DIY Electric Car Forums banner

1 - 13 of 13 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #1
Greetings guys n gals!
My name is William and the last many weeks I have been obsessed with the idea of building an electric vehicle. Ive read numerous websites, and a couple of books ("Build your own electric vehicle-Bob Brant) (Convert it! Micheal Brown)

My IDEAL goal is to have a highway friendly care (top speed atleast 70) and the more range, naturally the better. The perfect range would be 100.

That being said, after much reading I know that is a very tall order to fill...but is it possible/somewhat practical? What components would be needed? I have a hard time determing which brand of product is better than the other.

I am also not sure as to convert a truck or a car first. Truck more space, car lighter, etc etc. I read the other thread on the same question. I am a car man, but I would rather drive the truck if it met the above criteria. Which would have a better chance of reaching my goals? Car vs. Truck

I am going to pick up the donor vehicle first, and start ripping stuff in hopes of curbing my excitment.

Sorry, I feel like I am throwing alot of information out there at once, and if I am not 100% clear, please let me know and I will clarify the best way I can!

Many Thanks!
~*William*~
 

·
Registered
Joined
·
28 Posts
Hi,
If you want long range, you'll want lithium ion batteries (and lots of 'em :p). There's a bulk order getting organized on evforum.net if you're interested. You probably already know this if you've done a lot of reading, but you'll never get 100 miles with lead-acid, it would be too heavy. Plus lithium lasts longer and needs no maintenance.
If you're going to drive around town alot (stop and go), you could also consider an AC motor, to have regenerative braking (and 97% + efficiency). Of course this comes at a price, just like the long range :). Have a look at metric mind for an idea of pricing.
For the donor vehicle, basically go for what you prefer. A truck has more space, but usually has only 2 seats, is heavier and unaerodynamic. If you use lithium batteries, you'll probably have space to squeeze them in just about any car, so just convert whatever you prefer...
Hope it helps
Craig
 

·
Registered
Joined
·
372 Posts
Well, I wouldn't say you'll never get 100 miles on lead acid. It's possible, just not easy. I don't know about you, but as much as I woud LOVE to have lithiums and an AC system, I just can't afford them. :rolleyes:

Realistically, if you convert a light car like a Civic or something, and put maybe $7000 into it (sounds scary, I know. It depends on how many things you do yourself, how many parts you buy used, etc.), you'll probably end up with a good commuter car. Something that'll do at least 70 (you won't be tailgating cars in the left lane, but it'll do it ;) ), with maybe a 50-60 mile range at 50 mph. You'd probably be looking at your basic lead acid batteries (probably about 144V system) and a DC motor.

It all depends on how much time and money you want to put into it.
 

·
Registered
Joined
·
38 Posts
Would it be dangerous to have a half lead acid and half lithium battery pack, so there's a bit more power, but not quite as expensive?
 

·
Registered
Joined
·
372 Posts
Possibly. You would definitely need to charge the two packs independently. Seems to me it's been done before, though. I'll look around on the EV album later and see if I can find it.

A better solution would probably be a pack of lead acids with an ultracapacitor (supercap? I don't even know the diff anymore :rolleyes: ). The cap would give you amp surges for acceleration and level the load on lead acids.
 

·
Registered
Joined
·
38 Posts
I've read in many places that the maximum distance falls as you go faster. Are there any gears or ways to make this more efficient, or is it mostly wind drag that causes it?

If I could get a 150km rang on lead acids, i'd be able to get to the nearest capital city which would be great, but I wouldn't be able to get back. I'd really like to be able to do 300km but I guess that's completely out of the question with lead acids, and probably out of the question with lithium ion's as well. I wonder how fast I can charge the batteries if I was only at that city for a couple of hours...
 

·
Registered
Joined
·
372 Posts
It's mostly wind drag. Gearing can make it slightly more efficient, but not nearly enough to noticeably counteract the effects of wind resistance.

If I were you, I wouldn't be looking at an EV (at least not a conversion) as a long-distance car. It is much more cost effective to build a purpose-built commuter. If you build your car to get an amazing range that you'll only need once a month, and your acceleration and top end suffer as a result, it just isn't worth it. On the other hand, if you don't need to go fast, and you make long trips often, it might be worth it.

EVs are absolutely awesome as commuters and errand-runners. Mine (with just a 40 mile range) reduces gas costs to near zero for 90% of the trips I make. I'm happy taking a gas car for the other 10%.
 

·
Registered
Joined
·
28 Posts
A better solution would probably be a pack of lead acids with an ultracapacitor (supercap? I don't even know the diff anymore :rolleyes: ). The cap would give you amp surges for acceleration and level the load on lead acids.
That would work, but then you're paying quite alot for capacitors so you're saving very little compared to lithium, and that's without counting that lead-acid has to be replaced 2-3 times more often than lithium.

As far as the 300km range goes, it is possible (the tesla roadster can do almost 400km city/motorway), but it'll be difficult, and (very) expensive. You'll need a very aerodynamic and light car, efficient electronics (AC) and gears, regen braking, and, again, money.
Good thing is, if you want to do this, we'll all get a big discount on the bulk ltihium ion order :D.
 

·
Registered
Joined
·
2 Posts
Discussion Starter #11
Thanks for all of the input!

Another question, does it play a big difference if you use the equipment from metric mind (they are stating that their products were made for ev) or use other items that werent "made for it" but can do the job?
 

·
Registered
Joined
·
372 Posts
Depends on what you mean by "made for it." Metric Mind sells very high-end EV equipment. Good old DC motors and controllers do the job just fine as well, at a relatively low cost. With components like those from Metric Mind, you'll get excellent performance, but you'll put a lot of money into it.
 

·
Registered
Joined
·
320 Posts
As a rough rule of thumb for lead acids whatever percentage of your final vehicle weight is batteries double it for your range in miles. So to get 100 miles 50% of the vehicle must be batteries. Take a 1400kg truck and add 1400kg of batteries and you'll have something close to the range you want. That could be two strings of 24 batteries 6 volts each or a total of 48 batteries at 30kg each.

The lithium advantage is its weight or lack of it and the reactivity of the metal. How much of an advantage that is depends on the battery chemistry mainly to do with the electrode materials. Some lithium’s cannot be discharged very fast. The speed with which a lithium battery can be charged and discharged is indicated by its C rating, this is a multiplier for the Ah rating of the cells and gives the maximum amperage that the cell can safely produce or be charged at. So say a cell is rated at 2C. When discharged at its maximum rate it will take a half an hour to go flat.

I think the cells in the Tesla are rated at 0.3C for charging which is why the minimum time the car can be charged in is about 3.5 hours. The Tesla battery weighs 450kg and I think constitutes a third to a half of the total vehicle weight (it's a very light car) for a 400km range. The battery contains the equivalent energy of 8 litres of petrol (less than 2 gallons I think). The car is more than 4 times as efficient as an ICE car. The cell chemistry isn't the safe Iron phosphate but is the much more energy dense cobalt oxide and Tesla use systems other than chemistry to ensure the safety of their battery.

Kokam make 100Ah cells with a 5C continuous and a 8C peak rating (I think charging is 2C). These cells are the power dense and less safe cobalt oxide types. Charge recovery even at high currents is vastly better than lead acid so even though in terms of kWh/kg they are about 3 time as good as lead acid they should produce a range of at least 4 or 5 times as far. Google Electric Imp for someone using these. Cell balancing on the fly and good power management is crucial with cells like these.
 
1 - 13 of 13 Posts
Top