Rewind a cyclone 3kw motor for more power ?

[ZeroEm]

That does not look reasonable, to me. Do a 12T motor and gear it up. then take a 6T motor and gear it down.
Must admit I know very little about the gearing of a MAC. But looking at that would never own one.

 

[Sparfuchs]

As it seems like here are some experts around, i've got a short off-topic but related question about the battery i should use with my cyclone motor.
I'm using a hailong box for 65 cells and i'll use the molicel p26a 18650 cells CDR 25A/(35A <60°C). So i could build a 16s4p (64cells) pack with nominal 57,6V and CDR 100A/(140A <60°C), or a 21s3p (63 cells) pack with nominal 75,6V and CDR 75A/(105A <60°C). Yes, i know i don't necessarily need such high discharge cells and should probably get a bit more mAh instead but haven't found a better option for a good price. The controller will probably be the Kelly KBS72121X and i'm also thinking of using a fan to cool down the motor.

About my needs: I prefer torque more than speed and don't "need" to go faster than 40mph.. but if doesn't bring any disadvantages i don't have a problem if i could

So what is in your opinion the better configuration and why ?

I'd also appreciate a good link that helps me to understand the influence of the balance between volts and amps on a motor in general.

Thx a lot.

 

[john61ct]

> KBS72121X

Is that true FOC?

https://endless-sphere.com/forums/viewtopic.php?t=105139

The torque/ amps vs speed / volts was already beaten to death right? See my post #2 above for a summary

even though not all points are consensus there, no one has directly disagreed with any of those points AFAICT

 

[Sparfuchs]

> KBS72121X

Is that true FOC?

https://endless-sphere.com/forums/viewtopic.php?t=105139

The torque/ amps vs speed / volts was already beaten to death right? See my post #2 above for a summary

even though not all points are consensus there, no one has directly disagreed with any of those points AFAICT

I don't know about the FOC.

You are absolutely right about the beaten to death volt vs. amps and it might sound like a lame excuse but it feels like there is to much information an that makes it quite difficult to find the answers i need. I guess i quite understand how volts and amps and windings influence motors. But when it comes to battery building it seems like the only reason why people make less serial connections is to be able to get enough parallel cells for the wanted discharge. But what if you have enough discharge anyway no matter if you use 16s or 21s. Can the higher voltage also be an disadvantage somehow ?

I can understand if the question is to off topic or to often asked, so in case feel free to just ignore it

 

[john61ct]

I guess i quite understand how volts and amps and windings influence motors. But when it comes to battery building it seems like the only reason why people make less serial connections is to be able to get enough parallel cells for the wanted discharge.

The motor Kv/winding issue is completely separate from P vs S / V vs A at the battery level.

> But what if you have enough discharge anyway no matter if you use 16s or 21s. Can the higher voltage also be an disadvantage somehow ?

So first you determine your desired voltage from the motor POV - for efficiency, just a bit higher than what is needed to get your desired top speed.

That voltage changes if you are rewinding, but that's already been thoroughly discussed.

The point is yes, do not increase voltage unnecessarily, just what you need no more.

So, once you know your desired system / nominal voltage, that gives you your S-count, depending on chemistry but usually using li-ion 3.6-3.7V per.

16S if you wanted 60Vnominal

13S for 48V, 20S for 72V

Now you get into your need for current, peaks vs constant.

That determines your parallel cell count, depending on how many mAh / Ah per cell.

A 3Ah cell requires a lot more connections vs a 20Ah cell.

Range is a big factor, if you want a 50mile run per charge you have a bigger / heavier pack much higher Ah capacity

so lower C-rate discharge, do not need high-power cells, can choose those designed for energy density instead.

But low size and weight targets, "fun" level performance conversely reduces max Ah and range, might need to prioritize power density instead.

Does that help clarify?

 

[Sparfuchs]

I guess i quite understand how volts and amps and windings influence motors. But when it comes to battery building it seems like the only reason why people make less serial connections is to be able to get enough parallel cells for the wanted discharge.

The motor Kv/winding issue is completely separate from P vs S / V vs A at the battery level.

> But what if you have enough discharge anyway no matter if you use 16s or 21s. Can the higher voltage also be an disadvantage somehow ?

So first you determine your desired voltage from the motor POV - for efficiency, just a bit higher than what is needed to get your desired top speed.

That voltage changes if you are rewinding, but that's already been thoroughly discussed.

The point is yes, do not increase voltage unnecessarily, just what you need no more.

So, once you know your desired system / nominal voltage, that gives you your S-count, depending on chemistry but usually using li-ion 3.6-3.7V per.

16S if you wanted 60Vnominal

13S for 48V, 20S for 72V

Now you get into your need for current, peaks vs constant.

