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  • Charging car battery

    Hi everyone - I'm new here. I hope you can help with some simple advice. My recently widowed aunt has inherited my uncle's car - a 1984 VW polo. It had a new battery last year. She doesn't drive nowadays - although she thinks she could - at 84! We try and keep the car ticking over for her but the battery has now died, and she has bought a charger. Can anyone please tell me how I disconnect the battery from the car - connect it to the charger and then when charged replace it in the car? I know there is a certain way it has to be done. Thanks in anticipation

  • #2
    disconnect the earth lead on the battery, connect your charger up

    red clip to positive terminal, black to negative terminal, sorted

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    • #3
      You do not have to disconnect anything. Identify the battery terminal marked + (often coloured red) and the negative battery terminal marked - (often coloured black or blue). Connect the charger red lead to the battery positive (+) and black lead to battery (-) negative.
      Adjust your charger to around a two (2) amp charge rate and leave overnight. For long term charging adjust charge rate to 0.2 amps or around a quarter of an amp. A normal sized car battery will take this charge rate indefinitely.
      For chargers that only have a voltmeter, you must stage the charge rate, to avoid overcharging when the battery is flat.
      A car battery consists of six lead/acid cells connected in a chain, each cell has a working voltage range of 1.8 to 2.2 volts, with a nominal voltage of 2 volts.
      So your run down battery condition is (1.8 x 6) = 10.8 volts and your fully charged condition is (2.2 x 6) = 13.2 volts. In actual practice auto alternators are designed to supply around 14.4 volts to allow for cable loses. In the USA many cars manufacturers set the systems to 14.7 - 15.0 volts.
      If you can see the battery fluid, it should only show a gentle flow of (hydrogen) bubbles coming of the plates; during charging; and the battery sides should only feel warm (around body temperature).
      Albridge

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      • #4
        Originally posted by albridge View Post
        You do not have to disconnect anything.
        Whilst this may be true for older vehicles-on modern cars it is considered good practice to avoid 'spiking' the electronic control units and a lot of manufacturers specify this.

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        • #5


          As my freind has just found out and blew his ECM

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          • #6
            You do not have to disconnect anything.

            I am afraid this is just not true and in fact, is a garage fabrication used when they do not know why the ECU is not working. There are millions of auto and marine installation all over the world, but particularly in USA, Canada, Norway and Sweden, where battery installations in cars, boats and light aircraft are floated across a standard proprietary battery charger. They have been doing this every winter since the first auto and marine engines became available. Most cars have a socket around the front bumper area, as soon as you get home you plug into your existing wiring that runs back into a battery charger, and your charger is floated across your car battery.
            To suggest to this person (who is telling you in his request that he is without any electrical knowledge) that he should disturb the battery terminals, is certainly not best practice. There are basic skills that must be used in handling batteries, lack of these skills has over the years caused many injuries (some very serious). All garage mechanics are aware of these, however a rookie owner driver is not.
            Modern electronics is digital and is far more robust that the electronics that appeared in the 70’s and 80’s generation of vehicles. Basically because the circuitry does not rely heavily on inductance and capacitance to process data. The digital subsystem relies more on data switching. When the old analogue circuits were connected and disconnected, at the battery, sparks could be seen. These sparks did the damage, as they are proportional to the rate the circuit is switch on or off . In other words someone with a shaky-hand disconnecting a battery could as the terminals parted cause sparking, as the circuit was made – broken –made- broken, many times in a fraction of a second, inducing through the inductive circuits voltages as high as 90 volts. Which was more than enough to see off the older generation of electronics.
            This is no longer the case.
            Connect you battery charger across your battery without disconnecting anything. Once you have the leads securely in place switch on the charger.

            Albridge
            Last edited by albridge; 07-11-07, 13:02.

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            • #7
              In my days in the workshop I have seen ecu's and climate contol computers blown by putting booster packs and chargers on while the battery is still connected to the vehicle.

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              • #8
                Auto-elect damage caused by poor garage equipment?

                Perhaps you should have tested your booster/charger packs, these are often the cause of damage to electronics, that the motorist is charged for. Yes, some times many hundreds of pounds, Just ask yourself - when were they last tested for spurious emissions? Over 90% of ECU/EMU's returned for repair, are not faulty. Garages often misdiagnose, and the poor motorist pays the price.

