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Old Oct 01, 2003, 02:39 PM
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nose_first's Avatar
Riverview, FL
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computer power supply help

I had posted this in another forum and it was suggested this would be the proper place for this discussion...


ok - after following the directions from a link given earlier, I decided to convert an old computer power supply to one I could use to charge my packs while at home.

i have not yet placed a small load on the +5 volt side to get the max. output from the 12v line but I am currently measuring 11.68 volts at the posts. the ps. fan is also running fine. I plug in the charger and it is acting like a short as the fan on the power supply just stops and the posts measure no voltage. so long as the only thing connected is my multimeter - current flows just fine. once it 'shorts out', i unplug the supply from the wall for a little bit, plug back in and everything works fine.

how it is hooked up:
PS_ON is connected to a common (black) line
Power_Good is connected to a +5volt red wire
the yellow +12volt wires are hooked to the positive (red) female banana
the black common line is connected to the negative (black) female banana

i have also removed the banana connectors from the case to see if they were shorting somewhere on the power supply case with the same result.

from the other discussion the points brought up were:
1) I should have a load on the 5v line in order to stop this
2) the charger should be plugged into the power supply before the power supply is turned on
here's a link to the other discussion - http://www.rcgroups.com/forums/showt...hreadid=155508
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Old Oct 01, 2003, 03:07 PM
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Take the advice given.... Put a load on the 5V supply. If you don't have an appropriate resistor handy, use 1 or 2 automotive type light bulbs (taillight). I'll wager that this will fix you right up.
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Old Oct 01, 2003, 05:15 PM
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Riverview, FL
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so which resitor would be appropriate?

or should i stick with the automotive taillight bulb?
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Last edited by nose_first; Oct 01, 2003 at 05:24 PM.
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Old Oct 01, 2003, 05:46 PM
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I will take another look at mine. I don't believe I used the power good. Mine is an ATX power supplly. I could not get a good enough increase using the "load" on the 5 volt side of the PS. I took the cover off and adjusted the output potentiometer with my DVM connected to the yellow circuit !VERY CAREFULLY! I reached my desired volt/amp output. Mine is working fine and is still not running at max output. I run a Triton charging 3 amps with a cooling tube pulling .3 amps and it works great.
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Old Oct 01, 2003, 06:42 PM
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Just keep in mind when you are poking around these that there is 300 volts DC there and the heatsinks on the primary side are LIVE!!!!!!
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Old Oct 01, 2003, 07:04 PM
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I think if you can find a 1 ohm, 25 (or 50) watt resistor, it would work fine.
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Old Oct 01, 2003, 08:27 PM
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Riverview, FL
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Quote:
Originally posted by flatfour
Just keep in mind when you are poking around these that there is 300 volts DC there and the heatsinks on the primary side are LIVE!!!!!!
which is why i do as little poking and prodding as possible !
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Old Oct 01, 2003, 08:50 PM
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FYI: Don't spend too much time poking and proding trying to find a potentiometer to adjust... Most PC power supplies won't have one.
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Old Oct 01, 2003, 09:00 PM
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Riverview, FL
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i am happy to report the issue is solved. I need to have the charger plugged into the supply - and turned on - before plugging in the power supply. no need to put a load on the 5v side. the voltage is 11.95 with the light bulb on the 5v side and 11.32 without the bulb illuminated.

enough to do what i need - power up my hitec cg340 charger
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Old Oct 01, 2003, 10:08 PM
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You may still find that when you put any significant load on the 12V output, you will see the output voltage drop quite a bit. The only way to keep my Orbit happy with a 10-cell pack was to put a 1 ohm resistor on the 5 Volt output. This keeps the 12V output above 11.5 volts even when peaking the 10-cell packs. With a 5 ohm resistor, I would get low voltage shutdowns (input <10V) with 10 cells, and low voltage warnings (input <11V) with 7 cells. Now, with the 1 ohm resistor, the no-load 12V output is about 12.6V. With the 5 ohm load it was 11.8V.
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Old Oct 01, 2003, 10:27 PM
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so would charging 7 cell nimh for my slow stick and tiger moth constitute a significant load?
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Old Oct 01, 2003, 11:50 PM
Nimble with Gimbals
San Diego, CA
Joined Apr 2003
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Charging an 8 cell 720mAh NiMh pack at 500mA only takes about 600mA from the power supply. The 11V seems to be enough to make my CG340 happy but I'm quite sure other chargers would be a lot more picky.
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Old Oct 02, 2003, 08:28 PM
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Quote:
Originally posted by KnimRod
FYI: Don't spend too much time poking and proding trying to find a potentiometer to adjust... Most PC power supplies won't have one.
my words of wisdom are "if i dont know what the $%^# a pointa-whatever meter is - I probably shouldn't be adjusting it"
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Old Oct 02, 2003, 10:24 PM
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Riverview, FL
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and the finished result...

she aint pretty - but gets the job done. 11.98 volts to the terminals and i was able to charge a battery and transmitter at the same time without the magic smoke coming out of anything
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Last edited by nose_first; Oct 02, 2003 at 10:27 PM.
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