Custom (very) Quark esc heatsink...

[BrianG]

I've wondered that myself, but it may simply be the way the Quark operates. I made a thread a while back showing the differences on how the MM behaves vs the quark when the motor is forced to a stall condition. Basically, the MM simple increases the throttle until the motor finally moves (which is bad IMO and the root cause of a couple of them burning up) vs the Quark being MUCH more gentle about it. I know this is mostly firmware programming, but maybe the engineers at S&T decided to decrease the slew rate a little for control reasons? And if you decrease the slew rate, there is more time where there is an actual voltage drop AND current draw creating more power loss. I really don't think it's a matter of raw FET specs. But, even in your example, 10W is actually quite a lot of power to be dissipated on a small heatsink.

And, I've not found a reason to get crazy with heatsinking - just enough to pull the heat away from the case and dissipate it to the ambient air, which should have enough flow in a moving vehicle to do so effectively. I don't like heat - at all - so when I say the ESC isn't hot, it isn't. To me, 130*F is too much.

[coolhandcountry]

I don't run a heat sink on a quark 80b. I have great temps on my gmaxx.
That is one huge heat sink though.

[BrianG]

Yeah, I've never thermaled before I added any extra sinking, but I thought it got too warm for my liking. I guess I'm just funny that way. :)

BTW: What's up CHC. Haven't seen you around a lot lately...

[zeropointbug]

Originally Posted by GriffinRU

Looking on all this mighty heatsinks I am thinking how much power dissipates on Quark?

Lets say 7XL draws 50A continuously, so at 0.00036Ohms at 25C power loss should be 0.9W
Next say at 100C derating factors bring us to 3 times up, so 0.00036*3=0.00108 - power loss now 2.7W

To get even 10W requires Rdon to be at 0.004Ohm which is 11.1 times higher then at 25C.

So, is the ESC efficiency so low or there is something else?

LOL, okay now I know... are you sure you know what your saying?

The physical resistance is only PART of the heat output. Most of the power loss is the design of the motor, and how well it transforms the power input to it.

What is 2.7Watt? That would be barely warm to the touch....

The esc I am guessing is somewhere between 92 - 97% efficient. Couldn't tell you, it's probably about 10 - 25 watts of heat, which is alot for these little FET's to dissipate, that's why they can get so hot because of insufficient heatsinking. With a proper heatsink, 25 watts of heat is a piece of cake to keep the temps down (~15C Delta).

Is there a misunderstanding here about motor efficiency.

[coolhandcountry]

I think some times the driving styles effect the heat issues as well.

Not alot brian. Just figured i would show up and throw some input around. :D

[BrianG]

Originally Posted by zeropointbug

LOL, okay now I know... are you sure you know what your saying?

The physical resistance is only PART of the heat output. Most of the power loss is the design of the motor, and how well it transforms the power input to it.

What is 2.7Watt? That would be barely warm to the touch....

The esc I am guessing is somewhere between 92 - 97% efficient. Couldn't tell you, it's probably about 10 - 25 watts of heat, which is alot for these little FET's to dissipate, that's why they can get so hot because of insufficient heatsinking. With a proper heatsink, 25 watts of heat is a piece of cake to keep the temps down (~15C Delta).

Is there a misunderstanding here about motor efficiency.

Let's start by saying that motor efficiency has very little to do with ESC heat. The only motor spec that might effect ESC efficiency is the inductance value due to the phase angles produced, which can be more difficult to drive.

Assuming an FET goes rail to rail, the only time an FET dissipates power is when there is a voltage drop across the device AND current flow. If the output of the ESC were perfect square waves (0 rise time), then the ESC would be 100% efficient no matter what the motor is doing with that power. At the 0 point of the square wave, there is full voltage across the FET but 0A (0 watts). At the max point of the square wave, there is 0v dropped but there is max current (0 watts). But during the ramp up (the total time it takes to do this is the slew rate), there is voltage dropped AND current flow, which creates the heat. The longer the ramp, the more power loss and more heat. Higher frequencies have more pulses per second and therefore more "ramp up and downs" which can make them an ESC heat up more. However, too low of a switching frequency will cause the motor to not act correctly.

[BrianG]

Originally Posted by coolhandcountry

I think some times the driving styles effect the heat issues as well.

Not alot brian. Just figured i would show up and throw some input around. :D

I think you're right about the driving style. Of course, there are a ton of other factors as well.

While you're throwing input around, make sure it doesn't hit anyone. Someone can lose an eye that way! ;)

[zeropointbug]

Originally Posted by BrianG

Let's start by saying that motor efficiency has very little to do with ESC heat. The only motor spec that might effect ESC efficiency is the inductance value due to the phase angles produced, which can be more difficult to drive.

Assuming an FET goes rail to rail, the only time an FET dissipates power is when there is a voltage drop across the device AND current flow. If the output of the ESC were perfect square waves (0 rise time), then the ESC would be 100% efficient no matter what the motor is doing with that power. At the 0 point of the square wave, there is full voltage across the FET but 0A (0 watts). At the max point of the square wave, there is 0v dropped but there is max current (0 watts). But during the ramp up (the total time it takes to do this is the slew rate), there is voltage dropped AND current flow, which creates the heat. The longer the ramp, the more power loss and more heat. Higher frequencies have more pulses per second and therefore more "ramp up and downs" which can make them an ESC heat up more. However, too low of a switching frequency will cause the motor to not act correctly.

