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Battery and general voltage drop
Posted: Mon Oct 22, 2018 11:54 am
by Kabous
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
Re: Battery and general voltage drop
Posted: Mon Oct 22, 2018 1:05 pm
by boxedin
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
Re: Battery and general voltage drop
Posted: Mon Oct 22, 2018 2:02 pm
by mikew1972
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"
Re: Battery and general voltage drop
Posted: Mon Oct 22, 2018 3:14 pm
by Bob225
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
Re: Battery and general voltage drop
Posted: Mon Oct 22, 2018 5:35 pm
by Kabous
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
Re: Battery and general voltage drop
Posted: Mon Oct 22, 2018 6:20 pm
by kellys_eye
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.
Re: Battery and general voltage drop
Posted: Mon Oct 22, 2018 7:18 pm
by Bob225
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
Re: Battery and general voltage drop
Posted: Mon Oct 22, 2018 8:37 pm
by Kabous
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.
Re: Battery and general voltage drop
Posted: Tue Oct 23, 2018 5:31 am
by Ktuludays
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.
Sent from my HUAWEI VNS-L31 using Tapatalk
Re: Battery and general voltage drop
Posted: Tue Oct 23, 2018 9:33 am
by Bob225
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