higher or lower kv

[Tolkano]

Either way every time i play in the simulator the lower kv motor performs better at the expense of more heat

Im giving the high kv motor more benefit by lower controller resistance and giving the high volt battery more resistance because it has more series groups, what else am i doing wrong?

https://i.imgur.com/UNNxlVU.png

 

[danielrlee]

Either way every time i play in the simulator the lower kv motor performs better at the expense of more heat

Im giving the high kv motor more benefit by lower controller resistance and giving the high volt battery more resistance because it has more series groups, what else am i doing wrong?

https://i.imgur.com/UNNxlVU.png

The higher kV motor requires proportionally less battery voltage and proportionally more controller current. Leave the controller resistance alone.

 

[Tolkano]

Either way every time i play in the simulator the lower kv motor performs better at the expense of more heat

Im giving the high kv motor more benefit by lower controller resistance and giving the high volt battery more resistance because it has more series groups, what else am i doing wrong?

https://i.imgur.com/UNNxlVU.png

The higher kV motor requires proportionally less battery voltage and proportionally more controller current. Leave the controller resistance alone.

...

That's exactly whats in the simulator

And if i give them the same controller resistance the high kv motor would get slaughtered even more...

 

[neptronix]

Either way every time i play in the simulator the lower kv motor performs better at the expense of more heat

Im giving the high kv motor more benefit by lower controller resistance and giving the high volt battery more resistance because it has more series groups, what else am i doing wrong?

It likely has to do with the parameters you are using and what the continuous load is.
IE if you run a low kV hub motor on 48v and a high kV motor on 48v, the high kV motor will, of course, operate at a higher speed and have a higher continuous load. Once you adjust for the same continuous speed, the difference will disappear once the controller is set to produce adequate amps to hit it's top speed and the battery IR is adjusted to suit the amperage.

I have ran ultra low kV, medium kV, and ultra high kV motors and not encountered any notable differences between them, even in terms of efficiency, once you adjust for load and top speed.

Efficiency ( and thus heat generation ) between different motor windings will vary +/- 2%. That variance is mostly due to whether the manufacturer chose a slightly higher or lower copper fill for one winding versus another.

I find myself preferring lower voltage, higher amp setups VS higher voltage, low amp setups due to the ease of charging and managing balance in low voltage batteries. There are more good lower voltage chargers than there are high voltage chargers.

 

[minde28383]

what a discussion. minde, please read what john in CR and snowchyld wrote,

You read what TheManShaker asked about. There is emphases on low speed, torque from stand still, climb to hill.

Overall think about:
-different efficiency at low speed.
-about higher torque in low speed,
-about less load on battery in low rpm,
-better traction control on rear wheel (this might be not so relevant for most but still worth to consider when low speeds apply).

there is no such thing as a "high torque" or "high speed" motor. Different kV does not mean higher or lower torque or speed capability of the motor. It is just that simple. The magnetic circuit is the same, bearings are the same etc. Very simple to understand that they must be the same.

Actually there are things opposite of what you wrote.
It is simple indeed therefore true will come alive. No need to defend others opinion and simulators graphs (theory) instead try two different motors in real world. You will see and feel the difference then.
High or low Kv motors have the same torque but in different rpm range therefore different kV does mean higher or lower torque and speed capability of the motor.
Actually you even can see it in simulator. Low Kv better start torque. And if you ride steep, soft, rocky, rooty forests, you preffer higher torque in lower rpm range.

Imagine taking high Kv motor, riding it 30km/h, pouring Amps, generating heat, climbing slowly some steep, rocky terrain.
How many km / miles you ride compared with low Kv motor? Answer is: You will ride less amount of distance compared with low Kv motor when riding in low speeds and in difficult terrain.


On high Kv motor You can put FF and radiators but you will still be in disadvantage compared with low Kv motor and most importantly motor will behave differently in extremely low rpm range and of course it will have less torque.

