Checking Primary Cell Voltage During a Radio Current Pulse

A primary cell can show a healthy open circuit voltage and still reset a board during a radio transmission. Pulse current interacts with the cell’s impedance, state of discharge, temperature, and the board’s energy storage. Evaluate the voltage at the load during the event rather than using an unloaded reading as a pass criterion.

Use the relevant discharge information

Record cell type, pulse amplitude, duration, repetition, background current, and minimum system voltage. The Energizer lithium coin application manual discusses pulse effects, temperature, internal resistance, and the dependence of usable capacity on load and cutoff conditions.

Use the selected cell’s own current and voltage data. A capacity rating measured at a light continuous load does not automatically predict operation with repeated high current bursts.

Separate cell and connection drops

Measure voltage at the cell terminals and at the PCB supply input during the same event. Include holder contacts, traces, protection elements, and wiring. A poor contact can imitate an aged cell, while a measurement at the holder alone can miss a downstream drop.

A simple resistance model gives voltage drop as current multiplied by resistance, but real cell behavior can be time dependent. Use that model to organize the investigation, not to claim a complete electrochemical prediction from one pulse.

Evaluate local energy storage

Check the capacitor network supporting the pulse, including effective capacitance, ESR, leakage, and recharge time between events. For an illustrative ideal case, 10 mA supplied for 1 ms removes 10 microcoulombs; a 100 microfarad capacitor alone would drop by 0.1 V. The cell’s concurrent contribution and circuit losses change the actual result.

Increasing capacitance can reduce a short excursion but does not create additional average energy from the cell. Confirm that the repeated pulse schedule allows recovery and that capacitor leakage does not undermine long standby life.

Test the intended service conditions

Evaluate representative discharge states and temperatures using the cell manufacturer’s guidance. Record reset thresholds and regulator behavior so the endpoint corresponds to product operation. Check both the first pulse after idle and pulses within a sustained activity sequence. Avoid extrapolating from a fresh room temperature cell to the entire service life.

Save pulse waveforms, cell identification, contact arrangement, capacitor parts, and test conditions. A useful power budget establishes acceptable loaded voltage for the required pulse schedule and identifies the end of usable operation. It does not equate remaining open circuit voltage or nominal capacity with guaranteed ability to support the next transmission.