cmsc838 week 04 | lecture 08 | feb 19, 2015 · 2015-02-25 · week 04 | lecture 08 | feb 19, 2015...

Human Computer Interaction Laboratory

@jonfroehlich Assistant Professor Computer Science

CMSC838 Tangible Interactive Computing

Week 04 | Lecture 08 | Feb 19, 2015 I’ve Got The Power!

TODAY’S LEARNING GOALS

1. What is power? What is energy? What’s the

difference between a watt and a watt-hour?

2. Develop an intuition for high-wattage vs. low-

wattage

3. Understand how to calculate power in ohmic

circuits

4. Learn about batteries including: capacity, nominal

cell voltages, battery discharge curves, C-ratings,

energy densities, and internal resistances

5. Understand popular varieties of batteries and

tradeoffs between them (e.g., what are Li-Ion/LiPo

batteries and why are they so popular?)

volt∙age [vohl-tij] | measured in joules/coulomb or volts (V)

To get electrical current to flow from one point to another, a voltage

(electric potential) must exist between two points. A voltage across a

conductor gives rise to an electromotive force (EMF) that pushes free

electrons in a circuit

cur∙rent [kur-uhnt] | measured in coulombs/sec or amps (I)

Electric current is the total charge that passes through some cross-sectional

area A per unit time.

re∙sist∙ance [ri-zis-tuhns] | measured in ohms (Ω)

A material’s tendency to resist the flow of charge (current). In 1826, Georg

Ohm published experimental results regarding the resistance of various

materials using an empirical approach. He found a linear approach and

defined resistance as: R = V / I

QUICK REMINDER: VOLTAGE, CURRENT, AND RESISTANCE

[source: Scherz & Monk, Practical Electronics for Inventors, 3rd Edition]

WHAT IS POWER? In general physics terms, power is defined as the rate at which energy is transferred (or

transformed). There are many forms of energy: mechanical, electrical, chemical,

thermal, electromagnetic.

Energy can never be

created or destroyed,

only transferred to

another form!

[source: https://learn.sparkfun.com/tutorials/electric-power]

WHAT IS POWER? In general physics terms, power is defined as the rate at which energy is transferred (or

transformed). There are many forms of energy: mechanical, electrical, chemical,

thermal, electromagnetic.


Pic of led,

resistor,

electric

motor,

speaker. I

had this

slide but

lost it

LEDs transform electric energy into electromagnetic energy

Resistors transform electric energy into heat

DC motors transform electric energy into mechanical energy

Speakers transform electric energy into sound

Much of what we do in physical interactive computing is transform

different forms of energy to and from electric energy.

WHAT IS ELECTRIC POWER? Electric energy begins as potential energy, which is what we call voltage. When

electrons flow (current), this potential energy is transformed into electric energy.

Electric power is measured by combining how much electric energy is transferred and

how fast this transfer happens


pow∙er [pou-er] | measured in watts (W) or joules/second (J/s)

Power is the rate at which work is performed. In electrical circuits, power is

measured in watts. One watt is the rate at which work is done when one amp (I)

of current flows through an electrical potential difference of one volt (V). More

formally, Power = I * V. You have likely seen ‘watts’ listed on electronics. For

example, a 100-watt light bulb draws 100 watts of power at any moment when

turned on. Note: as it is simply a measure of work, a watt can be defined in non-

electrical terms (e.g., in newtons or horsepower).

QUICK DEFINITIONS


pow∙er [pou-er] | measured in watts (W) or joules/second (J/s)

Power is the rate at which work is performed. In electrical circuits, power is

measured in watts. One watt is the rate at which work is done when one amp (I)

of current flows through an electrical potential difference of one volt (V). More

formally, Power = I * V. You have likely seen ‘watts’ listed on electronics. For

example, a 100-watt light bulb draws 100 watts of power at any moment when

turned on. Note: as it is simply a measure of work, a watt can be defined in non-

electrical terms (e.g., in newtons or horsepower).

en∙er∙gy[en-er-jee] | measured in watt-hours W∙h or joules (J)

Energy is measured in watt-hours or joules. It is the amount of electricity

produced or consumed. It is simply the power rate (watts) multiplied by time

(hours). If we want to power our 100 watt light bulb for 3 hours, we need 300

watt-hours of energy. When you hear ‘watt-hour,’ you may think ‘watt per hour’

(like miles per hour); however, this doesn’t make sense. A watt itself is the rate

measurement—like speed—the watt-hour is more like the odometer (tracking

distance traveled or work over time). This is why electric companies bill in

watt-hours (it’s how much you’ve consumed for the month).

QUICK DEFINITIONS


CONFUSED ABOUT WATTS VS. WATT-HOURS? Then watch this video by ASUEnergyPolicy. It’s a bit slow, but you can watch at 1.25x!

[source: http://youtu.be/LpMoOFLPogc]

http://youtu.be/LpMoOFLPogc

POWER (WATTS) OF COMMON HOUSEHOLD APPLIANCES

[source: http://www.seattle.gov/light/accounts/stretchyourdollar/ac5_appl.htm; http://www.consumerreports.org/cro/resources/images/video/wattage_calculator/wattage_calclulator.html]

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0 1000 2000 3000 4000 5000 6000

Clock

Laptop

60-Watt Light Bulb

100-Watt Light Bulb

LCD TV (26")

Desktop Computer

Clothes Washer (Cold Water Cycle)

Refrigerator

Electric Coffee Maker

Toaster

Dishwasher

Microwave

Hot Water Heater (Energy Efficient) 40 Gallon

Clothes DryerTo gain a bit of intuition about ‘watts,’ let’s review the power consumption of various household appliances.

Can you name the top three most consuming appliances/devices in the home?



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0 1000 2000 3000 4000 5000 6000

Clock

Laptop

60-Watt Light Bulb

100-Watt Light Bulb

LCD TV (26")

Desktop Computer


Refrigerator


Toaster

Dishwasher

Microwave


Clothes Dryer



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0 1000 2000 3000 4000 5000 6000

Clock

Laptop

60-Watt Light Bulb

100-Watt Light Bulb

LCD TV (26")

Desktop Computer


Refrigerator


Toaster

Dishwasher

Microwave


Clothes Dryer

But remember, power is like mph for each appliance—an instantaneous rate of consumption—we need a measure like the odometer to get an indication of how much energy each appliance is using per day.



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0 1000 2000 3000 4000 5000 6000

Clock

Laptop

60-Watt Light Bulb

100-Watt Light Bulb

LCD TV (26")

Desktop Computer


Refrigerator


Toaster

Dishwasher

Microwave

Hot Water Heater (Energy Efficient)…

Clothes Dryer

72

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180

200

250

300

440

450

533.3333333

1400

4200

5000

6750

0 2000 4000 6000 8000

Clock

Laptop

Toaster

60-Watt Light Bulb



100-Watt Light Bulb

LCD TV (26")

Desktop Computer

Microwave

Dishwasher

Refrigerator

Clothes Dryer


ENERGY USAGE PER DAY (WATT-HOURS) OF COMMON HOUSEHOLD APPLIANCES

Power (Watts) Estimated Time

Usage Per Day (Hrs) Estimated Energy Use Per Day (Watt-Hours)

Hot Water Heater (Energy Efficient) 40 Gallon 4500 1.5 6750.0

Clothes Dryer 5000 1.0 5000.0

Refrigerator 700 6.0 4200.0

Dishwasher 1400 1.0 1400.0

Microwave 1600 0.3 533.3

Desktop Computer 150 3.0 450.0

LCD TV (26") 110 4.0 440.0

100-Watt Light Bulb 100 3.0 300.0

Electric Coffee Maker 1000 0.3 250.0

Clothes Washer (Cold Water Cycle) 600 0.3 200.0

60-Watt Light Bulb 60 3.0 180.0

Toaster 1200 0.1 100.0

Laptop 25 3.0 75.0

Clock 3 24.0 72.0

The hot water heat consumes 4500W of power for an estimated time of about 1.5 hours a day, so 6750Wh (or 6.75kWh).



