12020 heat

[BrianG]

Hey, I noticed after running for a while that the sides of the ESC seem hotter than the heatsink itself. Without removing the heatshrink, I assume that the PCB traces work as a heatsink for the lower layers and the heatsink is only on the top layer of FET devices? Since I've had my ESC for a few months now, I was thinking of risking the warranty by removing the heatshrink and attaching heatsinks to the sides of the ESC. While I'm at it, I'm thinking of adding a larger one in place of the current one. I could use a fan, but I'd rather not use one just for the sake of simplicity. Does anyone have detailed, close-up pictures of what a non-burned ESC (9920 or other would work too) looks like without the heatshrink? I don't want to remove the shrink unless I have a reasonable idea that what I want to do is possible.

[MetalMan]

I have a picture of the bottom of a 9918, and without taking the shrink off of my replacement 9920, the components look to be in the same spots. This controller was sent in to be repaired (hence the yellow circles), and was just recently replaced. Here is the only picture I have, of the underside:

[BrianG]

Thanks. I kinda figured the underside would be the same since that is where the "brains" and BEC of the controller are and that part won't change much between, if at all. However the number and maybe type of FETs will change depending on the current specs of the ESC and the nominal voltage.

The majority of the heat seems to come from the sides where there is no actual heatsink. That's why I'm still looking for pics of the sides. From what I know of how these are built, the FETs are probably stacked on top of each other with only a layer of PCB between them. The fact that they are stacked lets the heat from the FETs from the lowest level heat the FETs above them through the middle PCBs with only the circuit traces of the PCBs acting as a secondary heatsink until the heat gets to the little heatsink on top. If this is built like I suspect, I can procure a piece of mica insulator to electrically insulate the PCB edges from the added side heatsinks to prevent possible shorts (if needed).

After seeing the new Quark ESCs, it seems they have a better heatsink scheme. I think the 125B will be my next ESC purchase. But for now, I'd like to make my current ESC as cool as possible. Even if I did use a fan, it would only cool the heatsink and not do much for the ESCs further down...

Metalman, How did you get your ESC serviced. One of my old ones has been down for about a year and I'd like to get it back up.

[MetalMan]

Originally Posted by combatcm

Metalman, How did you get your ESC serviced. One of my old ones has been down for about a year and I'd like to get it back up.

I sent it to Mike, and he tried fixing it, but ended up sending it to BK.

BrianG, you are right about the FETs. I had not realized it before, but they aren't allowed much heatsinking. Maybe the idea is that the FETs on top that have a heat sink will be cooler, thus decreasing their resistance so they take more load than the non-heatsunk ones that will be hotter and have a higher resistance.

[BrianG]

Well, I removed the heatshrink from my ESC last night and they are indeed stacked with a layer of PCB in between. There is even heatsink grease between the top of the FET and the bottom of the PCB, but I noticed there is about a 1mm thermal grease-filled gap between the top of the FET and the board above it. Heatsink grease does help reduce thermal resistance, but only if used VERY thinly. It's only designed to fill in the microscopic inconsistencies between the mating surfaces, otherwise it really is useless when filling gaps. MOSFETs by nature conduct less with increased temperature, so they tend to sorta self-regulate to a degree, but this would explain why some people burn out one of the layers since the tops of the FETs don't mate closely with the PCB above it so they retain the heat until they ignite. As a matter of fact, that globbed thermal grease actually retains some heat. :(

All in all, I like the design of the BK ESCs, but I really wish a little more attention would have been made to some of these types of details. A small slab of aluminum between layers would help sink/spread the heat, and fill in the gap. Personally, I'd make this slab bigger so it can be extended out the sides to allow a larger heatsink to be attached. But that's just me.