I use a pwm to control a trolling motor on my kayak. What can I coat the pwm circuit board to make it water resistant? It can heat up a good bit when wide open for a long period and I need something that will disperse heat. The board is:
PWM 3500W Max DC Motor Speed Controller, DC 10V-55V & 100A Max Brush Motor LED Display Stepless Speed Controller with Forward-Brake-Reverse Switch & Adjustable Potentiometer

 

It probably depends on the layout of the controller but I'd think about putting it in a waterproof die-cast aluminium box with cable glands for cables coming out of it. Waterproof potentiometer for speed control, waterproof switch for forward/brake/reverse. Display in a waterproof transparent box. Heatsink on outside of die-cast box.

If it's got to withstand really getting wet then I'd question the effectivity of coating the circuit board.

 

Post pictures of the pcb, then we can advise you best.

 

 

Nice to see that the pot, switch and display are already on wires so bringing them out from a waterprooof box through cable glands should be fairly simple. Are the 12 heatsinks grounded? I'm thinking an aluminium bar across the top screwed into the heatsinks with self tapping screws between the fins which in turn could be screwed to the lid of a diecast box would help get the heat out - but if they are all at different voltage this won't do!

But how hot do they actually get? Your picture looks as if the whole asseembly is normall boxed and has been opened to show the innards. If that's the case, and there is no blown cooling, screwing the top of the enclosure to the lid of a dieceast outer enclosure should suffice

 

More than removing heat, I was trying to figure out if the board could be sprayed or brushed with a conformal coating to make it more waterproof. I have the board in a plastic box to protect it. The problem is that I use it in a kayak in the ocean. While in use, I crack the lid of the box to let heat out so that it does not overheat. This offers a chance for water entry depending on weather conditions. In my previous box I installed a small fan and small vents but it didn't really seem to move much air. When I'm running the trolling motor wide open it pulls about 50 amps which seems to generate a fair amount of heat. I'm not sure if conformal coating can prevent heat dissipation. Also when I catch bait with a castnet in such a small area, water splash is a concern. Though I keep a backup PWM, I'd really hate to blow them since the size of the kayak and the current of the water doesn't make paddling a real option. Basically, I do not want to cause problems with a conformal coating but using it would add another degree of preventing damage by water that may be beneficial. So I was wondering if a conformal could realistically be used without causing issues with one of the components on the board and allow heat dissipation. I'm just surprised that conformal coating is never mentioned in discussions about PWMs for fishing applications when discussing waterproofing or making them more water resistant unless it isn't an option for a PWM board. As you can tell, I'm pretty much a novice when it comes to electronic boards but im learning. Sorry this is so long and probably redundant.