🔋 Power Budget + Measurement

Why it matters

Power budget tells you if your design will work. Without it, you’re guessing how long the battery will last.

The idea

What Is a Power Budget?

A power budget calculates total energy consumption:

• Active mode: Current × time
• Sleep mode: Current × time
• Total: Sum of all modes
• Battery capacity: Total energy available

        <h3>Typical Values</h3>
        ESP32 power consumption:
        <ul>
          <li><strong>Active (Wi‑Fi off)</strong>: ~40mA</li>
          <li><strong>Active (Wi‑Fi on)</strong>: ~80mA</li>
          <li><strong>Deep sleep</strong>: ~10µA</li>
          <li><strong>Wi‑Fi transmit</strong>: ~170mA</li>
        </ul>

        <h3>Calculation</h3>
        For 5-minute cycle:
        <ul>
          <li>Active: 80mA × 3s = 240mAs</li>
          <li>Sleep: 10µA × 297s = 2.97mAs</li>
          <li>Total: ~243mAs per cycle</li>
        </ul>

        <h3>Battery Lifetime</h3>
        For 2000mAh battery:
        <ul>
          <li>Capacity: 2000mAh × 3600s/h = 7,200,000mAs</li>
          <li>Cycles: 7,200,000 / 243 ≈ 29,600 cycles</li>
          <li>Lifetime: 29,600 × 5min ≈ 103 days</li>
        </ul>

        <h3>Measurement</h3>
        Use multimeter in current mode:
        <ul>
          <li>Break circuit (series measurement)</li>
          <li>Measure active current</li>
          <li>Measure sleep current (may need µA range)</li>
          <li>Verify calculations</li>
        </ul>

Demo

Adjust Active Current, Active Time, Sleep Current, and
Sleep Time to see how battery lifetime changes.

Watch for:

• Total energy per cycle — lower is better
• Battery lifetime — days/months/years
• Impact of active time — reducing active time dramatically improves lifetime

Key takeaways

• Power budget = sum of (current × time) for all modes
• Deep sleep is essential — 10µA vs 80mA active
• Minimize active time to maximize battery lifetime
• Measure actual current consumption to verify calculations

Going deeper

Real-world power consumption varies with temperature, battery age, and component tolerances. Always add a 20–30% safety margin. For production, use a power profiler (like Nordic Power Profiler) to measure actual consumption. Consider battery self-discharge (~5% per month for LiPo).

Math details

Power budget formula:
  E_cycle = (I_active × t_active) + (I_sleep × t_sleep)

  Where:
  E_cycle = energy per cycle (mAs)
  I_active = active current (mA)
  t_active = active time (s)
  I_sleep = sleep current (µA, convert to mA)
  t_sleep = sleep time (s)

Battery lifetime:
  Cycles = Battery_capacity (mAs) / E_cycle
  Lifetime = Cycles × Cycle_time

Example:
  I_active = 80mA, t_active = 3s → 240mAs
  I_sleep = 10µA = 0.01mA, t_sleep = 297s → 2.97mAs
  E_cycle = 243mAs

  Battery: 2000mAh = 7,200,000mAs
  Cycles = 7,200,000 / 243 = 29,600
  Lifetime = 29,600 × 5min = 148,000min = 103 days

Implementation

LLM Prompt: Power Budget Calculator