Guide: Power Supply Sense Wire Modding

[Hell-Fire]

I dont see why it wouldnt work well for you.

The reason I use the 10Ks is so that I am as closer to spec values before adjusting the VR.

Almost any fixed resistor below 80 ohms is a good choice honestly.

[Alexius H [SLO]]

>The reason I use the 10Ks is so that I am as closer to spec values before adjusting the VR.
Why do you need that (safety, ...)?

[Hell-Fire]

Originally posted by Alexius H [SLO]
>The reason I use the 10Ks is so that I am as closer to spec values before adjusting the VR.
Why do you need that (safety, ...)?

Yes, mainly for safety. A lower beginning value (resistance-VR) forces the voltage up higher than maybe the user would like.

Lets say that all you want is around 12.25-12.5v, but the VR you put in is a low resistance. The lowest voltage you maye be able to achieve is 12.85v or more. See what I mean.

I do the same on many other mods I perform. If the Vdimm says to use a 1K, I may use a 5k-10k just make sure I can still close to the default voltages if I want to.

[Alexius H [SLO]]

I see what you mean.
How can I calculate which voltages will I get when I do the mod? What is the equation?

Edit: Another question: VRs must be set on max resistance, right? And then I lower them.

[pucky124]

hey i have a question u say to put the vr on max resistence to get pretty much stock volts right? y would the psu give the same voltage with a 10k vr set on max and b4 the mod with just the sense wire that has maybe 0.0001 ohms of resistence.

[Hell-Fire]

The sense wire itself has very little resistance, but there are internal resistances at work.

Not to mention the Vregs responsible for handling the regulation of the different voltage rails.

[pucky124]

ok but still y does adding 10k ohms of resistence not change the voltage very much but turning the vr down to say 8k ohms raise the voltage. to my understanding no matter what u do to the sense wires u can never take the resistence down (well significantly anyway) but u say that turning the resistence in the vr down raises voltage.

[Hell-Fire]

Ok, look at it this way instead.

Typcically there is something on the pcb that is regulating voltage/current, versus just using a ton of resistors and diodes.

These ICs are responsible for keeping the voltages per rail within their given specs (say withing 5-10%). Now, we add a resistance there and the regulators think they are not providing enough voltage and increase the current/voltage.

The other case is that we have an internal resistance in the circuit loop we are working on. When you add a VR in parallel with that internal resistance, you effectively lower the overall resistance of the system which increases the voltage. Everytime you adjust that VR you are lowering the total resistance even further which causes the voltage to increase even further.

Simple Case:

Current = Voltage / Resistance (Ohms Law)

If you lower the resistance in a system where the current/voltage are not variable, then the overall current/voltage must increase to even out the equation.

[pucky124]

ok thanks for the help i think ive got it now but couldnt u do that mod on any 12v and gnd wires since they r all in parallel? like couldnt u use an old molex and just run the vr inbetween the 12v and gnd wires (the 47 ohm resistor might still b needed) that would make it really eaasy to enable/disable the mod.

[Hell-Fire]

No, because a straight thru voltage line has no feedback and adding resistance there would lower the voltage.

On a voltage rail without feedback (sense wires, etc), the regulator has already compensated for the internal resistance and is feeding voltage as it sees fit. Adding a resistance into that voltage rail will only lower it.

I use to make my psu mods where you could disable them on demand if need be. I stopped doing that because it was extra work and no1 ever used the switches I installed.

An easy way to make the mod removable so you can get back to stock voltage, is to solder one of the GND (black) wires of an old molex plug to the ground pin of the VR and then plug that into a working molex off the psu. When its plugged in, the mod is in effect...unplugged and the mod is turned "off".

Here is an older mod I performed on an Antec TP550. You can see where I used old molex connectors, and plugged them into those pesky "Fan Only" headers for the mod to become active:

[pucky124]

now it seems the more i know (or think i know) the more it confuses me. the sense wires were all connected to the respective rails right? now is the vr there to change the resistence between the rail and the gnd or the sense wire on the psu pcb and the gnd? and y dont psu makers run the sense wires internally instead of off the mobo connector?

thanks 4 all the help

[Hell-Fire]

The sense wires are connected to the voltage rails at the ATX Connector, but they are connecting seperately from them on the psu pcb. They are running to respective traces that filter from the Vregs responsible for their regulation.

