A site has a long ramp between two floors. Trucks leave the charger fully charged and drive straight down the ramp. The engineering team asks how the lithium pack protects itself when regenerative braking pushes current into a full battery.
Regenerative braking returns current to the battery, and a full pack can accept little or no extra charge. The BMS sets a charge current limit, which falls as the pack fills or gets cold. The truck controller should read that limit, ideally over CAN, and reduce regeneration, with the service brakes taking the rest. If the controller ignores the limit, the BMS may disconnect to protect the cells. Agree the limits and test the full-pack ramp case before go-live.
Why the full pack is the hard case
At high state of charge, cell voltages are near their upper limit. Extra current from braking pushes voltage higher, so the BMS must limit or block charging. Cold cells accept less charge too. A truck leaving the charger and going straight down a ramp combines both.
How the parts should work together
- BMS. Calculates the allowed charge current from cell voltage, temperature and state of charge, and sends it to the truck.
- Controller. Reduces regenerative current to stay inside that limit.
- Brakes. The service brakes provide the remaining braking force; regeneration should never be the only brake.
- Last resort. If limits are exceeded, the BMS can open its contactor, which the truck must handle safely.
Our CAN bus article and low-voltage cut-off article cover the communication side.
What to test
- Full pack, loaded truck, longest downhill ramp.
- Cold pack at the start of a shift, if the site is cold.
- Check the BMS log for over-voltage alarms or disconnects.
Practical options
Some sites ask the charger to stop slightly below full, or plan a short level drive before the ramp. Discuss any change with the battery supplier first. Redway’s BMS and telematics page gives background.
Risk limits
Braking performance is a safety matter for the truck maker. Do not change controller settings without the truck maker’s approval, and confirm limits for your pack model. This article is general guidance.
Additional perspectives
Make sure the controller reads the BMS charge limit and reacts within a short time. A slow response is often the cause of over-voltage trips on ramps.
Redway Tech Editorial Team – Truck engineer perspective
Treat ramps as a special case in the risk assessment. Check that trucks brake normally even if the battery stops accepting charge.
Redway Tech Editorial Team – Site safety lead perspective
Send us the ramp length, gradient and truck mass. With those, we can estimate the regen current and check it against the pack’s limits.
Redway Tech Editorial Team – Battery engineer 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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