                At the first sign of ECU trouble - get yourself a can of "switch cleaner" (on no account WD40) available from Maplins or RS components. With everything switched off, disconnect ECU connectors and spray the contacts in both sides of the connectors. Repeat for all the sensor connectors - especially those mounted low down in the engine bay (speed sensor, when on crankshaft nose), these often have a hard life with road moisture. Connectors design for the old analog systems are just not suitable for digital systems (where switching voltages are often less than 0.5 volts). Being slow to recognize these problems, caused Mercedes to drop from being in the top three ranking cars for reliability, to being in the bottom three (from which they have now recovered). If you buy the bulk of your fuel from the supermarkets, regularly use injector cleaner. If the fault is still apparent find a person/garage that specializes in auto-electronics.
                There is a real and serious shortage of trustworthy garages, and I do not mean that purely financially, I mean garages that can diagnostic faulty digital equipment correctly and can give a true, honest and cost effective service to their customers.
                Last edited by albridge; 08-11-07, 12:59.

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                • #9
                  Sorry, wrongly edited.
                  Last edited by Rolebama; 08-11-07, 16:57.

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                  • #10
                    I have seen BMWs, Citroens, Rovers, Vauxhalls, Fords, Volvos etc suffer damage to ECUs and alternators damaged through having battery chargers used whilst battery still connected. On some vehicles, having been 'jump started' and then revving the engine will cause spikes and damage onboard electronics. Although older BMWs seem more prone to this.
                    Albridge wrote: Modern electronics is digital and is far more robust that the electronics that appeared in the 70’s and 80’s generation of vehicles.
                    In response to: a 1984 VW polo
                    Albridge then wrote: You do not have to disconnect anything.

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                    • #11
                      Originally posted by albridge View Post
                      There is a real and serious shortage of trustworthy garages, and I do not mean that purely financially, I mean garages that can diagnose faulty digital equipment correctly and can give a true, honest and cost effective service to their customers.
                      I agree, The problem is people take cars to mechanics and while they might be a dab hand with a spanner they know very little about electronic control systems and effectively fault finding them.
                      Its dreadful that people end up either paying for parts being changed that was not needed or paying hours of labour charges because the person does not really understand what the readings on the multimeter or 'scope are telling them.

                      I worked for a garage years ago that charged a whole days labour for a simple short circuit because the 2 technicians who worked on the car didn't understand what they were doing, they had even re-programmed the ECU 3 times. It took me less than 10 minutes to get the car started.

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                      • #12
                        I could not agree more with you. Working in the manufacturing side of the auto component industry we analysed all component returns, categorising what the faults were, in order to sort out any problems we were designing into the equipment. The numbers I have quoted in my mail to this forum were not guessed, they were quite factual, and speak volumes for the competency of garages in the auto electronic field.
                        The claptrap that mechanics give out as Bible, is endless and at times worrying. The problems are not limited purely to electronics either. When a friend of mine had a misfire in his V12 Jaguar, a garage charged him £1650 (ten years ago) to fit 12 new injectors, which made no difference what so ever. They then stated that this had to be done first, to eliminate the possibility that the injectors were the problem. Gross incompetence verging into criminal intent. Garages should be licensed to do only the tasks that they carry the proper tested and calibration equipment for, and have trained and certified mechanics for.
                        Albridge

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                        • #13
                          I have found garages where ALL the staff do not know how to use their basic diagnostic tools, including basic engine tuners and multimeters. I have also seen them use the wrong cartridges when using diagnostic equipment. As to a NOID lamp, they haven't even heard of them.

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                          • #14
                            Charging battery on car?

                            Hi, I have a merc CLK430 year 2000 and was wondering do you think it might be safe to top up battery charge with the battery still connected to the car, on previously owned cars I would remove the cars wrg to the battery terminals, however on this car I do not wish to disconnect the batt as I have no codes for the radio/sat nav system plus I would have to re-calibrate sunroof, seats, and windows positions according to the manual
                            Thanks, Graham

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                            • #15
                              Originally posted by morss View Post
                              Hi, I have a merc CLK430 year 2000 and was wondering do you think it might be safe to top up battery charge with the battery still connected to the car, on previously owned cars I would remove the cars wrg to the battery terminals, however on this car I do not wish to disconnect the batt as I have no codes for the radio/sat nav system plus I would have to re-calibrate sunroof, seats, and windows positions according to the manual
                              Thanks, Graham
                              Mercedes sell a charger which can be left on if the car is left for long periods without disconnecting the battery.

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