Reliable outage reporting is an energy budget written frame by frame. This paper gives the selection and sizing method for a collector or concentrator backup module: choose storage on the power-energy axis and the recharge duty, enumerate every millisecond of the last-gasp sequence and its retries, size the nickel-metal hydride module to finish them with margin, and design the rail topology, charge management and protection for a sealed cabinet that sees both summer heat and winter cold.
The animated scorecard compares a bulk/supercapacitor bank, non-rechargeable lithium and rechargeable NiMH on radio-pulse power, multi-frame energy, recharge from mains, cycle life across many outages, wide-temperature behaviour, abuse safety and cost. The capacitor wins pulse power but lacks energy; non-rechargeable lithium keeps a clock alive for years but is not meant for repeated recharge or high-current radio use; NiMH combines rechargeable multi-frame energy, strong pulse current and thousands of cycles with an aqueous, thermally benign profile.
Many robust designs therefore tier the storage: a small supercapacitor for the immediate rail hold-up and a NiMH module for the acknowledged, retried outage report and buffer flush - mirroring the layered timing approach seen in commercial smart meters but extending it to genuine two-way reporting.
Write the outage timeline as discrete current-time tasks: wake and detect loss; assemble the outage frame (node id, timestamp, last-good readings, downstream meter status); power the radio, attach and transmit; wait for the link-layer acknowledgement; retry on alternate channels up to a target count; flush the store-and-forward buffer and event log to flash; hold the real-time clock through the outage; and on restoration send the first gasp. Each task has a current and a duration.
The second animated figure is the energy waterfall: the initial frame, the acknowledgement wait (receive current), the retry frames, the buffer and log flush, the clock keep-alive, converter losses, and end-of-life and low-temperature derating, ending at the module capacity required for a fully acknowledged report rather than a single pulse.
The cellular or RF PA sets the peak current - a few hundred milliamperes for seconds per attempt - and the module must hold the converter input above undervoltage through the pulse and through the retries. Size cells and welded tabs for that peak; NiMH's flat plateau keeps the rail stable where a capacitor bank droops linearly and forces an oversized converter input range.
Choose the series count and a small buck-boost stage so the rail stays inside the radio and MCU operating window from a freshly charged pack down to end voltage, and use an ideal-diode or blocking path so the backup never back-feeds the mains supply.
The module recharges whenever mains is healthy, through a current-limited manager that restores full readiness after an outage and then holds a gentle maintenance current (at or below C/20) with a thermistor cut-back above about 45 C. Because the pack is recharged after every event, the chemistry must tolerate a lifetime of shallow cycles - a NiMH strength and a non-rechargeable-lithium non-starter.
A charge-status and self-test routine lets the concentrator report backup health to the head-end, so a module weakened by age or extreme temperature is flagged in maintenance rather than discovered during the next storm outage.
Pole-mount and underground collectors see a wider temperature span than indoor equipment. NiMH discharges reliably in the cold where lithium charge is restricted, though available capacity still falls and must be derated; in summer heat the controlled-charge rule prevents gassing. Welded cells, a fuse, an NTC and conformal coating suit a sealed, condensing enclosure, and the aqueous chemistry removes the thermal-runaway concern of a lithium pack in an unattended cabinet.
Apply an end-of-life capacity factor and a worst-case cold derating in the waterfall so the acknowledged last-gasp sequence still completes years into deployment and on the coldest night - precisely when grid outages cluster.
Record the loss-detection threshold, the radio profile and retry count, the buffer-flush energy, the temperature class and every derating. Where only a single unacknowledged frame is required, a supercapacitor may suffice; where the operator needs acknowledged, retried, multi-node outage reporting and clean restart, a NiMH DC-UPS module is the fit. Paper C validates the result against the DLMS/IEC 62056 stack, IEC 62052-11 and IEC 61000-4-11.
Weijiang Power manufactures sealed nickel-metal hydride cells and DC-UPS / last-gasp modules for AMR collectors, data concentrators and smart-grid endpoints. Send us your mains rail, radio technology and transmit current, the number of last-gasp frames and retry window, and the enclosure temperature range, and our engineers will design a welded, wide-temperature NiMH module with charge management and protection. See modules on the products page.
