Heat Sinks For the BBSHD Ebike Mid-Drive

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.

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I’m riding in the Class 3 lane on the street, not the Class 1/2 shared use path just to the right

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.

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The Stormtrooper – Now living the good life in Pacific Grove, CA where it is never hot, unless its on the inside of a freshly baked cheddar bagel.

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):

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The small heat sinks are placed in rows, 4-across.

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.

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You can see the thermal adhesive I applied to the center alloy section of the end cap, just at the top.  Hand cutting the adhesive strips to fit was a pain.

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.

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These 30mm-wide sinks were a lot easier to apply as you only have to go 1-wide all around the motor.

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.

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.