Ferrofluids : Join The Ebike Motor Cooling Revolution

There have been several major technology breakthroughs in the last few years with ebikes.

  • Lithium batteries have completely eclipsed all over battery technologies for ebikes due to their light weight and ability to put out massive amounts of power.
  • Neodymium Magnets (also known as rare earth magnets) reached the price point to be used in many less expensive ebike motors.

Justin from Grin Tec is working on building a commercial product for the next big breakthrough for ebike motors, using magnetic ferrofluids to cool ebike motors. The product is called Statorade and is currently sold on their website here for a whopping $25 for a 10ml syringe. They are currently in the testing phase of this product and are looking for technical people who are used to watching their motor temps pretty closely to participate in their experiment. Most of us know what amazing contributions Justin and Grintech have made to the ebike industry over the years and I’m sure that this will add to their impressive collection of ebike advances (Cycle Analyst, Cycle Satiator and more).

Ferrofluids are one of the most beautiful things science can show you

Ferrofluids are one of the most beautiful things science will ever show you

Everyone has seen the amazing youtube videos of ferro fluids but few of us actually know what they are. In short ferrofluid is a liquid that becomes strongly magnetized in the presence of a magnetic field. Just the tiniest amount of ferrofluid in an ebike motor can bridge the gap between the stator and the rotor and allow the extra heat from the electricity being run through the windings to make its way to the external case and cool off from the outside air. This setup is only useful with outrunner motors like almost every DD motor on the market where the copper coils are isolated on a stator deep inside the motor and the heat has to pass through an air gap to escape the shell. For motors like the BBS02 and BBSHD which are inrunner motors the coils are mounted on the case so they already get the case cooling effect without having to jump an air gap and the ferrofluids would not really benefit them.

Image from the Grin.ca website. Top is w/o Statoraid, bottom is same test with Statoraid

Image from the Grin.ca website. Top is test without Statorade, bottom is same test with Statorade

In the past if you had an outrunner motor and wanted to pump lots of amps through it there were 2 basic ways of cooling it.

  1. Cut large holes in the side of the case so that the coils can air cool
  2. Drill a tiny hole and add about a cup of automobile automatic transmission fluid (ATF)

Both of these approaches have serious drawbacks. Having large holes in the side of your ebike motor means that it is suddenly exposed to the weather, rain, salt, sand, etc. Any of these things can seriously shorten the life of your motor.

Adding ATF fluid to the motor you can have problems with it leaking out and getting everywhere and also the added weight of the fluid to the already heavy motor. This option adds a lot more cooling to the DD motors as shown by Adam Griffin who beat out every other ebike in 2012 to the top of the Pikes Peak race with a $1600 ebike with a 9c motor cooled with ATF. The ferrofluid cooling solution looks like it will give similar results to the ATF cooling without many of the drawbacks using only a tiny fraction of the amount of fluid that you would need to otherwise use (less than 5ml as opposed to a full cup of ATF).

The $1600 home built ebike that beat factory ebikes that cost over $15000.

Adam’s cheapo $1600 home-built ebike that beat factory ebikes that cost over $15000 at the Pikes Peak race. He would not have completed the race, much less won, without ATF cooling.

From their wind tunnel testing Grin has discovered that you can run about 40% MORE continuous torque and power through many ebike motors without overheating problems. To be clear this is a major game changer. Heat dissipation is one of the biggest problems with large DD motors like the Mxus as they generate insane amounts of heat when running thousands of watts through them continuously.

Although you can buy Statorade through the Grintech website you should understand that this technology is still in its infancy. As long as the motor side plates are sealed (as should always be the case anyways, to prevent water ingress) then leakage should not be an issue. If you get any leakage then it is pretty straightforward to fix by applying any kind of sealant on the side plates when they are screwed on. One of the main differentiators to ATF fluid is that it’s way easier to keep the Statorade from leaking than conventional oil fills, which even if you seal the side plates will end up leaking out through the wires, the ball bearings etc. Since Statorade stays mostly in the air gap it doesn’t ever splash around to find other exit points, and even on the tests where Justin drills tons of large holes in the side cover plates, there is no escape of the fluid. The original thread where Justin describes his initial experiments can be found on Endless Sphere right here. Geared hub motors spin about 5x as fast as DD motors which means that it is much more likely that the ferrofluids are going to be more useful with DD motors as they won’t spin so fast that the fluid can’t bridge the gap between the magnets.

