Originally Posted by NABBO
occamRazor thanks for the explanation of asic
to overvolt the GTX 780, I should not have + margin, having a fan over the vrm?
hybrid should give better results than other solutions to air, which is why I feel I can risk a little bit more ...
The only part of the card thats watercooled by AC Accelero is the core, the VRM´s are still air cooled; the heat produced in the VRM area is exponential with voltage, from 1,212v above on air you start to have temperatures above 85C in the VRM´s;
Here is another quote from one of my posts:
"The problem with added voltage is not the core temps but the VRM temps, and that temp increases as the voltage increases so you can increase the core speeds, so you could have perfectly acceptable temps for your core but having your VRM´s with temperatures well above the intended specs;
Power (Watts) = Voltage(Volts) x Current (Amperes) - adding voltage allows for more amperage as you increase the core speed, all that amperage (except what goes to the GPU) has to be dissipated in the VRM´s (especially by the MOSFETs**) thats why watercooling is needed; when you increase the voltage, you increase the flow of current (amperage) and the heat it produces in the VRM´s area needs to be dissipated(VRM´s, mosfets and power inductors*)
No air cooler that i know of is specifically cooling the VRM area that´s why you see VRM´s high temps with air coolers even at core 70C or below, while it covers the core area well it doesnt cover the VRM area properly! thats why EK blocks are the best for the titan/780, the cooling area covers VRM´s, mosfets and power inductors!
*(the inductors can sometimes generate a buzzing noise depending on the amount of current that is passing through…)
** normaly it´s the mosfets that you see burned (remember the 590?)
"Nothing in physics or as in the word it self (knowledge of nature) is safe as unpredictability runs in every aspect of it"
And another about voltages and temperatures!
"Please do NOT GO ABOVE 1,212v WITH SOFT VOLT MOD AND LLC DISABLE!
No air cooler has the capacity to dissipate the heat load out of the VRM area when OC with overvoltage! And you cannot know the VRM´s temps, only do an estimate calculation based on your power draw! HEAT KILLS!
Exactly what happens depends on how excess the power is. It may be a sustained cooking. In this case, the MOSFET gets hot enough to literally unsolder itself. Much of the MOSFET heating at high currents is in the leads - which can quite easily unsolder themselves without the MOSFET failing! If the heat is generated in the chip, then it will get hot - but its maximum temperature is usually not silicon-restricted, but restricted by the fabrication. The silicon chip is bonded to the substrate by soft solder and it is quite easy to melt this and have it ooze between the epoxy and the metal of the body, forming solder droplets! Excess heat leads to short circuit! Usually, a MOSFET will fail short first. This is because excessive heat will, by diffusion, mix the dopants enough to create a good conductor instead of the p-n or n-p barriers that were there originally. Often, the gate oxide will be taken into the diffusion, too, causing a short between all three terminals.
Only if the short circuit current after this first mode of failure is high enough to blow the bond wires or the entire transistor, there is an open circuit.
Another forgotten thing is the voltage controller NCP4206 itself! its rated for a maximum operating temperature of 85C and again no way to measure the temperature!"