What does motor MAX actually means?

Hey Just I was just reading a thread about someone having problems with a setup. I believe is was a 175kv motor and he had a 16t/36 system. He said he was overheating MOTOR MAX @ 35. He went up to 45 and his problem was fixed. How does the Motor max work? Someone care to explain? Thanks!

Motor max (A) is the maximum amount of current the VESC is supplying to the motor. A value that is too high will overheat the motor if it’s over the max rated watts (thus amps) of the motor as the motor can’t whitstand that amount of current because of physical limits (amount of copper etc).

When setting a too low value instead, especially going up hill and/or with an heavy load, overheating can happen because the motor can’t enter/maintain the “good efficiency zone” (where you have still some throttle left or at least going full throttle your board doesn’t decelerate) and it will run at lower RPM and in the end it will need a higher amount of total current to do the same amount of travel, that loss of current used to move the board will be converted to heat.

If you can get enough speed uphill so that your board maintains it or doesn’t decelerate greatly (in fact gaining enough speed before the hill/steep point helps) your board, even if the esc will give max amps, the board will decelerate and even stop. Having a better acceleration (via higher motor max) to use before getting to a steep point will help this too.

So if you’re not light or have a lot of hills you should set a higher motor max, instead if you want to maximize battery performance you can set a low motor amp but it’s really battery amps max the value that determines the amount of current the ESC pulls from your battery.

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The interesting part I wonder is does anyone know if this is an absolute max or can you still burst higher? I want to burst up to 120 amps (or 30 per motor), but I can’t do more than 80 con, I don’t want more than 72 personally (which is 18 per motor). But it seems like there’s only one setting.

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What issues are these, the sometimes dropping of brakes or acceleration? I definitely feel like I get some slightly weird behavior some times, but I’ve always associated that to my controller. I want to meet up and do some tests with my 4wd like you did with John. I seem to be getting way better range with 4wd than 2wd, by almost double. I did increase my battery from 3p to 4p, but I can get about 8 miles now instead of 4…

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so… following that logic… if i have an older space cell, or what i’m now calling a raptor cell to avoid confusion…

Batt Max: 45 Motor max: 540 Absolute max: 540

That seems odd to me. Usually those settings would look somethig like this:

Batt Max: 45 Motor max: 60 Absolute max: 130

I’ve seen several of your posts about the AC v DC thing. I’m just trying to straighten this out in my head because i’m not an EE and i get lost easily when you start talking EE stuff.

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I’ve seen his posts so many times all over forum even when it’s not related the topic at hand, and the more I see the less inclined to give his theory any credibility. It also makes no sense to me.

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That explains why raptors haul ass on a 45 amp fuse and why noone will ever need an 80 amp BMS and why Ollin told me i’d be lucky to ever see anything approaching 45 amps, all reasons i switched to 60amp BMSs and felt comfortable with the leftover headroom for cooler running.

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@devin like @longhairedboy I’ve struggled to understand your posts about this issue. It seems like a a compelling argument, but I don’t have the knowledge to unpack it. From a more practical perspective, has anyone applied this logic in a build and tested it? What was the result? I’m wary of frying a VESC to test the prediction.

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@devin, the only thing that your example above proves is that the battery limit didn’t have any effect in this case. Could have been set at 50, 60 or 100 Amps. No effect.

If we approximate the battery voltage to 43v (allowing for some voltage sag) we can conclude that hummies board used 43V * 44A = 1892 Watts as peak power.

Why the board didn’t use more that this peak power we can only guess. Hills not steep enough hummie not accelerating fast enough because he would have been thrown down motors too hot … ?

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thx @devin it helps to know that this approach hasn’t been tested “in the wild” just yet. I think your assertion concerns VESC owners because your recommendation asks us to exceed the default values by quite a lot.

Have you tried sharing this theory with the folks on Vedder’s forum for VESC? I think you’ll find a lot of people there with the right experience to comment on it.

@chaka @elkick Do you have thoughts on Devin’s theory about batt max / motor max/ absolute max ?

Because, it is IMPOSSIBLE… current is limited by the type of winding use inside the motor, witch can not exceeded maximum power of the motor… Like 500amp at 43v, the motor would need the tolerate the equivalent of P=VI… 50043= 21KW of power… EVEN ELECTRIC POWER LINE DOESN’T SUPPORT THIS KIND OF POWER…

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