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old battery charger

Discussion in 'Car Repairs / Maintenance' started by norseman, 15 Dec 2020.

  1. norseman

    norseman

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    Hi folks, I'd be grateful for some advice on this subject.
    I've not needed to charge either battery on our two cars for years, but with current restrictions limiting the vehicle's use I've had to dig out my 40 year old 10A charger with both 12 & 6v high/low options. I've done tests with a multimeter & come up with the following figures.

    !2v High setting 15.2v
    12v Low setting 12.2v
    When I tried to get mA (current?) readings on my digital meter the screen remained at zero, but when the charger is switched OFF the reading becomes something like 27 & runs down to zero in less than a second.

    All readings are taken from the croc. clips with clean contacts. Is there any life left in the old girl?
    Thanks all, stay safe, Merry Christmas :)
     
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  3. Burnerman

    Burnerman

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    The voltage readings are about correct when connected to a battery but current readings need to be in series with the positive output wire. Most multimeters can’t handle more than a few amps - can yours?
    Is there no indication of the current output on the charger at all?
    John :)
     
  4. norseman

    norseman

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    Thanks for the prompt reply John. These readings are obtained when NOT connected to a battery, just on the bench.
    I'm not that familiar with multimeters & mine is a pocket model Hilka with a 500v / 200mA limit. Assuming I'm right to use the mA range to read current, with the charger ON (again not connected to a battery) the screen remains at 00.0. Turn the charger OFF & the initial reading of around 27 is only momentaritly visible before the readings run down to 00.0 again in less than a second, barely time to read the pixels.
    Should I repeat the test(s) when the charger is actually charging a battery ?
     
  5. Burnerman

    Burnerman

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    Always best to test these things with a load.....if you don’t have a battery handy, a 12v bulb will do - you’ll get more accurate readings this way.
    200mA is much too small a current range, I’m afraid - ideally up to 10A is best. Bizarre readings from the meter are common on overload, before it blows the internal fuse!
    For voltage readings, its across the two crocodile clips, for current measurements you connect one meter lead to the clip and the other to the load terminal.
    John :)
     
  6. norseman

    norseman

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    Many thanks for your education in multi-meters, at least an overload means there is a current of some sort? I'll try to borrow a more suitable unit.
    nb: will the 200mA of my meter be enough to carry out a parasitic drain test on the car ?
     
  7. Burnerman

    Burnerman

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    In most instances, a 200mA drain is within the requirements of a car security system, clocks etc so you should be able to measure any battery drain.
    John :)
     
  8. cdbe

    cdbe

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    I blew the fuse on my meter trying to measure a current. Why not stick the charger on overnight and compare before and after voltages (after battery has had half an hour to rest from charging). I think it's only 0.5 of a volt or so between flat and charged.
     
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  9. jj4091

    jj4091

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    I agree this is the best way, measure the battery volts before connecting the charger & again with the charger connected & on the high setting. You will know if the charger is failing under load or not if the volts drop down to the level of the battery only reading. A good battery should charge up to approx 13.5 volts, dropping to 12.6 an hour after disconnecting the charger.
     
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  11. Harry Bloomfield

    Harry Bloomfield

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    You are a little low with the 13.5v. 13.5v will not charge a lead acid battery, it will just about maintain the existing charge. I would suggest the on-charge voltage should be nearer 14.1 to 14.5v. However an old design of uncontrolled charger like this, can go much higher and can cause excessive gassing and wrecking a battery, unless carefully supervised. Gassing has a risk of causing a very damaging explosion, spraying battery acid around [1]. Which is why modern chargers are voltage controlled or even better Smart Chargers. Personally, I would never use such an old charger these days, I threw all my old chargers out years ago.

    After an hour off charge, a good fully charged battery should have a voltage of 12.5 to 12.9v.

    [1] I had one battery explode in my face in my teens - lesson learned.
     
  12. jj4091

    jj4091

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    The op says that the o/p from his charger was 15.1 volts. I was saying the battery should charge to approx. 13,5v but not much more. As you say when the battery is charging I would expect it to drop slightly, but if it drops below the voltage of the battery being charged then the charger is probably faulty.
     
  13. Harry Bloomfield

    Harry Bloomfield

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    Difficult to measure an accurate voltage, when the output from the charger is a very raw DC - likely it will be much higher voltage. Were I checking it, I would add a cap across the output to obtain a more sensible value of DC.

    Which would mean little if any charge being put in the battery.

    The OP's best way forward, if he must use that old charger, is to connect the charger to the battery and monitor the voltage very carefully, especially when it nears the gassing voltage. If the voltage gets to 14.5 I would suggest he then calls it fully charged and disconnects.
     
  14. jj4091

    jj4091

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    I don't really think the accuracy of the reading he is getting with the charger connected to a multimeter is that important, but it shows that it is operating to at least some extent so he then just needs to know if is breaking down under load (connected to the battery). I think it is fair to assume the battery is giving a reading of less than 11.5v if he feels it is flat, so if the reading he gets when charging is above that value then the charger is doing it's job, if it is below that value then it is not. If it is OK & he then wants to leave it to charge for any length of time I would suggest he switches to the lower setting 12.2v to trickle charge it. It will not charge above that voltage but will charge it enough to start his car.
    I don't understand what you mean when you say little if any charge being put in the battery. It should give an output of 12.6v under normal conditions & should maintain that voltage during usage within the limits of it's rating. But that is getting away from what I think was the op's question was, is the charger working?
     
  15. norseman

    norseman

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    Thank you John & all who were most helpful in the content of their replies.

    I shall ditch the old charger (with full military honours) & treat myself to a new one. The largest of my batteries is 90AH & I'd want it to charge up overnight (say around 15 hrs.) so a 10A charger?
    I assume a modern charger will adjust the charge rate according to the battery's requirements?
     
  16. Keithmac

    Keithmac

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    I bought one of these for home and one for work.

    You can't really beat an ammeter to see how a battery is charging imho.

    This has done 90ah+ batteries and motorcycle batteries.

    Whenever I charge a battery I keep an eye on it, never leave one inside the house charging overnight.

    20191025_162640.jpg
     
  17. frutbunn

    frutbunn

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    I just ditched my dads old charger, it should be on its way to China by now to make one of the new MG's. he bought it when he was 18 he's now 83! I wonder if the new one will last as well.
     
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