An Electric Quantum 2+2

Weights

Weight estimates come from this kit car info page. The figures are:-
Component Weight
Engine 115kg (est)
Type 9 gearbox (and bellhousing) 33kg (+10kg)
Ancilliaries 50kg (est)
Fluids 10kg (est)
Total: 218kg

So if we use a single motor and batteries, they need to weigh less than 175kg if the car is going to stay the same weight. If we use a pair of motors with batteries, they need to weigh 218kg if the car is going to stay the same weight.

The Donor Car

My initial target is a Mark 2 Fiesta, one of the 1.3, 1.4, L or Ghia options. The 1.4 Ghia weighs 890kg naked, and have a maximum weight of 1225kg. My Quantum probably weighs 800kg, so that allows 643kg before the car (with no driver) is overweight.

The roadwheels of all the Mark 2 Fiestas are 13 size, which is a radius of 300mm. That gives 60mph as 1000rpm, and 1333rpm at our 80mph top speed.

The dimensions of the vehicle are Length - 3.83m; width - 1.63m; height - 1.38m. The ground clearance is about 0.3m. This leads to frontal area being 1.75m2. In fact,the front view is not perfectly rectangular, so that's probably nearer 1.1m2 by the time the slopes are taken off.

The engine compartment looks to be about 1m wide between the suspension points and maybe 1.2m wide further forward. The total length of the engine compartment looks like about 1m long, of which about half is the narrow part and half is the wide part. The under-rear-seat section is about 0.5m long and about 1.2m wide.

The drag profile of the Mark 2 Fiesta body shape is something I am waiting for a friend to measure. Now I have everything except the weight of their car, which means I almost have enough. I have found a way to measure a drag profile for a car in the Bosch Automotive Handbook. Until they get back to me, the performance is really a guess. In the meantime, my guess is about 550N at 75mph.

There is 325kg of payload to cut into: and the average passenger probably weighs less than 75kg. So five people would weigh 375kg. Oops. So much for the centre belt on the back seat. Four people might weigh 300kg, though, so that leaves 30kg before we no longer have a 4-person car. And the Quantum is a lighter car.

I'm planning to block the radiator grille and cover the underside of the engine compartment, probably with rigid plastic sheet (not film). This should significantly improve drag, and hence high-speed range, although by how much is yet to be seen. It will also protect the motors and reduction units from wet and from road grime.

Drag and Friction

The theory and practice of measuring drag and friction is discussed on the Drag and Friction Page.

Calculated drag

Figures for the Mark 2 Ford Fiesta are available online.

This gives a Cd figure of 0.35, and width and height figures of 1.631m and 1.321m respectively. If the bottom of the bodywork is at the same height as the wheels, then the frontal area can be approximated by a rectangle of 1.631 x (1.321 - 0.5) = 1.339m2. That's probably an over-estimate, since the side windows are sloped. So taking off the sloped bits, let's say 1.1m2.

Let us also assume that the rolling resistance adds, say, 125N to the total drag, using a rolling coefficient of 0.015 and a weight of 850kg. (850kg X 9.81m/s2 X 0.15 = 125N)

Lastly, let's assume air density, ρ, is 1.2 kg per m3.

Power is equal to the force in newtons times the speed in metres per second. So it's the force in newtons times the speed in miles per hour divided by 0.4444.
Speed Air Resistance Total drag Power Miles/kWh
5mph 2N 127N 282W 17.7
15mph 19N 144N 958W 15.7
25mph 52N 177N 1966W 12.7
35mph 102N 227N 3526W 9.1
45mph 168N 293N 5860W 7.7
55mph 251N 376N 9190W 6.0
65mph 350N 476N 13736W 4.7
75mph 467N 592N 19719W 3.8

