Students Guide

The Driving Range of Electric CarsSbastien Marcotte

Collge Montmorency

The Driving Range of Electric CarsContext

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.

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 Ah before it needs to be recharged.

You: What do you mean Ah?

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 cant 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, youre right Joel. Ill make calculations to check if the driving range is long enough.On the way back to the office, you think about the problem.

Three-Step CycleList 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 doWhat we need to knowSummary

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?

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

E

Left headlight

Right headlight

Engine

Batteries

Audio system

Taillight

PBL/Students Guide The Driving Range of Electrics Cars2