Choosing a Vehicle · 11 September 05
We had a survey a couple of weeks ago asking what types of cars folks were thinking of converting. I also get two to three emails a day from folks wondering if their vehicle might make a good EV or Hybrid.
Let’s take a look at how to determine what type of EV your vehicle will make and what it will take to get the range you need.
When I converted the Mazda, Bob at EV America printed up a spreadsheet of Electric Vehicle Calculations specific to that model.
The Mazda 626 had a starting weight of 3,392lbs and a drag coeff of 0.35. The calculations, based on a FB-4001 motor and SCS225 batteries, showed the anticipated range for a variety of speeds and road grades. It’s pretty hilly around here so I figure a 2% grade is a good average to work with. Driving 30mph on that grade worked out to about 35 miles of range. The furthest I ever drove that EV was around 30 miles, so that’s about right.
The thing is (there’s always a “thing is”) that this was under ideal conditions: relatively new batteries, moderate temperature, and steady driving. A New Hampshire winter can knock the range down by a third or more. Batteries get old over time. The range you design for should leave enough elbow room to take into account bad weather, aging batteries, and unplanned detours.
If you are thinking of making an EV you need to do two things: be honest with yourself and be realistic. Or be rich.
There’s a slim to none chance that the laws of physics are going to cut you some slack or you’ll discover an energy loophole during your EV construction. Me, I kept thinking they’d discover a new, cheap, long range battery before I was done or perfect hydrogen fuel cells. Ten years later and those two words (cheap & long range) are about as far apart from each other as they were then.
First off, why do you want an EV? Is it a knee-jerk reaction to high gas prices, part of your plan to help the environment, or an itch to tinker that you just gotta scratch? I get emails from folks with huge SUVs that think a set of batteries and an electric motor will magically solve their fuel cost problems. Don’t think so, sorry.
Environmentally I think an EV provides more options in “cleaning things up” but just like anything else this depends on the person. If you charge the EV with a gas generator, toss old batteries in the woods, and drive like an idiot then you are making little if any positive impact. On the other hand an EV makes it possible to use clean power and recycle dead or dying gas vehicles.
Of course making an EV is great tinkering….
Who you are and your driving style has a lot to do with what type of EV you make and the range you’ll get. Is your car part of your identity or is it a tool to get from point A to point B? Do you want something fast and furious or calm and conservative?
One fellow wrote that he wanted an EV which can make 0-60 in 4 secs, reach 120mph, and get over 100 miles range. Ok, Greg’s Yugo EV probably isn’t a good fit, but something over at NEDRA might do the trick. With enough money he might be able to get close, although 100 miles of range at 120mph is a little optimistic.
What do you really need? Keep track of your driving for a couple weeks or a month and determine the normal commute, not the exceptions. My commute is under ten miles and I drive it at least 250 days of the year. There are always exceptions, but if you build for the exceptions you will be spending more money.
Instead of converting your sole gas vehicle, maybe it’s better to find an old, small car to convert and use the gas vehicle just for the exceptions. You spend a little more for the donor car, but that will end up being cheaper in the long run than building and maintaining a higher range vehicle.
Where you drive makes a big difference in performance. You’ll get more range driving the flat expanses of Florida than the hilly knolls of New Hampshire. A Florida EV won’t need to worry about the effect of cold on the batteries but an Air Conditioner is probably mandatory.
When I built the first EV I was all excited to get regenerative braking going. People said that it might add a modest (i.e. 8-12%) amount to the range, but I was convinced otherwise. The regen controller died, I switched to a non-regen controller and bought a book on making a regen circuit.
It was a lost cause. We live on top of a hill and the only meaningful regen would be when I left for work with the batteries full. I’d either be damaging the batteries or burning it off into an external heat sink. It just wasn’t worth the extra expense and complexity.
Running the numbers
I’ve been doing “what-if” analysis using Uve’s EV Calculator (here’s another version). Plug in the car specs, motor, controller, and a variety of batteries and out comes all kinds of useful information.
These charts show information calculated for 2nd gear operation on a 2% grade. The top chart shows the old Mazda (near as I can get it) while the bottom shows the new Probe. With the first EV I almost always drove in 2nd gear: from starting off, on up to 35-40mph. I picked an AGM battery as a reference point for the comparisons. 2% grade is probably a realistic average for this area.
For an exercise in extremes consider these two charts. The top chart is for a ‘96 Dodge Ram and the bottom is a ‘92 Subaru Justy. Both of them are calculated using the same controller, motor, and batteries.
The Justy gets around five times the range. That doesn’t mean you can’t get the same range with the Dodge, it just means you’ll need more battery power. This means more money and not just out of pocket expense for the batteries, you’ll probably be consuming about five times the electricity and may need to buy a more powerful charger to fill them in a reasonable time frame.
This works the other direction as well: convert a motorcycle, moped, or bike to electric and you’ll spend a lot less to get good range than shown with the Justy.
Do it yourself
With Uve’s great calculator in hand and a little time spent perusing the web you can do the same what-if analysis of your own future EV donor. Here’s a few links to pages with helpful information:
- EV Battery Page
- Coeff Drag Tables
- Used car specs: automotive.com, NADA guides
- Tire sizes: Goodyear tire selector, Tirerack
Narrowing the search
Now that you’ve figured out what type of driving you do, the type of vehicle you want, and the range you’d like you can start working these tools to figure out what kind of EV configuration will do the trick.