can a 24pin PSU supply enough 5v though for an old AT computer,

I think that it is just a matter of connecting the 5volt converter to the positive 5 on the ATX psu, and connect the output (neg. 5volt) to the P8/9 connectors that go into the AT-Mobo.
Powerdraw is not really an issue, as most PSU's that I have seen, deliver under 1amp on negative 5volt.

Most modern PSU's that I have seen, that can do high amps on 5 and 3.3 are plus 800watt.
Wich are those in the shops in town. Way owerkill, yes. And they are expensive. Ohh well.... 😁

I kept the old 300W early ATX supplies around just for the early motherboards. New supplies are mostly built for 12v video cards.

Unknown_K wrote:

I kept the old 300W early ATX supplies around just for the early motherboards. New supplies are mostly built for 12v video cards.

At work we have kept atleast a dozen 250w ATX suplies from the badcaps plagued Dell Optiplex GX270 and retired GX260s. We only use SFF desktops today and no need for them anymore. Have to check them out before we throw the lot. Maybe i keep some for myself 😊
Edit: -5v is missing from Dell Optiplex GX260/270 PSUs.

All this still does not answer my question.
Does anyone know where to get a diagram for atx to at converter cable?

Just look at these pinouts:

http://pinouts.ru/Power/MotherboardPower_pinout.shtml

http://pinouts.ru/Power/atxpower_pinout.shtml

and make the adapter...

I used the first pinout to make miniature DC/DC AT power supply (you power it from 12V power brick), you can see it on the photo, but I will later 3d print a case and it will be even smaller.
I put an analog amp meter on +5V line and AMD 486 100 MHz with S3 PCI video draws only about 2 amps.
I used self made mc34063a converters to provide -12V and -5V, and +5V is converted by off-the-shelf step-down converter. Probably less than 10 USD for everything.

(it's just a prototype, sorry for messy look and the terminal blocks)

adalbert wrote:

Just look at these pinouts:

http://pinouts.ru/Power/MotherboardPower_pinout.shtml

http://pinouts.ru/Power/atxpower_pinout.shtml

Hmmmm....
It is something like this that I want to make.
I just need to know where the cables will go, from the P8 and P9 into the ATX.

The converter that supplies minus 5 volt is this..
http://www.instructables.com/id/Create-A-Nega … n-Analog-Circu/

Looking forward to study your pictures and the pinout stuff.
All in all... I just want to make one, for the fun of making one. 😉 😁

All you need to do is match the voltages on the pinouts, ignore 3.3V and get a ground wire and the PSU_ON pin to make the power switch connector. You can also be fancy and add a -5V regulator and/or a little addon board to create a latching circuit out of the momentary ATX switch (so you can install the board on an ATX case without changing the switch itself).

To make an adapter, just look at the colors. It should be simple. But to be perfectly safe, you can measure the voltages to be sure they are right before you plug it into mainboard, or compare the colors with pinout. The colors almost always should be standarized, but everything should be checked.

Now i'm talking about ATX connector:

You don't need orange cables (3.3V). Isolate them.
You don't need purple cable (5VSB). Isolate them.

All black cables are ground, then can be joined together or not, they are all the same, the order doesn't matter.

Now you can just connect yellow cables with yellow cables (12V) on AT connector,
black with black (GND), red with red (5V), blue with blue (-12V) and white with white (-5V - if it's there and it's working, you don't need the converter)

ATX is switched on by the switch connected to motherboard - AT doesn't have that, so you have two options now:
1) simple: take GREEN cable and connect it with BLACK cable. ATX supply will be turned on after you turn on the main switch, on the power supply itself, and will be working until you cut the power off.

2) additional switch: take GREEN cable, make it 30 cm longer, do the same with BLACK cable, and put an electrical switch between them.

That voltage converter from instructables looks nice and simple, but I'm not sure if it will provide enough current... anyway it's worth trying.

To make my converter i used this webpage - http://www.nomad.ee/micros/mc34063a/ Vin = 12V, Vout = -5V, Iout = 150mA, Fmin = 49kHz, Vripple 20mV.
With this parameters following parts are needed:
1x MC34063, 1x 270pF ceramic capacitor, 1x 0.68R resistor, 1x 165 (or more) uH inductor, 1x 470 uF low ESR capacitor, 1x 1k resistor, 1x 3k resistor.
I etched small 2x2 cm PCB for that, but it should be possible to make it on universal board too.

alexanrs wrote:

All you need to do is match the voltages on the pinouts, ignore 3.3V and get a ground wire and the PSU_ON pin to make the power switch connector. You can also be fancy and add a -5V regulator and/or a little addon board to create a latching circuit out of the momentary ATX switch (so you can install the board on an ATX case without changing the switch itself).