Now to the practicle advise: Choose your controller according to your windings. When you only can effort a cheap one, then go for the low kV motor, it does not need many phase amps to reach the max torque the motor is capable of. But most likely your are then stuck to low speed. If you want to use the full potential of the motor you can

a) use a high kv motor (12kV) and a high battery voltage (96V) to get the same top speed. You dont need a controller with high phase current (only 100 amps), but one that can work with high pack voltage (rated for 110V max)

b) use a low kv motor (6 kV) and a normal battery voltage (48V for example). You need a controller that can do high phase current (200A), but it does not need a high voltage rating (55V max is sufficient)

system a) and b) will perform the same

You mixed it. Things are opposite.
Nevertheless I believe you intended to write it opposite regarding you a and b examples, but if you believe of what you wrote in a and b than you should know that it's wrong.
Roughly, talking into perspective of what you try to give example. Let's say:
You get 9kv and set it to 250A phase
Or
You get 13kv and set it to 350A phase

According what you wrote you get the same results. Nop, you don't get the same torque, because you get that ''same'' torque in different RPM.
Low Kv motor will pull better in low speeds. And if you need better efficiently ie less heat ie less ampsm, MORE torque on low speed than you use low Kv motor. You don't simply get highest possible Kv motor and set amps to roof and say that all motors has the same torque. I'm trying to give examples to the point where I get smile, it feels that I'm repeating the same thing but slightly from difference angle.


It's not only about controller price and how much phase it has. Two controllers can have the same max phase; same motors, kv; same batteries, but motors will have difference torque, especially from stand still. It's not only about max phase amps on paper.

@bionicon:
there is an rpm for every motor, where it feels healthy. This point can be calculated an thus the ideal reduction ratio for a given bike (weight, wind and tire drag)

You need:
Motor resistance
Kv
Eddy and hysteresis loss constants
dissipation ability in watts at the desired conditions (max air temperature for example 40°C, max motor temperature, for example 100°C )
plus the above mentioned values for the vehicle

Yes,
Low Kv motor is more efficient in Low rpm, and it is more torque in low rpm.
High Kv motor less torque in low rpm, less efficient in low rpm, more heat when it is less efficient.

You say that high and low Kv motor has same torque. Fine.
If you still think so then try 'qs 205 17 Kv' version motor in 26'' rim (or 17'' rim, it will be still sluggish in low rpm) with some 500 phase amp controller and go to some difficult terrain, rocks, roots, hills, maybe some snow or sand.

 

[neptronix]

High or low Kv motors have the same torque but in different rpm range therefore different kV does mean higher or lower torque and speed capability of the motor.

I have tuned dozens of motors for an optimal power output versus heat and mechanical considerations and have not noticed this. You can affect the torque curve of any motor by tuning the ratio of phase amps versus battery amps. It will greatly affect the low to mid RPM torque.

The only difference between windings is how they respond to different combinations of amps and volts.

Imagine taking high Kv motor, riding it 30km/h, pouring Amps, generating heat, climbing slowly some steep, rocky terrain.
How many km / miles you ride compared with low Kv motor? Answer is: You will ride less amount of distance compared with low Kv motor when riding in low speeds and in difficult terrain.

That has everything to do with load versus RPM, then the controller programming determines how much power gets shoved into the motor. The motor determines what to do with that power. Continuously shove more power than the motor can handle and you will progressively get more heat and less thrust. This is not the specific winding's fault.

On high Kv motor You can put FF and radiators but you will still be in disadvantage compared with low Kv motor and most importantly motor will behave differently in extremely low rpm range and of course it will have less torque.

That's the effect of two different motor tunes that aren't equally set for each winding. Notice that you get more heat out of the motor that continuously pushes more power? low RPM is where electric motors are at their least efficient.

But you can gimp out the low RPM power on any motor to get more efficiency if that's your goal.

You don't simply get highest possible Kv motor and set amps to roof and say that all motors has the same torque.

I did exactly that with the leafmotor 4T. It is the highest KV motor on the market outside of say, a Crystalyte 5302.
The motor had more torque than i knew what to do across the band with on 48v x 87A. I had to adjust the phase to battery ratio to produce a flat curve so that the front wheel would just barely stay on the ground.

I also had to do this adjustment on a Magic Pie in a 20" wheel ( very low kV - 15mph on 36v ). It also produced more torque than i knew what to do with. Both motors were tuned the same and responded the same to the tune, despite big differences in their physical geometry.

But the magic pie COULD produce a little more power at super low RPM simply because of it's tallness and number of poles. But of course, this advantage falls apart at higher RPM due to increased eddy current and copper losses, unfortunately.

But that's a motor design issue, not a winding choice issue.

