Hi, I wonder what are the physical limits, that determine the max motor current. For example If I have SK8 140kv on which is stated the 42A current max. Is this really the maximum number that I can set on the ESC? Or if battery amps are lower then that (per motor - for example 80A total battery discharge on dual drive) I might be able to set higher current then 42A (for example 60A).
What will be the factors that really limits the maximum current the motor can handle in lower speeds? Just the dispation of heat/overheating? Or what else?
For us the limit is heat dissipation, if your motor is cool you can increase the current
Just be careful because if the motor is hot on the outside the windings will be even hotter, and if your motor has a internal temperature sensor, make sure it’s beta value is properly calibrated
Thanks, so if I have sensored motor, properly calibrated (through Focbox Unity app) and set up the temperature limit “motor cutoff start 75°C motor cutoff end 80°C” I should be fine with going higher motor amps in lower duty cycle?
It’s the firmware code in the vesc. On some versions of vesc, the max you can do is 120a motor and 60a battery, regardless of what the motor or battery maker recommends. That being said ignoring the manufacturing recommendations can cause damage, mostly from the production of excess heat.
So as long as I have sensored motors and the cutoff start/end temperature limits of motors set on ESC conservatively (75/80) I can go to 100A on motor even when it is stated as 42A max?
That why I started this debate I can imagine, there would be other limits like not enough thick cables for example… But as long as not exceeding the manufacturers limits too much (like using 55A instead of 42A) together with temperature monitoring, I should be able to use the motors without causing them any extra demage, right?
80c is very low. motors state some bull amp rating but not the actual wire temp rating. The temp rating of the wire if u can find it tells the temp the wire can do consistently for 20,000 hours. You’re likely nowhere near a worry at 80c. I use wire rated to 200c In motors I make and that’s common. I wouldn’t give the motor amp limit a thought related to motor longevity and the insulation and set the temp sensor higher if it’s actually in the windings
Yeah, the power rating of any motors means nothing
Motor heat loses are mostly due to cooper loss (winding resistance), and proportional to current², so if you keep the the amps constant and increase the voltage to make it spins faster, you increase the power since power is torque*speed
My bet on this ratings, since the inrunner has a smaller diameter rotor, the centripetal force is smaller and you can spin them faster to get this power rating
it doesn’t show the resistance compared. if the resistance is lower for the same kv its a better motor for doing the same job. with the inrunner having the airgap diameter (not thickness) being smaller it has less leverage and to still have such a low 300kv im guessing the windings must be many turns and thin to get the torque/inductance to compensate. either that or they have super magnets building the mag field strength in the gap
i think the amp limit of any motor should depend on the winding resistance and potential cooling alone.
I can imagine, there would be other limits like not enough thick cables for example… But as long as not exceeding the manufacturers limits too much (like using 55A instead of 42A) together with temperature monitoring, I should be able to use the motors without causing them any extra demage, right?