That determines your parallel cell count, depending on how many mAh / Ah per cell.

A 3Ah cell requires a lot more connections vs a 20Ah cell.

Range is a big factor, if you want a 50mile run per charge you have a bigger / heavier pack much higher Ah capacity

so lower C-rate discharge, do not need high-power cells, can choose those designed for energy density instead.

But low size and weight targets, "fun" level performance conversely reduces max Ah and range, might need to prioritize power density instead.

Does that help clarify?

Thanks a lot for taking the time to explain.
Everything you said sounds absolutely reasonable and understandable to me.
But sorry, i still don't understand what DISADVANTAGE i have if the battery has more volts than i really need if also the CDR of the battery is enough (so not more cells in parallel necessary) ? I also thought the Cyclone motor is quite efficient at about 72V ?

"Can the higher voltage also be an disadvantage somehow ?"
>"The point is yes, do not increase voltage unnecessarily, just what you need no more."

But why ? Is it because it's less efficient to use a motor below the max rpm that could be reached with the voltage of the battery ? Does that in reverse mean you get the highest efficiency at the max. rpm that the voltage of the battery pack supplies ? So if that's right, that would mean i'd get with average speed of 20-30mph more range with a 16s pack than with a 21s pack ?

 

[john61ct]

Yes, if I understand it correctly

the farther below your average rpm is compared to the maximum

the higher your Wh per mile.

Of course other factors like wind resistance have their impacts, but I believe that's a valid generalization.

 

[Sparfuchs]

Yes, if I understand it correctly

the farther below your average rpm is compared to the maximum

the higher your Wh per mile.

Of course other factors like wind resistance have their impacts, but I believe that's a valid generalization.

Yeees, finally i understood :thumb:
That's what i didn't know and what leaded to all those questions. The missing part of "my" puzzle was finally found. Thanks a lot for your great help john61ct

 

[john61ct]

See if my first post #2 here has a different meaning now that your "context knowledge" is greater.

Repetition really is the key to deeper understanding, eventually AHA the puzzle pieces fit together.

I'm still waiting for more expert members I trust to confirm my words, but meantime assume that from their silence [emoji14]

 

[daleag]

Running a higher voltage than you need to attain your desired speed does slightly reduce efficiency in the motor, and often in the controller as well. However, unless you're running GROSSLY more voltage than needed such that the controller is having to really pull back, I dont feel like it's enough % change in efficiency to matter most of the time. I would also note that the switching devices used in higher voltage controllers often have slightly higher resistance than lower voltage switching devices, so that adds a slight loss. Of course, running lower voltage at a given power means running higher amps, with higher resistive losses... but if you're running higher power then you're probably running high voltage to get the RPM anyways. I'd say stick to the motor manufacturer's specced voltage range as long as you're planning to run ballpark within the specced power levels and speeds and overall it balances out.

Suggested watching:

https://www.youtube.com/watch?v=dxJe_gygRGU&ab_channel=GrinTechnologies

 

[john61ct]

Well in this case turns/Kv is up to the OP, not pre-determined, similar to the question "which voltage range should I buy" ?

Some respondents on this issue respond "higher voltage is always better" within the limits of the circuitry involved.

Then OP asks, "since my to speed is under 40, and I want mostly torque is there ANY disadvantage going to top voltage possible? "

Hence my pointing out that inefficiency at low speeds issue, goal being to lower the speed where efficiency peaks

I am not saying it is a "very significant issue", just a counter to "always go for highest voltage" as well as "changing turn count matters not a whit".

And on the other hand, the advantages of lowering amps (faster turn count, higher voltage) is no need for fatter wiring and (more expensive) high-amp controllers.

 

[ZeroEm]

I'm with you John. I run 72v, the reason is not so simple. Wanted long distance batteries and more low end torque (i'm heavy). Yes your right, Voltage does not give distance. Thought about multiple battery packs (still think about it), seemed simpler and cheaper to have one big battery and at the time only one close in capacity was 72v 1.8kw. Still bought two for 3.6kw. would have needed 3 or 4 48v batteries.

I like that did not need more than 40a controller and did not need to mod the hub wiring. Still needed to get the speed down so ordered a 7T-leafmotor 53kph and only needed 45kph. Need to start building my own batteries then I can setup up my wheel, motor kv then match the battery Volts for the perfect top speed.

 

[Sparfuchs]

Thank you all so much for all your great answers. You helped me a lot !!
I made a new thread that was a bit to off topic to post it here but includes lots of things you were talking about here.
As you proved great great knowledge at topics like gear ratio, volt/amp balance, kw, torque ect. here I'd really like to hear your opinion to my new topic: https://endless-sphere.com/forums/viewtopic.php?f=30&t=116817&p=1722843#p1722843
Thanks a lot.