I see... Hmmm... 3.3 is ATX era!
What about ground? There are 7 ground on the ATX and 4 pins on AT. And probably the same issues on all the other rails.
Should I then connect some of the extra ones on the ATX Psu then?
For example. Should I connect the first grounds in pair's up to pin 16 on the ATX and having pair's go to the first 3 ground wires on the AT connectors?
And do the same kind of procedure with 5 volt and so forth? I am familiair with the procedure regarding power switch on the green power on signal on the ATX PSU. Or should I reserve a single ground wire on the ATX psu, for use with the green power on signal-wire?

adalbert wrote:

To make an adapter, just look at the colors. It should be simple. But to be perfectly safe, you can measure the voltages to be s […]
Show full quote

To make an adapter, just look at the colors. It should be simple. But to be perfectly safe, you can measure the voltages to be sure they are right before you plug it into mainboard, or compare the colors with pinout. The colors almost always should be standarized, but everything should be checked.

Now i'm talking about ATX connector:

You don't need orange cables (3.3V). Isolate them.
You don't need purple cable (5VSB). Isolate them.

All black cables are ground, then can be joined together or not, they are all the same, the order doesn't matter.

Now you can just connect yellow cables with yellow cables (12V) on AT connector,
black with black (GND), red with red (5V), blue with blue (-12V) and white with white (-5V - if it's there and it's working, you don't need the converter)

ATX is switched on by the switch connected to motherboard - AT doesn't have that, so you have two options now:
1) simple: take GREEN cable and connect it with BLACK cable. ATX supply will be turned on after you turn on the main switch, on the power supply itself, and will be working until you cut the power off.

2) additional switch: take GREEN cable, make it 30 cm longer, do the same with BLACK cable, and put an electrical switch between them.

That voltage converter from instructables looks nice and simple, but I'm not sure if it will provide enough current... anyway it's worth trying.

To make my converter i used this webpage - http://www.nomad.ee/micros/mc34063a/ Vin = 12V, Vout = -5V, Iout = 150mA, Fmin = 49kHz, Vripple 20mV.
With this parameters following parts are needed:
1x MC34063, 1x 270pF ceramic capacitor, 1x 0.68R resistor, 1x 165 (or more) uH inductor, 1x 470 uF low ESR capacitor, 1x 1k resistor, 1x 3k resistor.
I etched small 2x2 cm PCB for that, but it should be possible to make it on universal board too.

Thanks...
On the negative 5 volt. I seem se notice that negative 5 volt allways delivers under 1 amp on both early ATX and mostly all AT psu's.
I might be wrong on this one. If this really is the case. Then the circuit is good enough I think.
The reason for it, are that I then can use all the newest PSU's, as long as they are powerfull enough.
Most modern 400 watt's have too little on the 5 volt line. Only those of say, 700/800 or more, does the trick.
I might be wrong here too. Yet better to take modern outputs in the equation too.

Well, like I said before, my 486 only takes 2 amps on +5V... modern ATX PSU's have at least 10 amps on +5V, which should be more on enough.
My entire 486 setup takes under 36W of total power (i know that because I put 3 amps fuse on 12V input of my DIY power supply), but I use CF card for hard disk. Orginal IBM PC XT had 63.5 Watts power supply.

And in case of -5 volts: Yeah, even 0,5 amp should be enough. But that IC you linked looks to me like something based on charge pump which is able to provide 10mA of current, but maybe i'm wrong 😉

edit: http://electronics-diy.com/electronic_schematic.php?id=603 - here is stated that LTC1046 chip is a replacement for ICL7660 with improved current, but even while it's "improved", it can provide only 50 mA. So the original chip probably is really weak.
I found another replacement, which is MAX660 and it can have maximum 0,5 amp output. But i never tested it.

brostenen wrote:

I see... Hmmm... 3.3 is ATX era! What about ground? There are 7 ground on the ATX and 4 pins on AT. And probably the same issues […]
Show full quote

I see... Hmmm... 3.3 is ATX era!
What about ground? There are 7 ground on the ATX and 4 pins on AT. And probably the same issues on all the other rails.
Should I then connect some of the extra ones on the ATX Psu then?
For example. Should I connect the first grounds in pair's up to pin 16 on the ATX and having pair's go to the first 3 ground wires on the AT connectors?
And do the same kind of procedure with 5 volt and so forth? I am familiair with the procedure regarding power switch on the green power on signal on the ATX PSU. Or should I reserve a single ground wire on the ATX psu, for use with the green power on signal-wire?

