Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

CHEAP Power Supply

H

Hook948

Guest
Got a old computer laying around? Yank out the power supply and with a simple mod, you have a cheap 12.5-13.5 volt power supply. There are lots of wires coming out of the PS when you take it out of the computer. Snip off all wires at board except 6 black, 2 red & 4 yellow wires. Solder the 4 yellow wires together for a 12.5-13.5v HOT lead, Solder 4 black wires together for the GROUND, Next solder the other two black wires together for a 5v GROUND, Solder the two red wires together for a 5v HOT, solder the 5 volt hot and ground to a 3 ohm 20W resistor or (2 10W wired parralel) and mount the resistor/s to the vent in the P/S case so it will "sink" some of the heat and be in-line with the air flow from the blower. This will put about a 1 amp load on the 5 volt section and allow the regulator to work. If the power supply you have has a pot to adjust output, you can turn it up to 13.5v MAXIMUM out put (any more and you will stress the traces on the board) this will also increase the 5v a little but not much. If yours dosen't have a adjustment you can change the output by changing resistor values in the circut but you are on your own as to what will work as there is no "set" standard as how the manufacturer designs the circut. A 400W PC power supply will make a 20 amp continuous switching power supply. IF you pick up RF noise from the supply you can wrap the yellow hot lead about 15 turns through a torid and this should solve the problem.<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/wink.gif ALT=";)"> Use your prefference on a power switch and terminals. I used the switch from the old computer, a couple of 1/4" X 1 1/4" long bolts and drilled out a set of knobs from a old car sterio for insulators.NOTE If using bolts for the terminals, file off the shinny coating on top of the head before soldering the wires to the bolts. Total cost...$1.89(I had to buy the resistor). Add some rubber feet to the bottom if you want. Not bad for a small power supply <img src=http://www.ezboard.com/intl/aenglish/images/emoticons/happy.gif ALT=":D">


</p>
 

Got a old computer laying around? Yank out the power supply and with a simple mod, you have a cheap 12.5-13.5 volt power supply. There are lots of wires coming out of the PS when you take it out of the computer. Snip off all wires at board except 6 black, 2 red & 4 yellow wires. Solder the 4 yellow wires together for a 12.5-13.5v HOT lead, Solder 4 black wires together for the GROUND, Next solder the other two black wires together for a 5v GROUND, Solder the two red wires together for a 5v HOT, solder the 5 volt hot and ground to a 3 ohm 20W resistor or (2 10W wired parralel) and mount the resistor/s to the vent in the P/S case so it will "sink" some of the heat and be in-line with the air flow from the blower. This will put about a 1 amp load on the 5 volt section and allow the regulator to work. If the power supply you have has a pot to adjust output, you can turn it up to 13.5v MAXIMUM out put (any more and you will stress the traces on the board) this will also increase the 5v a little but not much. If yours dosen't have a adjustment you can change the output by changing resistor values in the circut but you are on your own as to what will work as there is no "set" standard as how the manufacturer designs the circut. A 400W PC power supply will make a 20 amp continuous switching power supply. IF you pick up RF noise from the supply you can wrap the yellow hot lead about 15 turns through a torid and this should solve the problem.<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/wink.gif ALT=";)"> Use your prefference on a power switch and terminals. I used the switch from the old computer, a couple of 1/4" X 1 1/4" long bolts and drilled out a set of knobs from a old car sterio for insulators.NOTE If using bolts for the terminals, file off the shinny coating on top of the head before soldering the wires to the bolts. Total cost...$1.89(I had to buy the resistor). Add some rubber feet to the bottom if you want. Not bad for a small power supply <img src=http://www.ezboard.com/intl/aenglish/images/emoticons/happy.gif ALT=":D">


</p>
 
Just don't leave out that resistor. Sounds nutty, but it has to be there. Really.



73




M3D.jpg
</p>
 
Question

So if I have 3 400amp Power supplies and stacked them and wired them toghter how many amps would it be?
 
just curious but y the resistor on the 5V????

why not just tie the green and one of your grounds together to turn the unit "on" permanently
and then use the switch on the back for "standby"


scott
 
Computers universally use 'switch-mode' technology for their power supplies. The 5-Volt output is traditionally used as the reference for the other regulated voltages. The regulator circuit will only be stable with a minimum power drain on that output. Since there is ALWAYS current being drawn from the 5 Volts by the motherboard and hard drives, no such load need be installed when it's used in a computer. If you plan to use ONLY the 12-VOlt outputs, they may not regulate properly if the 5-Volt output is runing without any load current.

Since a computer always places a sighificant load on the 5-Volt output, there is no need to build one into the supply itself.

Newer "ATX" supplies that also supply 3.3 VOlts may be different. My experience on that kind of item only dates to the "AT"-type cabinets, before the separate 3.3-VOlt output became standard. Newer "ATX" supplies may or may not use the 3.3-Volt supply as the reference, and need to be treated the way the 5-Volt side was on older "AT"-type supplies.

If you ever looked inside a "North Star" base radio, they used a "AT"-style computer power supply inside. That radio had a 10-Watt (can't remember the resistance) resistor on the 5-Volt output, and powered the radio from the 12-Volt side.

The power supply's fan opening on the rear panel would prompt some folks to think it must be "mean" and have a linear in there. In fact, that radio would deliver a bit less than similar-looking base radios, since you could not turn up the radio's operating voltage, like you can in a Galaxy/RCI/General base radio with the older linear-regulated power supplies in them. No trimpot to crank up to 15 Volts.

73
 
kinda makes sense now.............

ive always used just the 12V leads and tied the single green and a ground together


ive never had any troubles like that but next time i set one up ill try it your way

scott
 
And it's always possible that my info is out of date. Newer "ATX" power supplies may very well be different. Never looked inside one of those.

And if they build that 'minimum' load into the supply, you don't need to provide it. Older supplies meant for "XT" and "AT"-style cabinets with a hard-wired power switch probably need that load resistor on the 5-Volts. That's how far out of date I am on that stuff.

73
 
Re: Question

NCBamBam said:
So if I have 3 400amp Power supplies and stacked them and wired them toghter how many amps would it be?
Click to expand...

Do you mean 400 amp or 400 watt? If you did mean 400 amp, wiring them in series would still only draw 400 amps, but at 3 times the voltage. Wired in parallel would draw 1200 amps at the rated voltage of a single supply.

If you meant 400 watt, you would need to run some calculations using Ohm's Law to be able to answer that question.
 
I know this is old, but new here so I'll ppost anyway. A 400 amp PC power supply would be the size of a bedroom, he ment watt. I love Mr. Ohm, he gave me a great way to do mental gym on just about anything. So, 400 watt from a 110 circuit. Really 120, multiplied by 3. Well 400 devided by 120 is 3.1 amps, that was easy enough. 3x3.1= 9.3 amps. Lets get rid of the .3 for losses and say 9 Amps (probably a little less.) So we have a 9 amp regulated, switching power supply. Also, why put a resistor in the 5V circuit? I'm sure we can find something else to do with it. Maybe panel lights or to run an LCD or whatever, it just seems a waste to let it burn for nothing.

I am good with computers, but new to radio tech, what can we do with a regulated, 9Amp, switching power supply for about 5 bucks?

Ron
 
...or probably get rid of all those 'wall-warts' and just use the $5 supply.
- 'Doc

Make mine with cheese and 'Arby' sauce
 

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back