ATX PSU and 24V

A Former User

just take a ATX PSU with two independent 12V-rails

unlikely to be a success as most if, not all, ATX PSU use a common ground; so when wiring this is series you are effectively shorting 12v to ground.

arhi

As previously written, there are regular 24V psu bricks with 5Vsb and on/off .. most manufacturers make them. Also as @bearer said, those ATX psu boxes use common ground so pushing rails in series is not going to be easy task and using -12V rail to get to 24V is problematic too as -12V rail rarely have capability to push more than 200-500mA.

OTOH you can, fairly easy, make your PSU output 24V. Usually cheaper the PSU easier the mod. The general el-cheapo (and many expensive ones) have a single transformer inside and a pwm regulator (usually TL431) that's monitoring 5V rail. There's a voltage divider on the 5V rail feeding the sense pin. Change this voltage divider and you get different output. Pay attention that all voltages are related so if you change this regulated 5V with divider to be 10V your 12V rail will become 24V, your 3v3 rail will become 6.6 etc etc ... so ALL rails will change as PSU monitor only 5V and other one are related to it by winding relation in the transformer.

Check the 5Vsb voltage, that is often separately generated and is not affected by this but in any case make sure if you are connecting it to power duet or rpi or.. that it's an appropriate voltage.

Depending on how cheap the PSU is, often they cheap out on the output capacitors so you will have 15 or 16V caps on the 12V rail... you need to check all the caps and replace them with one with proper voltage rating for your new voltage.

Still IMHO cheaper and faster to get a proper PSU with "remote control" input for on/off

Veti

there is a psu power off modules
https://de.aliexpress.com/item/4000210923653.html

A Former User

@Veti said in ATX PSU and 24V:

and one which is fanless
https://www.meanwell.com/webapp/product/search.aspx?prod=UHP-350(R)

don't think that one has remote on/off btw

but when turning the power off when the duet is idle i doubt a psu fan is a problem as the hotend will likely make as much noise anyway (and if i'm not mistaken the fan is controlled on the 24v version of those Meanwell RSP series)

Veti

@bearer said in ATX PSU and 24V:

don't think that one has remote on/off btw

no but combine it with the psu power off module and then it does.

the uhp series is fanless. i use it myself. just mount it onto metal for heat transfer

zapta

@justus2342, are you sure that those 12V outputs are isolated and don't share ground?

Theoretically connecting two 12V in series gives 24V but there may be corner cases. For example, if one of the two detects over current and shuts off, will it see a reverse voltage on its output from the other power supply? Will it get damaged?

Dad003

in my 3d printer build , i have a 850 watt modular pc PSU that run the board for extruder and stepper motor , i have a 600 watt 24 volt for the heated bed connected via a mosfet controlled by the board,

that 24volt psu is very noisy , it make more noise than the printer running

zapta

@Dad003 said in ATX PSU and 24V:

that 24volt psu is very noisy , it make more noise than the printer running

I also had a noisy power supply (the high speed fan was turn on every minute or two and was very noisy) so I switch to a mean-welll UHP 500W (they came with a wide range of power) which are compact very efficient and thus don't need a fan and stay cool.

Thalios

From my RC days, i've been using HP server power supplies to feed 24V to my Powerlab 8 charger. Each pushes 900W for a total of 1800W at 24V. (12V each in series for 24V).

Works like a charm and is super stable, and was about 80$USD total if I remember right.

Phaedrux

@Thalios said in ATX PSU and 24V:

HP server power supplies

Do they come with noise canceling headphones?

Thalios

haha I wish.

They are a tad noisy!