 

[minde28383]

Im way late to the kv discussion but

Every time i look at high vs low kv in the simulator it ends up in a situation where the low kv makes more power but overheats faster, and the high kv makes less power but overheats slower

That's why im not sure theres a one size fits all solution

Assuming both motors are the same model and correctly wound (same copper fill), they will generate the same amount of torque per unit of heat. If you feed the low kV motor proportionally less current and the high kV motor proportionally less voltage, they will behave identically.

To note that we still talk about qs205 50H or very similar motor.

It might be identical on paper or simulator.
But if you take all things into proportion as you wrote - amps volts you will still get different torque in different rpm range. So you claim that motors behave identically is not true.
Low Kv motor will be more torque at low speeds.
High Kv motor will be more torque at higher speeds.

You can't expect from high Kv motor the same torque as low Kv motor and be efficient in the same RPM range in for example very low RPM range. So it is not identical.

 

[minde28383]

@neptronix
but these are different motors. It might be all true; these are all different motors and bikes.

I was intending to emphases differences in 9Kvlow and high 13Kv hub 205 motor hubs with 45mm or 50mm magnets regarding @TheManShaker intro question in this forum. He is asking what to chose, 9kv or 13kv hub for slow hilly terrain therefore all this follows his question.

For real world experience I know (not from some paper or I read somewhere or saw in simulator) that if you ride some heavy 60kg ebike and you put high 13Kv motor you will do worse in low speeds in slow terrain but you will do better in higher speed, ~40km/h and over.
Therefore 9Kv ~250A phase for the one who needs high torque from stand still, in slow terrain. If you put 13kv hub and set amps to 325A you won't get the same torque from stand still and up to 35km/h as with 9kv set to 250A.

9kv ~250A phase
13kv ~325A phase

 

[larsb]

Not much to add here really as it was already stated well enough

Just that all of you are correct in your opposing views!

except for this little bit:
You can't expect from high Kv motor the same torque as low Kv motor and be efficient in the same RPM range in for example very low RPM range. So it is not identical

This is simply not true..

The oldtimers: it doesn't matter what kV you get (since you buy the correct battery and a 600$/500A controller and go 100mph)

Newbies: it really matters! (As you buy the 250$/200A controller and get enough torque at low speed and go 50 mph). Who needs to go faster anyway, right?

 

[minde28383]

You are pointing to different transport. You don't need 100mhp in forest trails or paved city center.
The one running 100mhp is motorcycle and the one 50mhp is more or less still electric bicycle. They are in different weight class too and look differently. They are not better or worse; light vs heavy. If you don't mind to motorcycle look and weight than why not and vs.
And it is not about money because you can get bicycle very small controller for you stated motorcycle controller price. It is opposite, if you don't mind wight you can get cheaper therefore motorcycle parts are cheap, especially used ones.

 

[minde28383]

Did not notice small font before. Regarding small font follows.
All said is regarding hub 205 with 45h or 50h magnets. Not some a motor.
As you say it was well stated but well does not mean - correct.

Had you experience to compare these 9 and 13 kv hubs and you only reference is not literature and simulation or you had not need to compare as it was well stated.

 

[neptronix]

Therefore 9Kv ~250A phase for the one who needs high torque from stand still, in slow terrain. If you put 13kv hub and set amps to 325A you won't get the same torque from stand still and up to 35km/h as with 9kv set to 250A.

9kv ~250A phase
13kv ~325A phase

In order to get the same torque for both windings, you have to increase the battery current as well as the phase by a certain proportion.

You also have to have a power bus that is overbuilt because additional loss of voltage from your power wires, controller, or battery would skew the results. ( even -0.5v is enough to skew the results, because voltage helps produce torque also )

 

[neptronix]

Another confounding factor is what i mentioned before.. the fact that two different windings might contain a slightly different copper fill. A certain kV wind might have a tad more or less copper than another.

If you're going to disregard what the ebikes.ca simulator says, you'll need to do a controlled experiment, accounting for all things, on a dyno, to prove that winding choice affects torque potential / efficiency.

Never seen anyone prove that, but there's a lot of opinions out there.

