To repair and then convert ATX-300W PSU to a lead acid battery charger

[theslayer]

Hi guys,

Just joined in today.

I have a 300w ATX psu and having problem with it.It is operating but the regulation is poor .The voltage output from the +12 volt terminal is 11.2 at open and drops to 10.45 on a load which draws 1A.Similarly the +5volt and the +3.3 volt pins are a not stable too.

I have googled for repairing it.They said that their might be problem with TL431 chip but in my PSU this chip is not connected the regulation part.The pwm ic in it is ka7500.Downloaded Its datasheet but could not understand its totally.

I want to build a three-stage charger from it by modifying it .

Guys, please help me !! Having a lot of trouble here.

 

[4pyros]

1st off that PSU was made for the lower voltages, your 12 volt output current is probably pretty low, and its probably not worth fixing. What size batterys are you trying to charge? To make a three-stage charger you would have to redo the hole output so you may as well start from scratch. lead acid battery chargers are cheep. Buy one and then add the charge controller. Andy

 

[theslayer]

only one reply aren't there other member in this forum ??
can't any body help??

 

[Reloadron]

OK, a 300 watt ATX form factor PSU with the symptoms you are seeing would have me looking at the filter capacitors before worrying about anything else. Especially looking at the ESR of the caps. The problem with troubleshooting and repairing is I can buy a no brand name basic 400 watt or more ATX form factor PSU for about $29. That alone makes it less than practical to troubleshoot. However, if I was to troubleshoot I would start with the caps.

Next, when running correctly the 12.0 volts out on a PSU like this has a tolerance of +/- 0.6 volts. Matters not anyway as you will need to hack the regulator circuits to get the output voltage up around 13.6 volts (depending on type 12 volt battery you want to charge). So even if you get the thing working you have a way to go. Personally I don't see this as a practical project but not for me to say.

Just My Take
Ron

 

[MikeMl]

I dont either. By the time you fix the basic supply, modify it to put out 13 to 14.8V, add current limiting to protect the battery and charger, add a charging controller (microcontroller), what is left of the original supply? Cannibalize it; you might be able to salvage some parts; capacitors, rectifiers, diodes, etc...