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0 1000 2000 3000 4000 5000 6000

Clock

Laptop

60-Watt Light Bulb

100-Watt Light Bulb

LCD TV (26")

Desktop Computer


Refrigerator


Toaster

Dishwasher

Microwave


Clothes Dryer

72

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180

200

250

300

440

450

533.3333333

1400

4200

5000

6750

0 2000 4000 6000 8000

Clock

Laptop

Toaster

60-Watt Light Bulb



100-Watt Light Bulb

LCD TV (26")

Desktop Computer

Microwave

Dishwasher

Refrigerator

Clothes Dryer








Dishwasher 1400 1.0 1400.0

Microwave 1600 0.3 533.3


LCD TV (26") 110 4.0 440.0

100-Watt Light Bulb 100 3.0 300.0




Toaster 1200 0.1 100.0

Laptop 25 3.0 75.0

Clock 3 24.0 72.0

In this case, the clothes dryer is estimated to run once a day for an hour (this family probably has a baby), so 5000 watts x 1 hour = 5kWh



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0 1000 2000 3000 4000 5000 6000

Clock

Laptop

60-Watt Light Bulb

100-Watt Light Bulb

LCD TV (26")

Desktop Computer


Refrigerator


Toaster

Dishwasher

Microwave


Clothes Dryer

72

75

100

180

200

250

300

440

450

533.3333333

1400

4200

5000

6750

0 2000 4000 6000 8000

Clock

Laptop

Toaster

60-Watt Light Bulb



100-Watt Light Bulb

LCD TV (26")

Desktop Computer

Microwave

Dishwasher

Refrigerator

Clothes Dryer








Dishwasher 1400 1.0 1400.0

Microwave 1600 0.3 533.3


LCD TV (26") 110 4.0 440.0

100-Watt Light Bulb 100 3.0 300.0




Toaster 1200 0.1 100.0

Laptop 25 3.0 75.0

Clock 3 24.0 72.0

While the microwave consumes more power than a refrigerator (1600W vs. 700W), the microwave is used far less in this home (20 mins/day) than the refrigerator compressor (6hr/day). So, the refrigerator accounts for more energy.



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25

60

100

110

150

600

700

1000

1200

1400

1600

4500

5000

0 1000 2000 3000 4000 5000 6000

Clock

Laptop

60-Watt Light Bulb

100-Watt Light Bulb

LCD TV (26")

Desktop Computer


Refrigerator


Toaster

Dishwasher

Microwave


Clothes Dryer

72

75

100

180

200

250

300

440

450

533.3333333

1400

4200

5000

6750

0 2000 4000 6000 8000

Clock

Laptop

Toaster

60-Watt Light Bulb



100-Watt Light Bulb

LCD TV (26")

Desktop Computer

Microwave

Dishwasher

Refrigerator

Clothes Dryer








Dishwasher 1400 1.0 1400.0

Microwave 1600 0.3 533.3


LCD TV (26") 110 4.0 440.0

100-Watt Light Bulb 100 3.0 300.0




Toaster 1200 0.1 100.0

Laptop 25 3.0 75.0

Clock 3 24.0 72.0

[source:http://www.anandtech.com/show/4971/apple-iphone-4s-review-att-verizon/15]

Common Tasks

3D Gaming

3G/WiFi

IPHONE POWER CONSUMPTION

[source:http://www.anandtech.com/show/6330/the-iphone-5-review/12]

IPHONE COMPARISON

Pow

er C

onsu

mpt

ion

(Wat

ts)

Low

er is

Bet

ter

Device Power Consumption vs. Time Kraken Mobile Benchmark

This graph is based on the Kraken test suite, a Javascript test suite from Mozilla

CALCULATING POWER

[source: http://en.wikipedia.org/wiki/Volt]

Electric power (P) is the rate at which energy is transferred. It is measured in terms of

joules per second (J/s)—a watt (W). So, how is it calculated? We can get to

joules/second with just a few terms we have already covered in class.

CALCULATING POWER

[source: http://en.wikipedia.org/wiki/Volt; https://learn.sparkfun.com/tutorials/electric-power]




Recall that voltage (aka electric potential energy) is a measure of joules/coulomb (energy per unit charge).

CALCULATING POWER






Current is a measure of the total charge (coulombs) that pass through some area per unit time (seconds)—so, coulombs/second.

CALCULATING POWER







Thus, to calculate power, we multiply volts × amperes:

CALCULATING POWER








𝑝𝑜𝑤𝑒𝑟 =𝑗𝑜𝑢𝑙𝑒𝑠

𝑐𝑜𝑢𝑙𝑜𝑚𝑏 ×

𝑐𝑜𝑢𝑙𝑜𝑚𝑏

𝑠𝑒𝑐𝑜𝑛𝑑= 𝑤𝑎𝑡𝑡

voltage current

CALCULATING POWER








𝑝𝑜𝑤𝑒𝑟 =𝑗𝑜𝑢𝑙𝑒𝑠

𝑐𝑜𝑢𝑙𝑜𝑚𝑏 ×

𝑐𝑜𝑢𝑙𝑜𝑚𝑏

𝑠𝑒𝑐𝑜𝑛𝑑= 𝑤𝑎𝑡𝑡

To calculate the power of any particular component in a circuit, multiply the voltage drop across it by the current running through it: Power = Voltage * Current or P = V * I

voltage current

CALCULATING POWER A simple example

5V 3.3KΩ

I

How much power is dissipated by this resistor?


5V 3.3KΩ

I


Answer: 1. First, solve for the current running

through the resistor: I = V/R = 5/3.3KΩ = 1.5mA


5V 3.3KΩ

I


Answer: 1. First, solve for the current running

through the resistor: I = V/R = 5/3.3KΩ = 1.5mA

2. So, 1.5mA running through the resistor and 5V across it, then P = I * V = 1.5mA * 5 = 7.6mW

MEASURING POWER ACROSS A RESISTOR

[source: https://learn.sparkfun.com/tutorials/resistors;]

Power is usually calculated by multiplying voltage and current (P = IV). But, by applying

Ohm’s law, we can also use the resistance value in calculating power. If we know the

current running through a resistor, we can calculate the power as:

Given: 𝑉 = 𝐼𝑅

We can calculate power using current only with Ohm’s Law: 𝑃 = 𝐼𝑉 = 𝐼 ∗ 𝐼𝑅 = 𝐼2 ∗ 𝑅

MEASURING POWER ACROSS A RESISTOR

[source: https://learn.sparkfun.com/tutorials/resistors;]

Power is usually calculated by multiplying voltage and current (P = IV). But, by applying

Ohm’s law, we can also use the resistance value in calculating power. If we know the

current running through a resistor, we can calculate the power as:

Or, if we know the voltage across a resistor, the power can be calculated with voltage only:

Given: 𝑉 = 𝐼𝑅

We can calculate power using current only with Ohm’s Law:

𝑃 = 𝑉2

𝑅

𝑃 = 𝐼𝑉 = 𝐼 ∗ 𝐼𝑅 = 𝐼2 ∗ 𝑅

Pressure ≈ Voltage

(measured in

volts)

Flow ≈ current (measured in amps)

Hole width ≈ resistance (measured in ohms) Note: Hole width is inversely

proportional to resistance. Larger

hole, lower resistance.

