ATX PSU 24v mod

[bigone5500]

Has anyone ever had any luck making a 24v power supply from a computer PSU?

 

[KrisBlueNZ]

I haven't done it but I can tell you what you need to do.

You need to re-wind the 12V secondary of the transformer with twice the number of turns. You can remove the 5V and 3.3V secondaries, so you'll have plenty of room on the bobbin.

You may need to change the rectifier diode(s) on that rail because their voltage ratings may not be high enough. You'll have to change the smoothing capacitors to ones with higher voltage ratings.

You'll need to change the voltage feedback circuit so that it monitors the new rail instead of the 5V or 3.3V rail like it did before, and change the voltage threshold from 3.3V or 5V to 24V.

It would be REALLY helpful if you could find a schematic for the power supply so we can check that there's nothing else funny or special about it that might cause a problem. Having a schematic would also make it easier to specify what changes are required.

How many amps are you hoping to get from the 24V rail?

 

[Gryd3]

Has anyone ever had any luck making a 24v power supply from a computer PSU?

Should be able to use the -12V line and +12V line.
http://pinouts.ru/Power/atxpower_pinout.shtml

Keep your current use to less than the -12V line as it is usually far less than the +12V line.

Would this be a problem Kris?

 

[davenn]

Would this be a problem Kris?

on a 500W ATX PSU the -12V rail is only 1A compared to 22A for the +12V rail

its a serious mismatch. being restricted to 1A is almost a waste of time
Tho a lot of work to do Kris's suggested mod, at least you would end up with a 24V supply of ~ 10A capability

Dave

 

[bigone5500]

I can tell that this would be a waste of time. Easier to buy a 24v supply.

 

[bigone5500]

I haven't done it but I can tell you what you need to do.

You need to re-wind the 12V secondary of the transformer with twice the number of turns. You can remove the 5V and 3.3V secondaries, so you'll have plenty of room on the bobbin.

You may need to change the rectifier diode(s) on that rail because their voltage ratings may not be high enough. You'll have to change the smoothing capacitors to ones with higher voltage ratings.

You'll need to change the voltage feedback circuit so that it monitors the new rail instead of the 5V or 3.3V rail like it did before, and change the voltage threshold from 3.3V or 5V to 24V.

It would be REALLY helpful if you could find a schematic for the power supply so we can check that there's nothing else funny or special about it that might cause a problem. Having a schematic would also make it easier to specify what changes are required.

How many amps are you hoping to get from the 24V rail?

I was hoping that it could be done somewhat easy. I am only looking to get a couple amps @ 24vdc.

 

[davenn]

oops only 1A at 24Vjust buy one then, they are not overly expensive AU$34

http://www.jaycar.com.au/productView.asp?ID=MP3318

that one is 1.5A there may be other higher rated

oops 1A @ 24V


cheers
Dave

 

[davenn]

or this one at 2.7A

http://www.jaycar.com.au/productView.asp?ID=MP3248

 

[bigone5500]

or this one at 2.7A

http://www.jaycar.com.au/productView.asp?ID=MP3248

Oh crap! Why didn't I think of one of these? I think I have one!

Thanks!!!!

 

[davenn]

there ya go

tell us how ya get on

 

[Rleo6965]

I'm just curious. Was it possible to rewind a ferrite transformer with 1:2 winding ratio. primary will be connected to original ferrite transformer of for 12V winding. This will result 24V on secondary winding . Just add new components filter circuit and rectifier to produce 24V.

 

[KrisBlueNZ]

I'm just curious. Was it possible to rewind a ferrite transformer with 1:2 winding ratio. primary will be connected to original ferrite transformer of for 12V winding. This will result 24V on secondary winding . Just add new components filter circuit and rectifier to produce 24V.

Yes it is possible. I described this in post #2 on this thread.

 

[bigone5500]

there ya go

tell us how ya get on

Well, the supply I thought I had was actually from an old HP printer and is rated at 30vdc @2.5A. I don't know if I could use this or not.

 

[KrisBlueNZ]

Do you want to change the output voltage to 24V? If it's a switching power supply, that's probably pretty easy to do. Upload photos of both sides, and close-ups of both sides of the output section. Make sure we can see the components and tracks clearly. See https://www.electronicspoint.com/resources/how-to-take-photos-of-circuit-boards.6/

 

[(*steve*)]

If you have a more modern computer PSU with multiple 12V outputs the possibility exists (in theory) to change one or more of these additional 12V outputs to be references to something other than the common ground.

I say "in theory" because these power supplies are not built in a way that makes doing modifications like this easy (or indeed safe).

 

[Pablo Díaz Enrico]

Before of all, I hope this can help anyone. Sorry for my English...
To obtain 24 V for ATX psu you can (as mines):
1) Add two of them in series.
2) Mod one (more or less) as follow:
Remove the extra components for 3.3V, -5v and -12V (optionaly 12v ones).
Connect the +5v output diodes at the output of the +12v rail from the transformer (the +5v rail will be the new +24v one).
In my first intent, I taken an ATX psu with an AT2005 pwm supervisor, and, with a pair of circuits taken thanks google, I'd replace the resistors from Vref to get 2.5V from the new output.
This psu is actually not fully tested yet, but can manage a load of 60W without drop any mV. I connected a 24V lamp and its output remains constant. My first idea was to mantain the modified +12V rail (from the old +5V) to the fan, but this output goes high with the load on the other rail, which is reasonable. In fact, I plan to add a switching regulator (like the LM2586-12) to move the fan and discard all the rails but the +24V modified.
If anybody wish more details, tell me if I can help.
Thanks for this great place!
Regards from Argentina.

 

[(*steve*)]

If you connect two power supplies in series you need to ensure that the output ground is floating.

 

[Pablo Díaz Enrico]

Oh, yes, when you put two or more power supplies in series, they share the input voltage but not the ground-chassis, then, the ground-chassis is only connected to the bottom power supply. The ground of the upper power supply must be completely isolated from chassis (floating).

 

[(*steve*)]

If this involves removing the protective earth then you are risking a deadly fault

 

[Pablo Díaz Enrico]

The idea of two psu in series is not to remove the protective earth. This is connected to the entire case (psu cases screwed one by the another), then, the ground of the bottom psu is to earth and its +12v are connected to the ground of the upper psu, isolated from earth. Psu's voltages are added without loose security. I have a couple of burns in my figers that allways remeber me that electricity can be very, very dangerous.