I built a power supply from a computer ATX power supply

Thread Starter

nicklus

Joined Sep 11, 2017
12
I had watched a Youtube video by a guy named " Sorin-DIY Electrical Nerd". He used a 10W 43 Ohm resistor between one red and one black ground wire. He said a lower ohm resistor would get to hot... IDK. That is why I used the 10 watt 50 ohm resistor. The only difference between his and mine is he didn't use a rotary switch. And yes my switch is a " B before M" switch. I think I will probably have to back to separate output jacks. I really liked the rotary switch deal but just too many bugs.:confused:
 

Reloadron

Joined Jan 15, 2015
5,916
So why a 10 watt resistor? Not that I need an answer, I don't intend to hijack this thread.
While the power dissipated is only 2.5 Watts and a 5.0 Watt resistor would do fine a 10 Watt ceramic will run very cool. The former Radio Shack sold them making them very available. They could be had for under a buck each. Another popular choice was the aluminum housed 10 Ohm 10 Watt resistors. Either would run pretty cool the ceramic could be glued to the chassis and the slightly more expensive aluminum housed screwed to the chassis.

Ron
 

Tonyr1084

Joined Sep 24, 2015
5,862
My ATX didn't come with a switch on it. I added one. And I used banana jacks for the various voltages. No need for a meter.

I don't recall what load I used. [edit] I didn't use one. [end edit] I followed someone's YouTube on that part. I think it was the one green wire in my ATX that was connected to something. Either the 5V or ground - I don't remember for sure. [edit] it was ground. [end edit] Oh, and mine has -12V @ 1A.
View attachment 233345
 

AlbertHall

Joined Jun 4, 2014
11,222
The supplies are different.
Some will run just fine with no resistor.
Some will run fine with no resistor until you load the 12V and then they will trip (the 5V rail trips the overvoltage).
Some won't even get started with no resistor (the fan just twitches).
 

Reloadron

Joined Jan 15, 2015
5,916
I also have seen plenty where a load resistor was not necessary. Some will and some won't.

For years Intel published an ATX PSU Form Factor Design Guide. It is merely a design guide so keep in mind that manufacturers are not bound to it. Over the last 40 years the ATX PSU has evolved in a few dozen ways and directions. Years ago I designed a few load banks for testing ATX PSUs. Anyway, there is no steed fast specifications anyone is held to. Thus we end up with:

The supplies are different.
Some will run just fine with no resistor.
Some will run fine with no resistor until you load the 12V and then they will trip (the 5V rail trips the overvoltage).
Some won't even get started with no resistor (the fan just twitches).
Really pretty simple:
"Now some they do and some they don't
And some you just can't tell
And some they will and some they won't
With some it's just as well" :)

Ron
 
Top