JRK 12V12 overheating

Hello i run the JRK with 45A i cooled them with cooling fins and a fan and now i have the second JRK wich overheated.
what could i do better?
Should i take a lower amp number?

What is 45A? Continuous, peak, or rated on motor? Jrk is 12A continuous and 30A peak.

Maybe you have had Jrk for awhile now but appears you would have been better off with a sabertooth controller. Sabertooth 2x60 runs 2 motors at 60a continuous and 120 peak for each motor and with purchase of Uno too it costs about the same as 2 Jrk controllers. You may be able to use sabertooth 2x32 also in which case would be around $65 less than 2 Jrk.

That's why I'm moving from 12v12 to 2x60. 60a continuous, 120A peak... enough said

The Polulu JRKs use an ST H-bridge chip that has metal slugs that are designed to be bonded to the circuit board to dump the heat that way. If you check the datasheet (http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00043711.pdf) in Figure 2 they show the heat slugs and in Section 4 they discuss the thermal considerations with that chip. As practice has shown, you can mount a heat sink on top of the chip and cool them that way, but it's far more efficient to pull the heat out through the board instead. The split is about 80/20 - 80% of the chip heat is dissipated through the board and only 20% is through the plastic.

The bottom of the JRK board is free from all components so I mounted mine to cheap heat sink / fan assemblies with a thermal pad (electrically insulating but good heat conductors). You just want to be careful to clip any header pins flush or below before soldering them in place so you don't have anything to stick through and short out. At 12A continuous load, the temperature of the bare plastic top of the H-bridge only rose a few degrees. That was it. This method is overkill but it also makes for cool-running JRKs and handy mounting.

The red box in the photo was a test print before I had the idea to scavenge the cooling air from one side of the heat sink and duct it down into the mount/electronics bay below. The CAD render is what I'm printing now so no photos yet of it but hopefully it's clear how the duct will align with the heat sink to collect and redirect the air.

And here is the final version with the .stl file to print if anyone is interested. Not sure which other heat sink fan assemblies it will fit besides the Alpine. I didn't carry the duct up all the way on purpose so it wouldn't be grabbing all the air. I don't really think that matters, though, and maybe it should have gone all the way up to force more air into the box. The majority of the heat will be dissipated by the heat sink anyway but I wanted to get some air circulation through the lower electronics bay. Makes for a neat and clean installation, and too much cooling is way better than too little even if it is overkill. When I bought mine they were just $10. Looks like they are $16.99 each now. http://a.co/i5btPWy

@Zed in that first pic, the fan to the right, is it hooked up to the JRK and getting power via USB? Haven't read the docs yet, lots of random questions as going through posts finalizing purchases and getting ready to build

@gSeat - those are 12 volt terminals and the power comes from the power mains that run the motor. USB is only 5 volts. The fans won’t run until the power supplies are turned on.