I recently put together a smart charger to replace the dumb charger that I built using an LM317 Voltage Regulator. I wanted something that could fast charge a battery at C/2 or higher. The batteries that this charger is configured for are 12V 4.5AH SLA batteries. However, the modifications necessary to charge any SLA battery are easy to make by just changing a few of the resistor values and potentially adding wider tracks on the high current bus. It bulk charges at a current limit of 2.5 Amps until the voltage across the terminals gets to about 14.7 volts. Then it continues charging by regulating the charge voltage at 14.7 volts until the current drops to .25 amps. From there it switches to a float charge of 13.5 volts to offset the batteries self discharge rate. Because this was the first circuit that actually required me to design and etch my own pcb as well as calculate out some of the part values and select suitable parts, I started out with a schematic that was 99% of what I needed. The app note that I used is here:
http://focus.ti.com/lit/ug/sluu023b/sluu023b.pdf
The attached files include pdf's of the schematic and pcb layouts as well as the ExpressPCB and ExpressSCH files. I have also included a BOM with all of the appropriate Mouser part numbers.
Please note: I am not an Engineer! I am just an inexperienced hobbiest and tinkerer. I am not responsible for any adverse consequences that may arise if you try to build this circuit. As you probably know, improper charging of a battery can cause horrific outcomes, especially if your goal is to fast charge them.
http://focus.ti.com/lit/ug/sluu023b/sluu023b.pdf
The attached files include pdf's of the schematic and pcb layouts as well as the ExpressPCB and ExpressSCH files. I have also included a BOM with all of the appropriate Mouser part numbers.
Please note: I am not an Engineer! I am just an inexperienced hobbiest and tinkerer. I am not responsible for any adverse consequences that may arise if you try to build this circuit. As you probably know, improper charging of a battery can cause horrific outcomes, especially if your goal is to fast charge them.
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