If you open up the PSU, you'll see that all the grounds are shorted, same thing for the 5V lines. It doesn't really matter which ones you use. Also, for the PSU_ON signal, it shouldn't make a difference if you get a dedicated ground or not.

adalbert wrote:

Well, like I said before, my 486 only takes 2 amps on +5V... modern ATX PSU's have at least 10 amps on +5V, which should be more […]
Show full quote

Well, like I said before, my 486 only takes 2 amps on +5V... modern ATX PSU's have at least 10 amps on +5V, which should be more on enough.
My entire 486 setup takes under 36W of total power (i know that because I put 3 amps fuse on 12V input of my DIY power supply), but I use CF card for hard disk. Orginal IBM PC XT had 63.5 Watts power supply.

And in case of -5 volts: Yeah, even 0,5 amp should be enough. But that IC you linked looks to me like something based on charge pump which is able to provide 10mA of current, but maybe i'm wrong 😉

edit: http://electronics-diy.com/electronic_schematic.php?id=603 - here is stated that LTC1046 chip is a replacement for ICL7660 with improved current, but even while it's "improved", it can provide only 50 mA. So the original chip probably is really weak.
I found another replacement, which is MAX660 and it can have maximum 0,5 amp output. But i never tested it.

Thaks.. 😀 I will keep the IC in mind.

alexanrs wrote:

If you open up the PSU, you'll see that all the grounds are shorted, same thing for the 5V lines. It doesn't really matter which ones you use. Also, for the PSU_ON signal, it shouldn't make a difference if you get a dedicated ground or not.

Nice. I have never really opened up an PSU to date.
I usually just do some other type of soldering job's, like soldering different connector on stuff instead of the original.
Have converted many case-fans from small plugs to molex in the past years.
This little project should be a really nice one, once I get the rest of the parts and have the time for it.
At the moment, I am just gathering information and information.... And more information. 😁
Just to make shure I am doing everything the right way.

brostenen wrote:

... I have never really opened up an PSU to date ...

Recommended reading: Capacitor Safety In Power Supplies

brostenen wrote:

adalbert wrote:

Well, like I said before, my 486 only takes 2 amps on +5V... modern ATX PSU's have at least 10 amps on +5V, which should be more […]
Show full quote

Well, like I said before, my 486 only takes 2 amps on +5V... modern ATX PSU's have at least 10 amps on +5V, which should be more on enough.
My entire 486 setup takes under 36W of total power (i know that because I put 3 amps fuse on 12V input of my DIY power supply), but I use CF card for hard disk. Orginal IBM PC XT had 63.5 Watts power supply.

And in case of -5 volts: Yeah, even 0,5 amp should be enough. But that IC you linked looks to me like something based on charge pump which is able to provide 10mA of current, but maybe i'm wrong 😉

edit: http://electronics-diy.com/electronic_schematic.php?id=603 - here is stated that LTC1046 chip is a replacement for ICL7660 with improved current, but even while it's "improved", it can provide only 50 mA. So the original chip probably is really weak.
I found another replacement, which is MAX660 and it can have maximum 0,5 amp output. But i never tested it.

Thaks.. 😀 I will keep the IC in mind.

Usually you would use a linear regulator such as the generic 7905 to make -5V from -12V.

Well, it would be the simplest option, but also a waste of power (and that equals heat) - 7V * current, that would be 3,5W at 0,5 amp - you will need a radiator on that. It might be worth trying, but it will also lower the usable current of -12V rail (if it has rating of 1 amp, then it can provide 12 watts of power and that linear regulator will waste some of it as heat)

You are right, but that's the way it is done inside many PSUs.

There are not that many cards that even need -5V, and for those that do (like some Sound Blasters), they really don't consume that much so heating is usually not an issue.

So if you must have -5V, this just might be enough in many occasions.