1. Power Management Donald Heer 11/9/2011

2. Topics Battery Types Charging Schemes Instantaneous vs. Average Power Example Battery Life Example Battery Safety

3. Battery Types Alkaline - AA, 1.5V Nominal, 2.5Ah at 100mA, R INT ≈ 225mΩ, Digikey N107-ND NiCad (Rechargeable) - AA, 1.2V Nominal,.7Ah at 100mA, R INT ≈ 16mΩ, Digikey SY114-ND Lithium Coin Cell - CR2032, 3V Nominal,.24Ah at.19mA, R INT ≈ 15KΩ, Digikey N189-ND Lithium Ion (Rechargeable) - Prismatic Cell, 3.6V Nominal, 1.8Ah at 3.4A, R INT ≈ 320mΩ, Panasonic CGA103446 June 26, 2015 2

4. Charging Schemes – Simple June 26, 2015 3

5. Charging Schemes - Better June 26, 2015 4

6. Charging Schemes – Mo’ Betta’ June 26, 2015 5

7. Power vs. Average Power Power is the power used during a single action. Power over time gives you capacity used. - Motor Motion: 12V @ 500mA for.5 Seconds Average Power is power used over a fixed period of time. - Motor Motion: Door used 20 times per hour Eg. The motor uses: 20times *12V *.5A *.5sec * 1/3600 = 16mW/Hour June 26, 2015 6

8. Example Battery Life Example Imagine you are building a keypad activated door lock. You want it to run as long as possible. For some reason you are required to use a 9V alkaline battery. June 26, 2015 7 How long will the system work? Can the 9V system directly drive the Lock? If not how can we fix it?

9. Specifics for Example PropertyValue Keypad Use3.3V @ 5mA for 3 Sec Lock Cycle.02mAH @ 6V (200mA) Controller Active3.3V @ 2mA for 3 Sec Controller Stand By3.3V @ 2uA System Leakage2uA 9-6V RegulatorSwitching Regulator at 95% Eff. 6-3.3V RegulatorLinear Regulator Uses per Day200 9VRINT ≈ 1.5Ω, 600mAH @ 25mA June 26, 2015 8 How long will the system work? Can the 9V system directly drive the Lock? If not how can we fix it?

10. Battery Safety Short Circuits In low resistance batteries, you can quickly create LARGE currents that can easily melt components. Over Heating During charging (and discharging) battery chemical reactions produce heat. The faster the rate the more heat. The issue is some chemistries (Lithium Ion) can ignite! June 26, 2015 9

11. Take Away Check both your average power for battery life and your instantaneous power for intermittent use Pick the correct battery type, not just the newest