# Vesc max voltage. Again

I was wondering if using 12s with a 195kv motor, which is right on the edge of hitting the vesc’s Max erpm, and then what would happen if you were to go faster than the erpm by going down a hill coasting, and then you tried to use the brakes??

So ud be trying to have comutations faster than the 8600/max voltage = kv max number.

What would happen?

Where did you get the idea that 8600 is the vesc max rpm ?
I thought this was the rpm where Vedder found brushless motors to be most efficient.

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That’s what I thought as well but there’s a formula 8600/max voltage= your max possible kv. Read it here from Chaka. And then beyond that there’s also the vesc components voltage rating.

I’ve already told him about a million times

The max ERPM for the VESC is 100k. If you try to exceed that with too high kv per volt the VESC will generate a fault code and switches the motor off. So, not a good idea to try that downhill…

ERPM = kv * voltage * (motor poles / 2)

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Thanks for clarifying, now I see. It’s all about the voltage generated by the motor in regen.

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Chaka:
"If you are using the VESC, divide 8600 by your motor KV and that will give you the max voltage you should use. Of course this isn’t some golden rule just a general guide."
I’ve heard this a couple of times on here and if u search 8600 you’ll find it

With 100k Max erpm as the limit and 200 kv and 50 volts (nominal or actual…I’m using actual)
: 200 x 50 x 6 = wait for it…wait for it…only 60,000 erpm and well within limits

8600 / 200 = 43 volts
so not ok

I found the thread, perhaps @chaka can clarify: what is the limiting factor behind this ?

8600 rpm max is based on an observation in efficiency. 100,000 max erpm is based on the vesc throwing fault codes.

Is there a way we can fix the 100k max erpm issue?

@Chaka How are you able to reach 30-40mph speeds with this issue? Wouldn’t you hit 100k max erpm?

Happens on the bench but I think you can limit the erpm if you are using a high kv motor. I have a pair of 190kv on 12s that hits 35mph easy and 40mph in a full tuck. I would have to hit a pretty steep hill to go faster and throw a fault code while coasting up to the erpm limit.

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Not something you want to happen when going 40mph…

Yeah, having the VESC go dead while it reboots is scary at speed. I have had it happen when I triggered my overcurrent on a bms. I do not recommend anyone take their board up to these speeds, it’s a dance with death.

Find a local DH group that host slide clinics and practice braking techniques. It could save you some skin.

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