Measured Drag

Following the experimental method, I ended up with a table something like this:-

Start Speed End Speed Time (outward) Time (return) Average time
(out+return)/2
Mid-speed
(start+end)/2
Force
(weightX4.4444/time)
Power
(forceXspeed/0.4444)
20mph 10mph 20.8sec 20.3sec 20.6sec 15mph 198N 1268W
30mph 20mph 20.7sec 17.4sec 19.0sec 25mph 213N 2690W
40mph 30mph 14.6sec 15.2sec 14.9sec 35mph 273N 4042W
50mph 40mph 14.6sec 9.9sec 12.3sec 45mph 332N 7046W
60mph 50mph 10.9sec 9.3sec 10.1sec 55mph 404N 9855W
70mph 60mph 9.3sec 9.3sec 9.3sec 65mph 438N 12148W
80mph 70mph 7.5sec 7.1sec 7.3sec 75mph 556N 17839W
Starting weight 913kg Ending weight 913kg Average 913kg

Italic figures are guesses - when I have the real data I'll put it up. But I think it's something near.

For rough and ready calculations, this graph is all that's needed: it gives required motor torques and powers, and from that battery life and so range can be calculated.

The Electric Conversion

The Drivetrain

The plan is to use two motors. The selection of motors is discussed on a separate motors page. The Advanced DC motors are cheap and cheerful ($1100 each) but heavy (about 48kg). The Lynch motors are much lighter (22kg) but much more expensive (£1900 a piece - plus VAT)! The AVT "supermotor" seems like a happy compromise - it's cheaper and lighter.

I'm guessing that the motors and reduction units will add to about 30kg. That leaves 440kg over for batteries. That's assuming the AVT motors - the Advanced DC motors will add about 120kg or so, and so allow only 350kg for batteries.

The AVT motor should use a reduction unit of 6:1, to give a maximum roadwheel speed of 1083rpm. That gives a maximum speed of 77mph, which is almost legal. That also gives a traction figure of 2000N.

The Lynch motor should use a reduction unit of 3.5:1, to give a maximum roadwheel speed of 1143rpm. That gives a maximum speed of 80mph, which is almost legal. That also gives a traction figure of 2333N.

In conclusion, we will use either a single AVT motor for each front wheel, with a peak power of 35kW and a continuous power of 20kW, or a double AVT motor for each front wheel, with a peak power of 70kW each. The continuous battery rating will be for 70mph - that is, 20kW for both designs.

The Batteries

Given the above power/speed table, we can calculate the range at different speeds. We want 60 miles at 75mph, so we're using the 75mph power of 22.5kW to give an endurance, then (since we know the speed) turning that endurance into a range.

The power is divided by the motor efficiency, of course, and modified with Peukert's Equation and the number for the battery.

The choice of batteries (and Peukert's Equation) are discussed on a separate batteries page.

We need to calculate the battery packs based on several criteria: range; peak power; continuous power; weight; that sort of thing.

Battery packs

Battery max 550kg min 18kWh@22.5kW min 120v min 140kW peak min 70kW peak min 22.5kW continuous
Thunder Sky 100 32 46 194 (155) 97 (78) 94
Evercel 24 22 11 22 11 5
Optima 28 32 10 16 8 3

Results

Here are some packs made up with these batteries, arranged in weight order:-

Manufacturer Part Weight Lost payload Rated capacity Price Endurance,
Range
Layout Regen Current Regen Shunt Replacement interval Cost per mile Comment
Thunder Sky LP9393A 220kg 300kg gain 28.8kWh $10,000 71 min
88miles
1x40,144v 66A 2.4Ω
7.9kW
35,000 miles $0.28 Acceleration, speed shorten battery life; slows down at endpoint
Thunder Sky LP9393A 275kg 245kg gain 36kWh $12,000 89 min
112miles
1x50,180v 66A
7.9kW
45,000 miles
84,000miles*
$0.28
$0.15*
Acceleration, speed shorten battery life
Evercel MB-100 440kg 80kg gain 22.44kWh $7000 50 min
63 miles
2x10,132v 2x50A 2x2.9Ω
2x6.0kW
38,000 miles $0.19 none
Evercel M-100-12 460kg 60kg gain 19.72kWh $5180 44 min
55 miles
2x10,116v 2x50A 2x2.5Ω
2x6.0kW
33,000 miles $0.16 none
Thunder Sky LP9393A 495kg 25kg gain 64.8kWh $21,600 162 min
203miles
2x45,162v 2x66A 2x2.7Ω
2x7.9kW
81,000miles
122,000miles*
$0.28
$0.18*
top speed may slightly overheat
Optima D34 585kg 25kg 19.8kWh 4198.50 45 min
56 miles
2x15,180v 2x55A 2x3.6Ω
2x7.9kW
20,000 miles
40,000miles
$0.21
$0.11
overweight