WATER ANALOGY FOR DC CIRCUITS Let’s return to our water analogy for DC circuits to help explain power.

[based on figures from: Platt, Make: Electronics, 1st Edition]

Recall our basic analogy between pressure, resistance, and volume of water flow with voltage, resistance, and current


(measured in

volts)







With Ohm’s Law: V=IR or I=V/R. Thus, two easy ways to increase flow in a circuit.


(measured in

volts)







Increased

pressure (Increased

voltage)

More

flow

Hole width

held constant (resistance

constant)


1. Increase the voltage.


(measured in

volts)







Increased

pressure (Increased

voltage)

More

flow

Hole width


constant)

Hole width

increased (resistance

decreased)

Pressure

held constant (voltage

held constant)

More

flow


1. Increase the voltage. 2. Decrease the resistance.


(measured in

volts)







Increased

pressure (Increased

voltage)

More

flow

Hole width


constant)

Hole width


decreased)

Pressure


held constant)

More

flow



How does this relate to power?


(measured in

volts)







Increased

pressure (Increased

voltage)

More

flow

Hole width


constant)

Hole width


decreased)

Pressure


held constant)

More

flow



How does this relate to power?

Answer: Recall that P = I * V. So, in both cases, we’ve increased our power usage!



As power is measured in watts—a measure of work—Charles Platt adds a water

wheel to his analogy (imagine the water wheel hooked up to some machinery

doing some work). Note: in an electrical circuit, resistors actually dissipate power

as heat (that’s the work)—that’s not the case in this water analogy, which is why

we need the water wheel (helps to show off work).

ways to power a project

4 COMMON WAYS TO POWER A PROJECT

[source: https://learn.sparkfun.com/tutorials/how-to-power-a-project]

1. USB Cable. Perhaps the most

common way to power a project,

especially when prototyping.

2. External wall power (sometimes

called a wall wart). Perfect for long-lived

deployments.

3. Batteries. If you want to build a

mobile or wearable project, you’ll need to

power it off of batteries. There is a huge

variety to choose from. We’ll cover this

today.

4. Variable DC bench power supply.

This allows you to set a specific voltage

and also the maximum current allowed

(to provide some protection against short

circuits). We have one of these in the lab.

batteries

Alkaline AAA 1.5V, 750mAh

SAMPLE OF BATTERY TYPES

[images from sparkfun.com]

Rechargeable Lithium Ion 9V, 350mAh

Alkaline AA 1.5V, 1500mAh

Rechargeable Lithium Ion 3.7V, 2,000mAh

Alkaline 9V 9V, ~500mAh

Rechargeable Lithium Ion 3.7V, 110mAh

Rechargeable Nickel Hydride (NiMH) 1.2V, 2000mAh

CR2032 Coin Cell Lithium 3V, 250mAh


Exa

mp

le

Rech

arg

eab

les

Exa

mp

le

“Dis

po

sab

les”

A list of sample rechargeable (aka secondary) batteries and disposable (aka primary) batteries with different

chemical compositions (e.g., alkaline, lithium-ion, nickel hydride (NiMH))

Alkaline AAA 1.5V, 750mAh

SAMPLE OF BATTERY TYPES

[images from sparkfun.com]

Rechargeable Lithium Ion 9V, 350mAh

Alkaline AA 1.5V, 1500mAh



Rechargeable Lithium Ion 3.7V, 110mAh

Rechargeable Nickel Hydride (NiMH) 1.2V, 2000mAh



Exa

mp

le

Rech

arg

eab

les

Exa

mp

le

“Dis

po

sab

les”

A list of sample rechargeable (aka secondary) batteries and disposable (aka primary) batteries with different

chemical compositions (e.g., alkaline, lithium-ion, nickel hydride (NiMH))

Help the Environment Use Rechargeable Whenever Possible

TERMINOLOGY

[source: https://learn.sparkfun.com/tutorials/battery-technologies; http://en.wikipedia.org/wiki/Battery_(electricity)]

Capacity: Batteries store different amounts of energy. Interestingly, batteries are not rated in terms of an

aggregate value (watt-hours) but, instead, two values: nominal voltage and milliamp hours (mAh). If two

batteries have different voltages, use watt-hour to compare them (voltage * mAh * 1,000 = watt-hour).

Nominal Cell Voltage: The average voltage a cell outputs when fully charged. The word nominal here is key as

the actual measured voltage on a battery will decrease over time (as it discharges). This is known as the battery

discharge curve.

Battery Discharge Curve: The measured terminal voltage of any battery will decrease as it is discharged. There

is typically a fast initial drop of voltage to a plateau and then another fast drop (knee of discharge) when the

battery is near its end-of-discharge (or end-of-life) voltage (EODV). The mid-point voltage (MPV) is when 50% of

the initial capacity is discharged; it provides a useful approximation to the average voltage throughout the

discharge.

C-Rate: Rather than show off these discharge capacity curves, battery makers often use a ‘C-Rating.’ A C rating

is an informal way of describing how much current a battery can safely deliver. The higher the C, the more

current you can draw from the battery without exhausting it prematurely. To use the C-rating, multiply the

capacity times the C-rating divided by 1-hour.

Self-Discharge: Disposable batteries lose 8-20% of their original charge per year when stored at room

temperature (20-30C). This is known as the “self-discharge” rate and is due to chemical reactions that occur

within the cell even when no load is applied.

Energy Density: Batteries with higher energy density will provide more capacity at smaller weights. Often

expressed as watts-hours/kilogram (Wh/kg).

Internal Resistance: A battery can be modeled as a voltage source in series with a resistance. The internal

resistance of a battery is not due to an actual resistor but rather specific properties of the battery such as it’s

size, chemical composition, age, temperature, and discharge current.

POWER CAPACITY

[source: https://learn.sparkfun.com/tutorials/battery-technologies; https://learn.adafruit.com/all-about-batteries/power-capacity-and-power-capability]

Batteries store different amounts of energy. Interestingly, batteries are not rated in

terms of an aggregate value (watt-hours) but, instead, two values: nominal voltage and

milliamp hours (mAh). If two batteries have different voltages, use watt-hour to

compare them (voltage * mAh * 1,000 = watt-hour).

Rechargeable Lithium Ion 3.7V, 2,000mAh = 7.4Wh

Rechargeable Lithium Ion 3.7V x 1,000mAh = 3.7Wh

Rechargeable Lithium Ion 3.7V x 110 mAh = 0.4Wh

POWER CAPACITY


Batteries store different amounts of energy. Interestingly, batteries are not rated in

terms of an aggregate value (watt-hours) but, instead, two values: nominal voltage and

milliamp hours (mAh). If two batteries have different voltages, use watt-hour to

compare them (voltage * mAh * 1,000 = watt-hour).

Rechargeable Lithium Ion 3.7V, 2,000mAh = 7.4Wh

Rechargeable Lithium Ion 3.7V x 1,000mAh = 3.7Wh

Rechargeable Lithium Ion 3.7V x 110 mAh = 0.4Wh

This 2Ah capacity means, in theory, that we can draw two amps of current for one hour (or 8Amps in 15 minutes, 0.2A for 10 hours, 0.02A for 100 hours); however the amount of current we can really draw (called the power capability) is limited.

