just posted this for the information of anyone who wants to use a computer SMPS as a 12 volt power supply.
You can find ATX Power Supply Pinouts at this url : http://www.smpspowersupply.com/connectors-pinouts.html

Note that for using the supply you must connect pin14(/PS_ON -Green Wire) to pin13(GND -Black wire).
Pnly if the green and black wires are connected do you get any output from the other pins.

Avijit

Nice thing you brought up this Avijit. I recently bought a 12V/5A mini SMPS for my electronic workbench. the only reason was size. These Computer SMPS are much better choice and one can easily find these for Rs 200 in scrap yards, salvaged from old Pentium computers!! The best thing - they have a huge cooling can, apt for using with Lipo Balance chargers.

Just one advice, its better to install Fuse Holder on the SMPS case and connect the output thru them. They are fine when connected to Motherboards and lids shut. With Field/Workbench use there's good chances of short circuits.

Strangely, I find the 15/15.5V laptop power supplies a better choice. They can also be used to charge the flight box battery which a 12V supply cannot do. Also more compact and quieter.

Laptop Adapter is best option if one take my opinion, as it is compact, quiet and light weight. One can use a small Car inverter on these adapter very effectively. those inverters are  easily available in market at a cost of 1000 to 1500 for a 50 to 70W inverter. Just plug the inverter to your car cigarette lighter adapter and take 110- 220 volt out put to run the laptop adapter.

Yes Laptop/Adpter liek SMPS are more compact, but they barely come with > 5A rating. Those which come (Laptop OEM Adapters) are much much costly ( > 2K) . I bought a 12V/5A SMPS for Rs 400 from SP road Bangalore.

Avijit's idea is good for High Capacity Chargers, as Computer SMPS can easily duty 10 Amp and are cheap when sourced from scrap.

Unless you are charging a > 3S lipo, a good 12V 40Ah car battery should be good for directly feeding the charger. 12V -> 120V -> 15v would result in loss and low capacity charging, due to DC to AC to DC conversion and lower wattage rating of your DC-AC converter (150Wats peak )

QuoteYes Laptop/Adpter liek SMPS are more compact, but they barely come with > 5A rating. Those which come (Laptop OEM Adapters) are much much costly ( > 2K)

Not so in Mumbai. I have bought several of these for myself and friends at an average price of 875/=. This is for NEW units with a limited warranty.

Quote from: ujjwaana on November 20, 2009, 01:36:54 PM

Avijit's idea is good for High Capacity Chargers, as Computer SMPS can easily duty 10 Amp and are cheap when sourced from scrap.

Scrap is a good source  but even a new one just costs Rs 450/-  and I use the same SMPS to power  both my charges ( 10 amp 200 watts + 2 amp ) at the same time , so multiple chargers with 1 power source is an added advantage .

Sai

i also plan to use it as a power supply to heat up the foam cutting wire.
Plan to use the 5 and 3.3 volt outputs also to heat shorter bits of wire.

All the wires of the same colour come from the same point inside the SMPS circuit board. So 3-4 strands of yellow or black wire can be twisted to get a hogher current rating.

The car inverter thing is very useful. you can use your regular wall chargers on the field.

Avijit

Avjit

You will need some method of varying the output (best done at the input) as the amount of current required to heat the wire to the correct temperature varies with the type and length of wire.

there are also car "inverters" available which use the power in the car 12v dc socket to generate upto 1kva power which can be used to charge the batteries  on the go

while flying if the power is finished we can charge it then and there

will post links soon

Quote from: sushil_anand on November 20, 2009, 04:05:30 PM
Avjit

You will need some method of varying the output (best done at the input) as the amount of current required to heat the wire to the correct temperature varies with the type and length of wire.

i agree which is why i posted it here for ideas. I have been told by people who know that reducing the input in a smps will not alter the output. The clever design ensures that the output is fixed over a wide range of input voltages.
But the other thought i had was just to use a step down transformer and a fan electronic regulator for heating the thermocole wire. IT DOESN'T MATTER IF ONE USES AC OR DC power to heat a nichrome wire and neither is the voltage critical. The wire should be hot enough but not too hot.
so ideas are welcome.
Avijit