Best car characteritics for EV?

Technical discussion on converting internal combustion to electric
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Plugger
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Best car characteritics for EV?

Post by Plugger »

Hi, I'm new here and am not really a car person. I'm in the homework phase. My wife and I want to convert a car to a BEV for her to commute 50km to work and back (ie 100km all up)over fairly hilly country. I'm thinking of something smallish like a Suzuki Swift cino with a kerb mass of 795kg or Charade 845kg. Apart from low mass, range would also presumably be affected by aerodynamics and rolling resistance so something like a coupe such as Toyota's Paseo (1997) may also be a possibility. The Paseo's a bit heavy at 921kg but has a lower frontal area and better drag coefficient (0.31) to offset this. The one I'm looking at also has alloy wheels so may save say 20kg on the standard steel ones. The disappointing thing about the Paseo is its relatively low carrying capacity: GVM minus kerb mass of only 384kg. Most small cars are over 400kg. With LiFeP batteries I reckon we could still come in about 100kg under the GVM allowing 70kg for 1 passsenger and driver. I have tried to work out possible range/performance senarios with EV Calculator at EVConvert.com but end up with odd results.
Is it possible to deduce anything about EV suitability from the original ICE characteristics? I currently drive a little Hyundai 97 Excel lx. Its kerb mass of 943kg is greater than the Paseo and has a bigger frontal area and probably higher drag coefficient. The power output of the ICE is about the same for both at similar rpm (65 & 69 KW) yet according to redbook.com.au the non urban fuel efficiency of my Excel is only 4.8l/100km cf 5.2 for the Paseo. Shouldn't the sleeker coupe be best? Any suggestions on how to sort all this out?
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Richo
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Best car characteritics for EV?

Post by Richo »

So you want to know if a heavier car with better aerodynamics will be more efficient than a lighter car with worse aerodynamics.
I agree that there maybe some point where there would be a crossover point.
It would help if you gave us the numbers you used in the eV calculator for each car you are interested in.

Now with the GVM the ruling is you have to allow 81.6kg(min) per person.
So generally you could only take 163.2kg off the GVM to get the max convertered weight.
So the short answer is NO but the long answer is YES.
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Best car characteritics for EV?

Post by Plugger »

Thanks Richo. I'll just stick with the Paseo for now. For the frontal area I multiplied the width (1660mm) by the height (1296mm) to give 2.15m2. I'm not sure whether this is what is actually meant, I did email a few questions to EVConvert but so far haven't had a reply. Should I make a deduction for the space beneath the car? Also the cross sectional shape is not really rectangular. Should this be adjusted down? I noticed in another forum on the GM Volt that an 'adjustment factor' to the simple W X H area was made.

I made a notional deduction of 25% kerb weight for stripping out the ICE etc. and ended up with a final total combined weight of 1205kg which included 80kg ea.for driver & 1 passenger. BTW the 70kg for passenger weight was given to me by one of the registered engineers over here in NSW.He also said to allow 70kg for luggage. One problem with EVCalulator is that it doesn't seem to include the ThunderSky Li batteries as an option. Also the addition of more battery strings seemed to imply 'in series' rather than parallel as the total battery voltage increased each time. So it became a bit of a juggling exercise to simulate what I wanted.
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Richo
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Best car characteritics for EV?

Post by Richo »

You can reduce the Frontal area by the area under the car.
This will only give an error of around 5-10% on the Wh/km.

If you were say condisering a Impulse9 DC conversion.
Then typically you would need 160Ah TS LiFePO4 cells.
Using a 144V system this would be 23040Wh total capacity.
This is 18432Wh usable capacity at 80%DOD.
For flat ground with no wind would be about 110km.
Add wind and hills and 100km would be hard to achieve.

The options would be to increase the voltage to maximum of the controller.
This would give you extra range.
Or change from 160Ah cells to 200Ah cells.
This would give you extra range as well.

So the short answer is NO but the long answer is YES.
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Plugger
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Best car characteritics for EV?