POWER CAPABILITY


The amount of current we can really draw from a battery is limited. For example, a coin

cell that is rated for 1Ah cannot actually provide 1A of current for an hour. In fact, it

cannot even provide 0.1A for an hour without overextending itself. See analogy below.

Think about it like this: let’s say humans have the capability of traveling up to 30 miles on foot. For many of us, we could likely walk that distance (if in a pinch) but running it would be a whole other matter! It’s the same thing for batteries. A 1Ah coin cell would have no problem providing 0.1mA for 1,000 hours but even drawing 10mA (0.01A) would overextend the battery.

POWER CAPABILITY VIDEO

[source: http://youtu.be/cxkVxi9P0EA]

The power capability of a battery is dependent on its size, chemical composition, etc.

See the video explanation below.

POWER CAPABILITY EXAMPLE

[source: https://learn.sparkfun.com/tutorials/battery-technologies; https://learn.adafruit.com/all-about-batteries/power-capacity-and-power-capability; http://biz.maxell.com/en/product_primary/?pci=9&pn=pb0002]

Let’s look at the Maxwell CR2032H coin cell battery. The CR2032H has a nominal

voltage of 3V, a nominal capacity of 240mAh, and a nominal discharge current of

0.2mA. This is all in the battery datasheet: http://biz.maxell.com/files_etc/9/catalog/en/CR_13e.pdf

http://biz.maxell.com/files_etc/9/catalog/en/CR_13e.pdf







The graph shows the discharge capacity of the CR2032H under three example loads: 1kΩ, 3.9kΩ, and 15kΩ.

We can calculate the instantaneous current draw for each:

I=3V/1kΩ=3mA

I=3V/3.9kΩ=0.77mA

I=3V/15kΩ=0.2mA








The graph shows the discharge capacity of the CR2032H under three example loads: 1kΩ, 3.9kΩ, and 15kΩ.

We can calculate the instantaneous current draw for each:

I=3V/1kΩ=3mA

I=3V/3.9kΩ=0.77mA

I=3V/15kΩ=0.2mA

So, a minimum load of 15kΩ is required to meet the battery’s nominal discharge current of 0.2mA.

If you don’t meet this, the capacity of the battery drops precipitously. For example, with the 1KΩ load (3mA current), the capacity is effectively reduced to ~140mAh (if we consider 2.5V our cutoff)



POWER CAPABILITY: C-RATING

[source: https://learn.adafruit.com/all-about-batteries/power-capacity-and-power-capability; http://youtu.be/cxkVxi9P0EA]

This battery has a 20C rating, so it can discharge at 20 x C: 20 x 2.2Ah = 44A

Rather than show off these discharge capacity curves, battery makers often use a ‘C-Rating.’ A C rating is an

informal way of describing how much current a battery can safely deliver. The higher the C, the more current

you can draw from the battery without exhausting it prematurely. To use the C-rating, multiply the capacity times

the C-rating divided by 1-hour.

http://www.hobbyking.com/hobbyking/store/__8932__Turnigy_2200mAh_3S_20C_Lipo_Pack.html

POWER CAPABILITY: C-RATING

[source: https://learn.adafruit.com/all-about-batteries/power-capacity-and-power-capability; http://youtu.be/cxkVxi9P0EA]

Rather than show off these discharge capacity curves, battery makers often use a ‘C-Rating.’ A C rating is an

informal way of describing how much current a battery can safely deliver. The higher the C, the more current

you can draw from the battery without exhausting it prematurely. To use the C-rating, multiply the capacity times

the C-rating divided by 1-hour.



http://www.hobbyking.com/hobbyking/store/__8932__Turnigy_2200mAh_3S_20C_Lipo_Pack.html

BATTERY DISCHARGE CURVE

[source: https://learn.adafruit.com/all-about-batteries/power-capacity-and-power-capability]

The measured terminal voltage of any battery will decrease as it is discharged. There is typically a

fast initial drop of voltage to a plateau and then another fast drop (knee of discharge) when the

battery is near its end-of-discharge (or end-of-life) voltage (EODV). The mid-point voltage (MPV)

is when 50% of the initial capacity is discharged; it provides a useful approximation to the average

voltage throughout the discharge.

BATTERY DISCHARGE CURVE EXAMPLE

[source: http://biz.maxell.com/files_etc/9/catalog/en/CR_13e.pdf]

Let’s again look at the Maxwell CR2032H coin cell battery. Recall that the CR2032H has a nominal

voltage of 3V, a nominal capacity of 240mAh, and a nominal discharge current of 0.2mA. The

discharge curve in the datasheet is for four different temperatures. The datasheet specifies an

operating temperature range of -20 - +85C but you’ll note better performance at the higher range

of this spectrum. Regardless of temperature, note the three stages: fast drop, plateau, and then a

rapid voltage drop at end-of-life. The load here is 15kΩ, which is 0.2mA of continuous current.

ENERGY DENSITY

[source: Tarascon & Armand, Issues and challenges facing rechargeable lithium batteries, Nature, 2001]

Ener

gy D

ensi

ty (

Wh/

l)

Energy Density (Wh/kg)

The amount of electrical energy, expressed either per unit of weight (Wh/kg) or per unit of volume (Wh/l), that a

battery is able to deliver is a function of the cell potential (V) and capacity (Ah/kg), both of which are linked

directly to the chemistry of the system. Among the various existing technologies (Fig. 1), Li-based batteries —

because of their high energy density and design flexibility — currently outperform other systems, accounting for

63% of worldwide sales values in portable batteries (in 2001).

LI-ION HAVE HIGHEST ENERGY DENSITY Li-ion batteries are the highest energy density

battery available—meaning they store the

most amount of energy for a given size,

which is why we find them in our cell phones

and laptops.

[source: http://youtu.be/saxYilLJ7yw]

BATTERIES IN SERIES VS. PARALLEL

[source: Platt, Make: Electronics, 1st Edition; https://learn.sparkfun.com/tutorials/how-to-power-a-project]

What happens when you place two batteries in series?

1.5V 2,000mAh

1.5V 2,000mAh



What happens when you place two batteries in series?

1.5V 2,000mAh

1.5V 2,000mAh

Answer: The voltages of the batteries add together. Note: Batteries in series should be of the same chemistry and same age (depletion level). In addition, they should have the same amp-hour rating.


(measured in

volts)





WATER ANALOGY FOR SERIES BATTERIES Let’s return to our water analogy for DC circuits to help explain power.


Double

pressure (Double

voltage)

More

flow

Hole width

held constant (resistance constant)

≈

≈

EXAMPLE SERIES BATTERY HOLDERS

4 AA Battery Holder

4 x 1.5V AA = 6V output

2 AA Battery Holder


4 AA Battery Holder


There are lots of different battery holders that allow for different combinations of batteries.

8 AA Battery Holder


EXAMPLE SERIES BATTERY HOLDERS These battery holders are from Adafruit and have built-in on/off switches (though it’s easy enough

to solder on your own switch).



1.5V 2,000mAh

1.5V 2,000mAh

1.5V 2,000mAh

1.5V 2,000mAh

How about when batteries are in parallel?


[source: Platt, Make: Electronics, 1st Edition; https://learn.sparkfun.com/tutorials/how-to-power-a-project; http://www.allaboutcircuits.com/vol_1/chpt_11/5.html]

1.5V 2,000mAh

1.5V 2,000mAh

Answer: The voltage stays the same but the capacity is doubled. Note: all batteries in a parallel configuration must have the same voltage rating

How about when batteries are in parallel?

