BMS/Precharge

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Precharge is a BMS pre-ride startup function to charge the main power bus before closing the contactor.

The BMS has a precharge circuit for ensuring that the contactors can close without causing damaging current spikes to the controller or other components.
Precharge is necessary because of capacitors in the controller; connecting sets of capacitors electrically requires care to match voltages because of the rate at which capacitors will charge and discharge to each other to balance potentials.
See Precharge Theory for a detailed explanation.
Operation
  • When the motorcycle is keyed on, precharge supplies a low amount of power (fused at 10A) to the controller-side main bus.
  • Voltage should climb above 85V within 4-5 seconds of powering on.
  • At this point, the BMS measures the voltage on both sides and decides to close the contactors.
  • If this process fails, precharge will stop and then the voltage level will decay.
    You will likely see error code 25 for a precharge error on the dash (when error codes are selected for display).
Warning Warning: The precharge circuit is not isolated from the controller or accessory charging port, and can be damaged if a large transient current is induced from an outside source to a de-energized motorcycle.
Precharge Failure
A recent (mid-2016) firmware update improves the robustness of the precharge logic especially when used with accessory charging systems that are permanently connected to the vehicle.
If while starting the bike, the sequence completes before the contactor closes, the green run light for the motorcycle will flash until the contactor does close.
To address a failed precharge on startup:
  1. Key the bike off if after several seconds, the contactor has not shut with an audible click and the green run light is still flashing.
  2. Wait 2 seconds (ensuring the dash indicator goes fully dark) and then key the bike on again.
    This should allow precharge to get a boost from residual charge from the last precharge startup cycle.
  3. Repeat a few times if necessary. If the contactor never shuts, check the logs and any error codes.