Inside the Quark 125, pics.

[thesteve]

I don't think the voltage limit of the mosfets is the problem with supporting 6S in the ESC. Mosfets will keep operating just fine at higher voltages until they fail - and when they do fail you'll know cause you'll smell that lovely electronics smell. Without having one of the controllers to look at I believe the problem with higher voltages is simply a function of how fets work, in general you need/want a higher voltage on the gate(the on/off pin if you will). To get this higher voltage pretty much all ESCs have a voltage charge pump(booster) So even though you may have a 6 cell nimh pack connected the ESC is turning the fets on and off with 12 or more volts. I am guessing the charge pump in the Quarks isn't high enough to keep the gate voltage higher then the input voltage, and as a result the fets will not turn on properly.
The ESC above appears to have 36 fets (6 per phase) which is a very solid design. Even the Schulze U-Force which is a very good controller only has 18 fets in it(3 per phase)
Also the fets they are using are quite good - rated at 28 amps in real world conditions.

[GriffinRU]

Originally Posted by thesteve

I don't think the voltage limit of the mosfets is the problem with supporting 6S in the ESC. Mosfets will keep operating just fine at higher voltages until they fail - and when they do fail you'll know cause you'll smell that lovely electronics smell. Without having one of the controllers to look at I believe the problem with higher voltages is simply a function of how fets work, in general you need/want a higher voltage on the gate(the on/off pin if you will). To get this higher voltage pretty much all ESCs have a voltage charge pump(booster) So even though you may have a 6 cell nimh pack connected the ESC is turning the fets on and off with 12 or more volts. I am guessing the charge pump in the Quarks isn't high enough to keep the gate voltage higher then the input voltage, and as a result the fets will not turn on properly.
The ESC above appears to have 36 fets (6 per phase) which is a very solid design. Even the Schulze U-Force which is a very good controller only has 18 fets in it(3 per phase)
Also the fets they are using are quite good - rated at 28 amps in real world conditions.

And this story about FET's and high voltage based on?
And do not blame fet's control if you not sure how it works...

Artur

[thesteve]

Originally Posted by GriffinRU

And this story about FET's and high voltage based on?
And do not blame fet's control if you not sure how it works...

Artur

Based on education and several years experience working with, repairing and designing speed controls that use mosfets. And anyone thats knows basic mosfet operation would also know...

[jhautz]

I'm looking at this thing trying to think of how to get more heat out of it. Adding additional mass to the bottom seems to make a huge differeance in disapating the heat. But thats only taking heat off of the bottom layer of fets. I'm thinking that opening this thing up and adding somethiing to the sides of the heat spreader to help pull the heat out of the middle of this thing could be the ultimate way to heatsink it.

Do the sides of the heats spreader contact the aluminum sides of the case?

This is really interesting to see how its set up inside. I have been wanting to tear mine open, but didnt want to void my warranty.

Cartwheels, If you open it again can you get some pictures of the top board also? Anyone know what part of this thing is the BEC?

[GriffinRU]

Originally Posted by thesteve

Based on education and several years experience working with, repairing and designing speed controls that use mosfets. And anyone thats knows basic mosfet operation would also know...

Well, then any good (Quark is good) pump-charge based (not fixed 12V) fet driver has a feedback, which helps to set the voltage at level which guaranties FET's turning on and FET's safety (not to exceed GS voltage) and as well fast transition and...
Based on this your previous guess is wrong!

And any comments on Leroy's question as a professional?

Artur