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- 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.
- 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:
- 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.
- 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.
- Repeat a few times if necessary. If the contactor never shuts, check the logs and any error codes.