minicells have a max discharge of 45amps 35 continuous. wired in parallels a 4 p configuration should be able to output 140amps but my esc can alow my motors to pull a total of 200 amps of load. from the little i understand i would assume that operating outside of that boundary although possible likely damages the cells or makes them get warmer than normal. what are peoples real world experiences. is my thinking on the amperage capacity of these cells correct?
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Mostly? It’s all tradeoffs - more amps is more heat and cell aging. So fewer cycles before you lose capacity. Also you aren’t likely to be drawing max amps continuously either. If you ride really aggressively at the top end you could possibly see the full battery amps but you will also start to see sag.
168a for a 4p p42a is good but imho this is one of the applications where the p45b or 50b when it comes out from molicel is a good investment. Better test results from mooch for sag and a few more amps
Remember battery amps is high speed and true draw from the battery. Motor amps is low speed and isn’t actually what the battery sees. Motor amps can exceed the battery amps but battery amps shouldn’t exceed the battery rating for more lifespan and range.
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Raceboard? That’s a lot of battery amps but im a pansy. My 18s is set 40a battery and my 12s is at 70a battery. Motor amps are about double that and this is per side not total
what do you mean by battery amps is high speed. i was under the impression max amp draw is how many amps the battery can dump before overheating. motor amps is the max amps the motors can draw. which is why with high voltages you get more power out of the motors. so if a 3500 w motor pulls full power at 50 v the motor pulls ~70 amps 7000 watt motor ~140 amps or am i getting my wires crossed?
not overheating, but going into thermal runaway. it’s not exactly the same thing, and it’s also much worse. it’s best to stay within the lowest limits you have, and even a bit lower if you can. A bit of headroom is always good. The more often you run your cells to their limits the more dangerous it becomes that they will suffer internal damage and create another negative esk8 headline in the news.
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I don’t think sucking more amps from a cell than it’s rated is going to send it into thermal runaway if it’s for a short time. The voltage will sag a lot. Not that it’s a good idea.
Motor amps are amps sent to the motor after kinda being transformed by the esc and not true amps from the battery.
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Motor amps are partly decoupled from battery amps, the voltage (and frequency) delivered by the vesc is changed to run your motors at different speeds. (This is super surface level so find one of the esc designers to break it down further). This means that you can draw +/- amps at low speeds and lower duty cycles that exceed the battery amps setting. The motor amps for instance can be drawing 50a at 2mph but the battery amps at that same instant would only be 10a
Here you can see at 20 mph, 17batt amps, 42 motor amps. 50ish duty cycle. The motor amps can be set as high as your vesc can take (leave a little headroom if you want it to last). The higher your duty cycle the closer your batt and motor amps will match.
At high duty cycle and high speed the battery amps settings will be the limiting factor for your speed/torque as the battery amps will bottleneck what the esc can output. At lower speed/duty cycles motor amps will be the limiting setting and can easily exceed the battery amps to give you A snappy torquey low end. You can have lower battery amps to reduce high speed sensitivity or go nuts with lots of power on the high end also - battery amps.
Its not unlimited- you can’t do 10battery and 100motor but you can do a lot. Think of your duty cycle as a multiplier- if you have 20 battery amps at 50% duty cycle you can do 40ish motor amps. At 25% you could do more at 75% less
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To put it simply motor amps is low end torque and battery amps is top end torque.
At 10% rpm the motors might draw 20 amps at 10% voltage from the ESC and there will be a load of 2 amps on the battery.
This thread is helpful. Another example at 40 motor amps at 50% rpm the battery only has to output 20 amps. On the graph you can see where torque gets cut off in the top end by battery amps.
Controller amps is also important, a bigger motor or battery isn’t exactly more powerful it can just go for longer without sagging or heating up.
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interesting I see. because the DC current is converted into 3 seperate phases of AC in the ESC by the mosfets which emulate the sin wave. so beacause of that the amps pulled at the battery are not one to one. i remeber something about Pythagorean theorem and calculating this i think hang on
that’s probably thinking off in the wrong direction.
motor rpm = voltage * kv.
motor rpm = battery voltage * duty_cycle * kv. ( we don’t change voltage. we average it out by turning it off and on… duty_cycle )
at 50% duty_cycle the power is “on” 50% of the time and off the other 50%. so motor amps can be 2x battery before hitting the battery amp limit. (on average)
so… the diff between battery amps and max motor amps is a function of duty_cycle.
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i think i am wrong about the Pythagorean theorem thing. its true their is a conversion of dc to ac but the same power is being pulled. sure their will be voltage drops due to various sources of resistance. but at the end of the day it should be proportional to the total work done by the board. aside from voltage drop due to resistance and inductance what else might cause the motor to pull more amps propotionally to the dc amps at the battery and why?
i see because the esc lowers the voltage at lower speeds on the motor side it looks like higher amps but because the voltage is still 48v or whatever on the battery side. the amps drawn is proportional to the power divided by the voltage.
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thank you i never considered duty cycle.
Fess knows more about the voltage not changing but the effective voltage is lower… The average is lower? Whatever, i am just a novice and fess has the good good 
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I would start by thinking about a simple DC coil, as this question of motor current is mostly based around inductance.
Say you take a coil of wire and jam it onto some DC volts, the current will build up in a short period of time, and form a magnetic field. Exclusive of inefficiencies, the energy that it took to build up the magnetic field is stored in the coil.
Say there is 10A of current in the coil, and then the supply is switched off. The circuit is now of infinite resistance for ease of explaining. As V=IR: 10A X infinite resistance equals infinite voltage, simply put - for ease of an explanation.
In a BLDC motor, it’s not a dissimilar scenario. Energy is stored in the coil, and when it’s switched to the next coil the energy goes from one, to the next. So in a way, the motor is supplying itself with current, hence the battery current must be less.
I never finished the electrical engineering diploma though, I’m just a dropout Electrician / machinery technician who’s become fixated on skateboards.