Converting a PC Power Supply to a SLA Battery Charger

I modified a PC power supply to a charger for 6V sealed lead acid battery. It can also be used for powering a 6V halogen spot light. 

To charge a 6V sealed lead acid battery, a constant voltage of 7.3V is required. I looked into some details of the PC power supplies. In one of the PC power supplies I found that there is a resistor connected between the 5V output and a small transistor. I concluded that it was the feedback resistor that could change the output voltage. See the following steps for hacking the power supply.

1. Remove the feedback resistor from the PCB and measured its resistance.
2. Replace it with a variable resistor. Set the variable resistor to the same resistance and turn on the power supply.
3. Make sure that around 5V output is there. Then slowly adjust the variable resistor until it reaches the voltage you want (7.3V for my case). Never set it higher than 10V because some capacitors used in PC power supplies are rated 10V only. Setting the voltage higher than their voltage rating would cause an explosion.
4. Turn off the power supply.
5. Remove the variable resistor and check its resistance.
6. Find a resistor (or a combination of resistors) that has resistance close to it. Solder that resistor(s) in place.
7. Turn on the power supply and verify output voltage.
8. Find a case for it (I used a lunch box).

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End of the project

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