"high"ER voltage PC powersupply?

[gulio]

I don't post much here because I am electric challenged. Decent with math and formulas and good with diy though.

Here's what I wanted to do after using a number of pc power supplies to power chargers and always coming up short on the 12 rail. I want to get 14-15 volts out of a few of them.

Is it possible to hook the 3.3 in series with the 12?
Is it possible to hook 3 powersupplies together for 5 + 5 + 5 = 15 volts?

The 5 volts seems to always be the one with the high power. All the ones I've done do not have a voltage adjustment and seem to require a very high load on the 5 volt side in order to get close to 12 volts on the 12 volt rail.

thanks for help.

[Dan Baldwin]

All of the voltages on a normal PC power supply share the same common, so it would not be possible to add the 3.3 volt supply to the 12 volt supply, although it would be possible to connect from the -12 volts to the 3.3 volts for 15.3 volts. The problem with that is that the -12 volt supply is normally not rated for much current.

If the supply common on all three power supplies are not connected to the earth ground on the 110 volt power cord, you might be able to connect the 5 volt supplies of 3 power supplies in series for 15 volts.

Dan

[jeffs555]

The common on most PC power supplies is usually connected internally to the chassis and to the green wire ground on the power cord, so you usually can't connect multiple supplies in series. It is possible to modify the supplies to cut this ground connection. Usually this connection is made by the screws that mount the circuit board to the chassis, and cutting the traces from the pads around the screws will isolate the grounds. I had a link to a good step by step article with plenty of pictures, but can't find it now.

PS found the link http://www.procooling.com/index.php?func=articles&disp=52&pg=1

[Afroman]

How much current do you need to draw?
Dan's suggestion of using the 3.3V and -12V rails is good, but the -12V rail exists solely for the purpose of powering an rs232 port so sinking more than 0.5A may not be guaranteed.

[gulio]

I wanted to pull at least 10 amps (at over 14 volts) My computer guy says these are AT power supplies and they are all 200-250 watts with the 12 volt being rated at 9-10 amps and the 5 volt being rated at 27 amps.

Usually I can pull the 10 amps like I want to, but the voltage really falls off to around 10.5

[Rodney]

I salvaged some scrapped UPS's and found all had 115 VAC primarys and 17.5 VAC secondarys. Depending on the size, I think all of these are quite capable of putting out 10 amperes on the secondary. These even had the full wave rectifiers still good so made it easy to create a power supply providing over 15 volts DC.

[gulio]

Is there a site or tutorial that will show me how to do that? Can my AT power supply do that? I just junked about 4 of them,,,

[vintage1]

Give up and buy a fat ex CB battery eliminator PSU on ebay.

Less than the cost of a decent LIPO pack...

..and if you are electronically challeneged, its something else not to have to worry about.