 

[minde28383]

I don't have dyno. My Empirical evidence are from going testing bikes on road. So far I found that lower kv pulls me better to steep hill, out of sand or mud up to certain speed.
My batteries I had access to test were never the limiting factor, were allowing up 180A constant (Leafs, volts cells). Wiring beefed up too. Controllers - Sabvoton 72150. Never even bothered to try else. In worst scenario would look into Kelly 72300.

I'm not against digits. My practical evidence suggested that lower kv pulls better from stand still. Also I found ca simulator to support my empirical experience.
Can you show me simulation in ca sim; you'll need to copy past only address. Address line will have all information, I'll need to open in my browser. Like this:
https://www.ebikes.ca/tools/simulator.html?https://www.ebikes.ca/tools/simulator.html?bopen=true&motor=cust_13_0.12_0.2_23_0.77_0.0185_0&batt=cust_72_0.2_30&wheel=16i&motor_b=cust_9_0.15_0.2_23_0.77_0.0185_0&batt_b=cust_80_0.2_30&cont_b=cust_70_200_0.03_V&cont=cust_90_250_0.03_V&wheel_b=18i&blue=Lbs
*If above link B sim won't be viable you just press B sim and it will appear.

In my sim you can see that lower 9kv has 18'' wheel , 80v voltage it has more thrust up to certain speed.
In my sim you can see that higher 13kv has 16'' wheel, 72v voltage it has less thrust up to certain speed.
I tempered with copper internal resistence in sim too but int resist is just my guess.
I increased voltage in sim up to 80v just for simulation. I would want too see in your sim 72v voltage for both 9kv and 13kv to support your claim that 9kv and 13kv have the same torque.

I'm trying to compare specifically
qs 205 50h v3 3kw
9.03kv 24*5 65omhs and
13.28kv 33*4 38omhs versions

 

[neptronix]

There are a couple problems in your calculation..
The speeds are different and the different size wheel will skew the results.
The two motors must absolutely be at the same speed.

Also some motor parameters may be different than you specified, so i'm going to use some well known motors instead and exactly match the RPM. And we're going to change the mOhms of the battery to 0.0002 to rule out voltage drop as a factor. ( it was an issue in your calcs too )

Here is a nearly exact match. The only problem with getting an absolutely exact match is javascript rounding issues in the simulator itself. I've split hairs to as small as they get.

https://www.ebikes.ca/tools/simulat...mph&frame_b=road&frame=road&grade_b=0&grade=0



The efficiency difference varies across the curve, as you can see.

And yeah, like i said.. windings don't have exactly the same copper fill, so one motor can get a small advantage over another once we control for all factors. You'll see this difference in torque and efficiency overall.

 

[neptronix]

I forgot something.

If we rule out the variable of controller internal resistance by also using 0.01 mOhm, the efficiency during cruise for the two motors becomes identical. Although there is still a bit of a deficiency when hill climbing

https://www.ebikes.ca/tools/simulat...mph&frame_b=road&frame=road&grade_b=0&grade=0

But keep in mind that this difference is motor manufacturer specific and may not apply to the QS lineup. It might actually be the reverse..

 

[larsb]

I am guessing a bit here but one thing might be supporting the low kV / low current motors for torque in real life:

Every controller manufacturer i've tried (except maybe Lyen) seems to have a certain low rpm current reduction to protect the controller.

In the case of riding at low speeds like 0-5km/h on a hub motor this might make a difference to the torque
It's not related to the kV of the motor but to the controller output of phase current.

I am building a dyno currently, it'll be evident in the graphs how much we're talking about - should be easy to find some graphs on the www showing this also.

 

[crossbreak]

FYI, in your above 'a' & 'b' examples, you have the two motors the wrong way round!

thx, corrected, hope you got the idea anyway

 

[minde28383]

I am guessing a bit here but one thing might be supporting the low kV / low current motors for torque in real life:

Every controller manufacturer i've tried (except maybe Lyen) seems to have a certain low rpm current reduction to protect the controller.

In the case of riding at low speeds like 0-5km/h on a hub motor this might make a difference to the torque
It's not related to the kV of the motor but to the controller output of phase current.

I am building a dyno currently, it'll be evident in the graphs how much we're talking about - should be easy to find some graphs on the www showing this also.

@larsb
Can it be that 'low rpm current reduction' also called 'current ramp' by others. I'm not sure but maybe it is the same thing?


