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Power Management. Donald Heer 11/9/2011. Topics. Battery Types Charging Schemes Instantaneous vs. Average Power Example Battery Life Example Battery Safety. Battery Types. Alkaline - AA, 1.5V Nominal, 2.5Ah at 100mA, R INT ≈ 225m Ω , Digikey N107-ND NiCad (Rechargeable)

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Presentation Transcript
power management

Power Management

Donald Heer

11/9/2011

topics
Topics

Battery Types

Charging Schemes

Instantaneous vs. Average Power

Example Battery Life Example

Battery Safety

battery types
Battery Types

Alkaline

- AA, 1.5V Nominal, 2.5Ah at 100mA, RINT ≈ 225mΩ, Digikey N107-ND

NiCad (Rechargeable)

- AA, 1.2V Nominal, .7Ah at 100mA, RINT ≈ 16mΩ, Digikey SY114-ND

Lithium Coin Cell

- CR2032, 3V Nominal, .24Ah at .19mA, RINT ≈ 15KΩ, Digikey N189-ND

Lithium Ion (Rechargeable)

- Prismatic Cell, 3.6V Nominal, 1.8Ah at 3.4A, RINT ≈ 320mΩ, Panasonic CGA103446

power vs average power
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

example battery life example
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.

How long will the system work?

Can the 9V system directly drive the Lock? If not how can we fix it?

specifics for example
Specifics for Example

How long will the system work?

Can the 9V system directly drive the Lock? If not how can we fix it?

battery safety
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!

take away
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