How Hot is too Hot?

[Brendon1128]

Hey Guys,

Yesterday I went out for a cycle ride along the river here in Boston. I'll admit I was pushing my Smart Pie hard, a lot of hard accelerations and braking. Basically I was having fun After about 15 km or so, I hit a rough bump in the road and the motor started acting a little weird. The e-brake cut out for a few seconds and the motor started making a rumbling noise when accelerating like my old SP3 used to (the SP4 is normally silent accelerating with it's sine wave controller)

I was able to ride the rest of the way home fine; however, I noticed when I got home the motor was very hot to the touch. I let it cool down overnight and rode to work this morning fine. My ride to work is normally about 20 km, and when I touch the motor it doesn't get that warm. I was just wondering how dangerous/safe it is and how much heat the motor can take. Does the SP4 controller cut out if the motor is getting too hot? Also, do you think the bump in the road I hit caused anything? I just want to make sure I didn't cause any permanent damage. Thanks!

[Bikemad]

The maximum battery drawn current on the Smart Pies should not be set any higher than 18 Amps maximum.  If you try and push more current than this through the Smart Pie, the majority of the excess current will basically be producing unwanted heat within the windings rather than additional power because the efficiency of the Smart Pie can fall below 20% when placed under heavy load at low speed with high current draw, which means that over 80% of the battery's energy is simply being turned into heat under these conditions.

I'm pretty sure that the controller has inbuilt thermal protection which should prevent the controller from becoming too hot, but unless they have changed the design, there is no form of temperature sensor incorporated into the motor windings themselves.

I think it is unlikely that you will have caused any permanent damage, but I don't understand why hitting a bump in the road should have cause the motor to suddenly become noisy.

Alan