Here’s what one of the motor winding currents look like when my unloaded 18V Milwaukee BLDC router starts, runs, and stops. I imagine that the battery absorbs much of that braking energy (which needs to go somewhere). A diode in series with the VESC’s input power line would probably save the power supply, but might break the VESC - especially if it’s not rated for twice the motor’s operating voltage. So a big voltage clamp of some type (near the VESC) is probably the way to go.
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