1.5V 2,000mAh

1.5V 2,000mAh

PARALLEL BATTERY EXAMPLE


1.5V 2,000mAh

1.5V 2,000mAh

1.5V 2,000mAh

1.5V 2,000mAh

What’s the total voltage and capacity of this battery?

PARALLEL BATTERY EXAMPLE


What’s the total voltage and capacity of this battery?

Voltage: 1.5V

Capacity: 8000mAh

1.5V 2,000mAh

1.5V 2,000mAh

1.5V 2,000mAh

1.5V 2,000mAh

CAN I PUT BATTERIES BOTH IN SERIES AND PARALLEL TO REACH A DESIRED VOLTAGE LEVEL AND CAPACITY?

[source: http://www.batterystuff.com/kb/articles/battery-articles/battery-bank-tutorial.html]

The short answer is yes. Remember, however, that the batteries should all have the same capacity

(Ah rating), same voltage, same chemistry, and same age (depletion level). Generally, for

complicated configurations, it’s best to find preassembled battery packs that offer the voltage level

and capacity that you want.

MIXING SERIES AND PARALLEL BATTERY EXAMPLE

[source: http://itp.nyu.edu/archive/physcomp-spring2014/Notes/Batteries.html]

Voltage: 1.5V

Capacity: 8000mAh

The photo below shows two sets of two batteries, first put in parallel and then put in series with

each to provide increased voltage AND capacity. Each battery is 1.2V and 2340mAh

What’s the total voltage and capacity of this configuration?

MIXING SERIES AND PARALLEL BATTERY EXAMPLE

[source: http://itp.nyu.edu/archive/physcomp-spring2014/Notes/Batteries.html]

Voltage: 1.5V

Capacity: 8000mAh

The photo below shows two sets of two batteries, first put in parallel and then put in series with

each to provide increased voltage AND capacity. Each battery is 1.2V and 2340mAh

What’s the total voltage and capacity of this configuration?

Answer:

1. First, we have our two sets of batteries in parallel. So, 1.2V @ (2450mAh + 2450mAh).

2. Then, we have the two parallel configurations in series. So, (1.2V + 1.2V) @ 4900mAh

3. Total: 2.4V @ 4900mAh

TRADITIONAL ALKALINE Perhaps the most common disposable battery type is alkaline. Typical alkaline batteries

come in four different sizes: D, C, AA, AAA. All have the same nominal voltage of 1.5

volts but differ in capacity.

[source: http://en.wikipedia.org/wiki/List_of_battery_sizes];

AAA 1.5V

1000mAh

AA 1.5V

2700mAh

C 1.5V

8000mAh

D 1.5V

12000mAh

9V (PP3) ALKALINE BATTERIES

[source: https://learn.sparkfun.com/tutorials/battery-technologies]

A 9V battery (aka a PP3 battery) with a connector cable is a great, quick way to make a project

portable but don’t expect the battery to last very long! While it outputs 9V, the capacity of a 9V is

pretty low (500mAh to 600mAh)—a rechargeable 9V could be as low as ~200mAh!


9V battery 9V to barrel jack adapter Power Arduino off of a 9V

+ =

9V (PP3) ALKALINE BATTERIES



9V battery 9V to barrel jack adapter Power Arduino off of a 9V

+ =

We’ll come back to whether this is really a good solution or not later in the lecture

A 9V battery (aka a PP3 battery) with a connector cable is a great, quick way to make a project

portable but don’t expect the battery to last very long! While it outputs 9V, the capacity of a 9V is

pretty low (500mAh to 600mAh)—a rechargeable 9V could be as low as ~200mAh!

ALKALINE 9V (PP3) VS. 6 AA IN SERIES


Though an alkaline PP3 9V battery is much smaller and weighs less, it only outputs ~500mAh vs.

six AA alkaline batteries in series, which output ~1700mAh

9V battery

9V, ~500mAh 6 AA Batteries in Series

9V, 2700mAh

vs.

NICKEL METAL HYDRIDE (NIMH) NiMH are popular rechargable batteries that come in the typical alkaline battery sizes.

The first consumer grade NiMH battery became commercially available in 1989. Often

lower cost than other chemistries but suffer from lower densities than LiPo. NiMH

batteries also require less stringent charging curves than LiPo, which lowers the cost of

the chargers.

[source: https://learn.sparkfun.com/tutorials/battery-technologies; http://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_battery; amazon.com];

NICKEL METAL HYDRIDE (NIMH) NiMH are popular rechargable batteries that come in the typical alkaline battery sizes.

The first consumer grade NiMH battery became commercially available in 1989. Often

lower cost than other chemistries but suffer from lower densities than LiPo. NiMH

batteries also require less stringent charging curves than LiPo, which lowers the cost of

the chargers.

[source: https://learn.sparkfun.com/tutorials/battery-technologies; http://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_battery; amazon.com];

We have these Panasonic Eneloop

batteries in the Hackerspace along with

two chargers. The batteries are rated at

1.2V, 2000mAh capacity, and can be

recharged up to 2100 times. An 8-pack

is $24.72 on Amazon.

To compare, these Amazon Basics

batteries are rated at 1.2V, 2400mAh,

and can be recharged ‘hundreds of

times.’ An 8-pack is listed at $22.99 on

Amazon.

Panasonic also offers the Eneloop Pro

series, which has the same voltage

(1.2V) but higher capacity (2550mAh)

and lower recharge rate (up to 500

times). An 8-pack is listed at $39.54

NIMH VS. TRADITIONAL AA ALKALINE On the last slide you may have noticed that each AA NiMH battery nominally outputs

1.2V; however, an alkaline battery of the same size outputs 1.5V.

[source: https://learn.sparkfun.com/tutorials/battery-technologies; http://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_battery]

NiMH Nominal voltage:

1.2V Alkaline Nominal voltage:

1.5V

<

NIMH VS. TRADITIONAL AA ALKALINE Combining four AA NiMH will result in a 4.8V, which should work with many systems

that require 5V but note that you may experience issues after the batteries discharge a

bit (and the voltage dips).


4 x AA NiMH batteries, results in 4.8V






In contrast, 4 x AA traditional Alkaline batteries, results in 6V






In contrast, 4 x AA traditional Alkaline batteries, results in 6V

Again, Help the Environment Use Rechargeable Whenever Possible

CHARGING NIMH BATTERIES We have two NiMH battery chargers in the HCIL Hackerspace (that works with both AAA and AA).

We also have ~15 AA and 10AAA rechargeable NiMH batteries and C and D converters.

COIN (OR BUTTON) CELL

[source: https://learn.sparkfun.com/tutorials/battery-technologies; http://en.wikipedia.org/wiki/Button_cell]

Coin (or button) cell batteries are great for very small, low power projects and come in different

chemistries and sizes. They are often used for portable electronic devices like wrist watches,

pocket calculators, cardiac pacemakers, and hearing aids. Devices using coin cells are typically

designed for a long service life—e.g., a wristwatch may work for over a year.

The chemistries, sizes, and technologies of coin cells vary. Two popular versions are

alkaline and lithium. Alkaline coin cells have a nominal voltage of 1.5V while lithium

have 3V. Some coin cells are rechargeable. For example, the popular CR2032 has a

rechargeable version (the LR2032), but the capacity is much smaller.

ALKALINE VS. LITHIUM COIN CELL

[source: https://learn.sparkfun.com/tutorials/battery-technologies; http://en.wikipedia.org/wiki/Button_cell]

Alkaline button cells start

with an ‘L.’ This one, the

LR1154, is 1.5V measuring

11mm across and 5.4mm tall.

