Guide: Power Supply Sense Wire Modding

[aasmaukr]

Thank you for this mod, hell-fire!
Works like a charm, but i can't get the 3.3v rail lower than 3.49v, i used a 10k potentiometer. It doesn't really matter, since i am going to get a couple of bh5 sticks soon, anyway.

[zbogorgon]

very nice guide, i did it on my Antec True 480, worked perfectly, time to change PSU, i'll go for Enermax 600W Noisetaker and did sb perform this mod on Enermax Noisetaker PSU, does it work, how does it perform? thx.

[e268]

If you are going for a new psu, why won't you buy one with adjustable rails? I recall seeing some mentioned here in the forum.

[zbogorgon]

the only PSU i know who has that is OCZ powerstream, i want to have two seperate rail, so powerstream 600W, it kinda has a bad reputation at the moment and I am from Slovenia, Europe, OCZ PSUs are extreamly hard to get, even in Germany and it would cost me twice the cost of Enermax.

[phixie]

hi all,

First of all i want to thank hell-fire for this nice mod.
I am thinking of doing it with my own PSU cause my pc isnt stable at the moment. Reason? 12v rail is giving me 11.6-11.7. All the other rails are ok.
But now when i checked for the sense wires, i couldnt find one except the one of 3.3v. What can i do?

[wacky]

same here.. I guess u have native 24pin psu like me (i have OCZ ModStream 520w).. there is only orange sense wire, right? so.. where are u profi guys? We need your help, please.. how to mod 5v and 12v rails on 24pin psu?

tnx

[sluggo]

Sorry if this has been covered before, but I thought I'd chime in on the operation of the mod. Some of the explanations are simplified, but the concepts are accurate.

The PSU only knows what it's putting out because it compares it's output to a known 12 Volt reference voltage that's built into the supply. Inside the supply, this reference voltage is connected to one side of a resistor and the sense line is connected to the other side of the resistor. If the sense line is equal to 12 Volts, then there is 12 Volts on both sides of the resistor and no current flows through it. If the sense line is lower than 12 Volts, a very small current flows from the 12 Volt source through the resistor to the sense line. If the sense line is higher than the 12 Volt reference, current flows from the sense line, through the resistor and into the source node. The direction of this current flow is easily detectable by sensing the voltage across the resistor. These are the basics of a comparator circuit.

So when current is flowing from the sense line toward the 12 Volt reference, the supply knows that the voltage on the motherboard is too high and lowers it's output until there is no current flowing through the resistor. Similarly, if the current is flowing from the reference node into the sense line then the supply responds by increasing the output, raising the voltage on the sense line.

The mod adds a variable resistor between the sense line and ground. In operation, the variable resistor pulls a little bit of extra current through the comparator's resistor, forcing the supply to output a little more voltage, which returns the circuit to equilibrium. The fixed resistor is there to guarantee that at least some of the extra current comes through the comparator's resistor and not just straight from the motherboard itself.

When the variable resistor is at it's maximum value (10k or so), there is negligible current flowing through it, so the comparator circuit does not respond when initially setting the value. In fact, you need to reduce the value of the resistor quite a bit to get any response at all, but that's good. Much safer that way.

Of course, everything I've said about the +12 line applies to the +5 and +3.3 as well.

Nice mod.

[ElessarSI]

did the mod today and it worked very good first, i didnt think it work. I adjusted, adjusted and adjusted the pots, but no. Then suddely it came, and shut my psu off very nice mod. Thank you very much

[seaman]

Did the mod today,for training,on an old power suply wich has sense line only on the 3,3V line.
I read somewhere that modding such power supplies with only one sense line,will allow increase voltage on all 3,3 -5 -12V lines.
Before modding I had 3,36V on the 3,3V line.After modding I had 3,57V with variable rezistor set to max(10K).Reducing rezistance on VR,gave me increased voltage on the 3,3V.But when the 12V started to increase,I had allready more than 4V on the 3,3V rail.The 5,5V didn't seem to change.
Now,I want to do is to mod my PSU wich has sense lines on the 3,3V and 5V lines,but not on the 12V.Can anyone tell me if by modding the 3,3V line,will give me an increase on the 12V line?
I have now 3,23V and 11,78(11,71 load).It is not very low,but it looks like NF4 chipset and video card need more voltage.MB is Asus A8N -SLI wich I learned is power-hungry.