Yah, i agree! Power switching is a HUGE issue today!

Check out THIS , I don't really know how they do this, but they use 24khz switching. Something called 'Softswing", the switching is inaudible (first for EV inverters), and by far the most efficient EV inverter too, with 97% eff.

Also, (check my signature) they told to wait for their new 'Hybrid Synchronous Motor" to come out for my vehicle. Would you have any idea what it would be? They told me it would have very broad eff. range, and good torque range, just a very good motor all around...?

But yah, the internal resistance is only part of the losses of heat, a small part.

[BrianG]

The whole switching thing is a double edged sword. Too low and the motor speed suffers (not to mention erratic behavior). Too high and you have more losses due to having more switching pulses. By the sounds of it, they are actually decreasing the slew rate, which should cause things to heat up more. I'd be very interested to see how they do that! The only way I can see it working is if they use a tracking power supply, which I don't think is feasible/practical at anything close to the frequencies they are talking about.

I have no idea what kind of motor they have in mind. Personally, I think the motors we have now are pretty darn good since they approach 90% efficiency.

Just to clear things up; I'm not an electrical engineer, just someone with perhaps a less-than-healthy interest in this stuff. :)

[GriffinRU]

Originally Posted by zeropointbug

LOL, okay now I know... are you sure you know what your saying?

The physical resistance is only PART of the heat output. Most of the power loss is the design of the motor, and how well it transforms the power input to it.

What is 2.7Watt? That would be barely warm to the touch....

The esc I am guessing is somewhere between 92 - 97% efficient. Couldn't tell you, it's probably about 10 - 25 watts of heat, which is alot for these little FET's to dissipate, that's why they can get so hot because of insufficient heatsinking. With a proper heatsink, 25 watts of heat is a piece of cake to keep the temps down (~15C Delta).

Is there a misunderstanding here about motor efficiency.

Thanks, but I think you need to work harder before you can corner me :)

Well, FET dissipates heat during switching when it is in analog mode, defined by rise and fall time plus capacitance and inductance of load. Which means that load (motor) can influence and does on ESC efficiency as well. Well if you integrate over time then you can calculate power loss on ESC, would be difficult to do that over each individual FET. And yes ther are lots of them in parallel, so 10W over n-FET's with 23.4cm^2 (70mmx34mm) heatsink surface area would be great. Old rule of thumb 1cm^2 per 1W good for 50C.

Do not forget to drive those FET's you need some power too, FET's are field driven but speed cost power, current in this case. In addition do not forget about built-in diode and it's temp dependence, I am assuming you know what this diode does in pair with caps, right.

Brian, for motor to be sensitive to rise and fall of FET's switching motor system (motor and inertia of drive train) must have response time in microseconds at list if not nanoseconds. Our motors without load maybe have ms of response time.

For me it looks like Quark 125A controller might have problem with some component on board, based on Leroy's comment about his low temperature runs with 80A. Does anybody have a clear picture of 125A PCB with FET's control part?

[zeropointbug]

Originally Posted by GriffinRU

Thanks, but I think you need to work harder before you can corner me :)



Brian, for motor to be sensitive to rise and fall of FET's switching motor system (motor and inertia of drive train) must have response time in microseconds at list if not nanoseconds. Our motors without load maybe have ms of response time.

Corner you?


When you say response time, do you mean to say a motors inductance? What do you mean when you say a FET in analog mode? A transistor is a digital piece of hardware, it's either ON or OFF. AC Induction motors especially will smooth out a pulse (switching frequency) from an inverter because of inductance; to create a more sine wave looking shape (wave).

We don't really know how much power is dissipated by the Quark, could be 10 watts (average), also, this would be in a MT application we are talking.

So who knows, my guess for efficiency is roughly 96% efficiency. That's my guess? :032: :030:

[Serum]

I think he means slew rate.

The time it takes to activate a FET, and also important, the ripple it brings along in the signal.

'A transistor is a digital piece of hardware'

I don't think you get the basics of a transistor. because a transistor/FET is a analog as possible. that's what's causing the slew-rate. it's not an on/off operated thing. there are million steps in between.

[Serum]

another thing;

if it has got a 10W heat dissipation, and it's 96% efficient, the input power is 240W, a bl controller is more efficient than that.

[zeropointbug]

10 watts, no one said it was definitively 10 watts. The heat dissipation is totally dependent on power usage, does anyone have an EPA for RC MT? :005: :005:

So what is a transistor in half ON then? :032: A millions steps in between?

[Serum]

I missed the 'average' in the 10W part.

Since when is half on considered digital? if ON is close to 0 of internal resistance, and off is close to endless internal resistance, what is digital about that? The slewrate thing explains itself this way.
depending on the speed the signal is put on (and the speed of the transistor/fet) is one of the things that makes the controller more efficient.