I built a watertight PWM controller for my kayak trolling motor recently, and needed a way to let air circulate without letting water in.  After thinking about this for quite some time, and seeing several high-cost solutions, I came across the idea to use an old KN95 face mask as a filter.  I had remembered seeing where they won't pass water at all, but obviously pass air.  So, some vent holes backed by a face mask held in place with marine goop, and problem solved for no money out of pocket!  Just thought I'd pass it along. 

 

Also, the melting point of the face mask is about 160°C (320°F).  That's a good bit above what most electronics can handle, as many electronics components aren't designed to be operated above around 105°C.  So you'll likely fry your circuit before melting the mask material if that was a concern.  

You do you Magruber.

34 minutes ago, Deleted account said:

You do you Magruber.

You got no idea!  

 

And I am quite proud of my record.  1,246 DIY projects.  $14.37 lifetime total saved versus buying new.  0 significant structure fires.   

9 minutes ago, Bankc said:

0 significant structure fires.   

LOL.

Are you using the controller for speeds or charging controller, and why not just do a rheostat, shunt or the like? and doesn't the trolling motor have something built in?