Not so long ago, someone asked whether heat sinks had ever been applied to the BBSHD with any success. This reminded me to document what I have done for posterity’s sake. I turned a motor whose casing temp was 165 degrees fahrenheit and reduced it to 135. Still pretty warm but a 30-degree reduction nonetheless.
Whats The Problem?
Well, there isn’t one, actually, unless you are really beating on the drive. Even then its only going to be an issue under specific circumstances. The fact is, these motors are pretty well built and they generally don’t suffer from heat issues. Unless…
- You are running the motor on the street, say, on long city blocks, and either laying into a high level of continuous pedal assist, or the throttle
AND
- You are running the motor on a 52v battery, in its max 30 amp configuration
AND
- It is REALLY hot outside. We are talking 100-110 degrees fahrenheit (38-43 Celsius).
So, we’re talking summer commutes or midday shopping runs in Central California on streets like this, where my bike – which I geared for proper pedaling at 28+ mph – is putting out 100% power from the motor, continuously in between stoplights… and its a long way to the next light.
Put all of these things together and now you have a motor that gets hot. How hot? My Stormtrooper – A rescued Motobecane Lurch frame with carbon fiber 90mm deep dish wheels, 52v 30a BBSHD, and a Luna Lander front air fork – was seeing motor casing temps of 165 degrees. Yikes.
So…. what can you do? On this bike, I added a whole slew of 8.8mm x 8.8mm x 5mm heat sinks – purchased with thermal adhesive already applied so they are just peel-and-stick. Here is a link to the source I used. You can find them quite a bit cheaper buying direct from China but you will wait a couple of months for them to arrive. When done, the motor casing looked like this (I completely encircled the motor so there are many more of these things on than you can see here):
Next, I put on another large round heat sink on the end cap. Since it was sold to me in bare alloy, I used radiator paint (for minimal impact on heat transfer). I also had to apply my own heat transfer adhesive. I chose this style as it had the large center area that could be used for adhesive. Note I also had to fill the very center of the motor where there is a gap thanks to the laser etching for the logo. I did this with 3+ layers of thermal adhesive, cut to fit flush.
Here is a different motor where I used different heat sinks. These are 8mm x 30mm x 8mm in size. So they fit – again almost perfectly – in the smooth channel on the BBSHD motor casing. This time you only need to stack them as they fit the channel 1-across. Much easier. Also they are a bit taller, with more room between the fins. Is that better or worse then the little 5mm units? I haven’t done any testing so I don’t know. On this motor, I did the same end cap as pictured above.
Here is a link to the 30mm heat sinks I used. I can’t find a domestic source for these so if you decide to go this route you just have to order them from the source … and wait.
On the Surly Big Fat Dummy I recently built, I used them again. They make a major difference in the intense heat we get here in the California Central Valley
By the way, these identical heat sinks work extremely well on a mini-Cyclone… Those motors overheat if you give them a dirty look. The same combination of 30mm adhesive sinks mounted radially, plus the same end cap. Takes the surface temperature down to the point where the motor can be used with relative confidence once you learn not to overdo the throttle and cook it… The heat sinks cool the motor from the outside literally as much as is possible under the circumstances.
Something I read long ago; Heat is the enemy of electronics.
I Googled heat sink for BBSHD, and wa-la…
Thanks
I have found the small fins in the link provided. can you provide a link for the round heatsink in the photo. nice work. will use on my own bbshd build
Unfortunately there is no link as the sources keep changing. I can no longer get my original ones that have the Maltese cross of solid alloy that is such a good heat sink. I get these from EBay as-needed after searching. Sorry you have to do it the hard way.
I can not thank you enough for providing all of this valuable information on how to heatsink a mid drive motor. I have a number of hot rodded BBSHD builds that were running very hot, even though they all have the steel gear, stronger motor stator, and greased correctly. My Luna V1 controlled BBSHD powered 29er Kona Honzo was absolutely cooking at 145 degrees. I installed all of the heatsinks that you suggested, and took it out for a rigorous 10 mile ride at max settings and speed, up some of the SF hills here, and the temperature came back down to 105 degrees. A huge difference, as checked by my thermo gun. Cheers.
Did you glue the small passive coolers with thermal glue, or did you use the installed self-adhesive strips? It seems to me that the glue makes better contact, especially in case of a round motor profile.thank you
I always try and buy heat sinks with thermally conductive heat transfer tape already applied. Its just a lot more convenient. Thermal tape is not household grade double stick tape. Its a little thicker and that thickness, combined with positioning the sink so its minimally affected by the motor’s curvature (short side facing the curve, which also matches the vanes best position for airflow) makes for adhesion that lasts. I’ve never had the silver 8x30x8 sinks come off the curved surface, although I have had them come off the very bottom of the BBSHD, which is a completely flat surface. Thats probably due to their being directly in the path of road grit. Glue might be the solution to those, but in extreme summer heat here, an end cap and the circumferential sinks have been sufficient.
Does a bbshd automatically throttle itself back when it gets too hot? Mine started surging today, I put my hand on the case and almost couldn’t touch it. I’m hoping it was the heat that made it surge and nothing else wrong. Seems to be ok now that it has cooled.
As far as I can tell, no it does not. I have measured extreme temperatures and the motor was working fine. Word I hear is the first sign of heat failure is softened nylon gears inside that shred. But who knows… your controller might have been begging for mercy. If you are heating it up that much, take steps and cool it off as best you can. The heat sinks aren’t perfect but they do help.