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charging a lead acid battery bank with a 19v laptop charger

Dec 5, 2017 10:21PM PST

I am new to the forum and for my topic I feel some anxious because I can't

I find that a post in internet it as a question there about Lead Acid Battery charging from laptop psu so here goes the copy paste with an added video link I just uploaded:

I am new to lead acid charging and have been using a 19v 5A vaio laptop charger to directly charge the batteries, 2x used 12v 75Ah in parallel (=12v 150Ah) for a few months which in turn power some low watt led lights and a 12v table fan when main grid load-shedding occurs in this part of the world. I've noticed that the batteries can initially draw around 8amps from the 19v 5A psu without overheating the psu. The batteries no longer boil as they used to when charged four in series with the huge 48v controller which was required to overnight recharge an electric autorickshaw (their first hand use) and now remain cool whilst charging, I haven't needed to top up the water in over six months either despite the driver having had to top them up 2-3 times a week previously.

I am wondering if it's OK or whether I need to reduce the voltage output from the psu to ensure longevity of the batteries since the charger is usually left on until I switch the connector between the two sets of batteries which i charge and use alternately as the lights from one set begin to dim after 2-3 days. Any suggestions and links to diagrams if voltage reduction is helpful would be appreciated.

BTW, I also charge another set of four in parallel with another 19v Toshiba laptop charger (trickle charges a few points of a volt every day), i've noticed that smaller laptop chargers (I've got a small pile of them sitting around) tend to immediately begin to heat up upon plugging in (possibly due to lack of intelligence or inability to regulate amp draw?) So there appears to be some sort of intelligent co-ordination between the branded high amp chargers and the batteries - just added that in case it helps in drawing a clearer picture of how things are.

Here's a video with the pulsating voltage multimeter readings:

Charging lead acid batteries with laptop psu

Update: I found this circuit for reducing the voltage, does anyone know if it is efficient enough to charge my larger batteries through? Or maybe if I added a few more LM317 's in parallel in order to increase the load bearing capacity (datasheet shows max 1.5A each) - and would the transistor cope despite this? Any other workarounds?

Thanks all guys that are interested in laptop!

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I'm going to shortchange you.
Dec 6, 2017 8:44AM PST

Lead acid batteries, charging, care and such has papers galore on the web. I will shortchange you compared to what wealth there is for the taking today.

My view is the batteries are expensive and not worth hacking this found power supply. Over the last year I bought a few chargers and they cost less than the battery so my advice is go get a proper charger.

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Let's say I wanted to use that power source anyway.
Dec 6, 2017 8:58AM PST
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Dec 6, 2017 9:13AM PST

When you charge 4 batteries in series, the power for all four batteries goes through the first battery, so it would be the first to fail. If charged in series, then the voltage should be about 12-15V as ideal situation. I suspect the first and possibly second battery are the ones "boiling" and the last one at least probably doesn't. It would be the first 2-3 batteries that would suffer the most from evaporation.

If you charge them in parallel, then you can use higher voltage & amperage since each battery will "draw" or take the amount it needs due to equal access to become fully charged, so can use 48V (4x12V=48V), since all 4 batteries have equal access to the charging current supplied.

Series charging of multiple batteries should never be greater than you'd use to charge it alone.

Parallel charging can be as great as the multiple of batteries that need charging.

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You can use the 48V charger
Dec 6, 2017 9:19AM PST

on a 4 battery set so long as they are all hooked in parallel. That means a cable across all 4 positive terminals and another cable across all 4 negative terminals. That's the way it's done in RV's (recreational vehicles, campers) here in the USA.

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