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Discussion Starter · #1 ·
Would you guys with the experience and knowledge please read through my EV project scheme below and give me your opinion on it. Any recommendations based on your experience regarding the projected use of automatic transmission and low tech controllers would be very welcomed.
If you think that this schema makes sense could you possibly suggest some cost estimates for me regarding the batteries, motor and controller parts ?


My EV project scheme:

Purpose: To obtain a practical EV for daily use in rural areas.
Acceptable range is minimum 25 miles (35 kilometers).
Acceleration and speed requirements are modest and none beyond what is normally required for safe city traffic.
Preferred donor vehicle: A seven passenger 4x4 RV vehicle such as Mitsubishi Pajero / Montero or similar, with Diesel engine and automatic transmission.
These vehicles originally weigh around 1800 kg. empty and 2500 kg max load. Horsepower rating is close to 100.

Removing the Diesel engine with its accessories gives me weight headroom of some 300 kg and almost 500 kg if I also sacrify two passenger seats. By removing the low range/4wd components I may even gain up to 100 more kg if I have to.

I would opt to keep the automatic transmission since I believe that it gives me more flexibility in the motor controller selection and may even allow me to use a simple stepwise controller instead of the variable pulsewidth variety.

To retain the driveability I still need the power steering and vacuum for the brakes servo. If I keep the steering pump and vacuum pump (part of the alternator) and drive them via a fan belt from the traction motor I have all these systems ready and additionally some charging options for the legacy 12 Volt system if required. The torque converter in the tranny will let the motor and the pumps reach some hundred rpm’s before the vehicle starts moving so the pumps can build up pressure in time.

Braking power regeneration is currently not an issue but may be considered later.

I am inclined to opt for low tech solutions, lead acid batteries and a series wound DC motor, mostly because of the low cost and good availability of these proven components.

Cabin heating may be the largest remaining issue. It can be solved to some extent while charging the batteries, but returning home on a cold afternoon may call for warm underwear. :eek:
 

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Hello Agust-

You can look here to see if there are any examples of other vehicles similar to what you have done: http://www.austinev.org/evalbum

A 25 mile working range in city driving conditions (little or no time at speeds in excess of 50mph) should be pretty workable with a lead acid conversion, even with a midsize SUV like a mitsubishi montero, assuming that there aren't any extreme driving situations, like mountain passes, mud bogging, sub-zero temperatures or anything else that will require more energy than 'normal' driving would when you are planning your range. Shoot for battery weight about 1/3 of total curb weight as a minimum. A 120 volt system will give you freeway speed capability if you need it. Don't build it with less than a 96 volt system if you can avoid it.

While a montero will work (and is more sensible than some vehicles people want to convert :), if you don't need a truck, you can get the same performance (range, speed, etc) at lower cost with a smaller vehicle. If you need the interior space, what about an small or midsize older station wagon, maybe a 70's datsun or toyota wagon? If you do need a larger vehicle, that's fine, just expect to pay more to build it and keep it running.

If there is such a thing as a 2WD montero you might as well start there. Less overall work to do.

Series DC works great for vehicle propulsion. For a midsize SUV, a 9" motor is probably the best bet, even if you don't plan freeway speeds. You will want it for the torque. Anything bigger than that and the $ starts adding up fast. You can find forklift motors around this size, but forklift and equipment motors must be prepped a certain way to be reliable in an EV, heaps of info in other threads on this site.

As for the controller, in this day and age it really doesn't make much sense to go with a contactor controller. they are unsafe for a variety of reasons. A safe, modern PWM controller that can power that car starts around 1500 USD brand new. Yes, a PWM controller (and a main contactor, fuse, and emergency disconnect) all add cost but I'm guessing you really don't want to have to explain why you ran over your neighbor's dog (or kid) because your contactor controller shorted out or welded closed and you could not stop the car.

For batteries, flooded lead acid (FLA, aka golf cart batteries) are the best bang for the buck without going to a much longer timeframe for lithium to pay off, and FLA, despite needing a bit more maintenance for best performance, is by far the most forgiving type of battery to cut your teeth on. Expect battery pack replacements every 3 to 5 years depending on how they are treated and your range needs.

Using an electric heater will sap your range. a 1.5KW heater will tax your range by about 10% assuming it is run continuously. You will want more than that unless you only need modest heat. some people in colder climates choose to use various portable propane/kerosene heaters instead to save their range and provide some safety if the weather gets cold enough for danger to life. Just make sure the installation itself is safe. As you already implied however, there is nothing stopping you from keeping the cabin heated while the car is plugged in, at no cost to your range.

Cold temperatures also decrease battery performance, both in terms of peak power and usable energy. Insulate your batteries if you intend to operate the vehicle in cold weather. You lose about 1/3 your usable capacity at freezing vs. 80 degrees farenheit. It gets worse as it gets colder. Its cheap and easy if you plan for it, and a pain to retrofit.

Good luck, and keep doing your research.
 

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Discussion Starter · #3 ·
Hi mr. madderscience and thanks for your comments on my EV scheme.
I have a few more points to support my preference for donor vehicle and the “low tech” solutions which you seem to be a bit wary of.
Firstly I use one of these Diesel RV vehicles for my daily chores as well as occational longer trips around the country. I do most of the service work on it myself, know most of the internal works and feel at ease when doing it.
Secondly I prefer to start with a donor vehicle with reasonably large headroom in regard to weight and space. I would hate to start with a car which turns out to be too narrow and/or too weak for my purpose unless some major rebuilds were done on it.
Thirdly I am a kind of technical adventurer. I get more satisfaction from finding a useful technical solution myself, and building it, than buying somebody elses solutions ready off the shelf.
When I talk of stepwise and low tech I am not referring to the use of mechanical contactors etc. I am aware of the existence of semiconductor switches. Actually I am referring to the ideas described on this web page under the moniker of “batpack”: http://www.redrok.com/images/batpack.gif
Of course this schema would require a computer to keep track of the discharge state of the individual batpack units and manage their disposition accordingly in some intelligent way.
I believe that a vital part of my EV schema is a mission to find out how well the combination of stepwise motor controllers (batpacks) and automatic transmission will perform. Perhaps it will turn out that automatic transmissions and electric motors do not go well together at all and the use of switched “bat packs” may be too jerky for a comfortable ride. In that case I would probably rest the case and start looking for other interesting solutions. :)


Anyway, I will gladly accept continued feedback on these matters and look forward to receive advice from you and other experienced EV builders.

Agust
 

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Hi again Agust-

I consider myself a pragmatist so that colors much of my advice and decision making. If the problem has been solved already, I build on it and experiment someplace else where the problems are still bigger. I get something working first, then try the custom things. I know that I get what I pay for. (whether the currency be time or money) I learn as much as possible from other people's experience before I try something.

I've seen quite a few EVs running, and very, very few are running homebuilt motor controllers. I have not seen any modern EV running and driving on a contactor controller. The few people who are expirementing with homebuilt controllers have a stack of blown up boards to prove it.

It is fairly easy, cheap, and safe to build a homemade charger (for flooded lead) if you are reasonably adept at working with electricity, so if you want to cut your teeth on something, you might want to start there.

All that said, its a free country. Do whatever you want as long as it makes you happy.

Good luck.
 
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