Hi all,
I’ve built a small cart powered by two hub (BOT) wheels, each driven by its own ODrive S1. The system is normally powered by a 24 V Greenworks Li-ion battery (link). Regenerative energy from the wheels is fed back into the battery.
However, I’m curious what happens when the battery is disconnected, but the cart is still moved (pushed by hand), causing the wheels to spin and generate energy.
Where does the regenerative energy go in this case?
Is it potentially harmful to the ODrives if there’s no sink (like a battery or brake resistor) for that energy?
Thanks in advance for any clarification or advice!
The current caused by back-emf will flow through the FET body diodes into the main system bus, with a voltage roughly equal to the motor’s speed constant times the motor velocity. Generally as long as the total current draw from the rest of the system is less than around 5-10A, this should be safe.
Hi, can I ask a follow-up question on this post?
My application is similar, with:
battery → contactor / pre-charge circuit → DC converter to step down voltage → regen clamp → ODrive
When the contactor is open (no supply voltage into the regen clamp) and the vehicle is manually moved, will the regen current pass through the clamp back into the DC converter, or will the regen clamp dissipate the current through the brake resistor?
Thanks!
The clamp only passes current from IN to OUT (ideal diode), so nothing can flow back into the converter whether or not the input is live. With the contactor open, the input side is dead, so as soon as the back-driven bus gets above the clamp’s own undervoltage lockout (~5-6V – it self-powers off the output side) it’ll start dumping into the brake resistor and hold the bus down around there. The only side effect is some drag on the wheels once you push fast enough for the back-EMF to get past that, since the motor’s then effectively working into the brake resistor.