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Charging a 12v SLAB

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raynerd:
I have recently got my foundation licence for amateur radio and I want to go portable. I tried lugging a 12v car battery around with me but even between two of us, my dad and I struggled to carry it and gave up half way up the hill to set up camp before getting to the peak. I`ve kindly been given two SLAB - sealed lead acid batteries from work that are apparently ideal for portable use. They are these:
http://www.prolite-lamps.com/products/batteries/lead_acid/pdfs/NP7-12DataSheet.pdf

They are 12v/7Ah, will a standard car charger do the job of recharging? I don`t want to fry them so I was hoping someone might know the best way to charge them.

Chris

andyf:
Hi Chris,
You could certainly charge them using a car battery charger, but the problem with sealed batteries is knowing when to stop. Old-style car batteries had a removeable cap on each cell, so you could see the electrolyte and stop when it was gassing freely.

Unless you are sure that your charger can sense when the job is done and switch itself to a trickle charge, it might be better to get one like Maplins stock number JC87U, though they are currently out of stock, and cheaper versions are doubtless available. Or you could roll your own: http://www.myra-simon.com/bike/charger.html

Edit - that circuit is for a trickle only charger, rather than a full charge which switches to a trickle when the job is done, but the author says it will charge his battery up overnight.

Another option which occurs to me is that it might be worth investigating the chargers for 12v battery-powered golf-club carts and lawnmowers. They may have the trickle facility.

 :scratch: I don't know if keeping the batteries in the car connected to the cigar lighter socket so that they charge up as you drive around would work. 

Andy

HS93:
a lot of the model boat people just put a 12 car dashboar light bulb ( the type in older car instruments ) in line when charging with a car charger, dont use the chrger on BOOST. just solder a pair of wires on the bulb so it can go in series, you will see the buldlight densety chang over the charge time. ill take a picture of the type I mean and get the watage.
that type of battery can be obtained cheap from alarm companys second hand for free, as the have to change them by date not condithion and you will get a year or two out of them.

Peter

has there been a post removed ???

John Rudd:
I use sla batteries in my flight box for powering my starter and glo panel and have the following advice to offer.........


Sealed lead acid batteries require a constant current constant voltage (CC/CV) charging regime to prevent damaging the cells.

Generally speaking charge termination occurs when the cells reach around the 2.2v value (a typical 12v sla battery terminates around 13.8v)..

You are best following the manufacturer's recommendations for charging. Do not use a standard car battery charger.............

Dont allow the battery voltage to fall below the minimum either(data sheets...) else the battery will not recover....

You could build your own charger that will suffice, built from readily available components....

here's one I built that works very well.. http://shdesigns.org/gcellchg.html

HS93:
""Sealed lead acid batteries require a constant current constant voltage (CC/CV) charging regime to prevent damaging the cells.""

yes I know, that is what the bulb is for to keep the voltage constant, the charger itself keeps the curent constant

AS I SAID BOAT model boaters have been using this methoud in our are for years, with no problems..

Peter

G0PAH

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