voltage drops by about 1-1.5V. I have no idea what causes this – new bulbs and all.

Any thoughts?


02 Ford Focus estate 1.6 zetec petrol

Kabous


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PostPosted: Mon Oct 22, 2018 2:05 pm 
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Sounds like its on the way out with a low voltage reading of 12.3v, I would get another asap as the clocks are going back and temperatures are due to drop


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PostPosted: Mon Oct 22, 2018 3:02 pm 
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Kabous wrote:
When the engine is running at idling speed the voltage across the battery reads about 14.6 - 15.2V


That sounds high to me?

From Google "The typical charging voltage is between 2.15 volts per cell (12.9 volts for a 12V 6 cell battery) and 2.35 volts per cell (14.1 volts for a 12V 6 cell battery"

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PostPosted: Mon Oct 22, 2018 4:14 pm 
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anything above 11.5v engine off is ok, also the alternator may be ecu controlled meaning it will only output 20-50% at idle

15.2v is too high, I would get the alternator checked in should be no more than 14.8 @ 2500rpm, ideally it should be 13.8-14.4v when running

a over charge is a sign that the rectifier is going bad, over charging the battery can kill it, And now add the drop in temperature

A local parts shop / motor factors will be able to check it (normally FOC) with there test equipment, after 16 years its bound to have gone though a few battery's and alternators anyway


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PostPosted: Mon Oct 22, 2018 6:35 pm 
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Thank you for the replies. I'm going keep log of the voltage pre/post driving this week. It's going on on Monday for rear brakes.
This is the 2nd battery and original alternator


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PostPosted: Mon Oct 22, 2018 7:20 pm 
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Are you running any other high power devices - rear demist etc? The alternator regulator may be faulty. The battery sounds fine to me. 12.3V after standing is 'good'. If the regulator is externally mounted it's a simple matter to change.

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PostPosted: Mon Oct 22, 2018 8:18 pm 
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I don't think I have seen external regulator on anything newer than a mark 2 escort

5-7 years is about right for a battery, wow a focus on its original alternator it must be a low mileage car


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PostPosted: Mon Oct 22, 2018 9:37 pm 
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That high voltage reading taken over the battery was with the headlights on. I'm trying to find the reason for the dip in beam intensity, slight but annoying. Car has almost 140K, and doing 2250 miles per month, last 7 months, commuting.
Lots of thing going wrong, but can't afford to replace it.


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PostPosted: Tue Oct 23, 2018 6:31 am 
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Does your focus have smart charging, my 06 connect did and it was a pita, it is ecu controlled and are notorious for causing issues with charging.

Normally the 3 pin cable which differentiates battery voltage to alternator output is the cause and at £20 is quick and easy to change.

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PostPosted: Tue Oct 23, 2018 10:33 am 
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Get the alternator and battery checked asap, the over voltage can kill electronics, blow bulbs and cause many other problems


Put it this way if it kills the ecu the car is scrap


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