Putting those old ATX power-supplies to good use  :

I got myslef a PC ATX SMPS. This is how you can do the mod and use it to power up your Batt chargerrs. Copying verbatim from my original post in another forum
***start***
This is about how you can use an SMPS (PC ATX power supply module) to get 12 V upto 14 amps output. I was in need of a relaiable power supply for my Hyperion EoS 5i DP charger and the smps I had (12V 2Amp) became useless when I wanted to use it to charge LiPo's of capacity >2000mAh. So I got myself a PC ATX SMPS and it works great and can supply upto 12V 14Amps.

ATX-1 Shows the pinout of the 20 pin connector. The commonly available PC ATX SMPS has a 4 pin connector attached to the 20 pin connector. This is removable. Read the pin out based on the main 20 pin connector.

1) Short the pins 14(Green) and 13(Any ground: Black)

2) Use Pin 10 (Yellow: +12V DC) and Pin 3(Ground: Black) for 12V DC power supply.
***end***

For electronically inclined, you can change the feedback circuit to avoid the need for load at 5V that just wastes power. I had done this a few years back and I could get stable 12V at over 10A.

Also nowadays you can buy off the shelf SMPS similar to laptop adapters for a similar or little higher price. This gives a compact ready made solution for people who don't want to tinker. These are available upto 5A or so typically. Ready made SMPS with higher rating are also available, but tend to be much more expensive than PC supplies.

Just remembered that I also raised the voltage to nearly 14V to charge 8 cell NiMH packs.

I used the 12 VDC tap of a Computer SMPS as power source for my Duratrax AC/DC digital peack charger and B-6 charger for sometime to charge 7 cell and 8 cell Ni-Cd and Ni-mH battery packs. It worked okay for 7 cell battery packs but the PC SMPS could not provide enough Amps to peak charge 8+ cell Ni-mH/Ni-cd battery packs because the voltage from PC SMPS varied between 11-12 VDC. I tried several different units because I could get them for free from my local PC Hardware seller who solvaged them for me from the junked PCs available with him.I also used a brand new SMPS purchased for Rs.600/-.But the result is the same in every case. One could modify the PC SMPS to give 15VDC or 18VDC but you need some Electronics savvy and assembly skills and simply not worth the time and money spent to do it because SMPSs specifically designed for use with Battery Chargers are available off the shelf at a very nice price from RC Suppliers.Now I am using a 15VDC @ 5 Amps SMPS purchased from RC FORALL and it is working fine. Also I never tried the PC SMPS to charge Li-Po batterypacks.

Another good video to convert computer SMPS to 12 power supply for chargers.
http://www.youtube.com/watch?v=CT1tiQOz3LU&feature=player_embedded

pic 1: My setup of the SMPS supply. I have built a box which decodes all the wire to different voltages, and also adds a variable voltage resistor. I have been using this since long time but did not find time to post. you can connect any power supply just by plugging in the mother board adaptor and a spare IDE/sata adaptor to the box.

pic2 : using 2 of my chargers at once. Turnigy 200 watts charger rocks.

Looks great 

Can you post the circuit diagram for the same please.

I am in need of a 350 Watt supply at 20 volts + if possible... any suggestions

Hi Saurabh, as discussed on the phone last week, the voltage on the 12 V line is falling below 11 volts when I load it with 60+ watts. I have connected all the same voltage wires in parallel, except the sata connector, probably adding that also in parallel may help. I am not sure if one can connect all the same voltage (example 12 v) wires in parallel if there are different 12V rails.

Iam using a zebronics 450 watts SMPS. with 16 Amps on 12 V SINGLE RAIL version.

Note: All the gaming power supply has a huge marketing show off saying they have 12V1 and 12V2 rails, which are indeed very bad. For my gaming computer I picked up a 750 watts corsair with a single 12 V rail on 60 Amps Split rails are bad for health.  

Here are the links I have used. I havent incorporated the temperature controlled fan yet. Use a high guage wire and a bigger box then I used. Else it becomes a huge clutter inside and no much space left for fan, so the 5V resistor is hanging out  .

I used to following links for my knowledge. - Well all Ideas mixed UP to the max  

http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/step2/Planning/

http://www.marcee.org/Articles/PCPowerSupply.htm

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

http://www.wikihow.com/Add-Variable-Voltage-to-Your-ATX-Based-Bench-Power-Supply

http://www.eleccircuit.com/temperature-controlled-fan-12v-dc/

Thanks a lot Vinay... Will read them and see which one to use... 

I used the first link one as the circuit diagram.

Got the idea for pin diagram from the last part of link 2.

Used the link 3 to to get an idea of exposing all the voltages. Not just 5 or 12. but 3.3 -12 etc. and cable colour decoding.

I got a 12V DC - 5 Amp adaptor to use it for my lipo charger - GT Power.

Unfortunately its not working anymore. I checked with a meter and its dead.

Any ideas what went wrong ? It was brand new in btwn..

12 Volt Computer SMPSs are though written as 14 A or higher, but most of them of cheap SMPS use underrated rectifier diode using oversized heatsink.

I have seen that 3A Schottky rectifier diode 1N5822 used in 12 Volt rectification but used a metal tab soldered and screwed up with heatsink. Dont select that for higher Amp supply. They lost reliability beyond 6A (As used in center tap mode).

So, check the rectifier diode so that it should at least MOSPEC 12C20. I Prefer to use MOSPEC 30C45 which have 30A current rating with 45 Volt+ PIV. you can also just replace existing rectifier and use this.

Moreover, in primary HV oscillating MOSFET/BJT check the good transistors are used (Like 13007 or 13009 at least). Generally this i have seen OK except a cheap SMPS uses 13005.

Again, if higher current required, please use proper wires too and if use parallel conductor like 3 yellow and three black for a single charger.

If your 12V SMPS outpur required less that 1Amps or 2.5 Amps, you can use low cost SMPS (LG make IC based for 1A and Samsung make Transistor based for 3A), readily available as power adapter.

Pics added with 12V 3A Transistorized SMPS also opened and ther MOSPEC 30C45. The cell size reference are 3xAA sized NiMH Battery Pack. 

Thanks

i simply usee my broadband modem power supply(BSNL modem)

Isnt the BSNL broad band supply AC? My mt882 modem Power supply is AC not DC.

Mine is surely not.
Mine is a 10VDC 550 mA,good for charging a 2S of low capacity.
I also sometimes use a SMPS

my modem is something called a UTSTAR UT300r2u