Conference terri::cars_uk

    Is it being drained, or not charged ???

    How flat is flat ??? Would it just not start the car, or wouldn't
    it even light the ignition lights on the dashboard ???

    What did you do with the car yesterday i.e distance travelled, 
    lights on/off, wipers on/off etc etc.

    How old is the battery ???

    More information may lead to a cause and cure being found ...

  Mark

    
    Re: -1
    
    >>How flat is flat ???
    
    Enough to light the ignition lights but only enough to turn the
    car engine over twice and very slowly.
    
    >>What did you do with the car yesterday
    
    I only used the car to and from work, distance 2.5 miles in each
    direction. Used lights on the way home. No wipers, stereo on.
    
    >>How old is the battery ???
    
    Approximately 2 to 2.5 years old (if I remember correctly)
    
    When I started the car to go home last night the engine turned over
    quickly before starting which to me meant the battery was OK. My
    voltmeter also showed (if its working correctly) that the battery
    was charging at between 13 and 15 volts.
                                            
    If the battery was just not being charged correctly (rather than
    being drained) then I would have expected the engine to turn over
    more and more slowly each time I went to start it. Thus I think
    there must be a drain rather than a recharging problem ?.
    
    Hope this provides some more useful information. Thanks.
    
    /Steve
    

Take it to Lucas Electrical in Reading off Bsingstoke road. For about �13 or
is it �18 they will do an half hour leccy check.

Simon (they cured my Landy...)

    
    Recently we had the same problem with our EFI Maestro and it turned out
    to be the boot light - even though the boot was shut the light was
    still on and voila, one flat battery.
    
    Karen
    
    

Charge it up and drive to your local garage and have them load test it.  This
involved putting a dirty big resitive load on it and seeing if the battery
can handle it!  If it can't, you've probably got a cell gone.  The voltage
indicators in most cars indicate the volts at the regulator box, not what's
at the battery - misleading!

    To flatten the battery that much, I would expect to find more than
    the boot light on.

    Cars always require more battery power to start in the morning after
    they have been left out all night, that they do in the evening after
    work (first law of car electrics :-), so perhaps the battery is on
    the wane.

    The �13 electrics check sounds like a good idea. Saves spending lots
    replacing different pieces until you find the problem.

    Having said that, I would suspect the battery ...

 Mark

    
    is this a volkswagen ?
    
    'cause if it is, I know what your problem is....
    
    I had it.

    			Battery Drain??
    
    Altough you don't give age to the car and more info would be
    useful.....Here goes..
    
    		lets assume that its Alternator based system so that
    the figures you saw on your voltmeter were at idle 13.8volt is about
    right for a Alternator system {Zener based} this of course is not
    absolute and the amps delivered could be marginal. Buts lets make
    a safe bet and say it is charging. Then the problem is going to
    be either bad connections to the battery/starter, duff Battery or
    Battery being discharged by some source within the car.
    
    			To check the discharge rate assuming you have
    still the multimeter and it has a amps range. Switch everything
    off at the ignition and disconnect one lead from your battery and
    connect it to your mutlimeter lead place the other lead on the battery
    terminal from whence the lead came and assuming all doors shut,
    lights , radio off etc you should see a reading of less than 100ma
    anything greater and somethings draining. More detailed instructions
    can be given to trace this. If you don't have a multimeter and want
    to establish battery or drain from car....simply disconnect the
    battery lead overnight if it fails to start in the morning the most
    likely cause is your battery {don't forget to reconnect in morning}.
    
    			Hope this helps ...
    
    					Mike.
    

    About 6 months ago the wifes Astra battery died, and the battery was
    replaced by a very nice AA man. 
    
    Just yesterday, the new battery died completely (twice) not enough
    juice to turn the engine or activate the alarm. 
    
    The AA man was called and performed some tests on it. 
    
    He recokened that the alternator was producing too much current and
    that it was overcharging the battery and that may have killed it. He
    suggested a 'Heavy discharge test' - what is that ? 
    
    It the battery was being overcharged then the new battery selected by
    the AA man may have been wrong. 
    
    Reading the Astra manual yesterday, it suggested that the
    alternator/battery current rating should be in the range 35-65 Amps
    depending upon climate and conditions of various countries.
    
    Is there an easy way of testing or finding out what the alternator
    rating is, as if it is the battery problem, i'll make sure that a
    correct battery is chosen.
    
    He also suggested changing the alternator, is this necessary if I get a
    correct battery ?
    
