Switchable KV

[mrass]

For my ebike motor (prima powerbike with 9 pole ABB brand motor) to go any faster I need a higher kv motor or switch the windings from (3 times) 3 in series to 3 parallel
and how cool would it be to make it switchable on te go?
0-15mph low kv (series windings) and 15 to probably 30mph higher kv (parallel windings)??
The practical bit would be rather complex but should be doable.
Haven't heard about it at all, any reason why not?
Seems like a good idea?
Any scientifically sound input much welcomed.

 

[Miles]

https://endless-sphere.com/forums/viewtopic.php?f=2&t=9215 et al

No real advantage over a fixed change to delta...

 

[learningrc]

If you have a motor with windings for the field and armature (series DC motors, shunt wound DC motor, etc.) instead of permanent magnets on the field as brushless motor are, then you essentially have a motor that can have adjustable Kv. Provide less current to the field winding and Kv goes up; provide more current to the field winding and Kv goes down. The disadvantage is that these types of motors require commutator and brushes.

Otherwise, field weakening in brushless motors can be viewed as doing the same thing.

 

[mrass]

Thanks miles, however I'm not talking about switching from wye to delta, it remains wye.
Switching from one configuration to the other:

(P means pole number, L means leg number)

 

[mrass]

If you have a motor with windings for the field and armature (series DC motors, shunt wound DC motor, etc.) instead of permanent magnets on the field as brushless motor are, then you essentially have a motor that can have adjustable Kv. Provide less current to the field winding and Kv goes up; provide more current to the field winding and Kv goes down. The disadvantage is that these types of motors require commutator and brushes.

Otherwise, field weakening in brushless motors can be viewed as doing the same thing.

Thanks, you're right, I'm talking about something different, made the above simple diagram to explain.

 

[John in CR]

I have some motors with switchable series/parallel, which doubles the Kv when in parallel. Like Miles said it doesn't change much as there's little change in torque even with the same controller and settings. It's just that in the low Kv setting it's a bit more efficient at going slow. Since the added complexity adds failure points and resistance, I'd much rather they be simple locked into high. As I put the motors into service, that's exactly what I'll do...ie gut the switching mech and hard wire them to the parallel connection. For a true dual use ebike, off-road and high speed on-road, I will instead make a simple 2 speed gearing with dual sprockets front and rear. Then I'll stop, release the idler/tensioner, and move the chain over to the lower gearing for better off-road performance and efficiency with about half of the top speed and double the thrust at the wheel without giving up durability or regen, and little added weight.

 

[mrass]

I have some motors with switchable series/parallel, which doubles the Kv when in parallel. Like Miles said it doesn't change much as there's little change in torque even with the same controller and settings. It's just that in the low Kv setting it's a bit more efficient at going slow. Since the added complexity adds failure points and resistance, I'd much rather they be simple locked into high. As I put the motors into service, that's exactly what I'll do...ie gut the switching mech and hard wire them to the parallel connection. For a true dual use ebike, off-road and high speed on-road, I will instead make a simple 2 speed gearing with dual sprockets front and rear. Then I'll stop, release the idler/tensioner, and move the chain over to the lower gearing for better off-road performance and efficiency with about half of the top speed and double the thrust at the wheel without giving up durability or regen, and little added weight.

Good point, indeed it's a dual use ebike but high-speed to me is just 25mph also like riding thru the mud in the forest at 5mph.
As it is the current consumption (measured between battery and controller) is approximately 10 amps at 5 mph and 4 amps at 20mph, would like to flip that around..
A other solution would be increasing the battery voltage for higher speed and limit the current at lower speed by the controller or just feeding the controllers output
stage with a lower voltage by (again with a relay) switching to half the battery pack, or better the two halves paralleled with low drop schottky diodes.
I'm running 32 10ah GP nimh cells in series, could add more..

The mechanical solution is not for me but curious about what you described, you have a mid drive driving a separate chain to the wheel without a freewheel to be able to have regen?