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.
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.
The theory and practice of measuring drag and friction is discussed on the Drag and Friction Page.
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 |
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 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.
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 | 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 |
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 | 3Ω 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.
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.
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.