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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#41
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Car battery charger
On 23/07/2020 13:26, Paul wrote:
Martin Brown wrote: On 22/07/2020 22:57, Theo wrote: jon wrote: I used an old 19v x 4A laptop power supply with a couple of 55W headlight bulbs in series to charge my flat battery. It started at 2.5 amps and dropped to 1.8 amps over a couple of days, giving a full charge. That's a handy idea.Â* I have some 12V 20A PSUs, and a headlight bulb in series would limit the initial current to 4.5A which would be sensible. That would be enough to get it off the floor, and then a regular charger can take over.Â* It wouldn't be the fastest but it would be good enough to begin with. 12v is nowhere near enough to make the lead acid battery charge. A lead acid charger needs to source at least 14v (usually about 17v no load). Putting the headlamp in series with your existing dumb charger will probably solve the problem by stopping it overheating. You might actually need to find a 6v 20W filament bulb to match the voltage drop. He's bringing it off the floor though. If the battery has been discharged to below half its nominal terminal voltage for extended periods it is probably scrap metal anyway. Not doing a complete charge cycle with this bodge charger. Just lifting the battery high enough, so a standard charger will accept the battery and finish the job. That will happen automatically as the battery terminal voltage rises and the filament bulb no longer has sufficient current to maintain a white hot filament its resistance will decrease allowing more current. -- Regards, Martin Brown |
#42
Posted to uk.d-i-y
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Car battery charger
In article ,
Martin Brown wrote: If the battery has been discharged to below half its nominal terminal voltage for extended periods it is probably scrap metal anyway. Yes. The essence it to recharge a 'flat' lead acid as soon as possible. And of course before it gets too low. Given the high price of a new one, and how long they can last when looked after, makes sense to treat them kindly. -- *Velcro - what a rip off!* Dave Plowman London SW To e-mail, change noise into sound. |
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