I was thinking of, how to charge batteries of Alfred. Suddenly I have realized that my old and probably dead computers psu can help me. If you think it supplies constant 12 volt for long long time. Maybe i can tune it make it work for Alfred for some time also. These batteries have 6 cells, each are 2.2 volt meaning fully charged battery will be around 13.2 volt. So I may need to modify the power supply a bit.
Here is the little trick for you. If you look closer there is a green cable, in the bunch of power supply socket that is connected to mainboard of the pc. If you short circuit that green cable with any of the black ones(ground) your power supply will start to operate. Be careful! There is still 220v somewhere inside that power supply. As you can see, I used a grey cable to short circuit green cable the 4th one and the black cable 5th one.
When I managed to start the PSU, I have found out that I can only get 12.16 volt from the power supply unit which is a problem. If I think to charge the batteries with this PSU I should get more than 13.2 volt. Then the challenge has started and I decided to open the PSU 🙂
I was lucky the chipset inside the PSU was AZ7500BP-E1 which is open to modification. If you put a resistor pin 1 and 7(IN1 and Ground) you could get higher voltage. I have tried several values but could not reach to 13.6 volt. Luckily I have found Thanh Long in the internet and he had a similar video at Youtube. I have contacted him and advised to use 33K. resistor. So I soldered 33K resistor between 1 and 7.
I also realized that there are lots of cables coming out of the power supply which I really do not need. I only need 2 yellow cable and 2 black cable. Maybe 2 more black cable can help me as a spare in the future. Here are the color codes and their values:
yellow: 12.16 volt
purple: 5.17 volt
red: 5.24 volt
gray: 5.22 volt
orange 3.23 volt
Clearly it is not one of the best PSU in the world but can handle my issues. At least it says 12 volt 20 Amps output 🙂 (Note to myself the batteries needs to be charged much slower. Get a big resistor to slow down the charging.)
yellow: 13.67 volt – voilà
purple: 5.20 volt – maybe for powering raspberry pi 3 in the future
red: 5.86 volt – I don’t care
gray: 5.84 volt – I don’t care
orange 3.38 volt – I don’t care
and dark blue – 12.99 volt, which is important in case I sue 24 volt engines in the future.
I have checked the 3 batteries. They are 1.3 AH each so I have a total of 3.9 AH capacity.Specs of the batteries say that they should be charged at 7 hours. Basically, V = I x R. We have 13.67 Volt in hand and a requirement of 3.9 AH / 7 hours = 0,56 Amps capacity. I have checked my storage and found a 22R resistor at 50W (This should handle my requirement!)
When you make the math 13.67 Volt gives out 0,62 Amps per hour. This is still a bit higher than what I need but I think this is the solution I am looking for. So I decided to use this resistor. Well done!
Last but not least, I need a charge controller to stop charging at 13.2 volt. I searched the house and found out an old charge controller that has been left unused from sisters house. I think it can sort out my issues.
I know, I know, I am too lazy to draw an original one. I copied it from internet but so what? It works the same!
When we connect everything the out put is like in this video. Thanks for watching!