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Battery Workshop
February 4, 2017
Battery Workshop
What you will learn in today’s workshop:
• What is a battery?
• Learn by building a simple battery
• Selecting the best batteries for the two races
• Sprint race test – Max current for 30 seconds
• Endurance race test – 90 minute load testing
• Peukert’s Equation and how to use it in the endurance race
• “End of Useful Life” test – Measuring internal resistance
Battery Workshop
Approximate Times
• Presentations – 60 minutes
• Building a working battery – 10-15 minutes
• Demonstrate the three different tests
• Break ~ 10:15-10:30
• Hands on testing – Perform the actual tests on your own
batteries
• Reserve a test kit to do the tests back at your school
• End around noon
Battery Workshop
This workshop
• New workshop this year
• All materials are new
• Please let us know which parts are unclear
• All criticisms and suggestions are welcome!
• Please stop us at any time to ask questions or make a
comment.
Battery Workshop
Why Do These Tests?
• It’s impossible to tell the condition of a battery by measuring
it’s voltage with a voltmeter.
• No single test can tell you everything you need to know
• You need to test your batteries early to better plan your
budget.
Battery Workshop
What is a Battery?
1.5V Alkaline Battery
1)
2)
3)
4)
Case to hold things together
Positive Metal Electrode at top
Negative electrode at botom
Electrolyte (thin brown line)
Battery Workshop
A Lead-Acid Volt Battery
1) A lead-acid battery cell consists of two lead plates:
- A positive plate covered with a paste of lead dioxide
- A negative made of sponge lead with an insulating
material (separator) in between.
- The plates are enclosed in a plastic battery case
- The plates are submersed in an electrolyte
consisting of water and sulfuric acid
- This cell is capable of storing 2.1 volts.
Battery Workshop
A 12 Volt Lead-Acid Battery
1) A 12 v battery consists of:
- 6 individual led-acid cells
- Each cell can store ~ 2.1 volts
- Each cell has multiple plates connected
in parallel to increase the current
- All cells are connected in series
- Total of ~12.6 volts
Battery Workshop
Differences in the two types of batteries
Battery Workshop
Making a Battery?
1) Copper Penny – Anode
1) Zinc Nail – Cathode
1) Lemon – Citric Acid
Use a meter to measure the voltage between the nail and the penny
See if you can light an LED with multiple lemons wired in series!
Battery Workshop
Battery Testing for the Solar Cup
There are three test we will demonstrate today:
1. Carbon Pile Load Test – Determine which of your batteries
is best for the sprint race
2. Constant Load Test – Match up your batteries for the
endurance race.
3. Battery Quality Test – See if your batteries are reaching
the end of their useful life.
Battery Workshop
Selecting a Battery - Sprint Race
It’s all about CCA (or HCA)!
• CCA - The amount of current the battery can supply for 30
seconds at 0 degrees F.
• MCA - The amount of current the battery can supply for 30
seconds at 32 degrees F. (sometimes called CA)
• HCA - The amount of current the battery can supply for 30
seconds at 80 degrees F.
Battery Workshop
Selecting a Battery - Sprint Race
A formula:
• CA (@32 ) X .80 = CCA and HCA (@80) X 0.60 = CCA
• Some companies use the above formula to give these
numbers
• Others do the measurements at the different
temperatures.
Battery Workshop
Battery Workshop
Carbon Pile Load Testing
• -Measures the resistance of the entire battery
circuit – not just the internal resistance of the
cells.
• Unfortunately the DC load method gets similar
readings from a good battery that is partially
charged and a marginal battery that is fully
charged. State-of-charge and capacity
estimations are not possible.
• So, make sure your battery is fully charged!
Battery Workshop
Selecting a Battery - Sprint Race
Testing for CCA (or HCA)
• Battery must have an SoC of 100 percent.
• Load the battery with half the rated CCA for 15 seconds at a
temperature of 50º F or higher.
• After 15 seconds read the voltage.
• The battery is good if the voltage stays above 9.6V
Battery Workshop
Carbon Pile Load Testing
1) Meter on the left is tuned to match ½ of the
CCA of your batteries
2) Quality of your battery is shown on the meter
on the right
3) Knob in the middle is used to adjust the current
load on the battery
4) If your battery is not fully charged, this test is
useless.
Battery Workshop
Selecting a Battery - Endurance Race
It’s all about Reserve Capacity!
• The “Reserve Capacity” of the battery is defined as how
long your battery will supply 25A, measured in minutes.
• Reserve Capacity is difficult and costly to engineer into a
battery and requires higher quality cell materials.
• Be careful of how different manufacturers define
“Reserve Capacity”.
Battery Workshop
Selecting a Battery - Endurance Race
It’s all about Reserve Capacity!
Battery Workshop
Gives 25 amps for 87 minutes
Battery Workshop
Endurance Load Test
1.
