Battery Current Sensor

Posted on May 29, 2012

These controllers have an inhibit input and the effect of shorting this down to ground is to turn down the internal demand speed. So with the battery current limiter fitted, the internal demand speed can only ramp up to a value which engages the limit. Some enthusiasts of electrically assisted cycles believe constant power acceleration is the ideal response. Although personally I am not convinced that constant power acceleration is the ideal, limiting the battery current gives constant power acceleration whenever the limit is engaged.

Battery Current Sensor
Click here to download the full size of the above Circuit.

Controllers are very nearly 100% efficient, motors rather less. So there is an inaccuracy due to motor losses. However, ignoring these, all the power taken from the battery is delivered to the motor. For a particular system, the battery voltage is essentially constant, so limiting the battery current drain during acceleration forces the system to take a constant power from the battery, and thus to deliver a constant power to the motor. Certainly there is no simpler way of incorporating a constant power throttle system!

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