Modifying a Hub Motor

[markz]

An interesting read
https://avdweb.nl/solar-bike/hub-motor/permanent-magnet-dc-hub-motor-tuning

 

[BobBob]

An interesting read
https://avdweb.nl/solar-bike/hub-motor/permanent-magnet-dc-hub-motor-tuning

Yeah, but but it misses the key point of the OP's question and possibly confuses the issue because people won't get past the first line on windings which is misleading due to oversimplification and unstated assumptions.

It says "As we shall see, changing the number of windings W has no effect on the motor performance. "
He later says "It only determines the motor voltage and current."

That's as daft as saying "voltage has no effect on your system performance, it only determines the current, what motor windings and controller you choose" and then shortening it to "voltage has no effect on system performance"

For anyone who hasn't read the full thread:
Most people are happy to agree that increasing the voltage on its own will have an effect (more torque, more power, no better efficiency so more overheating)
Some seem to understand that changing the voltage/current relationship proportional to the number of windings cancels out - talking about a trade off (see mobius motor above) https://endless-sphere.com/forums/viewtopic.php?f=2&t=110990&start=25#p1652021
There seems to be controversy and confusion regarding reducing the windings having the same effect as increasing the voltage.

Just to be clear, yes, increasing the voltage has the same effect as reducing the windings whilst maintaining copper fill
Yes this does have an effect though it might be a bad effect depending on what you want.

Did you like the Mobius motor?

 

[markz]

Comparing two exact same motors with exact same windings.

Change the voltage, without changing the amps = you change the speed, torque is exactly the same. It changes total power.
Power = Voltage times Amps

Change the amps, without changing the voltage = you change the torque, speed is exactly the same. It changes total power.
Power = Voltage times Amps

Change one or the other or both, changes the power.
Power = Voltage times Amps

For anyone who hasn't read the full thread:
Most people are happy to agree that increasing the voltage on its own will have an effect (more torque, more power, no better efficiency so more overheating)
Some seem to understand that changing the voltage/current relationship proportional to the number of windings cancels out - talking about a trade off (see mobius motor above) https://endless-sphere.com/forums/viewtopic.php?f=2&t=110990&start=25#p1652021
There seems to be controversy and confusion regarding reducing the windings having the same effect as increasing the voltage.

Just to be clear, yes, increasing the voltage has the same effect as reducing the windings whilst maintaining copper fill
Yes this does have an effect though it might be a bad effect depending on what you want.

Did you like the Mobius motor?

 

[BobBob]

Comparing two exact same motors with exact same windings.

Change the voltage, without changing the amps = you change the speed, torque is exactly the same. It changes total power.
Power = Voltage times Amps

Change the amps, without changing the voltage = you change the torque, speed is exactly the same. It changes total power.
Power = Voltage times Amps

Change one or the other or both, changes the power.
Power = Voltage times Amps

Torque is a function of the real world, you can change it by applying your brakes.
Going down a hill can have the opposite effect or you could release your brakes. You could be on a large hill where you can choose to go uphill, downhill or accross the hill on the flat for example.

Speed is a function of power and torque, if you hit a steeper hill you will slow down
Happy to discuss this in theoretical or real world scenarios

So, it doesn't matter how you increase the power if you succeed.
To do so you must have sufficient volts to drive the current through the coils so, if you haven't, then it doesn't happen,
Assuming you do, then the power must go somewhere:

Increase the volts by 10% or increase the amps by 10% then you increase the power by 10% and it doesn't matter how, it must go somewhere.

With 10% more power, you can go faster or have more torque, you might go up a hill or down a hill and the power output will exacty and perfectly match the input, including losses due to copper and iron and air resistance etc.

Speed will be force X distance, with the same power, if you hit a hill (need more torque) you will go proportionally slower and vv

Losses will be greater for copper at low speeds and iron at high speeds but largely irrelevant for this discussion.

If you increase the power then fix the speed you must have increased the torque, regardless of voltage or windings etc
If you didn't increase the torque you will go faster using the same power.
By applying brakes you can change the torque at will, so the torque / speed thing is entirely up to how hard you pull the brakes
Where else could the power go?

There is no relation to whether you increased voltage or current unless the voltage is limiting the current due driving it through the windings / rest of system.

 

[markz]

Comparing two exact same motors with exact same windings.