The VRs are there to change the resistance between sense wire (on pcb) and GND. Which is actually changing the resistance between the Vreg and GND. Think of the sense wires as just a longer trace from the Vreg and not as a totally independent component.

The reason the sense wires run to ATX Connector is to monitor the onboard voltages and to use that reading to maintain those rails at spec.

[pucky124]

thank you i think i finally understand that part i still dont understand how the voltage regulators work but im gonna use google to figure that out because it would take to long for u to explain it to me and im sure u have better things to do

again thanks

[Hell-Fire]

Was my pleasure.

Good luck and keep learning man.

[mysticdrew]

My brand new (kinda shiny) Antec TP550 just arived, and I've been debating on what I need to remove out of my 5.25 bays for that front panel that comes with it, then I found this awsome thread (thanks a bunch Hell-Fire). So if I do the sense mods I wont need the front panel correct?

[Hell-Fire]

No, you wont need the front panel, and in fact it can be dangerous to use it after the mods honestly.

The front panel puts another VR in parallel with the VR you just added....which lowers the total resistance even more...almost to the point of a short circuit depending on the value of the VR.

[mysticdrew]

I almost forgot, without the front panel, how do I get my fan at Max speed then?

[Hell-Fire]

You would need to take off the housing again and solder the fans power wires straight to the 12v wires going into the psu pcb.

You can do this by soldering the red wire from the fan to the yellow wire of the psu. Obviously solder hte black ground wire of the fan to the black ground wires of the psu. You should be able to solder these wires to the silver capped wires running into the pcb.

You can ignore the yellow wires from the fan.

[Boyne7]

that is definately the best psu sense mod ive ever seen.
Im sooo glad i traded my friend now lol, i traded my raidmax 500watt (no sense wires) for his TP430. reason was that the tp430 had problems with his motherboard (abit av8) its almost a shame i have a powerstream 520 on the way, but not really.

[Boyne7]

one more thing, approximately what voltages can be achieved with this mod before the ovp kicks in?

[mysticdrew]

Thanks a Lot HF for this great guide.

Also what do you use for Hot Glue? I've tried High Heat and Multi Temp glue and it doesnt stick to PCB's very well and it's all stringy.

The first time I tried to glue the Pots to the inside of the PSU the glue didnt stick so I sanded the case down a bit so it wasnt smooth and it stuck fine, but I cant really do that to a PCB.

[Hell-Fire]

Originally posted by Boyne7
one more thing, approximately what voltages can be achieved with this mod before the ovp kicks in?

Depends on the psu, but with the Antec TP430:

+5V trip point < +6.5V
+3.3V trip point < +4.1V
+12V trip point < +14.4V

Originally posted by mysticdrew
Thanks a Lot HF for this great guide.

Also what do you use for Hot Glue? I've tried High Heat and Multi Temp glue and it doesnt stick to PCB's very well and it's all stringy.

The first time I tried to glue the Pots to the inside of the PSU the glue didnt stick so I sanded the case down a bit so it wasnt smooth and it stuck fine, but I cant really do that to a PCB.

I use an Arrow Dual Temp Hot Melt Glue Gun and the matching Dual Temp Hot Glue that comes specifically for this particular gun.

The best advice I can give is to clean the area you plan to glue to with Acetone or rubbing alcohol first. Then, apply the glue to the area and use the gun tip to "smear" it around a bit to make sure good contact is being made with the pcb.

This has always worked for me.

[mysticdrew]

ya, i just have one of those $2 guns from walmart heh. I'll look into getting a better one then.

[Hell-Fire]

I definitely recommend something that is Dual Temp.

You can find them cheaply at Lowes, Home Depot, and on Ebay.

[David302]

I have a question, the PSU from thermaltake 480watts not PFC don't have the v-sense wire in 12v rail and the 5v rail, how made this mod work on this PSU or only works in Antec PSU's ???


PD: Sorry if my english is not clear