Low Speed Sepex

[mjroman20]

This has been discussed before but rather than dragging up an old thread I thought I'd begin a new one.

I have read about and experienced Sepex motors heating up when running at low speeds. All of my know how is with controllers and component level design so motor design is a bit of a mystery to me. Since I am the inquisitive type and not one to just accept facts without data...does anyone have knowledge of the theory behind that? Obviously at lower speeds the armature is being pulsed giving an average voltage lower than the battery, I assume this has something to do with it.

[Sergio]

I think the main issue is related to the thin wire used for the field coils.

As the Sepex motor heats up, the field coil cannot dissipate the heat effectively and it gets hot.

The increased temperature also increases the resistance of the Field coil which limits the Field current (10% to 50% decrease in Field current with heat according to Curtis).

That in turn can lead to increased armature current as the motor is now operating inefficiently and it that leads to more heat being generated.

On a Series motor, not only the "Stator" coils are much thicker and able to better dissipate heat, when its resistance increases it limits the current on the entire motor, not just the "stator".

[mjroman20]

I would agree with that, but something needs to start it down that path. Since more current would be needed to start a vehicle running to overcome the resting position, I would say a lot of start and stop movement would result in rapid heating.

On that theory I would say since the field current drops at higher RPM then lower speeds where the current is higher would result in rapid heating. Am I on the right track here?