Outage recorder backup
CJ Ackley | Electrical | Project brief

STATUS
Power brief; load profile needed. Detailed design and analysis pending.

THE PROBLEM
A machine event recorder loses its supply at the moment an electrical interruption occurs. A local DC backup could preserve the final events without keeping the whole machine powered. The design must fit a defined load, outage duration, and enclosure.

DESIGN QUESTION
What storage and power path preserve the recording window without backfeeding the machine?

SCOPE
- Develop the recorder load profile and compare capacitor and battery storage.
- Size stored energy for conversion losses, voltage limits, and aging allowances.
- Specify source isolation, charge control, protection, and low-voltage shutdown.

CONSTRAINTS
Interface: Nominal 24 V DC; actual input range to be specified
Load: Recorder only, with measured startup and steady demand
Duration: Required recording window to be agreed
Environment: Enclosure space and temperature range to be defined

ENGINEERING DECISIONS (PROPOSED)
Storage sizing and power transfer
Size the storage against both the recording energy and the power path at minimum voltage. Include converter limits, storage resistance, startup demand, and source isolation.

ALTERNATIVE
A capacitor bank avoids a battery charge cycle, but its falling voltage and available enclosure volume may limit the recording window.

TRADEOFF
A battery can extend the window with less volume, while adding charge management, aging behavior, and maintenance requirements.

PROPOSED TOOLS AND METHODS
Time-domain power model, Component datasheets, Bench-test plan

VERIFICATION SCENARIO (NOT YET RUN)
The supply drops during peak recorder demand
Apply the measured peak load at the lowest allowed state of charge and temperature case, then remove and restore the input supply.

PASS CONDITION
Recorder voltage stays above its specified minimum for the agreed recording window, source backfeed stays within the allowed limit, and shutdown preserves the required records.

EVIDENCE TO RETAIN
A discharge model, independent energy calculation, component operating-limit checks, and planned voltage/current traces across dropout and recovery.

MEASUREMENT AND LIMITS
Treat transfer interruption, total recording time, and shutdown integrity as separate acceptance checks. Datasheet ratings and assumed derating must be traceable to the chosen parts.

COMPLETION CRITERIA (PLANNED)
- The actual load profile and recording window are established.
- The candidate power path meets voltage, energy, and component limits in the agreed worst cases.
- A bench procedure can verify dropout, backfeed, recovery, and record retention.

VERIFICATION PLAN
Energy balance
Compare time-domain discharge with an independent energy calculation.

Worst case
Evaluate peak demand, low charge, temperature, and component tolerances.

Transfer test
Specify a bench test for dropout, recovery, backfeed, and saved records.

PLANNED DELIVERABLES
- Power budget and storage comparison workbook
- Functional schematic, component criteria, and protection rationale
- Discharge model and low-voltage bench-test procedure

SCOPE NOTE
This is a low-voltage design brief, not a released circuit. Battery integration, protection, and hardware performance remain to be validated.

NEXT STEP
Measure the recorder load and establish the minimum uninterrupted recording time.