Change the voltage, without changing the amps = you change the speed, torque is exactly the same. It changes total power.
Power = Voltage times Amps

Change the amps, without changing the voltage = you change the torque, speed is exactly the same. It changes total power.
Power = Voltage times Amps

Change one or the other or both, changes the power.
Power = Voltage times Amps

Ok so starting with two of the same motor - yup

Torque is a function of the real world, air resistance and hills and applying your brakes so basically variable at will. Speed is a function of power and torque, generally, in the real world. Happy to discuss this in theoretical or real world scenarios

So, it doesn't matter how you increase the power.
To do so you must have sufficient volts to drive the current so, if you haven't then it simple doesn't happen,
Assuming you do, then:

Increase the volts by 10% or increase the amps by 10% then you increase the power by 10%.
if you are able to do this then it doesn't matter how, you are dissapating that power somehow

You now have 10% more power, you can go faster or have more torque, you might go up a hill or down a hill and the power output will exacty and perfectly match your input, there will be losses due to copper and iron.

Speed will be force X distance. if you go faster there will be less torque, if you go slower there will be more.

Losses will be greater for copper at low speeds and iron at high speeds but largely irrelevant for this discussion.

If you increase the power then fix the speed you must have increased the torque
If you didn't increase the torque you will go faster, where else could the power go?

Where will the power go? It could go into heat loss. Say going up a % slope will reduce speed and increase heat loss. But I am going off on a tangent with you on purpose there. 1000W = 50V x 40A, lets say thats 30mph which can get you up a hill at say 20mph. But now you go 1000W = 60V x 15A which is 31mph but can only get you up a hill at 8mph. 15A less torque to get up a hill. Lets throw a curve ball in there just for ya. Whats the optimal speed to go up a hill in terms of Wh used and heat. Do you go up that hill fast or slow?

Speed will be reduced due to air resistance the faster you go, which requires more power to get over that air resistance. More power means more battery, means bigger battery, means costs more, means a new controller or modify your current controller with larger capacitors and better mosfets and beef up the shunts.

 

[BobBob]

Where will the power go? It could go into heat loss. Say going up a % slope will reduce speed and increase heat loss.

But you said:

Change the amps, without changing the voltage = you change the torque, speed is exactly the same. It changes total power.
Power = Voltage times Amps

With the same battery, opening the throttle changes the PWM which just changes the (average) current,
Assuming you are not at WOT then opening the throttle would result in an increaase in speed.
I should conclude at this point that you're pulling my leg
That extra torque is going to make you go faster unless you apply your brakes at the same time, no way you are staying at the same speed with more torque.

It is also possible that you are talking about motor voltage and current without PWM, so you don't have a motor controller...
In this case you will get an increase of torque at slower speed and vis versa.
At a fixed voltage, you can only increase torque / current by slowing down (eg going up a hill)

But I am going off on a tangent with you on purpose there.

No probs, it's fun

1000W = 50V x 40A, lets say thats 30mph which can get you up a hill at say 20mph. But now you go 1000W = 60V x 15A which is 31mph but can only get you up a hill at 8mph. 15A less torque to get up a hill.

You're gonna need more torque and therefore less speed to get up that hill with that same 1000W
Hate to point it out but your 50V X 40A is 2Kw whereas the 60V x 15A is 900W, however your 31 mph which can't change is also 8 mph so I don't mind

Lets throw a curve ball in there just for ya. Whats the optimal speed to go up a hill in terms of Wh used and heat. Do you go up that hill fast or slow?

Generally around 15-25 Mph but for steeper hills go faster to reduce copper losses
For shallower, slower for reduced air resistance losses

Speed will be reduced due to air resistance the faster you go, which requires more power to get over that air resistance. More power means more battery, means bigger battery, means costs more, means a new controller or modify your current controller with larger capacitors and better mosfets and beef up the shunts.

I guess you could go slower or pedal harder if you have less money?
Get huskies, depending on the cost of meat locally vs electricity

Or you can reduce copper losses with more windings for more efficiency
Maybe you can reduce the time on the hill with more power from fewer windings allowing you to go faster and more efficiently depending on how steep the hill is (no I'm not about to do the maths on that one)
Don't forget that the bigger battery weighs more and you have to lug it up the hill and you only get around 10% back on regen

Cheers for the chat- lots of variables and sometimes more than one good answer