This Instructable started to solve a problem i had. I needed to charge a 9 amp hour SLA battery but i only had a standard car battery charger. The car battery charger was way too high of amperage to properly charge my SLA battery.
I started to dig around in my parts boxes to see if there was something i could piece together to make a low amperage battery charger.
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Step 1: Charge Controller and Wall Wart for Power.
Digging through my extra parts i found a 3 amp solar charge controller.
3 Amp 36 Watt @ 12v maximum input.
Has overcharge protection. This feature allows the controller to shut off the power going to the battery when it hits a specific voltage. This controller cuts off at 14.4 volts which is the maximum charging voltage for the SLA battery.
The undercharge protection feature is not really needed if you plan to use it as a battery charger. This allows you to draw up to 3 amps of power from the controller (the Load port on the controller). If you discharge the battery to a specific level (this controller 11.1v) the controller shuts the power off to that port.
I will use a 14.4 volt 1 amp (14 watt) wall wart power supply for power. The wall wart is low enough amperage that it will not fry the controller or hurt the battery.
Step 2: Connecting Battery and Power
The controller has 6 ports for wires. 2 wires for solar panel input, 2 for the battery, and 2 for devices.
The battery is connected to the controller and a small light is installed into the devices port. The wall wart power supply is connected to the Solar panel port on the controller.
The wall wart is providing voltage to the solar panel port just as a solar panel would. When the battery gets to maximum charge the controller will stop charging it.
Step 3: Ideas and Future Use
Since this charged my SLA battery quick and safely on wall power i want to make a dual charging rig.
Putting a power plug on my 15 watt solar panel that matches the plug on the wall wart will allow my charger to run on wall power where available and on solar power while out in the field just by switching the source at the power input socket.
In an extreme emergency it would also work on a much larger car battery. If i am camping and the headlights get left on in the car running down the battery. I could hook this setup up to the battery with a solar panel and possibly get enough charge in a day to start the car.
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