Why Run 12s on a VESC?

ESK8 Electronics
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78

I don’t think anyone makes a BMS for 11s

79

bestech does! http://www.bestechpower.com/407v11spcmbmspcbforli-ionli-polymerbatterypack/BMS-D163.html

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81

You posted this chart previously based on the Vesc having a 60000 erpm limit. 8570 RPM ---------------/50v = 170kv - 12s ---------------/42v = 200kv - 10s ---------------/33v = 260kv - 8s ---------------/25v = 340kv - 6s What changed?

82

Bestech is the best!

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83

Those numbers are for maximum reliability. Personally I wouldn’t go this high on 12s with larger motors, I was getting faults with 200kv maytech motors. 200kv at 12s is still risky business on smaller motors if you gearing is too low, it can be very easy to overrun the erpm on hills if you electrical top speed is only 20-25mph.

@Blacksheep 149 sk3’s are great at 12s but you will want to keep your gear ratio low or you could overheat the VESC when climbing. What tooth # are you running on your pulleys?

84

Ok, Thanks for the clarification. As for me, I’ll stick to the chart and play it safe.

85

I’m using 15/36

86

If you are running 83mm wheels you should be OK on moderate hills but you may overheat on 90’s.

87

I do have 83 wheels

88

OK apparently you guys don’t get why there is a disparity between the resistance calculations. You forgot to account for back EMF.

21.6V @ 54A

43.2V @ 27A

since we don’t know the rotational velocity we can’t assume that the back emf for both test cases are equal, but let’s just assume they are for the sake of demonstration.

| Rdc + jw1L | = (21.6 - KBw1) / 54A | Rdc + jw2L | = (43.2 - KBw2) / 27A

(KBw) is the back EMF. You can probably solve that and obtain a value for |Rdc + jwL| and (KBw) assuming w1 = w2.

And on that related note. Higher battery voltages will do the following:

  • For a given output motor voltage and current, a higher battery voltage will draw less BATTERY current. (Explanation for experts: the controller acts like a buck converter, and having a higher input voltage for a given output voltage and current means you will be drawing less source current) Another way of looking at this is if you are limited by battery current in a certain load scenario, higher voltages will solve this.

  • Higher battery voltages will let you achieve higher motor voltages. (maximum output of a buck converter is 100% duty cycle so Vout = Vin) Another way to look at this is if you are limited by motor voltage in a certain load scenario, higher voltages will solve this.

For the first case, the only time this will be an issue is perhaps at stall/startup or at some point in the acceleration profile. But this will likely be a very short transient in your acceleration profile so unless you’re doing some crazy drifts or something will likely not affect you other than slightly slowing your 0-30mph time or whatever metric fancies you. And from what it looks like nobody is really limited by battery current anyways.

For the second case, whenever you hit 100% duty cycle, that’s basically when you’re motor voltage limited. If you’re not satisfied with the performance you get when you put 100% duty cycle and whatever you get from your contraption, having a higher battery voltage will help.

It’s infuriating to see how ignorant hobbyists are and base their understanding on extremely rudimentary electrical models like “P=IV”. BLDC motors are extremely complex and what I described is barely opening the can of worms.

People spend their entire lives optimizing motors, and some other people spend their lives making incredible VVVF drives. Electric skateboards combine those two together and there is so much to discover. Please don’t limit yourself with “ohm’s law” and call it a day.

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89

sorry to geht this thread up here but im just curious about the 12S thing.

I am currently running 10S3P and just bought 50 30Q cells…

so i am thinking of 12S4P or 10S5P, and i really cant decide. Is it a safe option or is it really pushing the limits? i am suing esk8 VESC 1.1

maybe @esk8 did some testing with 12S? a 190KV motor should be fine or am i wrong?

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90

I too would like to hear the latest thoughts on this, and am having similar internal debates. Especially now that people have been running 12s for a while now. I was also thinking about ordering a couple 11s D140 BMSs from Bestech amd splitting the difference. I am using 190 kv BTW.

91

12s for the win. Less current more range…190kv perfectly fine in bldc and in FOC no need to worry about erpm limit :slight_smile:

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or probably less range as youre riding further from the no-load speed (if youre going faster you’ll have less range as well), likely putting out more power at the slow speeds too (just cause everyone cant help themselves with more power potential), and while the true wiring may be a bit more efficient with less battery amps needed I think the esc will also be a bit less efficient as it’s probably going to be operating also further from the no-load speed and have more switching.

93

because I can run 57V without breaking mine.

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94

I am running since a year on FOC without problems. It is just better and i would not go any voltage lower :smiley:

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95

Which VESC using?

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12s for the win. Just limit the erpm to 60k for 190kv and your all good.

I will be using an extra cap bank to smooth voltage spikes. 63v 19800uf bank for the win

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97

You’ve tried 14s Lion/16s LiFePO4?