VESC Heat sinks - How much does it help?

Hello guys, in my current build i have serious problem with over heating due to my enclosure being completely sealed and almost no air inside, very tight.

My plans for the next build is milling a heat sink that clamps to booth sides of the FETs and has the fins exposed under the board direct in the air stream. I know that the epoxy side has a poor thermal conductivity, but i think it’s better than no contact with the outside

So for the people who tried heat sinks on the fets, it at least helps to get up some hills?

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Heat sinks will help but it will just delay the onset if you do not have a fan to remove the heat or some passive airflow. Is this a single drive? You can also reduce your gear ratio, and top speed :sob: , but it will reduce your current consumption while climbing.

That’s the idea, the fins will be outside of the enclosure, and i will also lower the gear ratio a bit, currently i’m on 2,78, just waiting for the pulleys to try 3,0, and yes, single drive, no money right now to go dual, unfortunately

Would something like this work?

If you can expose the fins then you should have good results.

@SirDiff Those little fans don’t really push air too well. If you want results from an induction fan setup you need to run something larger off a buck converter.

Might have to try this, I added a buck to power some 12v led strips but it runs hot too since 50v -> 12v. and it shares a box with my vesc…

this style fan moves more air and would work with a low profile…

After thinking of ways to cool my vesc would it work to use a pc liquid cpu cooling system for the top of the vesc and mount the back to an 1/8" peace of alumanum that’s the top of my board, cause a have a corsair cpu cooler and I could replace it with a fan

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Im sorry to burst your bubble, but the heat transfer from the mosfet to the outside package is very low, adding heatsinks will probably reduce your temps in the range of 1-3 degrees tops.

I installed heatsinks on my mosfets and it made a substantial performance difference to me. As Chaka said, it only delays the onset, so heat eventually builds up. Wether it helps or not depends on how you ride. In my case, I have some longer hills followed by flats. Adding heatsinks enabled my board to barely make it up and everything cools off on the downhill. If the uphills were any longer, the heatsinks wouldn’t be enough and I’d be pushing my way up those hills.

Also note that different VESC’s have different levels of performance.

That’s why you need to use heat transfer plaster. Sometimes you need to actually try things before spouting off. :wink:

The key point is heatsinks wont lower temps unless you have some airflow. Without airflow you are simply adding more thermal mass which can help for burst currents ect…

I’m not spouting off, its simple science. As per the mosfet datasheet, the Thermal Resistance to the case (in this mosfet it would be the underside pad) is 0.4 C/W, now the Thermal Resistance to ambien (in this mosfet that would be the package) is 40 C/W.

Adding thermal plaster will not lower that 40 C/W thermal resistance.

This 0.4 C/W would not be from the silicon die from the metal of the underside? And this 40 C/W would be from the epoxi to air, if we replace the air with a cooper mass, this value would not be much lower?

What I am saying is you are using a myopic view by siting the data sheet alone without actual experimentation i.e. “actual” science. It has already been well documented that adding heat sinks with thermal plaster adds significantly to heat reduction.

Heatsink = bigger surface to dissapate heat. Plaster = better heat transfer between mosfet and the heatsink

You can also pack plaster into the void, bridging the gap between pcb and heat sink.

Thermal plaster is often used alone on smaller chips to provide better heat dissipation.

So you’re telling me if a stick a heatsink with thermal plaster outside my oven it will lower the internal temperature by a considerable amount? wow!

No, I’m not. I’m just explaining heat transfer.

How about some kind of heat pipe and radiator system?

The problem is that the case epoxy doesn’t have a high enough thermal conductivity to have a heatsink make a considerable difference. Lets see:

DYE --(40)–> EXPOXY --(0.3 aprox)–> (HEATSINK) —> AIR

Now tell me, will the thermal resistance of the epoxy lower because there’s a heatsink?

To give you a real world test point, I have heat sinks on all my Ollin VESCs (the high-output package VESC from Ollin is the only speed controller I use on my builds). I weigh 225 lbs and rip up hills with no overheating issues. VESCs are in large, but sealed, enclosures.