Author Topic: Flat battery  (Read 548 times)

JazzMan2018

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Flat battery
« on: May 09, 2020, 12:13:42 PM »
Hi,

Battery is only about 6 months old

Last couple of weeks it is flat after maybe 3 days of non-use

Looking on-line, appears it could either be battery or alternator or something draining it even when off (parasitic charge)

Plan is to get a meter on it to check a) voltage when not running b) voltage under idle c) voltage under idle & load, to try and isolate it

If no problems found, start removing fuses one by one to isolate which circuit is draining it

Does this sound the right approach?

Cheers

Jocko

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Re: Flat battery
« Reply #1 on: May 09, 2020, 12:24:09 PM »
Do you have an alarm fitted? If so that can eventually drain a battery. You say "Last couple of weeks" and "3 days of non-use". To me, this means it has failed to start more than once. Did you fully charge the battery once you got it going or did you just go for a short run or even leave it ticking over? That is not enough to fully charge it.
Does your car have air-con? Have you checked all the interior lights are off, especially the boot?

JazzMan2018

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Re: Flat battery
« Reply #2 on: May 09, 2020, 01:22:15 PM »
Hi,

No alarm

Has a bluetooth receiver in cigarette socket but unplugged that last time so not the problem

Will double check the boot. No a/c

I drove it for 10 miles, around 30 mins. Will idle speed not work or just take longer?

Thanks for the pointers


Jocko

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Re: Flat battery
« Reply #3 on: May 09, 2020, 02:32:27 PM »
Cigarette lighter socket is controlled by the ignition switch. As long as the ignition is turned off completely (0 position) before the key is removed (some posters have found they can remove the key in the Aux I position), then the cigarette lighter/power socket in not live.
The best way to charge the battery with the Jazz's charging system is to drive with the lights and possibly the rear screen on. At tick-over or low revs, there is hardly any charging happening.

JazzMan2018

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Re: Flat battery
« Reply #4 on: May 09, 2020, 02:58:05 PM »
Thanks

Will take it out for a decent run with lights/screen on

BIGFELLAH

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Re: Flat battery
« Reply #5 on: May 09, 2020, 03:19:37 PM »
Cigarette lighter socket is controlled by the ignition switch. As long as the ignition is turned off completely (0 position) before the key is removed (some posters have found they can remove the key in the Aux I position), then the cigarette lighter/power socket in not live.
The best way to charge the battery with the Jazz's charging system is to drive with the lights and possibly the rear screen on. At tick-over or low revs, there is hardly any charging happening.

Hi Jocko can you please explain for me ref Headlights etc on to increase charge rate,I have today taken the jalopy for a 40 mile run with only AC on have I wasted my time.
Thanks

Jocko

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Re: Flat battery
« Reply #6 on: May 09, 2020, 03:45:53 PM »
Most modern cars have a charging system which puts more volts out as the load is increased. With little load, the alternator will trickle charge the battery, fine when the battery is fully charged but not really enough when it is flat. As you increase the load the alternator puts out more, as you would expect, and the increased output makes for better charging.

culzean

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Re: Flat battery
« Reply #7 on: May 09, 2020, 10:06:36 PM »
Hi,

Battery is only about 6 months old


Despite the fact battery is only 6 months old you may have a dodgy battery, just like anything else they can be faulty from new.   If the alternator is capable of kicking out 14.2 + volts there is not much wrong with it.  In the past I have seen an alternators that have 'lost a diode' in the diode pack and could not reach 14 volts ( something around 13.7 to 13.8 which will not charge a battery ).

I have never heard of a battery discharging back through alternator.  If alternator is kicking out over 14.2 volts it should keep battery charged easily,  but frequent starts and short journeys can run a battery down. You really need to get a voltmeter and check voltage at battery terminals with engine running - it should be around 14.2 to 14.5 volts, should let battery stand for an hour after engine has stopped ( to get rid of 'surface charge' which can artificially raise the terminal voltage ).