Post by Plugger »

Again thanks Richo, I had tentatively pencilled in 2 strings of 90Ah TS LiFeP04 at 144V to give a total capacity of 26KWh and mass 270kg. Drawing down only 70% would supply 18.2KWh & would return a range of 121 km if the car used 150W/km. The big if is the 150. I notice that resellers generally talk (optimistically)of figures below this but (the few) actual values for real vehicles on EVAlbum for example are usually 200+. Which is in the same ball park as EVCalculator.
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Best car characteritics for EV?

Post by antiscab »

I would steer clear of parralleling cells if possible.
having more than one string makes the wiring more complicated.
you are better off with either 160AH or 200AH units than 2x90AH strings.

150wh/km from the batteries should be about right for an excel or similar small car.

is there any possibility of a charge at work?
this would increase the cars usability significantly.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells
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Richo
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Best car characteritics for EV?

Post by Richo »

The Wh/km is related to your driving style.
The heavier the accleration the worse it would be.
The higher the speed the worse it will be.
It also depends on the motor you use as they will have different points of efficiency.

The values on EVAlbum factor all this in plus thier terrain.
So it's only a guide and would be hard to do a comparison as you don't know thier driving style or area of driving.
Also watch out for the Wh/mile -> Wh/km.

In city traffic where you are going slow you could get under the 150Wh/km.
So the short answer is NO but the long answer is YES.
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Richo
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Best car characteritics for EV?

Post by Richo »

I agree one string of 160Ah or 200Ah would be better.
Also consider that the cost of the BMS for double the cells could go towards the extra range with one sting.
So the short answer is NO but the long answer is YES.
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Plugger
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Best car characteritics for EV?

Post by Plugger »

Thanks guys for the advice on batteries. The thinking behind the 2 strings in parallel was redundancy. If a cell fails does the overall voltage only drop 3.2V or is the whole string compromised?
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acmotor
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Best car characteritics for EV?

Post by acmotor »

Plugger,

All battery technologies require you to stop drawing current if one cell in a series string fails. If you continue then permanent or catastrophic damage may result. Immediate failures are less common than just flat cells. The latter can sometimes be nursed through with reduced current to next charge.

FWIW, I have no problem with 2 strings of 90Ah in parallel provided you have BMS on each cell and you monitor the current from each string to know what is going on. Extra cost and complexity though. It does give the option of battery bank series parallel switching that may be advantageous in some designs. Image
iMiEV MY12     110,230km in pure Electric and loving it !
Plugger
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Best car characteritics for EV?

Post by Plugger »

The other aspect to 2 sets of batteries in parallel is cost. We may have to abandon the idea of 120km range for the moment and just use the EV for local trips (<50km). And if prices fall (or our dollar recovers) then add in another set later. Or drop the whole idea of long range, which may increase the variety of vehicle shapes and be not so tied to streamlining.
We had another look at a 97 Paseo on the weekend. Pretty good condition really-the only drawback was that the bottom of the gearbox was very wet-oil, rather than hydraulic fluid. Got no idea how much that might cost to remedy. The Paseo is supposed to be a 4-seater, but as someone said 'seats 2 adults comfortably and 2 in agony'. So we'd take out the back seats and use the space for batteries. One thing that was obvious driving was the incredible solar heat load due to the heavily raked windscreen & rear window. I notice the same thing in my wife's Elantra hatch(fast)back. Incredibly some sports coupes also have a sun roof as standard! I'm not a fan of a/c and had planned to take it out to reduce weight. I liked the long crumple zone out front and the safety rating of the no airbags Paseo is as good as light cars with. So- many factors to consider. Thanks everyone for the input.
antiscab
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Best car characteritics for EV?

Post by antiscab »

Hi Plugger,

re the gearbox, you could use the gearbox leak as a bargaining chip for a lower price.
retaining the gearbox is only the cheapest route if you already have a good and usable one.
If you dont, then getting a gear box costs around the same as getting a more powerful motor/conrtoller and going direct drive.

another point, a smaller battery pack means less instantaneous power.
50km range worth of lithium is only good for around 40kw.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells
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