The transmitter pack for a crane remote has to satisfy two masters at once: the operator, who demands a full shift of uninterrupted control and a fast turnaround between shifts, and the functional-safety architecture, which demands that the battery never cause an uncommanded stop of a suspended load and always retains enough energy to send an emergency-stop command. This second paper turns the safety-critical load profile into a concrete nickel-metal hydride pack design. It covers sizing capacity to a full shift of continuous radio and display duty, choosing high-rate, low-internal-resistance cells, building the redundancy and monitoring that support a Performance Level d, Category 3 control architecture, reserving a guaranteed E-stop energy margin, designing hot-swap and rapid-charge workflows for multi-shift plants, and hardening the pack for cold, vibration and the occasional drop. The result is a pack treated as a safety-related subsystem rather than a consumable, with every design choice traceable to the crane-control standards.
Capacity sizing starts from the measured continuous duty, not a standby estimate. The designer logs the current of the scanning, radio-transmit, duplex-receive, display and backlight states across a realistic duty mix, computes the average for a worst-case shift - including frequent transmission at extended range - and sizes the NiMH capacity so that, after ageing and cold derating, the pack still clears the shift with the E-stop reserve intact. That reserve is deliberately excluded from the usable runtime the fuel gauge offers the operator.
Because NiMH cells span a useful capacity range in AA and sub-C formats with high-rate variants, the designer can trade pack size against shift target without sacrificing pulse capability, and the flat 1.2-volt discharge plateau keeps the regulator in its efficient region across almost the whole discharge. The deliverable is a pack whose predicted runtime, verified against a recorded shift waveform, comfortably exceeds the longest real shift rather than matching an idealised bench average.
Cell selection prioritises internal resistance and high-rate behaviour over headline capacity, because the safety case depends on holding the rail through repeated transmit peaks. High-rate NiMH cells with charged internal resistance in the low tens of milliohms and proven several-ampere discharge capability are specified in matched sets, so series strings behave uniformly and no single cell becomes the weak point that sags under a radio burst.
Matching matters because a transmitter pack is usually a multi-cell series arrangement to reach the radio and logic rail; mismatched cells reach end-of-charge and end-of-discharge at different moments, eroding both runtime and the predictable plateau the fuel gauge relies on. Procuring sorted, lot-consistent high-rate cells and welding the interconnects for minimal resistance and maximum vibration tolerance gives the pack the stable, repeatable electrical behaviour the safety argument assumes.
The protective functions of a serious crane remote target PL d, Category 3 under EN ISO 13849-1, which requires redundancy and diagnostics so a single fault does not remove the safety function. The battery design supports this at the power layer: dual or paralleled energy paths, monitoring of cell or string voltage and temperature, and a fuel-gauge that gives graded, early warning of depletion rather than relying on a single threshold, so an operator is never surprised by a dead pack during a lift.
The monitoring feeds the same diagnostic philosophy as the command channels: it detects a degrading cell, flags it for replacement and ensures the transmitter enters a controlled, announced state - finishing or safely pausing the current motion - rather than suffering an abrupt link loss. Designing the power subsystem with this diagnostic coverage is what allows the overall control system to claim its performance level credibly, rather than having the battery as an unexamined single point of failure beneath a redundant safety chain.
A non-negotiable design element is the E-stop reserve: a defined amount of energy, walled off from normal runtime, sufficient to transmit the stop telegram - and any required repeat frames - even when the usable pack is exhausted. It is implemented either as a firmware floor below which normal operation is inhibited while the stop channel remains powered, or as a small dedicated reservoir, and it is validated at end-of-life and low temperature, the worst conditions.
This reserve embodies the principle from IEC 60947-5-5 and EN ISO 13850 that the stop function must always be available: the operator's red mushroom button must work on the very last Joule. Testing proves the reserve survives after a full shift, after cold soak and with aged cells, closing the loop between battery design and the functional-safety requirement that a stop command can never be starved of energy.
Plants running two or three shifts need a battery workflow that never grounds a crane: spare packs charge in a dock while the operator swaps to a fresh one at break or shift change, ideally without losing the transmitter's binding or configuration. NiMH is well suited to this because it tolerates the repeated, sometimes rapid charge cycles of a shift dock when the charger applies a proper -delta-V or thermal termination with timer backstop, and it does not require the elaborate per-cell management of lithium-ion.
The pack and dock are co-designed for correct charge current relative to cell capacity, temperature monitoring during fast charge, and clear state indication. Because NiMH can accept some charge below freezing, a cold pack returning from an outdoor yard can still be topped up where a lithium pack would have to wait - a practical advantage in winter logistics. Robust, keyed contacts and a latching mechanical design make the hot-swap one-handed and prevent intermittent connection during operation.
The pack is built for abuse: welded tabs and rigid cell retention survive vibration and the drops that industrial remotes inevitably suffer; the enclosure and contact design exclude dust and rain to the transmitter's rating; thermal sensors and current protection prevent a fault from becoming a hazard; and the materials tolerate the same wide temperature span as the transmitter. Weight and balance are tuned because the operator wears the device for hours.
Validation replays the worksite: an electronic load runs the recorded shift waveform at high and low temperatures to confirm runtime and rail stability; vibration and drop tests confirm mechanical integrity; the E-stop reserve is proven at worst-case condition; and cycle testing across the equivalent of the service life confirms capacity and impedance stay within bounds. Passing that programme - followed by the functional-safety and radio certification in the final paper - yields a pack that protects both productivity and safety across years of shifts.
Weijiang Power designs and manufactures sealed nickel-metal hydride cells and matched industrial packs for remote, off-grid and safety-related equipment, and supports OEM partners with IEC 61951-2 performance files, IEC 62133-2 safety evidence, pulse-load characterisation, wide-temperature testing and charger/pack co-validation. Tell us your duty cycle, peak current, temperature envelope, autonomy target and the standards your product must meet, and our engineers will specify a cell-and-pack combination that protects runtime, reliability and service life. Review the range on the products page.
