Battery

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saint gaz
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Battery

Post by saint gaz » Wed Sep 20, 2006 2:16 pm

Is there a correct type of battery for my car? This problem has happened on two different batteries. The sticker on it says it’s got a 47 amp hour and is 425 amps cold cranking (can some one explain what that is)? Part of my problem is that I probably don’t do many miles. I do use it most days. I guess I do about 50-100 miles week

But I have to recharge the battery at least 2-3 times a year. It’s a new (ish) battery 2 years old. On the bench over a few days holds its charge. On the car I have checked with a multimeter and the voltage across the terminals is 12.5 engine off. With engine running and warm voltage across terminals is on average 14.2. Again with engine running and warm with lights on full beam hazards, heated screen, fog lights, wipers, heater all on full. The reading drops a little to 13.5 average. So by that I presume the altenator is working fine.

I had this problem checked two years ago at an auto electricians and the only “drain” they could detect was the alarm, radio back up and clock. They said that they would have expected that and tested the then battery. The battery had gone passed its useful life and hence they replaced it with this one. He said I should be looking at 14 – 14.5 volts under normal conditions with it dropping to between 13- 13.5 under load.

Is there any thing else I can look at?
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Kitch
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Post by Kitch » Wed Sep 20, 2006 2:31 pm

Pretty much most common batterys fit. But the best you'll probably fit is an 096 (UK number). They're plenty powerful enough and fit ok. Mines got one.

Others that could work are the 075, 065 and 063 but the 063 is probably a little bit gutless for the BX. I know the 063 is 44Ah from memory, and the 065 is 55Ah. Think the 096 is 66ish?

Basically not using the car alot will shorten the batterys life. The best you can do is get something like an 096, make sure its Calcium plated, like the Bosch silver range. If you go to Euro Car Parts, buy one of the Lion range....these are Bosch silvers in a different colour for half the price! 8)

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Post by Way2go » Wed Sep 20, 2006 2:52 pm

Best way to check your current drain is to put your multimeter on its highest current range and insert in series between the battery and one of it's terminals with all acessories, lights etc turned off. The current reading in this state should be very low. (Remove multimeter immediately after test to protect it.)
With this measurement you can calculate how long the battery will last without charge by dividing this expected figure in milliamps (convert to Amps) into the battery capacity figure in Ampere hours.
However, in real life you cannot run the battery this long without recharging because it will go into so called "deep discharge" and from this state it is almost impossible to revive the battery and replacement will be the only option.

Regular recharging by use is preferable to battery chargers and will prolong the life of the battery.
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saint gaz
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Post by saint gaz » Wed Sep 20, 2006 3:46 pm

Way2go wrote:Best way to check your current drain is to put your multimeter on its highest current range and insert in series between the battery and one of it's terminals with all acessories, lights etc turned off. The current reading in this state should be very low. (Remove multimeter immediately after test to protect it.)
way2go
can you explain in laymans terms step by step. :oops:

was up early and its already been a long day... :wink:
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Post by Way2go » Wed Sep 20, 2006 4:31 pm

saint gaz wrote:way2go
can you explain in laymans terms step by step. :oops:
Hi Saint Gaz,

Basically this check will test whether there is something draining the battery when everything is switched off. Some things will take a small current from the battery even when the car is switched off ie clock, radio memory and possibly ecu and alarm. The current taken by these devices in the "off" state will be small and insignificant compared to the heavy currents taken by the lights etc. Your multimeter will probably have a range that can test up to maybe 300mA which will probably be enough to check these small drainage currents. (Older AVO 8 meters were better for cars as they could measure up to 10 Amps)

Say that your drainage was as large as 250mA then a 47 A/hr battery would be flat in 188 hrs (1 week) if you did not use the car but you would find difficulty to start the car within a few days.

To check the your actual drainage, switch your meter to the highest current range and replug the probes into the "current" holes which are different to those used for voltage. Then disconnect one of the car battery terminals and touch one probe on the connection you have removed and the other probe on the battery terminal whilst they are separated. The reading will be your drainage current.

