Charge Controller - Another successfully charged battery!
I decided to make an iPhone charger for my truck. I guess I could have bought one, but this was more interesting.
I scavenged a USB port from an old PC. I destroyed the first one I tried to remove. The solder on computer motherboards does not easily melt. I found that a little butane torch will get the solder to melt, and then the solder sucker will remove the solder. This works well!
USB ports serve out 5 Volts. For the sake of simplicity, I used a 7805 regulator to provide the power. I added two capacitors and a diode for the regulator.
The USB ports have a +5 and a Ground pin. The case is also Grounded. I tested the real iPhone charger and found that the two USB data pins are set at 2.0 and 2.7 volts. I duplicated these values using 100k/140k and 100k/80k resistors.
It worked! But, it got really hot - about 140F. I added a heat sink and fan from an older computer CPU. I could not let this run all the time, so I added a roller-lever switch that activates when a USB cable is plugged in.
The prototype works. A future version will have a LM3524 switching power supply.