[UTF Nightmare]

I've got a Tagan 480W-U22 but when I put a 47 ohm resistor between the 3,3V sense wire and put a VR to it. The 3,3V rail becomes 4,77V

Any ideas ?

[Mussels]

use a smaller resistor! or use a VR as described earlier in the thread.

also, what was the reading before you modded?

[Calderbrae]

I've got a Tagan 480W-U22 but when I put a 47 ohm resistor between the 3,3V sense wire and put a VR to it. The 3,3V rail becomes 4,77V

Any ideas ?

Can you post pics of your mod?

[UTF Nightmare]

Sorry pics are a bit impossible because i haven't got a digicam.

3,3V wire is 3,45V (quite high too imo) before modding.

Why a smaller resistor? I also tried this with same VR en resistor on a Sweex psu and there i could turn it up to 3,75V and if higher it shut's down, think because of OVP.

Resistor I now used was 47Ohm and VR 10Kohm

[aasmaukr]

Well, to get higher voltage at the 12v rail, open up your PSU case and look for VRs inside, in my old AOpen 250w, there were 3VRs, one increased 3,3v, one for both 5v and 12v and another one that doesn't have any affect on 3,3/5/12v.

I will use this PSU for tec, so i'm running the 12v line @ 13,9V and 5V @ 5,95V, the PSU shuts off if i turn the VR more. The 3,3V line is @ 3V (lower voltage @ the 3,3v rail resulted in higher voltage at 5v/12v)

Oh, and btw, the VR for the 5v/12v lines that was soldered on was about 0,9 KOhm and that gave me a maximum voltage at the 12v line of 13,15V, so i added a 0,5KOhm VR in series with the other one to get 13,9V.

[zero3]

wow.. gosu guide!

[BarboneNet]

Hi,
Can i modd my Enermax NoiseTaker 600W??

I can't find the wire sense of Rail 12v and 5v.....

Can anyone help me?

Thanks


P.S. Sorry for my bad english

[Hell-Fire]

wow.. gosu guide!

Thank you sir.

Hi,
Can i modd my Enermax NoiseTaker 600W??

I can't find the wire sense of Rail 12v and 5v.....

Can anyone help me?

Thanks


P.S. Sorry for my bad english

Your power supply may already have internal variable resistors. You will need to take the cover off and look around for them. They aren't always easy to spot, and they will not look like the ones in this guide. They can be small and silver as well.

[C_B]

is the 3,3V sense mod the same on an 24Ppin ATX connector?

[Hell-Fire]

If the sense wires are present, doesnt matter how many pins are on the connector.

[detractor]

very good

[AsAsIn8eR]

I have an ideea of making t3h mod without opening the PSU-thus not voiding warranty.I made the scetch for the 3.3v since that's what interests me but it can be done to all the vsense wires.Tell me your opinions.Thnx.

[kurt]

Hi

I'm new here. Anyone tried to replace the resistor(s) of the TL431??? It is the one who is regulating the 3,3V line.

If not. I'll do so and i'll be back if everything works fine or not. ..

[loopy83]

Hello,
i have done the mod a few moments ago and I have a problem.
Insteat of the 47 Ohm i used a 33Ohm resistor und insteat of the 10k var res. i used an 50k var res..... in my opinion the same function.

When I srew the var res to increase the voltage nothing happens.
I want to be sure an turn the poti to nearly 0 Ohm, so the PSU have to shut down.... but nothing happens too.

The Mod is very easy and i am sure that i am done no mistakes!
What can be the reason for this?

BR Loopy

[TiN_]

AsAsIn8eR

It won't work in your way properly ;-)

loopy83

maybe you made some mistake?


My way of mod, properly working with resistors 33ohm and VR 10k

[loopy83]

I am sure made no mistakes.....
Like this:


Thats a easy mod.... no chance to make a mistake