making a bench top PSU with a old school PSU

I remember the thread on makign a bench top PSU with a computer PSU, and how you have to ground the green pin. Well wanted to make a PSU for myself and all I have is a really old mitac PSU. It has 2 sets of wires that go to the mother board. on is as follows (black, black, white, red, red, red) and the other is (orange, red, yellow, blueish turquoiusish, black, black). Anybody know what wire to ground, I tryed all of them but none work.

it sounds like an old psu (before atx) most old ones like that have either a switch on them or smaller wires that plug into the motheboard…if its the latter connecting 2 of them should turn it on. its been a while so im only 90% shur thats how they work. if you could take som pics of it that might help.

Does it have a power switch hardwired to the powersupply (or some empty terminals)? (I don’t mean the one on the back, beside the plug.) If so, it’s likely an AT power supply, which means that there is no need to ground the +5VSB line (because it isn’t there). Cross those, and hold them, and it will operate.

In any event, the connector you describe sounds like an AT.

To use an AT power supply just flip the switch(sometimes they are on the back i have a bunch of compaq like that) and connect to the power leads you want using the pinout from tristan

Hey hey guys watch it… computer power supplies only made to handle resistive loads…

that means no inductive ones. i.e. brushed motors

To turn on an ATX power supply, simply short the PS_ON pin to any of the GND pins… but this wierd one I don’t know. :confused:

I suggest plugging the power supply in, put your multimeter on vdc, hold the black probe to ground and look through the pins with your red probe until you come to one floating at an unstable or strange voltage… then try grounding it with a resistor. If it goes right down, then you’ve found a floating control line.

The only problem you might have is if this one uses sourcing instead of sinking logic… but I don’t think it would.

If you need any other help hit me up.


Very good point on the ATX PSUs but the old AT PSUs usually dont have logic circuits, they just supply as close to dteady voltage as possible.

After so much speculation… just drop us a pic of it, easier to make deductions :smiley:

You also may want to consider that some supplies will not turn on without a minimum load. As stated above, these supplies do not play well with motors as loads. It is not so much the inductance as the stall current. A motor that is not moving is stalled and as such the current demand for many motors exceeds 30 amps when starting. Kit motors like the Chalupas and FP motors exceed 90 amps.

in other words… DANGER WILL ROBINSON!!! :ahh:

One way to run such motors safely is to throw in a relatively large wattage resistor of a certain amount of resistance calculated from your motor, to limit the inrush current. You should end up with a slow-starting motor.

I will have a picture up in about a day or so. I am NOT using it to run a huge motor with, I have no idea where people got that idea from. Honestly I dont know who in their right mind would run a robot motor off a bench top power supply.

Atx power supplies will normally shut down if you try and demand too much current from them, then you just unplug the power cord, and plug it back in and dont do what you just did agin lol.