Using a PC PowerSupply as a bench power supply.

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- Tim -

Thanks

I will look it over, but at a glance it answers everything .

Not stated if these are AT power supplies (IBM PC or AT vintage) or ATX power supplies. Older supplies had a power switch attached to the supply. Newer ATX supplies are controlled by a power supply controller and front panel switch.

This assumes ATX type supply. Power supply controller ordered the PSU on via the green wire. Then gray wire (Power OK) would tell the power supply controller that power supply was working. You don't care about the gray wire signal (unless you put an LED on it to see that message). But you need a non-momentary switch to connect green wire to any black wire (to reduce green wire voltage from above 2.0 volts to below 0.8 volts).

Some power supplies need a m> I have the need to for a cheep 5/12vpower supplyand have a lot of

The article discussed minimum loads, but it I don't recall where it stated AT or ATX. You stated the gray (power good) wire could be ignored, but I thought that the board needed to put a signal back on this wire to turn the PS on for the rest of the system ? Is this not right ?

Power supply controller ordered the PSU on via the green wire. Then gray wire (Power OK) would tell the power supply controller that power supply was working. You don't care about the gray wire signal. But is using a power supply controller, then the controller does care about the gray wire voltage.

Posted were wires defined by color. Color was defined in ATX specs; not in AT power supply specs. That posting assumed ATX wire colors. And then some ATX type supplies don't use industry standard wire colors. If in doubt, this graphic helps identify what each wire is by connector position:

Every voltage has sense connection. Usually sensing is performed inside the power supply. However, some supplies may locate the sense connection via motherboard so as to compensate for wire voltage losses. IOW might use one 3.3 volt supply lines, instead, as a 3.3 voltage monitoring wire. If that sense is implemented and not connected to other 3.3 volts (orange) wires, then the sense will instead monitor 3.3 volts via a diode inside power supply. This will cause the 3.3. volts to be maybe 0.5 volts higher than what the power supply believes it to be. IOW if a power supply needs a sense connection between "a brown and orange wire", then connecting all three 3.3 volt wires together (at twenty pin connector - see chart in previous citation) will cause the power supply to drop maybe 0.5 volts to be closer to 3.3 volts.

Most supplies don't use a sense wire. Instead the sense wire is used as another source for 3.3 volt current as shown in that chart.

Best is to connect all same voltage wires together at the load - to eliminate any unexpected variation - such as using one 3.3 volt wire to monitor 3.3 voltage.

Thanks for all the input ! One last question, no where did I see the discussion of how much current can safely be drawn from each circuit. Is there no hard-set rules on this or just a fucntion of the size of your PS.

Thanks

You don't know anything about electronics and you're too stupid to learn, so why do you post here? You have very little comprehension of the technical material, so reading can't be it.

Power supply should list a maximum current for each voltage. A number that decreases when other voltages provide higher currents. How much for each voltage when all lines are loaded? Charts for this are found in the ATX power supply standards. Easier is to just use a larger wattage supply. Smarter is to look at those charts anyway to learn from the experience.

How much power on each circuit - each wire? Bottleneck is defined by Molex connector specs. Typically 6 amps per wire - less if concerned for contact resistance, temperature, or environmental degradation - which would be irrelevant as a bench power supply.

If I look at the pinout at

Am I reading this correctly ?

Thanks

Nobody can really answer that question without better understanding circuits for each voltage source. Typically, when two power supplies drive a common load, one supply with slightly higher voltage provides all current until the load wants too much current from that one source. Then that source goes into current foldback limiting; dumping the entire load on the other supply. Second supply also goes into current foldback limiting. Both supplies combined cannot provide enough current until power is recycled to reset that current foldback limiting condition (a safety feature).

Some of the tricks to better make two power supplies work in parallel were to use bipolar transistors rather then Fets; put a small resistance power resistor on the output of each supply (voltage decreases slightly as current increases), or an interconnecting signal wire between two supplies so that one power supply voltage regulator will track the other.