DrkAngel wrote:¿Isn't it more important to base current protection (fuse) on the lighter gauge wiring and circuits of the motor and controller than the much heavier supply wires?
No, if you mean the phase wires, because it does not see battery current, it usually sees higher currents than the battery provides to the controller, in spikes as commutation occurs, dependent on settings, inductance, etc.
So a fuse rated for what the motor might need to see in pulses or startup could let the constant currents in the battery allow a fire, depending on how great your motor phase currents are.
If it is a brushed motor, then the currents are different, but still higher than battery currents, in the PWM pulses.
If the motor fails in a way (overheats and two phases shorted together from melted wires in the axle, etc) that draws damaging levels of high current from the controller, then if the fuses are in the phase wires, it might prevent damage to the wires themselves--but it probably won't blow fast enough to save the electronics (FETs, gate drivers), if it's really high enough to instantly damage things anyway. And if the FETs fail, they'll probably blow up and open the circuit anyway.
A battery-wire fuse of any size, small or large, wouldn't stop the motor failure itself--it would just blow once the system drew enough current long enough, and protect the battery (and other) wire insulation from melting and potentially causing a fire if they then allowed the conductors inside to short to each other.
If the controller fails in a way that draws high current from the battery, then a battery-wire fuse sized to save the wires would also blow then, too, and again protect the rest of the system (whatever's not already damaged) from the heat generated from the failure.
FWIW, a motor probably wouldn't be damaged by anything that a fuse could prevent, anyhow. It could *cause* damage that a fuse could prevent, under some circumstances.
You *can* size the fuses to protect the motor wires, or the controller, but the motor itself doesn't need protecting via fuse--generally anything the motor does that would cause a fuse to blow means the motor is *already* damaged.
If the motor is overheating to cause the damage, then there there is something *else* wrong; probably it's overloaded, which you can prevent with limiters in your system elsewhere, throttle, cotnroller, etc., or you could add thermal cutoff or rollback to prevent overheating to the point of damage.
But a fuse won't do anything to stop the overheating, unless you simply size it to blow when the current is high enough to cause such overheating. That also means it'll blow on startup from a stop with "instant start" controllers that don't ramp up current to the motor, because from a stop they'll draw whatever current the controller can put out...whcih means that if that's enough to blow a fuse to prevent overheating, it's also enough to blow a fuse *anytime* the controller draws that much current.
Controllers also won't blow a fuse unless something is wrong (already failed) if everything is setup right and the fuse is already sized high enough to allow normal operation, and the cotnroller is sized right for the motor, and has limitations in place to prevent overcurrents or overheating. Unfortunately, most controllers are *not* well-designed like that, whcih is why so many blow up so easily...they don't have internal thermal rollback or cutoff, they don't have anything beyond basic *battery current* limiting, etc.
So either you have to add that limiting or rollback or cutoff to the controller (or system), such as with thermal sensors and a Cycle Analyst v3 or similar, or you could fuse it so that there is no way you can pull enough battery current long enough to overheat anything...which again, also means that unless it is a soft-start controller it'll also blow the fuse at startup from a stop. And it also means you probably can't climb much of a slope, if doing so draws current high enough to overheat the motor, cuz that would also blow the fuse, if it's sized to prevent overheating.
So...the fuse is there to prevent a number of things...but in our application on ebikes/etc it isn't going to be able to protect the motor or controller from a number of types of damage--unfortunately they are the most common types. It's just going to protect the battery and it's wiring, and hopefully prevent an on-bike fire or other lesser damage should the worst happen and short across the supply wiring to the cotnroller either inside the cotnroller or between it and the battery.