2.
The endurance race is 90 minutes
We all also know that the reserve capacity of the PC1100 battery
is 87 minutes.
a. It will give 25 amps for 87 minutes
b. However it will be completely dead at 87 minutes
c. It will stop powering the boat long before 87 minutes
Battery Workshop
Endurance (90 minute) Load Test
Battery Workshop
Endurance (90 minute) Load Test
1. The constant current load tester is
placed across the batteries.
2. A datalogging multimeter records the
battery information and sends it to the
PC
3. The PC displays the numbers in real time
4. End the test manually when the battery
voltage goes down to 10.5 volts.
Battery Workshop
Peukert’s Equation
• Rated versus useful Capacity
• Discharge rates
• Utilizing Peukert’s (poo-kert’s) Equation for lead acid
batteries and winning the endurance race
• Battery condition
Battery Workshop
Rated Capacity
• Manufacturers specify this
quantity
• Rated Capacity is calculated in
ideal conditions, for a specific…
• Temperature
• Discharge rate
• Capacity dependent on
availability of ions
Battery Workshop
Useful Capacity
• Affected by
• Environment (temp)
• +/- 10 degrees
• Discharge rate
• Varying loads
• Internal resistance and how it changes
• Faster the discharge rate the more energy is loss
Battery Workshop
Peukert’s Law
𝐶𝑓
𝑡=𝐻
𝐼𝐻
𝑘
Where
H is the rated discharge time (typically 10 or 20 hours)
Cf is the manufacturer rated capacity
I is discharge current
k is Peukert’s constant
t is time (hours)
𝐶 = 𝐼𝑘 𝑡
C is the current battery capacity
Battery Workshop
Proper use of Peukert’s Law
• Utilizing with Useful Capacity
• Endurance Race
• Compensation methods
• Determining battery condition
• Peukert’s constant typically increases with battery’s age and use
Battery Workshop
Battery Workshop
Curves Drawn for Peukert’s
Battery Workshop
Battery Workshop
“End of Useful Life” test – AC Conductance
• AC conductance meters are commonly used
to measure CCA.
• The single-frequency method sees the
components of the Randel's model as one
complex impedance called the modulus of Z.
Battery Workshop
1) For reference – A PC1100 battery has an
internal resistance of about 5.1 mohm when
new.
2) It is important to measure the resistance of
your batteries when they are new
3) Watch for the value to increase as the
battery ages.
Battery Workshop
1. Clip the meter across the battery, be
careful not to reverse the leads.
2. Set the CCA rating of the battery
3. Read the internal resistance
4. Then read the CCA
Battery Workshop
Possible Sources:
1. Electronic Load: Ebay – Search for:
KL283 300W 80V 30A LCD Dual Channel DC Electronic Load Instrument
Adjustable
2. Data Recording Multimeter: Ebay – Search for:
Data Logging Multimeter or Data Logging DMM
Battery Workshop
Possible Sources:
1. Carbon Pile Load Tester: Ebay – Search for:
500 Amp Carbon Pile Load Tester
2. Battery Internal Resistance Tester: Ebay – Search for:
12V LCD Digital Car Battery Tester Auto Battery Load Analyzer Flooded AGM CCA
Battery Workshop
Cycling your batteries
• New batteries should be run through the 90 minute test at
least twice to increase their capacity.
• Cycle old batteries to rejuvenate them.
• Don’t worry about wearing them out doing this.
Battery Workshop
• Example of a Lead Acid Battery
• Odyssey PC1100
Battery Workshop
Why use the Odyssey PC1100 Battery for an Example?
• If you were to design a battery that was perfect for the endurance
race, this is the battery you would design(almost).
• Use it a your standard when searching for other batteries.
• Reserve Capacity 25 amps for 87 minutes
• 400 Charge – Discharge Cycles
• This battery was designed for the M1 Abrahams tank
• It is used in the Humvee
• It also goes into most military jet aircraft
• This might not be true of the sprint race.
Battery Workshop
Connecting to an Odyssey PC1100
Battery is made for One Time Connection!
L Terminal Adapter Kit
Battery Mart #: - ADAPT
$5.95
Battery Workshop
• How to Increase Battery Lifetime
• Charge the batteries after heavy use, do not let them sit overnight in a
discharged state.
• Use an approved charger. Some chargers have a very high “finish charge
voltage” that might be ok to use in short – high current charge cycles, but daily
use will burn off the batteries liquid and eat away plate material
• Keep terminals tight and clean, use a good battery terminal spray to minimize
corrosion
• Using a battery with high internal resistance is asking for trouble. The high
impedance of the battery can cause battery failure and possibly damage the
controller or motor.
Battery Workshop
•Workshop Presentation
•Will be on the solar cup web site
•You can also request a test kit on the web site.
• Keep the kit for two weeks and then return it to Oxy.
• www.solarcup.org