Paralleling ATX power supplies

Can you put ATX power supplies in parallel?

I have a few salvaged ones but, for 12V, they can only supply around 18A.

My RGB LED cube will consume a maximum of 512 x 3 x 17mA = 27A.

No, you cannot safely parallel them. But perhaps you can run half the cube from one, and half from the other.

What is the wiring arrangement of your LED cube? If it is multiplexed, is the average current per active LED really as high as 17mA?

dc42: No, you cannot safely parallel them.

What would happen out of interest?

dc42: But perhaps you can run half the cube from one, and half from the other.

That would be possible although it would probably be easier to just buy a beefier ATX off ebay

dc42: What is the wiring arrangement of your LED cube? If it is multiplexed, is the average current per active LED really as high as 17mA?

The 8 x common anode RGBs are mounted on 4 vertical straightened support wires with the the RGB leads splayed out at right angles. But there is is no electrical connection with the support wires except through 470R resistors on the cathodes. Each of the vertical support wires with the RGB cathodes will be controlled by a BC327 with its base sinking to a TLC5940 port. 8 x 8 = 64 x 3 = 192 BC327s = 12 x TLC5940s.

The common anode leads will be electrically connected in rows and controlled by another 64 xBC327.

These will be multiplexed with a further 8 x BC327s controlling rows of BC327 bases and 8 x TIP225s controlling rows of BC327 emitters - 1 additional TLC5940.

It will mean that all the RGBs in a spire will have to have the same brightness and colour, however this limitation will not limit the animations to a great degree.

Both power supplies would work against each other trying to force the common point to the voltage each thinks it should be, causing a lot of current to flow in the process.

You can put a 1 ohm 17 W resistor in series with each one to isolate them a bit, but you will waste a lot of power.

boylesg:

dc42: No, you cannot safely parallel them.

What would happen out of interest?

Switch-mode PSUs track the output voltage and use feedback to increase/decrease the power as needed.

If one is aiming for 11.9V and the other is aiming for 12.1V (perfectly possible) then they'll fight each other. The 11.9V PSU will be trying to lower the voltage and the 12.1V PSU trying to raise it.