    Raj
    
    
    
    

    If the altenator is overcharging, you will either have to change
    it, or the regulator pack. Overcharging tends to cause the battery
    to heat up and loose all the liquid that is in it. You basically
    boil the battery. I assume that overcharging is caused by the altenator
    not realising that the battery is completely charged, and so it continues
    to charge it. Changing the battery won't help in this case. The new battery
    would die too ...

    The different battery types are more to do with the amount of charge
    that a battery can hold in terms of time. They are measured in amp/hours.
    Heavy duty batteries hold more charge and so can sustain a constant
    discharge for longer than a normal battery can.

    Your best bet is to take the car to an auto electrician. A specialist
    tends to know more about the subject than the average AA man, and 
    just replacing parts for the sake of it is a costly way of doing things.

  Mark

Here's my undertanding (probably wrong) of it:

The electricity-producing reaction in a battery is reversible. ie you can
charge and discharge the battery in your car as much as you like, but *within
certain limits*.  If it is over-charged by too much, or discharged too much,
then the reaction becomes irreversible, and the battery is said to have become
"high resistance".  That is, it's dead.  Whether you can repair it by flushing
out the liquid (dilute sulpuric acid) and refilling with fresh, or whether the
electrodes have become contaminated necessitating a whole new battery, I don't
know.

The "heavy discharge test" involves connecting the battery terminals across a
very low resistance load, thus drawing a high current.  Measuring this current,
and the drop in voltage between the terminals due to the internal resistance of
the battery allows the battery condition to be measured.  Qualitatively, the
greater the voltage drop, the greater the internal resistance.  Quantitavely,
the resistance is the voltage divided by the current.

Batteries are rated in Ampere-Hours: the number of hours for which they can
supply one amp, or the number of amps they can supply for an hour, etc.  Check
the car specifications against those of the battery fitted; if the battery's
rating is higher, no problem.  If it's lower, get the proper one.

Scott

    I race 1/10th scale electric cars and use a 12v battery to fast charge
    the nicad cells.  I started with a bog standard car battery.  After
    about a year it started to give trouble and would not hold a charge. 
    It was still under gaurantee so I took it back.  ATS told me that it
    had died due to incorrect use.  They said that car batteries are
    designed for short periods of high currect discharge, not long periods
    of low current discharge (typically several hours at 4-8 amps).  They
    sold me a replacement leisure battery (with an allowance for the dead
    one) which I have used for about 3 years with no problems.  I also use
    it in my caravan.
    
    I always thought a 12v battery was a 12v battery but it seems I was
    wrong.  The leisure battery has a built in carry handle and is rather
    more expensive than a car battery.
    

    I have heard (or read) somewhere that batteries will hold more
    of a charge if they have first been run completely flat.
    If they are only 'partially drained', then they will not
    'charge up' so well.
    
    Could someone tell me if this is the case - and if so, why ?
    
    Thanks,
    		John Rutter

    re .13
    
    This is a known characteristic of NiCad batteries. Newer batteries do
    not exhibit it as much as older batteries. A battery which is only
    partially discharged before being charged will show an increased
    internal resistance when it discharges to the same point again. I think
    this is due to some difference in the layer of chemical deposited on
    one of the plates when you first start charging. It may be reversed by
    fully discharging the cell (which would remove the bad layer). Actually
    you should never totally discharge a cell, just take it down to some
    point where the open circuit voltage drops off sharply.
    
    I dont think this applies to Lead Acid batteries. The chemistry is
    different and the plates are more porous so the surface area is greater
    anyway.
    
    Andrew

Certainly for NiCads this is true, but for lead acid I don't know.
What happens for NiCads is known as memory effect.

If you discharge a battery to 50% then recharge it, after a couple of times you
will only achieve a 50% charge (50% discharge?). To overcome memory effect you 
must discharge the battery completely, and then charge completely. This cycle
must be performed several times to regain full use.

Another effect on NiCads is the build up of hairs or filliments between the 
cells. This can cause the battery to hold less charge, or even reduce voltage.
To 'burn off' these hairs the battery must be zapped. To zap a battery you must
'charge it' with, and I not sure which way it is, either a high voltage and low 
current for a very small time, or it is a nominal voltage, eg 2.5v for a 2.5v
battery, and a very high current for a very small time. This is usally done via
capacator discharge across the battery.

As for lead acid battery I don't know.

Simon

.14 is right - it is a characteristic of Nicad batteries that they last longer
if they are used in a charge - discharge cycle.  It can also be beneficial to 
discharge them at high currents occasionally as this destroys neddle shaped
crystals which can short the plates together if allowed to grow.

Car batteries do not like charge - discharge cycles and can be destroyed by
being run flat only a few times.  On the other hand, traction batteries are
designed for this type of use.

Mike.