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Battery charger hacking

Dacflyer

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Joined
Jun 5, 2020
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349
I have acquired 2 Lestermatic 12V 25A chargers, they supposedly turn off when the batteries are full.
I am wanting to use these to charge my SLA batteries, but these chargers were designed for FLA use..
Has anyone hacked such chargers so that they'll cut off at a lower voltage so that they'll be fine for SLA charging?
 
Would a diode drop do the trick?
 
Post a link to your specific model charger, a glance at Lester's site shows several models can be adjusted for AGM etc.
 
These chargers are not supported on the Lester site any more.. they are obsolete.
The relay board in them has no adjustments. I'm sure a resistor could be changed, but without a schematic, i have no idea which item to change.
 
That might be an idea,, but the charger would never reach a cutoff point, and i'd like the charger to cut off when the batteries are full.
With 0.7V diode drop, 14.7V cutoff point should be reached with battery at 14.0V
Problem would be, battery can't really drive a mA or uA to charge controller for it to see voltage didn't drop to zero, or even to recognize battery when first connected.
Possibly parallel a Schottky diode oriented other way for 0.4V drop, or a megohm resistor.
 
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