After a lithium retrofit, operators report that the truck sometimes stops lifting while the pack still shows charge, and on another truck the pack switches off suddenly with no warning. The maintenance lead wants to understand how the two cut-off levels should relate.
The truck controller and the BMS both protect against low voltage, but they should act in a planned order. The controller should warn first, then reduce lift and drive power, while the BMS cut-off stays as the final safety step. Set the controller thresholds from the lithium pack’s voltage curve, ideally using state of charge sent over CAN rather than voltage alone, and test the sequence under load before returning the truck to service.
Why the two levels clash
Controllers set up for lead-acid often cut lift at a voltage that suits lead-acid’s sloping curve. A LiFePO4 pack holds a flat voltage for most of its range and then drops quickly near empty. With lead-acid settings, the truck may cut lift too early under a heavy load, or the pack may reach its own cut-off before the controller has warned the operator.
A sensible order of events
- Warning. The display shows low charge, giving the operator time to finish the task and drive to the charger.
- Lift cut-back. The controller limits lift so the truck can still drive.
- Drive limit. Speed reduces, so the truck can still reach the charger.
- BMS protection. Only if the pack keeps discharging does the BMS disconnect it.
How to set it up
Ask the battery supplier for the pack’s discharge curve and its cut-off values, and give them to the truck dealer who programs the controller. Where the truck and pack can communicate, use the CAN state-of-charge signal for the warning and cut-back steps; see our CAN bus article and voltage window article. Test with a loaded truck, because voltage sags under current and settings that look right at rest can trip too early.
Records to keep
Note the final controller settings and the pack firmware version for each truck. If either changes later, repeat the test.
Risk limits
Only qualified technicians should change controller parameters, following the truck maker’s instructions. Thresholds depend on the pack model and the truck, so confirm values for your order. This article is general guidance.
Additional perspectives
Log voltage and current on one heavy-duty shift before changing anything. The log shows whether the trip comes from voltage sag under lift or from a genuinely empty pack.
Redway Tech Editorial Team – Service technician perspective
We need the pack’s discharge curve and cut-off values before programming. With those, the cut-back points can sit safely above the BMS limit.
Redway Tech Editorial Team – Truck dealer perspective
Train operators on what the warning means. A clear rule, such as returning to charge at the first warning, avoids most sudden stops.
Redway Tech Editorial Team – Fleet manager perspective
Specifications are taken from Redway product pages as of October 2026. Where a figure isn’t published, this article says so. Confirm current specifications for your model with Redway before ordering. This article is general guidance, not a site-specific engineering assessment.
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