Choosing the right motor kv for the VESC

thanks. Its too bad there arent more lifepo4 builds

if I have an 80kv motor I could do much higher voltage except the components in the vesc are only capable of …what? Aren’t the components voltage ratings not their true ability and while the capacitors are rated to 60 volts they maybe could do 20% more? I’d like to try 14s if it won’t blow up

This is lifpo4 8s on an ezrun 6s esc. As long as I kept the charge level at or below 28v it wouldn’t trigger the esc’s overvoltage shutoff.

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im suprised that actually works

The problem you run into when going with as high a voltage as possible is the loss in capacitance due to the increase in voltage. Better to have some headroom. 12s systems are way more finicky than 10s in that regard.

if I have an 80kv motor I could do much higher voltage except the components in the vesc are only capable of …what? Aren’t the components voltage ratings not their true ability and while the capacitors are rated to 60 volts they maybe could do 20% more? I’d like to try 14s if it won’t blow up

This is a bad design ethic in my opinion. I have always thought leaving 20% headroom in relation to factory spec was a more successful way to get a robust system. The cold hard reality is we have limited space and fairly large current usage especially for us bigger guys in the 180+ lb category. Higher voltage components start to increase the total size of the package. You will end up going through a lot of perfectly good hardware if you push everything to its absolute max.

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Awesome!! Great write up, @chaka
How does dual motor in the equation affect that formula. Say, I’m running 230kv on a single 10s pack. Does running dual change anything?

Hi Chaka, what was your thought behind choosing (4.2V/cell),… rather than a more average Voltage when riding ??

The only thing running dual motors does is split the work into two systems, less amps per VESC and motor. So in regards to the calculation nothing changes.

@Randyc1 I run really big packs and I think everyone should :wink: so the voltage does not sag much when you have a full charge. My cells stay up around 4.05 to 4.10v per cell for quite awhile. Plus this gives the calculation a little headroom.

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'‘I like to make my voltage calculation based on a fully charged voltage so 12s would be roughly 50v’'
Would you mind to explain this? I thought each cell voltage was 3.7V, so how come you are saying that the voltage of an 12s is 50v rather then 44.4v?
Thank you

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50.3v to be exact, but yes a fully charged 12s li-ion will be about 50v fully charged.

Thanks for clarifying it.
btw any news about those new motors?

They are in Ohio right now, I should have them by Thursday. I need to do some testing to be sure they perform before finalizing the order for the first batch, this was just a sample run. We are going to do some minimal branding with motor specs etc.

Sounds good man:thumbsup:
keep me posted.

I found this very informative so I checked it out in VESC active monitor and found my actual measurements much lower than the pure calculations you have above.

230kv TB 6355 motor at full throttle
in BLDC
6s is 32,000 ERPM
9s is 48,000
12s is 66,000

in FOC
6s is 30,000
9s is 46,500
12s 61,000

It seems that 12s in FOC for my 230kv should be perfect
but I’m probably missing something

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If that motor is actually 230kv than you are lucky it is still working. I ran a 245kv motor on 12s and it caused a drv failure, full disclosure is the VESC was twitchy to begin with which is why I sacrificed it for science.

@Bender I just ran my TB 230kv motor and you are right, it is showing the same results as my 192kv sk3 so it is not an actual 230kv motor. I double checked by running an sk3 149 kv and a few others and the all gave the erpm values expected so the TB 230kv motors must be 190kv.

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Very interesting…
That makes sense
Thanks so much for checking
I really appreciate your contributions to the forum
This info is invaluable, especially for people to be able to design systems that work reliably

So it also depends if you are running in BLDC or FOC correct ??

Another question Chaka ,…do you always charge your cells to full capacity 4.2v ?

Does that diminish cycle life ??

that seems kind of sketchy… i wonder what’s up with that.

back on topic: i’m working on a 12S4P liion build, dual 190kv 63mm cans. Hopefully i’m not bumping up toooo close to the edge here. i figured 200+ would be too much, even splitting across two motors.

This is very helpful info and a great guideline.

No, not really, FOC will knock a few thousand rpm off your top speed but it has the same erpm limitations from what I understand.

I tend to do full charges each time but it will give you more cycles if you only charge to 4.14v per cell. For me it makes better sense to abuse my gear and see when and where it fails.

@longhairedboy It is actually kind of a plus in my opinion. 190-200kv works well for kids and total beginners @ 6s, a good all around board @ 8s, a rocket ship @10s. @12s the extra voltage is wasted and you only exceed 60k ERPM with a tail wind or when going downhill so it is better to drop your KV down and keep that headroom.

I should add that I have only experienced the 60k wall when running 190-200kv motors @12s. Traveling at around 32-34 mph.

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