I may have written my question a little bit strange …
you said
buck converters decrease in efficiency if the voltage difference gets higher. In case that’s also true for our ESC a higher voltage battery without ever using it (speed limit never reaches full duty cycle) should also lower efficiency again. I don’t know if the efficiency gets worse with a bigger voltage difference so that’s what the question was meant to ask.
Yes you are correct, the switching losses are higher, but at these power levels and configurations, it’s not that much of a difference.
I haven’t been able to stop thinking about this. pretty excited to understand it better.
I did another version of the power curve comparator on desmos. parameterized it in terms of NsMp cell counts. and added a “gearing” component.
In the default comparison, 10s6p (blue) and 12s5p (red) the power curves are the same. Red has more top speed but the torque/amps continues to drop as the rpm/volts (dutycycle * volts) goes down. keeping max power the same. (!!!)
bingo light going offf for me. 
That power curve staying the same is why:
Now,
if I were to gear it down to the same top speed. I do gain torque. but only where motor amps previously limited blue. and only where it stays under the max power curve. ( red is now virtual amps/torque relative to blue. but really it’s gearing )
so higher S count’s extra speed can be traded for more torque but only where previously limited by motor amp max. it can’t exceed max power. This is the tradeoff I was thinking of. but now I can also see the max power curve and how it limits the effect of that trade off.
But more series and less parallel would be more battery sags on startups and then quicker decrease in capacity/voltage/longevity, no ?
Good point!
10S6P at 90A and 12S5P at 75A (in above example) result in the same 15A/cell current though.
But the graphics above represent a “perfect” discharge scenario,
When you start powering an electric motor, the sag is 5 or ten time (?) The nominal amperage of the motor for a fraction of second.
The biggest the sag, the harder the strain on the cells, which impact the discharge speed in a non proportional way.
If you’re motor’s sag is of 200A, on a 10s6p pack it’s 33A by cell so a sag of 18A which is probably ok for sush a short time,
If you have a 12s5p, it’s 40A so 25A sag which is a lot less ok.
Or am i mistaken ? (It’s been a long long time I-ve seen this at school, i’m probably missing something)
I’m not sure any of that possible initial spike in motor current “gets through” the ESC’s current limiting and whether the motor current spike if present) would remain at the same level even though the gearing is changed in the above two examples.
I don’t know enough about an esk8 setup to answer this. You are very right about battery voltage sag though. The internal resistance of each cell causes an internal voltage drop that increases as more current is drawn.
You know those big electrolytic caps that keep killing antisparks (and causing sparks in the first place) they make sure the current through the battery does not spike as described.
The TOTAL voltage sag is higher on more cells in series BUT the sag PER CELL is the same regardless of configuration for the same power levels, so the excursion on each individual cell is the same.
Bottom line, higher s count configuration is always better, so long as your electronics can handle it.
200 motor amps from standstill would most likely start at 2-3 battery amps and ramp up from there as you speed up.
The real sag happens the higher up you go in speed under load, since you increase the volts that get to the motor, and in consequence the total power (W).
Now, do you want to sag from 42v to 33v or from 50.4v to 42v?
There’s efficiency to calculate as well… a cable “rated for 100A” can carry a bit over 5000W at 50.4v, or 4200W at 42v. Exact same heat, resistance, induction, flying pidgeon losses in both scenarios
hmmm i was sure those caps were there to prevent current inconsistency (due to resistance differential between the s groups and between + and - because of the long wires) to dammage the ESC.
I guess it works in both sense, never thought about it before.
i saw some small escs like makerx or maytech ones doesn’t have the caps, do they compensate in an other way or do they just table on low current/less surges ?
They have tons of ceramic caps in there. Capacity does differ between esc makers but it’s always there and the higher the better (until it fries antisparks)
So 12s1p will have the same load on individual cells as 3s4p?
Yes, about so for the same output power.
I am still eagerly waiting on your esc!
I tweaked this thing a bit more. Now it’s got even more parameters. 
now you can adjust for each board kv, gearing, wheel diameter, and some other things and see torque to ground vs speed.
cc @computers
updated with more params. fub, effeciency, per board battery and motor amps, …
please note that motor amps is total so multiply by number of motors.
[ desmos doesn’t let me update an original shared url, makes a new one for changes. lame. ]
latest. added a rudimentary readme section.
This tool is awesome! Definitely gonna use this to compare different setups to get an idea of how different they’d feel.
Haters gonna hate
based on the convo in that other thread. I still need to refactor this to take into account IR of the motors, and a torque/amps equation that factors that in will likely diverge at that point based on voltage. ( or maybe not… maybe only changes to motor internal resistance change it. )
