I am new to the forum and I notice that you have decent positive discussion and tips which also includes noobs on any given electrics related topic,
I was requested to post it as a new question here:
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?
http://renewablekinabalu.blogspot.com/2013/07/homemade-12v-sealed-lead-acid-battery.html?m=1
Best Answer
1 - Look, the first thing you need to do is get a cheap DMM. As it stands you have no idea what is actually going on in your batteries, and frankly I'm surprised at how durable lead-acids can be when subjected to the abuse that you are apparently putting them through. Once you have a meter, you can look up "lead-acid charging algorithm" online and learn how to do this right.
2 - Your 48-volt charger was an abortion. Never, ever, use a charger that boils the electrolyte. I suspect that the only reason the PSUs don't cause boiling is that they simply can't produce enough power, while the monster can. And does. Get rid of it, or learn enough electronics to figure out the charging circuit and modify it. You are causing long-term damage to the batteries if you use it.
3 - There is no "intelligent coordination" going on. All of your PSUs are in current limit, and the smaller ones simply don't handle it as well as the larger. The exact hows and whys depend on the circuit design and components/assembly techniques, but it's not a matter of coordination, intelligent or otherwise.