Alarms and other parasitic drains like the boot light or interior lights are most likely, a relay stuck in would drain the battery in a very short time, ( measured in hours not days ) relays are used to supply heavy loads - Aircon relay stuck would drain a full battery in about 10 hours, rear screen about 3 to 4 hours.  Interior or boot light drawing 5 watts ( about 0.5 amps ) would take about 60 hours to drain a full battery.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

Jocko

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Re: Flat battery
« Reply #8 on: May 09, 2020, 10:17:39 PM »
The first page of text tells all you need to know regarding charging with a load.
https://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=1011&context=auto_pres

BIGFELLAH

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Re: Flat battery
« Reply #9 on: May 10, 2020, 10:43:20 AM »
The first page of text tells all you need to know regarding charging with a load.
https://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=1011&context=auto_pres

Thanks Jocko having perused your above  link twice.
I understood your previous explanation more easily so many thanks again for the knowledge.
But I must say it does seem very involved, it makes me wonder how my 1948 Austin 12 with its dynamo managed,as If I recall correctly it very rarely let us down.

Jocko

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Re: Flat battery
« Reply #10 on: May 10, 2020, 10:56:13 AM »
Yes, it comes down to shaving decimal places from emission figures.



Not a lot to go wrong back then. Dynamo put out as much as it could with no concern over what it did for fuel consumption or emissions.
First of the alternator equipped vehicles were even better.

Darryl

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Re: Flat battery
« Reply #11 on: May 10, 2020, 07:48:13 PM »







I have never heard of a battery discharging back through alternator.  If alternator is kicking out over 14.2 volts it should keep battery charged easily, 

Sorry Culzean but it can definitely drain back through the alternator if the Diode is faulty.

It should only allow current to flow one way ie charging but if defective it will allow it to flow in either direction and yet still be capable of producing a charge rate of 14.2 when running

https://www.youtube.com/watch?v=oUhgyqm0wro

« Last Edit: May 11, 2020, 10:16:23 AM by Darryl »

Jocko

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Re: Flat battery
« Reply #12 on: May 11, 2020, 11:11:01 AM »
I went to the shops this morning after the car sitting in the garage since last Wednesday. Battery seems lively. I set my ScanGauge E to monitor the battery voltage, and it sat at 14.6 volts with and without the rear screen heater switched on.

John A

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Re: Flat battery
« Reply #13 on: May 11, 2020, 11:42:22 AM »
I went to the shops this morning after the car sitting in the garage since last Wednesday. Battery seems lively. I set my ScanGauge E to monitor the battery voltage, and it sat at 14.6 volts with and without the rear screen heater switched on.

I have a simple voltemeter in my 12v power source on my 2015 CVT Jazz and on the short journeys I'm doing it's conssitently showing 14.5v with or without the heated rear screen / lights / air-con being on.

Something like this:

https://www.ebay.co.uk/itm/Dual-Double-Car-Charger-Quick-Charge-Fast-12-24V-4-8A-2-x-USB-LED-Display-UK/273670682262?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 or

https://www.ebay.co.uk/itm/USB-LED-Car-Charger-Cigarette-Lighter-Socket-Power-Digital-Voltmeter-Thermometer/133395772738?epid=2175513440&hash=item1f0f01f542:g:S14AAOSwHk9epV75

Jocko

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Re: Flat battery
« Reply #14 on: May 14, 2020, 11:43:53 AM »
Had a 15-mile trip today and monitored the battery voltage. On startup it indicated 14.6 volts then after a couple of miles, it setted back to 12.7 volts. Then every two or three minutes it would cycle back to 14.6 before returning to 12.7 volts a minute later. One time it dropped back to 12.7 volts, so I switched on the rear screen heater, and it immediately increased to 14.6 volts. As soon as I switched the heater off, it returned to 12.7 volts. This voltage cycling indicates to me the ECU seeing the increased load and adjusting the charging rate accordingly.

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