PC Power Supply Project!

guido

Well-known Member
Hello,

I would like to make a battery charger out of this power supply. So
far I have been able to make it turn on (green and black white tied
together did the trick).I also after trying a few resistors to load
it, it is now up to about 12.25 volts with a .3 Ohms resistor which it
gets too hot. I tried a small computer fan, and it was able to power
my Hobby charger. Have not tryed to charge higher then 12 Volt
batteries yet. So stay tuned....


Guido.
a238197.jpg

a238197.jpg
 
PC power supplies are switchers! That's why you can't get any voltage out of it without a load. And I don't think you'll be able to get enough voltage out to charge a 12 volt battery without making some changes to the voltage sense circuitry. If you can find where it senses the voltage, you can use a couple of resistors to create a voltage divider to make it think the output voltage is less than it really is.

I did a little research on this unit, and found where someone had taken one apart. From the pictures, it uses two different IC to control the voltage: A CM6800 PWM controller and a PS223 overvoltage protector. Datasheets for each are available online; you'll need to fool them both.
 
To properly charge a flooded lead acid battery that's around 12.6 volts settled, you're gonna need a charger that's producing at least near 13 up to 14+ volts under load plus have the capacity to pump current INTO the battery under those conditions. I don't have enough info to know if the unit you posted will do that or not. The older cheaper noisy buzzing heat producing RV Converter/Chargers were more like a 13.4 to 13.6 constant voltage energy sources which sure powered your 12 volt appliances and charged the battery but NOT to the extent and quality the modern so called "Smart" 3 or 4 stage chargers are capable of.

Good luck, let us know

John T
 
I have no idea what you guys are talking about, I would just go to the hardware store and buy a battery charger, but it sounds like some of you guys like to have fun with a challenge like that. Good luck with your project.
 
The "standard" charge voltage for a 12V lead acid battery is 13.8V. Lower will not get you a full charge and higher tends to boil the battery.

Cliff(VA)
former Automotive Electrical Engineer
 
My 3 Stage "Smart" charger, all computer controlled based on charge state, first apples a BULK charge at 14.2 to 14.4+ Volts,,,,,,,,,,,Then it slows down to the 13.6 Volt ABSORPTION stage, finally it settles in at a 13.2 Volt FLOAT. You're right if you maintain too high voltage once the battery is fully charged it outgasses excessive and can boil out electrolyte and even ruin a battery grrrrrrrrrrr

Love sparky chat

John T Retired Electrical Engineer
 
Hello Cliff(VA),

Actually automotive charging voltage is between 13.8 to 14.2 volts. But I neglected to state that I want to make a cordless tool charger. I'm thinking the 5volts leg ought to be adequate for the lithium single cell battery. It already has enough power for the hobby charger,

Guido.
 
Hello John T,

You have the right stuff! Most people have no clue that it takes more then a fast charge to archive 100% saturation. Fast charging is just that, not a 100% charged battery. I have seen 16volts on a maintenance charging mode, but @1/4 amp input all is well on a 12V battery- system. Still have one of those chargers with a built inverter with a single 120V ouitlet. Automatically switch the a/c on, on power outage.
May be I can dig it out and do a show and tell?

Guido.
 
Hello MarkB_MI,

I am much better on letting the smoke out then putting it in! I just wanted to use it for cordless tool charging, the twelve volt seams able to power my hobby charger. The charger is capable of charging 15cell 18v packs. The only leg the has to be loaded is the 5volt orange leg. All other have no effect on raising the twelve volt leg voltage. This power supply keeps shuttng down when I overload a leg or cross a wire. I have not been able to let the smoke out!

Guido.
 
Hello John T,

I have so far been able to load the 5volt legs and have enough power for my hobby charger. I will need some type of variable power resistor for the 5volt leg for charging LiIo 4.2v cells. I think I have one rate at 12 to 15 volts. I don't recall the wattage though. It should be at least two watts if I recall correctly. Need to dig it out I guess. More sparky talk coming.......

Guido.
 

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