Injecting Statorade into a hub motor, it will bridge the air gap with almost zero friction.

Injecting Statorade into a hub motor, it will bridge the air gap with almost zero friction.

If you use large hub motors and are constantly having heat problems from an overpowered motor then you might want to consider jumping on the ferrofluid bandwagon as it is one of the most exciting recent developments in ebikes. The benefits of motor cooling don’t have any effect on the immediate performance of the motor, a hub will feel exactly the same in terms of torque, power, acceleration etc. whether you have the Statorade fill or not.  It’s only when you are pushing it on long continuous duty high power runs that the additional cooling effects can become appreciated, either by keeping the motor from burning up or by allowing you to run at higher power levels before the thermal rollback kicks in.

It’s great to see the whole industry move forward like this.

  • Build
  • Innovate
  • Disseminate

In 10 years ferrofluid might be a standard item with every hub motor you buy, till then let’s just keep pushing the envelope.

Thanks to Justin at Grintech for helping me edit this article and to Jarkko for the tip. Jarkko knows he is twice the badass I will ever be, because he double downed on the K’s in his name. I tried going by KKarl for a while, but everyone thought I had a sticky keyboard.

Ride On.




13 thoughts on “Ferrofluids : Join The Ebike Motor Cooling Revolution

  1. The first question many people ask is: how much extra drag does the FF cause? The continuous no-load drag is roughly one newton-meter at 300-RPMs. A 26-inch tire doing 336-RPMs is roughly 26-MPH. That is a tiny amount of drag in exchange for a 40% increase of heat-shedding ability. Conversely, a significantly smaller motor with FF can now produce the same power as what we would normally recommend a larger motor for, without fear of overheating, due to short and temporary peaks of power/amps. https://endless-sphere.com/forums/viewtopic.php?f=2&t=48753&start=675#p1095860


    • Hey Ron, this is a bit misleading, as the additional drag from FF is WAY less than 1 Nm. Part of the whole point and excitement of this was that at the fill levels that achieve the majority of the heat transfer effect, the actual additional drag loss was very minimal. In fact, it’s more like 0.1 Nm! It’s only when you keep adding more FF unnecessarily that the drag starts to increase similar to what you’d have with a normal oil bath.

      Look at the 5mL fill point at the two graphs at the end of this post:


  2. At first I wondered if FF was conductive but apparently it isnt. I wonder if there’s also a boost in power from better magnetic field propagation over air gaps.


    • There is no change whatsoever in the motor characteristics. The small amount of FF doesn’t come close to filling the gap volume or having any meaningful effect on the permeability of the air gap. So you don’t get any boost in off the line power, but you do get a boost in the long term sustained power you can run the motor at without it overheating


    • You can make ferrofluid for almost nothing out of bulk toner and vegetable oil. I wouldn’t put it in my hub motor though…

      There is many different kinds of ferrofluid, as it is just a liquid that can be magnetized. Different ferrofluids are used in different applications.


  3. My first contact with Ferrofluid was in 1998, when I overpowered two home made 12″ car subs 160wrms each all the way up to 1500wrms, two professional 18″ subwoofers with 3x more coil and magnets couldn’t handle that task back on the days. I was able to pump all that power continuously without frying the speakers thanks to Ferrofluid filling up the air gap and mechanically limiting the excursion so it wouldn’t hit the bottom of the magnet under extreme power levels. I was only 15, really really wanted that kick ass performance but didn’t have much $$ that would be impossible without this little thermal trick. =]


    • I was about to ask you if you´ve seen this already and what about BBSHD… obviously you did 😉
      (as you are one of the guys having the mid drives opened more often than other people on this planet)


  4. Pingback: 2015 : A Nucking Futz Year For Electric Fatbikes and 2016 Looks Even Better | Electric-FatBike.com

  5. I’m cautiously optimistic that the ferrofluid does not react poorly with the magnet epoxy. I am not recommending it to our customers yet, until we’ve had sufficient time and testers to vet the process, but if it’s good news, you can bet we’ll be marketing the heck out of it ourselves.


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