If this drainage current is large then it is necessary to start disconnecting the things like radio's, clocks etc one by one until you find which one is causing the higher than acceptable current drain.

Warning: Do not feel tempted to measure lights or other car electrics or switch the ignition on because your meter will not be strong enough on the current range as standard to take this. To measure these higher currents you will need to purchase a meter shunt from Maplins or similar.

Good luck and ask again if there is anything that is not clear.
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Post by citroen7 » Wed Sep 20, 2006 4:44 pm

i have found the boot light switch is a good place to start, esecially if you have a parcel shelf fitted , this has happened to me twice.

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Post by Way2go » Wed Sep 20, 2006 4:55 pm

Further thought, when you check the current make sure that the car doors are closed so that the interior lights are not on.
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Post by jeremy » Wed Sep 20, 2006 5:10 pm

The problem here is that most cheap multimeters have a 10 amp scale but it is unprotected - so put more than 10 amps through it - and - you've blown the meter.

What you are looking for here is devices that drain teh battery. In fact if the current drawn was say 5 amps - the thing wouldn't start the car after 10 hours or less - so its a fair assumption that its actually 1 amp or less. To be safe you can use a test lamp in series and when I had to test my father's Range Rover for this problem I soldered an indicator bulb with 2 wires and put this in between the battery earth and the earth lead. I then found if I left it there I could do the rest of the job with my meter used on a law voltage scale by putting it across the buld (a shunt)

Have you got the original radio in your car or another with a positive on-off switch? I ask this as I had the same trouble with my TD BX when I replaced the old Philips radio with a CD player - which has an electronic on-off switch. The CD player is now functioning without problems in our ZX - and the difference is that the BX only has an unswitched supply for the radio which is fine if the radio has a proper switch in it. The electronic ones draw a standby current which is quite hefty - and this was flattening the battery over several days.

The answer if I want to use the CD player in the BX is to arrange a supply from the ignition switch - and for convenience it may be easier to tap a convenient switched supply and use it to operate a relay to switch the existing supply.

1st step - everything off - and measure current between battery earth and its lead. This should be minimal.

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Post by saint gaz » Fri Sep 22, 2006 10:13 am

I looked at my multimeter (7.99 cheepo) and works multi meter (39.99 not a cheepo but rated similar) and both only go up to 200Ma so i presume there is a chance of blowing.

I have checked to boot light by removing parcel shelf and closing lid. The light goes off. I also checked glove compartment light and that goes off with the door half shut, so I can rule that out. The only things that i know about that would be taking a feed is the clock, alarm and radio back up.
The radio is a sony mp3 player so i would imagine there could be a higher drain when in use.
I will keep my eye on things but the next time i have to recharge i may get the battery checked and possibly upgrade form a 063 to 075.

thanks guys

gary
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Post by jeremy » Fri Sep 22, 2006 12:32 pm

The real question with your MP3 player is - does it have an old fashioned 'click' switch - or an electronic one. The click switch will break the circuit positively - ie operate it - circuit physically broken. The electronic switch simply turns off the set but if its like the one I had willdraw a substantial standby current.

The answer is to wire the thing so that it is on an ignition controlled circuit. The BX wiring leaves the set on all the time - which was intended to prevent tape tangling when the starter was operated repeatedly etc. When this is done - key out - circuit broken - and the separate memory lead will keep all the settings.

The alarm may also consume a noticeable current.

To check using your meter - use the bulb method I described above - what you are looking for is a substantial drop in the reading and you will probably find your problem.

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Post by tom » Fri Sep 22, 2006 2:15 pm

Ok: All stuff on and 13.5 volts across the battery. The Alternator should be making 14.4 volts even on load, so the regulator is not good. 50-100 miles per week won't be doing the battery any favours either. Ten miles and two starts a day will be fairly marginal for charge at the best of times but if that alternator is 900 millivolts low, then that reduces the maximum charge you can put into the battery by an astonishing amount. I would not assume that your alternator is well. If the alarm is taking more than 10 mA then you may have a problem here. They can drain batteries quite quickly.