Lithium cells are prefixed with a ‘C’ rather

than an ‘L’ (yes, that’s confusing) This one,

the popular CR2032, is 3V measuring

20mm in diameter and 3.2mm tall.

Note: the images below are not to scale.

LITHIUM COIN CELL You can get coin cells for very cheap in bulk.


This box of 100 CR2032 lithium

coin cells is $28.98 on Amazon

with free shipping (roughly 29

cents a battery)

These blister packs of 100 CR2032

lithium coin cells are $9.99 on

eBay + $5.99 shipping. So,

roughly 16 cents a battery.

LITHIUM CR2032 COIN CELL Because lithium CR2032 coin cell batteries have a nominal voltage of 3V, they are great

for testing LEDs (even without a current limiting resistor!)


CR2032 LITHIUM COIN CELL HOLDERS Adafruit, Sparkfun, and other online store websites (e.g., Digikey) sell different types of

CR2032 (and other cell size formats) battery holders. Here are two from Adafruit.

USE LITHIUM COIN CELL WITH ATTINY The ATtiny series of microcontrollers are super small, cheap ($1-3), and relatively easy to use. The

ATtiny45 and ATtiny85 have eight legs (ATtiny85 has twice the memory). The ATtiny44 and

ATTiny84 have 14 legs, so more I/O. ATTinys also have low-power modes (e.g., 210μA at 1.8V and

1MHz in active mode and 33μA in idle mode.

[source: http://www.atmel.com/devices/attiny44a.aspx]

ATtiny!

We will not be covering how to use/program the ATtiny chips in this course; however, you are welcome to investigate this option on your own for your projects. Some helpful links: • An HCIL Hackerspace video on programming

Attiny mcus: http://youtu.be/_ZL-YNOH_jA

• A Sparkfun ATTiny hook-up guide: https://learn.sparkfun.com/tutorials/tiny-avr-programmer-hookup-guide/attiny85-use-hints

• Google for more! There are a number of ATtiny projects on Instructables, for example.

http://youtu.be/_ZL-YNOH_jA




https://learn.sparkfun.com/tutorials/tiny-avr-programmer-hookup-guide/attiny85-use-hints














CHIRP! THE PLANT WATERING ALARM

[source: http://wemakethings.net/chirp/; https://www.tindie.com/products/miceuz/chirp-plant-watering-alarm/]

Atmel ATtiny44A 8-bit, 20MHz microcontroller with 12 I/O pins. Chip operates between 1.8-5.5V

The Chirp plant watering alarm uses capacitive humidity sensing (as opposed to resistive humidity

sensing) to sense moisture. If low-moisture levels are detected, Chip emits (infrequent) short

chirps. An ambient light sensor ensures that Chirp does not make noise at night. The chirp board

uses a ATtiny44A mcu and is powered off of a 3V CR2032 lithium coin cell battery (which

should last up to roughly a year).

Takes a 3V CR2032 lithium coin cell, which is expected to last ~1 year

SPARKFUN BIGTIME WATCH KIT

[source: https://www.sparkfun.com/products/11734/; https://www.sparkfun.com/tutorials/309]

This SparkFun “geekishly stylish digital watch” kit uses an ATMega328—the same microcontroller

that is in an Arduino Uno—and four 7-segment displays to show the time. This is all powered off

of a CR2032 coin cell, which is estimated to get two years of run time! The designer of this watch

documented his “low-power” hackery here. The system voltage is ~3V and draws ~1 microAmp!

https://www.sparkfun.com/tutorials/309

SQUAREWEAR

[source: http://rayshobby.net/cart/sqrwear-20]

SquareWear is an open-source, wearable, and Arduino-compatible microcontroller board with a

built-in ATMega328 and LIR2032 rechargeable Lithium coin cell battery. It also has built-in

charging circuitry, a temperature sensor, push-button, light sensor, and RGB LED.

GOOGLE FOR MORE LOW-POWER ARDUINO PROJECTS

LITHIUM-ION (LI-ION) BATTERIES Recall that lithium-ion batteries have the highest energy density and are the most

common batteries in mobile phones, laptops, quadcopters, etc.

Ener

gy D

ensi

ty (

Wh/

l)

Energy Density (Wh/kg)

LITHIUM-ION (LI-ION) & LITIHIUM-ION POLYMER (LI-POLY) BATTERIES There are nearly a dozen of different chemistries of rechargeable lithium ion batteries but here we

will focus on two: lithium-ion (Li-Ion) and lithium-ion polymer (Li-Poly or LiPo)

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/rechargeable-lithiums-names]

Lithium-Ion Polymer (LiPo)

The two silvery rectangles with yellow tops

above are LiPo batteries (the yellow top

contains control circuitry) LiPo cells tend to

be thin rectangles in a silvery bag. They are

soft-shelled and have an easy to damage

casing. They often weigh less than Li-Ion

and come in smaller capacity.

Lithium-Ion (Li-Ion)

Li-Ion cells tend to be either rectangular or

cylindrical (above, two packs made of

cylindrical Li-Ion batteries). Li-ion batteries are

hard-shelled with a strong casing (hard to

puncture) and come in larger capacity than

LiPo. They are often used for laptop batteries

or remote control (RC) vehicles.

LITHIUM-ION (LI-ION) & LITIHIUM-ION POLYMER (LI-POLY) BATTERIES There are nearly a dozen of different chemistries of rechargeable lithium ion batteries but here we

will focus on two: lithium-ion (Li-Ion) and lithium-ion polymer (Li-Poly or LiPo)

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/rechargeable-lithiums-names]

Despite the structural differences, Lady Ada tells us we should treat them similarly and consider them two versions (‘gentle and light’ vs. ‘tough and strong’) of the same battery.

Almost all LiPo batteries have 3.7 nominal voltages (the maximum voltage is often 4.2V, which then

quickly drops to 3.7V). The lower minimum is around 3.0V.

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/voltages]

LITHIUM-ION POLYMER (LIPO) BATTERIES


Rechargeable Lithium Ion 3.7V x 1,000mAh

Rechargeable Lithium Ion 3.7V x 110 mAh

Here are the discharge curves for LiPo batteries. The voltage starts at the 4.2 maximum, quickly

drops down to ~3.7V for the majority of battery life. Once 3.4V is reached, the battery is dead. At

3V, the cutoff circuitry automatically disconnects the battery.

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/voltages]

LIPO BATTERY DISCHARGE CURVE

Li-Ion and LiPo batteries are extremely power dense, which is great for reducing size/weight of projects but they are not

‘safe’ batteries are require extra care. Charging and using the batteries incorrectly could cause an explosion or fire.

[source: http://youtu.be/saxYilLJ7yw; https://learn.adafruit.com/li-ion-and-lipoly-batteries/protection-circuitry]

PROTECTION CIRCUITRY

Li-Ion and LiPo batteries are extremely power dense, which is great for reducing size/weight of projects but they are not

‘safe’ batteries are require extra care. Charging and using the batteries incorrectly could cause an explosion or fire.



There are five main things to watch for when charging and using Li-Ion or LiPo batteries:

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/protection-circuitry]


1. Do not charge them above their maximum safe voltage (say 4.2V) - usually

taken care of by any on-cell protection circuit

2. Do not discharge them below their minimum safe voltage (say 3.0V) - usually

taken care of by any on-cell protection circuit

3. Do not draw more current than the battery can provide (say about 1-2C) -

usually taken care of by any on-cell protection circuit

4. Do not charge them with more current than the battery can take (say about

1C) - usually taken care of by any on-cell protection circuit but also set with the

charger by adjusting the charge rate

5. Do not charge the batteries above or below certain temperatures (usually

about 0-50 degrees C) - sometimes handled by the charger, but often not an

issue as long as the charge rate is reasonable.

