silly/wild idea to improve ESC current handling capability

[Ron van Sommeren]

Sand/file (SMD) FET housing(s) open, glue/epoxy aluminium to housing.
What about moist? Lifetime expectancy? Deterioration?

Vriendelijke groeten ;) Ron
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[Comatose]

Ron, there are FET packages that do exactly what you describe, but without all the modifications. Toshiba's SOPA package is a thinned, thermally enhanced version of SO-8 that's used in most airplane ESCs. http://www.toshiba.com/taec/components/Datasheet/TPCA8004-H.pdf is an example.

International Rectifier's DirectFET is even closer to what you describe.

These solutions take the thermal resistance of the FET from about 20C/watt to more like 2C/watt.

If you figure a typical motor driver generates 1 watt per FET at max load, and shuts down at a delta T of about 100C, this would give you about 20% more current capacity for a given size. That's generally not worth the extra cost of the package compared to simply using one more fet in our application.

[Ron van Sommeren]

That much??? I would expect a current increase by a factor 10 in that case. What am I missing?

Prettig weekend ;) Ron

[Comatose]

The majority of the thermal resistance in an ESC is between the PCB and the air, not between the FET and the PCB. If we had water cooling availiable, or huge heatsinks, then there would be a much bigger benefit.

[birdofplay]

Any thought to just removing the OVER WRAPPER ?

and or adding a heatsink ?

Or better yet ( schematic and fanout dependent ) ...

paralling larger FET's , aka piggybacking FETs ?

[Ron van Sommeren]

That's what I meant, adding a heatsink.

[Trisquire]

Don't all the car/boat ESCs have huge heatsinks?

Tom

[duhh]

just look at the cc esc. for cars ... mamba max .... is has some heatsink there !!!but it should be as close as possible to the switching point ...

[Bruce Abbott]

That much??? I would expect a current increase by a factor 10 in that case. What am I missing?
RonPower is proportional to current squared, so 10 times greater current would cause 100 times greater power loss! Even if a super heatsink did allow your ESC to handle 10 times the current, its efficiency would be horrible :(.

[Ron van Sommeren]

Not bad for an EE huh (me, that is).

[z-matrix]

That's what I meant, adding a heatsink.
hi Ron,
i whouldn't sand the so-8 packages, that will decrease reliability of the device, i whould also suggest DirectFET(tm) by irf
though i don't like heat sinks, the excess heat generated must be dissipated somewhere.
This can be difficult inside of a foam plane without airflow for example, or under the heat shrink...


That much??? I would expect a current increase by a factor 10 in that case. What am I missing?

Prettig weekend Ron

You should take in count the mosfet's internal drain source resistance, that is slightly increasing at higher currents,
and a stabe P_D=I*I*R_DS_ON conducting state power dissipation, so if you want 10 times current with same R_DS_ON you will have to dissipate 100 times more heat.

Z

[coro]

I guess that ESC fets do have maximum specified in datasheets. They are not resistors to simply heat more or less, they are fets - current passing thru fet is allmost exactly stabilised to value specified by temperature and gate voltage. I mean that You cant use higher current with existing fets, even if You would use water cooling.

You have to exchange fets in esc. It is possible to use couple of them in parallel, but.. Using more powerfull ones, You can go for many times higher currents - it depends on exact type whether it has bigger surface for better thermal resistance, or it is tiny smd with extremely low RdsOn, to achieve higher power parameter in price list.
In addition, using heatsink You are increasing flight weight and You are wasting batery power, so I guess that using better fets brings better efficiency.

The only point of troubles to keep is mind is gate capacitance, slowing down the fet switching thus leaving the fet in linear mode for fraction of time. This is the reason for extreme heat and fet destruction. So, using hundreds of fets in parallel is possible, but You have to drive their gates by appropriate power - very probably, small ESC is insufficient as talking about powerfull fet driver.

As for me, I found ESC heating ONLY when using linear BEC - it is wasting energy and can fail with fatal results.