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Topic: Help with converting psu to 5v powersupply for arduino (Read 422 times) previous topic - next topic

dsaisho

I got a mini atx psu that I was hoping could power my arduino with the 5v power output.

Link to product (click Additional Information for specs)

I currently have it hooked up like this:



When I use the paperclip I see the psu fan turn on for 1/4 second then turn off and nothing happens.

Any idea on what I need to change to get this thing to stay on?

Thanks :)

JCA34F

You probably need a higher minimum current than the 10 mA with a 470 Ohm resistor, try a 47, 106 mA, and you may need minimum loads on the other outputs.
What does the supply's documentation say?

Paul__B

There may be a misunderstanding here.  The "Power on" connection of the power supply is not the same as the button on the front of the computer.

The power supply will operate only as long as the "Power on" connection remains connected to ground.

A paper clip is not an appropriate means to do this.  :smiley-roll-sweat:

dsaisho

There may be a misunderstanding here.  The "Power on" connection of the power supply is not the same as the button on the front of the computer.

The power supply will operate only as long as the "Power on" connection remains connected to ground.

A paper clip is not an appropriate means to do this.  :smiley-roll-sweat:
Im following this tutorial



And ive seen a few like it, power on shorted to ground will turn on the psu, there is no current going through the paper clip(or very little).

Ron_Blain

Over the years I have read dozens of "tech tips" on how to do just about anything with an ATX form factor PSU. Every tip I have read seems to have a different view of which voltage the PSU regulates off of and should have a load applied and loads have ranged from a 10 Ohm 10 Watt resistor to what I am seeing now. I have also had some power up and work just fine less any load so go figure?

I agree that the suggested load of 10 K on the 5.0 volt rail is pretty light at 0.0005 Amp (5.0 / 10000 = 0.0005) and makes no sense at all to me. I suggest a much higher load current. I would try it on the 5.0 and 3.3 volt rails and see what works. I would start with a 10 Ohm 10 watt load which at 5.0 volts would be a moderate 0.5 Amp load and 2.5 watts. The 5.0 volt rail seems to be the rail of choice.

Also, as Paul B points out, a paper clip is hardly a good substitute for a switch and the connection between PS_ON and Ground. That connection must be maintained.

So my guess is you need a much higher load resistance on the 5.0 volt rail.

I see there were more replies as I typed this and fed the dogs, and ...  :)

Ron

Ron_Blain

In your link, Step 5 won't work, Step 5: Solder on Your Dc Jack for Arduino Power. Using thet DC connector with an Arduino you need to apply > 7.0 volts actually applying an external 7 to 9 volts is ideal and 7 to 12 will work but remember what you apply on that connector is applied to the Arduino 5.0 volt onboard regulator.

Ron 

dsaisho

You probably need a higher minimum current than the 10 mA with a 470 Ohm resistor, try a 47, 106 mA, and you may need minimum loads on the other outputs.
What does the supply's documentation say?
Thats what I was worried about, setting up minimum loads to other outputs.

Is it one of the 3v to ground and one of the 12v to ground ontop of the 5v to ground?

If so, what resistors should I use for the 3v and 12v?

I posted a link to the PSU documentation, I did not see or notice any info on what was needed to have a load in order to start the psu.

Thanks

dsaisho

In your link, Step 5 won't work, Step 5: Solder on Your Dc Jack for Arduino Power. Using thet DC connector with an Arduino you need to apply > 7.0 volts actually applying an external 7 to 9 volts is ideal and 7 to 12 will work but remember what you apply on that connector is applied to the Arduino 5.0 volt onboard regulator.

Ron  
Ah ok, so I should hook up the arduino to the 12v out?

Ron_Blain

Ah ok, so I should hook up the arduino to the 12v out?
That's what I would do. I would also try a single load I suggested earlier on the 5 volt rail. I would try 10 Ohms 10 watt using a ceramic or aluminum block wire wound resistor.  A few bucks on Amazon. That will give you a .5 Amp actual 2.5 watt load. I suggest a 10 watt resistor simply because 10 Ohm 10 watt resistors are inexpensive and won't cook. An aluminum housing one is easily mounted to the PSU case.

Ron

dsaisho

I tried a 25 and 10 w resistor with the 5v and had no luck :(

Do you guys think I need to use the same ground pin for the 5v load and the power on, so something like in the below image vs my image where I use two different ground pins:


Ron_Blain

On an ATX Form Factor I think you will find Ground is Ground and all black wires share a common bond. It shouldn't matter which ground is used.

Early ATX PSUs often used a 3.3 Volt sense wire which was if I remember this stuff correctly, pin #11 of a 20 pin connector and was brown or orange depending on who made the PSU. While ATX Form Factor has published design guides from Intel:

https://www.intel.com/content/dam/www/public/us/en/documents/guides/power-supply-design-guide-june.pdf

It is worth noting that a design guide is merely a guide and there is nothing forcing compliance to any specification. Years ago I was involved with testing power supplies for a hardware test forum and it was amazing how well and how poorly made many were. Some required a load and some didn't.

You are absolutely sure you have a known good PSU correct? I would try the load on the 3.3 volt rail. The symptom you describe is what they do when they start but no load condition. You may find more about that in the design guide I referenced.

Ron

dsaisho

So I fixed this problem...

the problem was that im an idiot (still an existing problem).


Initially when I got the psu I cut the 5v and ground off a molex. I soldered them up to a power end that would plug in the arduino. I didnt think anything of it.

The problem was that when I used my heatshrink to cover the cables the damn 5v wire was touching the ground which essentially shorted the psu.

So after buying a crapload of resistors, trying every different combo, soldering all the 24pin power connections with female sockets to easily swap out resistors. I took off the heatshrink on my arduino power connector, separated the cables and boom psu turned on no problem... even powered my arduino which was the goal.

now gonna finish this thing :)

Thanks everyone who provided input on how to solve, even though I had a dumb issue I learned a lot more about psu's than I knew before.

**im pretty sure this is the programming equivalent to spending hours debugging code only to find out you forgot a comma.




Ron_Blain

It's just a learning curve at work. I would venture to say anyone in the game for any length of time has made a boo boo or two along the way. When I retired my boss and I were talking and he mentioned "well Ron, great career and you never smoked anything along the way" Looked back at Mike and said "fortunately nothing you saw". :) 

It's a mistake you won't make again which is what we were after right? So you have a working PSU and a lesson learned.

Ron

srnet

It should be mentioned that that PC power supplies are obvioulsy not intended to be used uncased as bench power supplies. 

They are far better in boxes, PC cases etc, so that there is little risk of poking in screwdrivers or dropping bits of wire that can be at mains voltage, which is not good.

I guess it depends how lucky you feel. 

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