@neptronix
Thank you for sims. Never managed to draw different kv motors performance graphs so almost identical my self. So I get idea of different kv motors being of equal torque and power in simulator.
Different kv motor needs more / less volts and amps accordingly motor kv and it can show almost identical mtr power, torque, speed, efficiency.

Also batt and controller resistance plays a role in all this game too. Therefore we throw it out of equation in sim. Never did it before in my previuos sim. I see it makes results more ''fear'' when comparing two motors.

Again, if you take two 205 50H 3kw hub motors. One 9kv and another 13kv.
Choose different voltage batteries, set controller amp settings accordingly. Overall set bikes to have identical speed, power and torque in simulation, but when you take to bikes on road, they will accelerate differently from stand still. Low kv hub will be more agile to start. And I'm talking about these motors, because different motors, different controllers can have less noticeable results.

I think different kv hub acceleration differ mostly due two factors:

- First factor. higher kv needs almost two times more battery amps, therefore to get declared 190Nm with 'qs 205 3kw 13Kv' you'll need 150 battery amps (350A phase);
- Second factor. Controller takes longer time to ramp up amps therefore higher wound 13kv hub will start slower due controller specifics.

First factor is solved by installing proper battery capable of needed const amperage.

Second factor can be solved by using controller with fast ramp. I know two controller: Sabvoton XXYYY and Kelly 72300. It's known from practice that Sabvoton has quicker ramp start - faster acceleration. Kelly slower ramp - slower acceleration.

 

[larsb]

@larsb
Can it be that 'low rpm current reduction' also called 'current ramp' by others. I'm not sure but maybe it is the same thing?

Yes, and no. The current ramp up can be set, what i mean is exactly what you describe in Kelly controllers. They don't output even close to the rated current at low RPM. No matter what is set.. But that's not a good controller either.

Never used a Sabvoton but if it's better in this regard then it'd be fine with a high kV motor

 

[parajared]

If the wattage is the same and the RPMs are the same the bike will perform the same.

 

[neptronix]

Also batt and controller resistance plays a role in all this game too. Therefore we throw it out of equation in sim. Never did it before in my previuos sim. I see it makes results more ''fear'' when comparing two motors.

I believe this is how most people come to the conclusion that low speed windings are better. And in experiences in real life where they're not rearranging the setup to account for the fact that it needs more amps and less volts.

I think different kv hub acceleration differ mostly due two factors:

- First factor. higher kv needs almost two times more battery amps, therefore to get declared 190Nm with 'qs 205 3kw 13Kv' you'll need 150 battery amps (350A phase);
- Second factor. Controller takes longer time to ramp up amps therefore higher wound 13kv hub will start slower due controller specifics.

First factor is solved by installing proper battery capable of needed const amperage.

Second factor can be solved by using controller with fast ramp. I know two controller: Sabvoton XXYYY and Kelly 72300. It's known from practice that Sabvoton has quicker ramp start - faster acceleration. Kelly slower ramp - slower acceleration.

If there is a few % better efficiency at low rpm with the low speed windings, this would explain the lower performance from a start even with a throttle ramp.

I use infineon clones that don't have this throttle ramp feature.

 

[Chalo]

Also batt and controller resistance plays a role in all this game too. Therefore we throw it out of equation in sim. Never did it before in my previuos sim. I see it makes results more ''fear'' when comparing two motors.

I believe this is how most people come to the conclusion that low speed windings are better. And in experiences in real life where they're not rearranging the setup to account for the fact that it needs more amps and less volts.

Providing more amps is usually more expensive, complicated, and heavier than increasing voltage.

 

[neptronix]

Providing more amps is usually more expensive, complicated, and heavier than increasing voltage.

The only place where you get more expense and weight is in the power bus ( wiring, interconnects ) and maybe the controller.
Lower voltage chargers are plentiful and not unobtanium though.
And amps are easier to scale than volts.

IE if you had a battery capable of 48v 100A, you could run a tiny geared motor or a massive hub just by getting the right winding and changing the amp settings. That is how i like to do everything.

Otherwise you need a different battery pack ( or add on pack ) to increase power through adding voltage.

The more cells in series, the more expensive and complicated the BMS and charging get.
More cells in parallel to produce more amps doesn't have this problem

 

[Antenor]

Here do you buy your controllers?
I would like one without soft start...
Thanks