What’s the hot side of a JK?

[Skypower]

I’m running the JK B2A20S-20P’s and now I’m about to commission #3. The previous two are mounted large flat side toward the vertical mounting surface (wood) with 3/8” spacers so that convection cooling can occur. The thing is now if I can do the same thing except flip it bump side with spacers to the mounting surface, my battery cables run will be be about the same as the other two batteries(no double back). Just wondering what side of the JK gets the hottest (both?)from the MOSFETs or does the top need to be the coolest? Or am I overthinking it?

 

[RCinFLA]

There are twenty power MOSFET's on each side of PCB, so both sides get hot.

 

[Skypower]

Thanks RC!
Should have known you’d be the one to have the answer. You are the data base. I was tempted to have a peek inside, but passed experiences and always having Murphy sitting on my shoulder just waiting has taught me better. Does RC stand for remote control or your initials?

 

[upnorthandpersonal]

Keep in mind that, unless you constantly draw high loads, they don't get hot at all. Mine don't even help keep the batteries warm in winter...

 

[RCinFLA]

But you don't want BMS only warming up some of the cells. Overpotential voltage is temperature dependent, particularly at cooler temps. Same as having mismatched cells.

Drives greater wear on some cells and accelerates cell misbalancing.

 

[upnorthandpersonal]

Sure, I was just trying to make the point that the BMS doesn't get warm enough to make a difference inside the box.

 

[Skypower]

Thanks guys. To my surprise, with my use patterns it seems the bms’s don’t really get that warm but I always plan for the worst case scenario. They probably are benefited by the air gap. I used FLIR to find any hot spots and found the DC to DC converter was pushing some heat through 1-1/2” of ply and warming the upper part of the last cell a few degrees. I spaced off the converter and added a mirror shield in the gap. Now there’s virtually no difference in the end cells. Those two batteries have a fan on timer that blows over them in the cool morning hours that pulls heat out via the terminals. This gives them a running head start to offset the heat gain of the day’s charge and afternoon discharge. The bench top protects these but the new one is on the floor and has higher sides, covered top, ends and is on heavy duty casters. It has a cooling fan with differential thermostat and several thermal fuses in the outlets so it can’t feed the flames if SHTF. The wood is treated with fire retardant and painted with silver gray 2000 degree header paint. Like the others batteries, it has side by side 8 cell modules so it can easily be separated and moved. This also shares the centralized compression springs but this one has the cells with two hole terminals and laminated flexible busses.