i have a smps power supply 24 v 3 amps can i modify this to charge my car battery 12 v 70 amph by connecting 2 similar value hi watt resistors across 24 v out put and tap the 12 v across one resistor to charge battery. if possible what value should be the resistors.
Two series resistors will waste a lot of power. If they have the same value then they make 12V with no load and make maybe only 9V or less with a load. But a 12V lead-acid battery is dead when it measures only 12V, it is fully charged at about 13.8V.
You need a supply that is about 15V at about 15A and a battery charger circuit that limits the current and limits the voltage, detects a full charge then turns off or switches to a trickle-charge.
The most efficient, and probably the cheapest, method is to use a buck converter. This one you can set for 13.8V output and set up at to 3A charging current.
car battery charger
Posted - Sep 05 2013 : 08:14:38 AM
