How slow can you wind a motor?

[Skedgy Sky]

We all know winding style determines whether motor will have more torque or speed (and I have read some of the "Science, Physics, Math, & Myth" thread. What a long discussion that is ).

The well know Turnigy C80100 as an example. Pretty fast spinning motor, with Kv of 130. It's noisey at high RPMs, like many RC motors.

How slow can you wind a motor?
The intention is having a powerful motor without the noise. The drive system can be altered to still drive the vehicle at reasonable speeds. ... or will the motor be so slow (despite having lots of torque), that the overall power and efficiency will suffer?

I'm talking rewinding a 130Kv C80100 using only a few strands of thin wire to get a Kv in the single digits.

 

[Thud]

I have gotten them to 50ish kv using 14g wire.

low rpms =lower power in the 80-100 architecture.
the issue with low kv is the amp carrying capacity of the wire required to make the many turns.....all you are trading is the output dynamics of the motor.

Unless you adjust the affected parameter to make up for the re-configuration.....you are making a less powerful motor.

ex: my single 14g 14-turn motor will sustain about 30amps.....& the motor will spin efficiently up to 8500 rpms before the iron losses take over & start really contributing to the heating profile.

on 24 volts it is effectively a 720 watt motor. 1200 rpms
on 36 its 1kw @1800 rpms.....& so on thusly.

it wont get back to its 5kw potential until you hit it with nearly 170 volts
(if its really 5kw to start with....I suspect in a traction application they are more correctly named "4kw" motors)


sorry-No free lunch.

 

[Skedgy Sky]

the issue with low kv is the amp carrying capacity of the wire required to make the many turns.....all you are trading is the output dynamics of the motor.

To compensate for less amp carrying capacity due to thin wire, voltage can be increased to bring the motor's power back up, no?

100W is same whether it's 1A 100V or the other way.
Same with Amp Turns. 10AT, whether it's 1 (thick) turn @ 10 amps or 10 (thin) turns @ 1 amp. .. the overall amount of magnetomotive force from the winding remains the same.

 

[Thud]

your absolutely right...
but no matter how you measure.....your still spinning 8k rpms to deliver the power required for serious fun.

doesn't matter if the kv is 45 or 180.

I think the math works out for higher voltages to deliver slightly better efficiency on the bench, but in real world operation its all going to balance out.

if your going to the trouble to design reductions, you may as well reduce for the most powerful set up you have in hand.

 

[Skalabala]

A slower turning motor should make more heat? Because mosfet is on longer and current flows through motor winding longer?
More losses?

 

[Thud]

A slower turning motor should make more heat? Because mosfet is on longer and current flows through motor winding longer?
More losses?

Naw, if your feeding the motor correctly, it will run indefinatly.
If you dumping more amperage than the windings are rated for, your wasting energy generating heat.

High pole count motors create more heat in iron loss lower in the rpm range...but as long as you inside the design parameters...you should have no problems.

Higher pole count motors also requier more comutation events (mosfet switching) per rpm. This will generate heat in the mosfets themselves.

This is why you need low Rds on the mosfets. & my favorite for the 80-100 is the 3077. They run much cooler than the 4110
on equal set ups. Since they are limited to 75v I wind a kv to optomise the voltage i am running. If i was going for 48ish volts, i would use 3006's
I typicly run 18cells & charg to 75v. Motors Are wound 2in hand 14g 6 turns & terminated wye. Or 15g 2 in hand 7 turns.

 

[Punx0r]

There has been a lot of discussion on this lately. Basically, you should choose a winding that maximises copper fill. That will give you the greatest torque potential at the highest efficiency to produce the greatest power at any given speed. More conductor cross-section area = more amp-turns = more mmf = more torque = more power at any given shaft speed.