I have a few old power supplies lying around, so I picked one to become a bench power supply. The choice was mainly based on the fact that I could find a manual that specifies the minimum load for each output of this thing.
The minimum load is just a power resistor that is not too small (that would be a waste of available current for actual work), and not too large (then it wouldn't be enough of a load). As the resistors would just dissipate heat, I'll see if they need any cooling and provide that with a small fan, or by just hanging them into the air that flows through the power supply.
A mainboard power adapter and a few old HD power adapters will be used to connect to the power supply, so I'm actually building a big adapter instead of modifying the power supply itself. This has a great advantage: The power supply can be replaced with an older/newer/really working/more powerful one.
Components
1×
Enermax EG465AX-VE(G)
ATX Power Supply
1×
Piece of wood, 300 mm x 300 mm x 16 mm
to hold the aluminum front and the power supply
1×
U-shaped Aluminum, 90 mm x 50 mm x 3 mm cross section, about 250 mm long (or something like that, I had that lying around)
This holds all the connectors, switch, LEDs
1×
A few Connectors (4mm banana jacks)
A pair for each voltage you want to have access to, plus one for protective ground
1×
Old ATX power supply adapters
The power supply will be left untouched, it can even be swapped later.
Create drilling templates for the front and base plates
Figure out how many 3.3V, 5V, 12V, -5V, and -12V banana jacks you want to have in your front plate. I used two each for the high-current voltages (3.3V, 5V, and 12V) and one each for the low-current ones (-5V and -12V, prepared a hole for -3.3V just in case I need it later).
The front plate will also hold a switch and two 3 mm LEDs (red for standby and green for power good). I also added holes for two cable glands.
Mark the positions of each hole on a piece of paper (or print the whole thing, it doesn't matter).
Do the same thing for mounting the front plate on the base plate. I used 4 M8 screws for that.
Here's a picture of my front template:
It's missing the marks for the switch and the LEDs, I added them later.
2
Step 2
Drill front and base, mount front on base plate
Straight forward: My banana jacks needed 8 mm holes, the cable glands needed 12 mm-ish (12.5? I'm not sure what I used), then there's 5 mm for the switch and 3.2 mm for the LEDs, and finally 8.5 mm for the mounting screws:
I used additional spring washers for the M8 screws.
3
Step 3
Drill front and base, mount front on base plate
Straight forward: My banana jacks needed 8 mm holes, the cable glands needed 12 mm-ish (12.5? I'm not sure what I used), then there's 5 mm for the switch and 3.2 mm for the LEDs, and finally 8.5 mm for the mounting screws:
I used additional spring washers for the M8 screws.
hi christoph and thanks. i'm a total beginner with this, but have used atx psu's to power arduinos and motors in my sound installations for a couple of years now.
usually i only need to connect the green cable to a black ground and it works fine but i tried this on a new unit i just bought and it's runs for a fraction of a second then cuts out... is this where the minimum load comes in?
and do you need to add a minimum load on every output as in this project, or usually only on the 5vsb output?
also, if i am unable to get my hands on these power resistors (or even this doesn't work) do you have any other suggestions please?
This is the second time I read someone mentioning the use of a resistor to load the power supply. How much current did you end up running through your resistor? Could you add a resistor and an LED in series so you can use it as a power indicator AND dummy load at the same time?
The power resistors (resistance, resulting current and rating) are included in the parts list. The biggest load is on the 12 V line with about 1.6 A.
Of course, I could have added an LED with current limiting resistor to each output, but I used the power supply's "power good" output instead. Another option would have been to monitor the current drawn by the "real" load (ie. what I actually want to supply with power) and switch off the dummy load with a transistor when it is not needed.
hi christoph and thanks. i'm a total beginner with this, but have used atx psu's to power arduinos and motors in my sound installations for a couple of years now.
usually i only need to connect the green cable to a black ground and it works fine but i tried this on a new unit i just bought and it's runs for a fraction of a second then cuts out... is this where the minimum load comes in?
and do you need to add a minimum load on every output as in this project, or usually only on the 5vsb output?
also, if i am unable to get my hands on these power resistors (or even this doesn't work) do you have any other suggestions please?