Download The Driving Range of Electric Cars Sébastien Marcotte

Student’s Guide
The Driving Range of Electric Cars
Sébastien Marcotte
Collège Montmorency
The Driving Range of Electric Cars
Context
You and your two friends, Annie (an electrical engineer) and Steve (a mechanical engineer), decide to
realize your dream of building a small automobile business, Lynxx. You intend to take the larger
companies by surprise by launching the Lynxx Spirit on the North American market, an entirely electric
car with a longer driving range than models available from large manufacturers.
In the design process, you want to estimate the driving range of the Lynxx Spirit based on the engineers’
current specifications.
You:
Hi Annie! Could you show me the electrical circuit diagrams of the Lynxx?
Annie: Yes, of course! Here you go.
Left headlight
Right headlight
Audio system
Engine
E
Batteries
Taillight
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You:
How many batteries do you recommend for the power supply?
Annie: I suggest using 25 12-V batteries connected in parallel.
You:
Does the voltage remain constant when the engine is running?
Annie: Yes, you can consider that the batteries’ voltage is always 12 volts.
You:
And what charge can these batteries deliver?
Annie: Each battery can deliver a charge of 210 A×h before it needs to be recharged.
You:
What do you mean A×h?
Annie: I mean 210 amps × hours, which is a charge unit. For instance, the battery could provide
210 amps for 1 hour or 21 amps for 10 hours.
You:
OK. Great! Oh, I forgot to ask…
Are there any other questions you want to ask Annie? (If you can’t think of any, you can come back later
as needed.)
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You then go see Steve, the mechanical engineer. Steve is trying to find out the resistance forces
that will be exerted on the moving vehicle.
Steve: I built models for a speed of 100 km/h. At that speed, I estimate that the car will
experience a total frictional force of 130 N (friction of the tires on the road and friction of
the parts) plus an air resistance of 110 N.
You:
And do you have any idea of the mass of the fully equipped vehicle?
Steve: I estimate that the car will have a mass of about 1,200 kg plus passengers.
You:
Okay, thank you Steve!
You confer with Joel, a friend in marketing:
Joel:
To sell you car, it must absolutely be able to run on the highway long enough for you to
make a decent trip without recharging the batteries. For example, for the Quebec market,
you must absolutely be able to drive from Montreal to Quebec City and back without
recharging the batteries, with all electrical components running.
You:
Yes, you’re right Joel. I’ll make calculations to check if the driving range is long enough.
On the way back to the office, you think about the problem.
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Three-Step Cycle
List all the relevant information you have gathered from the problem. Based on this information,
state what you need to know to solve the problem. As new information comes in, you will want to
summarize and update the relevant information you have gathered and ask new questions.
List the Following:
What We do
What We Need to Know
PBL/Student’s Guide – The Driving Range of Electrics Cars
Summary
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Guidance Questions (To Be Provided to All the Students)
1) This problem is based on both electricity and mechanics. As for any physics problem, you
need to begin with a large quality diagram. In this case, you need an electrical and a mechanical
diagram of the forces acting on the car. For the electrical diagram, use the diagram provided and
complete it by correctly illustrating how the batteries are wired together.
2) What could be the link between mechanics and electricity in this case? Would it help you to calculate
the driving force to be provided by the engine? Since you know the speed at which the car is running
(100 km/h), what can you deduct?
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3) What could be the links between the current and voltage of each cell and those of the
engine?
4) Extra assignment:
a) Calculate the driving range of the car going up a five-degree hill.
b) Calculate the driving range of the car with all electrical components turned off on a level road
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