charge a 12 vdc sla ftom cars 12 v system ?

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hi, any one got any ideas on how to charge a 12 v sla from a cars 12 vdc
supply ?
i suppose a boost converter circuit to get the voltage up ?
all i need is to charge the 12 vdc sla for a torch. i want to leave it
pretty well connected up permanetly, so its always charged, ready to go ,.
any schematics , links etc....

thanks.
mark k



Re: charge a 12 vdc sla ftom cars 12 v system ?


On Mon, 1 Feb 2010 10:15:33 +0930, "mark krawczuk"

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For starters to *properly* manage the charging of SLA/VRLA's you need
something like the old Silicon Chip kit (Altronics K1685).  They use
the Unitrode/TI UC3906 controller chip, which has arguably the best
charging regime around.  Check out the AppNote by googling for
SLUA115.PDF.

The problem then resolves to providing enough regulating headroom for
the series pass element.  Either EA or SC published a design (which
was kitted, don't have the details to hand) to reputedly charge an SLA
from a  vehicle supply.

If at all possible, cut your losses and convert the torch to 6 volt
operation, then you just need the standalone K1685 charger.  I've been
running a couple of Dolphins for about 14 years using that design with
6V4Ah SLA's, and it DOES look after the batteries.  I've only had to
replace ONE in that time.

PS if you do go to 6V, the transistor will require a bit of a
heatsink.

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