The battery’s protection circuit can monitor the battery voltage, current draw, and charge rate to ensure proper operation

LiPo batteries sold from Sparkfun and Adafruit have protection circuitry, which is underneath this yellow tape. You should consult the battery datasheet

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/protection-circuitry]

vs.

Lithium-Ion Polymer (LiPo) with

protection circuit.

Lithium-Ion Polymer (LiPo) without

protection circuit.

PROTECTION VS. NO PROTECTION CIRCUITRY

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/rc-type-batteries]

vs.

The regular Li-Ion/LiPo batteries are the

kind you would find in your iPod, camcorder,

phone, etc. They are meant to last for over

500 charges, stay safe, and prove a C or two

of current

RC Li-Ion/LiPo batteries are meant for RC

cars, UAVS, planes. They provide a lot of power

at once and are designed to never ‘cut off’ so

that the battery will be damaged rather than,

say, a plane falling out of the sky. These

batteries can be less expensive because there is

no protection circuity.

When purchasing batteries, be aware that there are two families of Li-Ion/LiPo: regular

(normal) and RC (radio control)

“RC” TYPE LI-ION/LIPO BATTERIES

Lady Ada suggests that it is best not to hook up your own Li-Ion or LiPo batteries in parallel or

series configurations and that, instead, you should just find them preassembled from a trusted

manufacturer.

[source: https://learn.adafruit.com/li-ion-and-lipoly-batteries/multi-battery-packs]

LI-ION/LIPO BATTERIES IN SERIES OR PARALLEL

EE folks like lady ada discourage hooking up your own parallel configurations of batteries because one battery can discharge into another, damaging it or causing a fire. Instead, just find a premade, professionally manufactured battery that fits your requirements.


LI-ION/LIPO BATTERIES IN SERIES OR PARALLEL

Though the above battery packs contain Li-Ion batteries in parallel configurations (the voltage remains at 3.7V but the capacity is large), these packs were assembled by a company that is experienced and certified to test and assemble battery packs. Moreover, the individual batteries are tested and sorted by a machine so that each pack has matching batteries with the same capacity and internal resistance… we don’t have the same sort of equipment


HOW ABOUT LI-ION/LIPO IN SERIES?

This is also discouraged because the battery won’t be able to charge in a balanced manner. Again, you should purchase a Li-Ion/LiPo battery pack that is preassembled and tested by professional manufacturers.

LI-ION/LIPO CHARGERS Both Adafruit and Sparkfun sell Li-Ion/LiPo battery chargers that can charge off of USB or even DC

via a barrel jack. See the individual webpages/datasheets on how to use these.

USB Li-Ion/LiPo Charger: $12.50 For charging 3.7/4.2V batteries. 500mA charge current but adjustable from 100mA to 1000mA by soldering in a resistor. Chip also supports a 10K thermistor, but this also needs to be soldered into place. https://www.adafruit.com/product/259

USB Li-Ion/LiPo Micro Charger: $5.95 For charging 3.7/4.2V batteries. 100mA charge current but adjustable up to 500mA by soldering a jumper closed. https://www.adafruit.com/product/1304

USB/DC Li-Ion/LiPo Charger: $12.50 For charging 3.7/4.2V batteries. 500mA charge current but adjustable from 100mA to 1200mA by soldering in a resistor. Safety timer will stop charging after ~14 hours. Has three LEDs, green for power, orange for charging, and red for error. Orange blinks when charging full. Chip also supports a 10K thermistor, but this also needs to be soldered into place. https://www.adafruit.com/product/280

https://www.adafruit.com/product/259






Both Adafruit and Sparkfun sell Li-Ion/LiPo battery chargers that can charge off of USB or even DC

via a barrel jack. See the individual webpages/datasheets on how to use these.

USB Li-Ion/LiPo Charger: $12.50 https://www.adafruit.com/product/259

USB Li-Ion/LiPo Micro Charger: $5.95 closed. https://www.adafruit.com/product/1304

USB/DC Li-Ion/LiPo Charger: $12.50 https://www.adafruit.com/product/259

LI-ION/LIPO CHARGERS

USB/DC Li-Ion/LiPo Charger: $14.95 https://www.sparkfun.com/products/12711

Sparkfun LiPo Mini-USB Charger: $7.95 https://www.sparkfun.com/products/10401

LiPo Charger/Booster: $19.95 https://www.sparkfun.com/products/11231







https://www.sparkfun.com/products/12711






You can even charger your Li-Ion/LiPo batteries with solar. This unit is rated for 8V open voltage

and 650mA short circuit.

LI-ION/LIPO SOLAR CHARGER

SparkFun Sunny Buddy MPPT Solar Charger: $24.95 https://www.sparkfun.com/products/12885

Solar Cell Huge: $44.95 https://www.sparkfun.com/products/9241





SUMMARY OF BATTERIES

[source: http://itp.nyu.edu/archive/physcomp-spring2014/Notes/Batteries.html; http://batteryuniversity.com/learn/article/whats_the_best_battery]

Chemistry Picture Power Capability

Power Density Price Pros Cons

Lead-Acid +10C 30-40 Wh/kg ~$20 for 12V, 12Ah

Cheap, high power capability, rechargeable

Heavy, large, and toxic

Alkaline 0.1C 100 Wh/kg $1 for AA, 3Ah Popular, long shelf life, high amp-hours when compared to equivalent rechargeable

Non-rechargeable, low power capability, and bad for the environment

NiMH 0.2C 100 Wh/kg $2 for AA with 2.5Ah

Rechargeable, high power density, common sizes

Self-discharge quickly (though there are new low-discharge varieties), a bit more expensive than alkaline

Li-ion and Li-Poly 1-10C 160Wh/kg for Li-ion and 30-200 Wh/kg for Li-poly

$10 for a cell with ~750mAh

Rechargeable, ultra-light, high power capability

Expensive, delicate, require special circuity, can explode if misued

Lithium Coin Cell 0.005-0.01C

270Wh/kg $0.35 for CR2032 with 220mAh, $1.50 for CR123 with 1.3Ah

Small, lightweight, cheap, commonly found in stores, long shelf life

Most varieties are not rechargeable, very low power capability

WHAT BATTERY SHOULD I USE FOR MY PROJECT? To help select a battery, answer the following four questions:

1. What are your voltage requirements?

2. What are your current requirements?

3. How long would you like the battery to last for?

4. How will the battery be used? For example, is it for a wearable project where weight is a

significant factor? Is size an issue—e.g., must it fit within a square-inch?

WHAT BATTERY SHOULD I USE FOR MY PROJECT? To help select a battery, answer the following four questions:

1. What are your voltage requirements?

2. What are your current requirements?

3. How long would you like the battery to last for?

4. How will the battery be used? For example, is it for a wearable project where weight is a

significant factor? Is size an issue—e.g., must it fit within a square-inch?

You can measure these empirically, try to calculate them by hand using datasheets and circuit formulas, use a circuit simulator, or some combination of all three!

In this example, the designer consults a datasheet for an IC that he is using (an audio amplifier). He finds that the

IC requires an operating range of 10-30V. He then visits a battery website (batteryspace.com) to find batteries

within that range and finds a battery with an average of 21.9V. Using this value, he sets his variable DC desktop

power supply to 21.9V and observes the current draw of 1.1A. So, the designer goes back to the datasheet for

the battery he is considering and notes a peak current rating of 7A. The designer has found his battery.

