Hi All,
I would like to remove the brake resistor as we’re using a battery bank and wanting to confirm the safest procedure and settings. I’m putting my understanding based on the ODrive documentation and various posts below but would love a confirmation. Thanks!
To start I am following the Startup Guides’ advice on estimating max braking power required:
When braking at max speed and with maximum motor current, the power that is dissipated in the power resistor can be calulated as: P_brake = V_emf * I_motor where V_emf = motor_rpm / motor_kv.
In our case, we are estimating max brake power of 60A at 900RPM with the D6374 @ 150kv where P-brake would == 360W if I’m doing my math right. Not really a major issue for us with a 48ah battery @24V that would be something like a 15A regen (0.3 C charge rate) if it was completely instantaneous.
So after confirming that the brake power can be absorbed by the battery bank I’m looking at the available config values:
odrv0:
brake_resistor_armed = True (bool)
brake_resistor_saturated = False (bool)
config:
max_regen_current = 0.0 (float)
brake_resistance = 2.0 (float)
dc_bus_undervoltage_trip_level = 8.0 (float)
dc_bus_overvoltage_trip_level = 59.92000198364258 (float)
enable_dc_bus_overvoltage_ramp = False (bool)
dc_bus_overvoltage_ramp_start = 59.92000198364258 (float)
dc_bus_overvoltage_ramp_end = 59.92000198364258 (float)
dc_max_positive_current = inf (float)
dc_max_negative_current = -9.999999974752427e-07 (float)
Based on a few posts the only information I can find is that odrv0.config.brake_resistance should be set to zero. Which I have done and removed the resistor, all seems fine enough. I’m leaving brake_resistor_armed = True (bool) alone as I’m not sure it really matters with the value set to zero.
That said, my intuition was to change a few more of these configs and is confirmed by a couple posts including this and this.
// Set Max Regen to Max Battery Recharge , 0.5C Charge Rate
max_regen_current = 24 (float)
// Leaving undervoltage trip alone
dc_bus_undervoltage_trip_level = 8.0 (float)
// Setting Over Voltage to Max Recharge Voltage From Battery Manufacturer
dc_bus_overvoltage_trip_level = 30 (float)
// Setting Max Negative Current to (-1 * Max Regen Current)
dc_max_negative_current = -24 (float)
That’s it, this appears to be functional and looking forward to any others’ insight.
