Improving thermal efficiency

With a hub motor we know that temperature is likely to quickly rise during a steep and long climb.

In order to avoid this behaviour, for sure there are some options that can be taken when ordering the hub motor.

For exemple if we know that we are going to take long and steep climbs we would choose “slow windings” hub motors. 

In this case the motor is optimised for climbing (not for speed): temperature would be kept lower than with “fast windings”.

In my case (Falco Hub motor) there was no possibility to choose  “slow winding” option.

Last year during my trip from France to Italy I had huge overheating issues: the worst was during the climbing of the Brenner pass where I had literally to push the bike several times.

As soon as the temperature raises to 80° the controller cuts the power down to around 200watts.

In this case when steepness is more than 8 or 9% it becomes very hard to keep pedalling uphill.

Last year tests

Last year I have done several tests on the same itinerary (see below from Strava): it is around 20 km, 1000m altitude gain, with and average grade of 5%.

Of course there are few sections up to 15% and some parts almost flat.

Before half distance the temperature was already up to 76°: I was using 400/500 W to be able to keep a speed of 20km/h to try to reduce overheating.

Last year I had to stop TWICE (for roughly 10′ each time) to let the motor cool down:

1) I had to stop for 10′, in order for the hub motor temperature to go down to 60°.

2) But after few KMs it reached 85° and I had to stop again to let the motor cool down: then I was able to continue till the end of the climb.

                                               This year modifications

After having explored various solutions, I decided finally to try to inject a special liquid called ‘Statorade’ from Grin Technologies:

This is also called ‘ferrofluid’: it provides a better transfer of heat from the internal side (stator) to the engine housing (rotor).

In this way the heat can be moved out much better.

In order to accomplish this modification, I had to drill a small hole in the external side cover (2mm).

Then I was able to inject 5ml of this special fluid.

Here below we can see how I was able to complete this modification.

Statorade injection
Statorade injection

                                         This year’s tests

At this point I was able to start doing similar tests I have performed last year.

In this way it would have been much easier to compare the results.

1) First test

For this first test  I just wanted to try to go up as fast as I could to Casera Razzo plateau at 1750m of altitude. (roughly 20kms, 1000m altitude gain, 5% average grade with sections at 14%!)

So in this first test I was using 500/600w of assistance: unfortunately I had to stop twice because the hub motor was overheating (more than 80° Celsius)…

Average speed was 19km/h.

2) Second test

Here the objective was to go up using lower assistance in order to try to avoid overheating.

In this test I was using an average of 400W of assistance: unfortunately even this time I had to stop because the hub motor was overheating (more than 80° Celsius).

Average speed was slightly lower (18km/h).

3) Third test

At this point my objective was to go up :

– with MINIMUM power used 

– and considering also at the same time the impact on TEMPERATURE of Falco hub motor.

To be noted that external temperature was 4° lower than previous tests.

So I was using between 150 and 250W of power with an average of 185W.

I NEVER had to stop for the hub motor temperature: it stayed pretty constant with a peak of 52° .

Average speed was lower (16km/h)

This was an excellent result: for the first time I was able to climb 1000m without having to stop to let the motor cool down!

4) Fourth test

For this last test my new objective was to go up :

– considering ONLY the impact on my hub motor TEMPERATURE, WITHOUT any worry for the power used. 

So I was using:

– in the first part of the climb around 300/350W 

– then I was increasing the power level to 400/450W 

– and only in the last 5km I was able to use up to 600W on the steepest sections.

I NEVER had to stop for the hub motor temperature: it was going up slowly till 72° .

Average speed was 18km/h.

This was also a very interesting result: not only I was able again to climb 1000m without having to stop but I also increased the speed without reaching the upper temperature limit of 80°! 

In the following chart we can see a graphical comparison of the most relevant data:

–  Maximum temperature reached in C°

– Average power used in Wh

– Average speed

Max Temperature relation with power/speed

This Post Has 4 Comments

  1. Marc

    Hi Daniele,

    Any reason why you restrict the motor temperature at 80°C? Since the temperature sensor is located in the stator windings, you should be able to go at least to 100°C.

    Also, I’d send the guys from an email, if they got a version that will fit the Falco. The don’t offer a similar big step in keeping the hub motor temperature down, but might add an other 15-20% better cooling.

    1. daniele gonano

      Hi Marc, in reality I am not allowed to change any parameter on this type of hub motor!
      In fact in this FALCO hub motor those temperature limits are unfortunately ‘hard coded’
      I think that they have ckecked that 100° would be too much (the controller is INSIDE the hub motor…)
      It’s a good idea to check if they make a version compatible with my motor, thanks!

  2. daniele

    Merci Alain pour ton commentaire.
    Mais si un jour tu decides de mettre le Statorade, comme t’as vu c’est très facile!

  3. IETTER Alain

    merci pour toutes ces dernieres infos, très intéressantes …
    alors j espère ne pas avoir à faire cette injection de liquide special, comme mon nouveau moteur NINE CONTINENT RH212 est équippé d une sonde température, que je paramètrerai mon C.A. , mais bon, c est vrai que cela n empêchera pas le moteur de chauffer, mais je serai prévenu à l avance par mon C.A. et je réduirai alors ma puissance d assistance.

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