SELECTING A BATTERY: AN EXAMPLE (VIDEO)


HOW LONG WILL MY BATTERY LAST?


To answer this question, you could:

1. Determine the average current draw of your project and use the capacity (mAh) rating of

your battery to figure out how long the battery will last. For example, a 3V CR2023H coin

cell battery has a capacity of 240 mAh. If your current draw is 0.2mA, the battery should last

240mAh/0.2mA = roughly 1200 hours (50 days).

2. Setup an experiment! Using the battery that you think is best for the project, log how long

the battery lasts. Of course, this works best for projects where the battery is only expected to

last a day or two. One simple way of logging is using a webcam in timelapse mode or you

could use a multimeter that has a time-series logging capability.

HOW LONG WILL MY BATTERY LAST? Imagine that we have a very simple project using the Arduino Uno that simply turns on

and off two LEDs every 500ms. We want to deploy our project in a context where we

can’t use wall power, so we have to use a battery. What battery should we use?

HOW LONG WILL MY BATTERY LAST? Imagine that we have a very simple project using the Arduino Uno that simply turns on

and off two LEDs every 500ms. We want to deploy our project in a context where we

can’t use wall power, so we have to use a battery. What battery should we use?

Power (Barrel Jack): The recommended input voltage is between 7-12 volts, which can be supplied via an AC-to-DC adapter (wall outlet) or battery. This voltage is stepped down via a voltage regulator to a smooth 5V.

We are going to use the barrel jack and a battery to power this project. What battery should we choose?

STEP 1: PREPARE PROJECT TO MEASURE CURRENT DRAW In Step 1, I am going to prepare a 9V battery pack to be used in series with my digital

multimeter. I will use the multimeter to measure the current draw of my project.

1. My 9V battery pack (which has a built-in on/off switch—which is a bonus feature)

2. Cut the supply and GND wires. 3. Strip the ends of the wires 4. These wires are stranded so I twisted them to make them easier to work with.

STEP 2: ADD IN THE MULTIMETER (IN SERIES) Now we need to add our multimeter. Remember, current is measured in series—this is

why we had to cut the 9V battery connections. We need all of the current coming out of

the battery to go through our multimeter and then into the Arduino.

[image source: http://www.sciencebuddies.org/science-fair-projects/multimeters-tutorial.shtml]

STEP 2: ADD IN THE MULTIMETER (IN SERIES) Here, I’ve added in the multimeter in series with my simple circuit. Note: the battery pack

is currently in the off position because my circuit does not yet have a load (I haven’t

connected the Arduino yet).

STEP 2: ADD IN THE MULTIMETER (IN SERIES) Here, I’ve added in the multimeter in series with my simple circuit. Note: the battery pack

is currently in the off position because my circuit does not yet have a load (I haven’t

connected the Arduino yet).

Make sure you move your multimeter leads (wires) to the ‘current’ measuring ports. This multimeter has two ports for measuring current: the one on the far left (which I’ve connected) supports up to 10A. The one next to it (currently open) supports up to 1A. Both ports have a backing fuse that will automatically blow if more than the rated current is drawn. If you’re unsure how much current your project will use, better to start with the higher rated amperage.

STEP 3: ADD IN ARDUINO AND BEGIN MEASURING Now I’ve added in my Arduino Uno and turned it on. The Uno is currently running a

completely empty sketch (no code), which consumes 0.059A or 59mA.

STEP 4: RUNNING ACTUAL CODE – NO LEDS ON In the last slide, I had the ‘negative’ lead (the black multimeter wire) connected to the

high current draw port (10A) of the multimeter. Here, I moved it to the more precise port

for lower current (the 1A port). I have also now uploaded and started running our

simple Android sketch that simply sets D0 and D1 to HIGH/LOW every 500ms. With the

LEDs off, our project consumes 52.6mA.

STEP 4: RUNNING ACTUAL CODE In the last slide, we saw that with the LEDs off, our project consumes 52.6mA. Here, we

examine what happens when our LEDs turn on.

With no LEDs on, the Arduino Uno draws 52.6mA of current.

With one LED on, the Uno draws 56.8mA (4.2mA more current than idle).

With two LEDs on, the Uno draws 62.9mA (a total of 10.4mA more of current compared to with no LEDs)

STEP 4: RUNNING ACTUAL CODE In the last slide, we saw that with the LEDs off, our project consumes 52.6mA. Here, we

examine what happens when our LEDs turn on.

So, our peak current draw is 62.9mA but because the LEDs are only on for half the time, our average current draw is 57.8mA.


With one LED on, the Uno draws 56.8mA (4.2mA more current than idle).


STEP 5: DOING THE MATH Recall that our simple Arduino program simply flashes the LEDs on and off every 500ms

(500ms on, 500ms off ).



Because our LEDs are only on half the time, our average current draw is:

(Idle current consumption + current consumption with LEDs on) / 2 = (52.59mA + 62.94mA) / 2 = 57.8mA


(500ms on, 500ms off ).





With a 9V battery rated at 500mAh, our project should last for roughly:

Capacity / current draw = 500mAh / 57.8mA = 8.6hrs


(500ms on, 500ms off ).





With a 9V battery rated at 500mAh, our project should last for roughly:

Capacity / current draw = 500mAh / 57.8mA = 8.6hrs

So, our project will last for a maximum of 8.6 hours on a single 9V battery.

If this is insufficient, then you will have to find a battery with greater capacity. Search on batteryspace.com or some other online store.

http://www.batteryspace.com/

SOME ADDITIONAL BATTERY RESOURCES The Battery (electricity), Wikipedia Article http://en.wikipedia.org/wiki/Battery_(electricity)

Battery Technologies, Sparkfun Tutorial https://learn.sparkfun.com/tutorials/battery-technologies

All About Batteries, Adafruit Tutorial https://learn.adafruit.com/all-about-batteries

Li-Ion and Li-Poly Batteries, Adafruit Tutorial

https://learn.adafruit.com/li-ion-and-lipoly-batteries

How Do I Choose a Battery?, Robotshop.com http://www.robotshop.com/blog/en/how-do-i-choose-a-battery-8-3585

Battery Amp-Hour, Watt-Hour, and C-Rating Tutorial, Afrotechmods http://youtu.be/cxkVxi9P0EA

How to Choose a Battery: A Battery Chemistry Tutorial, Afrotechmods http://youtu.be/saxYilLJ7yw

Battery University http://batteryuniversity.com/

Sew Electric: Understanding Your Circuit http://sewelectric.org/diy-projects/bookmark-book-light/understanding-your-circuit/

http://en.wikipedia.org/wiki/Battery_(electricity)

http://en.wikipedia.org/wiki/Battery_(electricity)

https://learn.sparkfun.com/tutorials/battery-technologies




https://learn.adafruit.com/all-about-batteries
















http://www.robotshop.com/blog/en/how-do-i-choose-a-battery-8-3585
















http://youtu.be/cxkVxi9P0EA

http://youtu.be/cxkVxi9P0EA

http://youtu.be/saxYilLJ7yw

http://youtu.be/saxYilLJ7yw

http://batteryuniversity.com/

http://batteryuniversity.com/

http://sewelectric.org/diy-projects/bookmark-book-light/understanding-your-circuit/












cmsc838 week 04 | lecture 08 | feb 19, 2015 · 2015-02-25 · week 04 | lecture 08 | feb 19, 2015...

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