* at 55miles per charge
...italic values are estimates.

Auxiliaries

There is neither servo assisted braking or power assisted steering on a Mark 2 Fiesta, so we don't need to worry about them. For the more lary options, these could be fitted: it'd mean an electric motor to drive the steering pump, and an electric vacuum pump to drive the servo. MetricMind have both.

The cabin heat exchanger must be replaced with some sort of electric heater. A 110v domestic fan heater is probably a good choice. A 110v hairdryer element is another possibility.

A secure compartment with an exhaust would be useful for a generator to do recharges on the vehicle. The alternative is a tow-hook and a generator on a trailer.

Performance Estimates

Here is a table comparing these motor and battery options to the factory Fiesta.

Plan 1 2 3 4 5 6 7 Ghia RS Turbo
Motor 2xAVT, 4.5:1 2xAVT, 4.5:1 LEMCo, 3.5:1 AVT, 6:1 AVT, 6:1 AVT, 6:1 AVT, 6:1 1.4 ICE 1.8? turbo ICE
Storage 40 Thunder Sky 50 Thunder Sky 50 Thunder Sky 50 Thunder Sky 20 Evercel 90 Thunder Sky 30 Optima petrol tank petrol tank
Weight 600kg 655kg 639kg 625kg 810kg 840kg 945kg 890kg 910kg
Payload 625kg 570kg 586kg 600kg 415kg 375kg 280kg 335kg 315kg
Power 80kW/108bhp 80kW/108bhp 46kW/62bhp 40kW/54bhp 40kW/54bhp 40kW/54bhp 40kW/54bhp 56kW/75bhp 99kW/133bhp
Top Speed 102mph 102mph 81mph 77mph 77mph 77mph 77mph 100mph 131mph
0-60 5.8sec 6.3sec 8.0sec 9.3sec 12.2sec 12.7sec 14.3sec 13.4sec 7.9sec
50-70 2.1sec 2.3sec 3.0sec 3.5sec 4.6sec 4.8sec 5.4sec ? ?
standing 400m 13.7sec 14.3sec 16.5sec 17.6sec 19.3sec 19.8sec 20.8sec ? 16.1sec
range 88miles 120miles 120miles 120miles 67miles 222miles 60miles 200miles? 150miles?
fuel/mile
55 miles
£1=$1.85
£0.17 £0.09 £0.09 £0.09 £0.09 £0.11 £0.06 £0.09 £0.10

These give various examples of the things that could be done with electric cars. The first item is, well, a bit mad. It assumes that those nice people at AVT would rebuild a Lynch supermotor to their superior specification, and that we put one of those on each wheel. On the other hand, there'd be a problem with traction on a front wheel drive car, unless all the batteries were piled onto the front wheels. Which leads, naturally, to Plan 2.

Plan 2 is the right option if all we care about is seeing some kid in his XR2 off the lights - but for economy, the choice of batteries is most important. The economy choice, I'm afraid, is plan 7. Unfortunately, for my 45-55 mile per day commute, that is sort of close for comfort. It'd confine me to one route rather than another.

The other plans show alternative battery chemistries built into the project: as it can be seen, the costs are pretty much all in the same order. Every one of them makes sense here in the UK: but it is worth remembering that this is because of the amount of tax we pay for our fuel.


This page is part of an Open Source Electric Car Project, and is written and maintained by Simon. At this stage these pages are constantly under revision. Thoughts and comments are welcome.