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Old 08-12-2010, 11:42 PM   #1 (permalink)
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New guy looking at Metro EV conversion

Quote:
Originally Posted by MetroMPG View Post
Got these questions via e-mail:

Hate to throw cold water on your plans, but for $2500, building a highway capable car with a 50 mile range is a very tall order. Maybe an impossible order with lead acid batteries (you'll be way over the car's GVWR if you fill it with enough lead to go 50 miles at highway speeds).[/URL]

Hey there folks, I'm actually the writer of the email, well after talking and researching, let me rephrase my first question; Is it possible to go 40 miles on one charge, be capable of going highway speeds w/ a max desired of 60mph, but not the entire duration of the trip? PLease consider I am a 'experienced hypermiler as well, with a personal best of 55+ mpg in my 98 Saturn SW2 with no mods, but after finding out that when i turn the key off far enough to just not be locking the steering wheel-it doesn't count miles. Therefor my calculations were way off unless i knew the entire distance with out turning off my car.... but i can't not do that.

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Old 08-13-2010, 07:43 AM   #2 (permalink)
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To go 40 miles, lets estimate the average usage of 300Wh/mile, you need a pack capacity of 12kWh if you drain your batteries to 0% state of charge. To get this, you could use 12 12V batteries that have a capacity of ~83Ah. A group 27 battery would give this to you. However, you will be dishing out ~$90 a piece for these new, or $1080 plus tax. Thats almost half your budget.

Now, lets factor in the other things that really show how not easy this is. 40 miles is your range you want, but the above calculation shows us pushing the batteries way harder than they should be. Generally you don't want to go below 50% SOC to maintain decent battery life with lead acid batteries. So, now you need a $2200 battery pack and weighs twice as much (~63lb per battery, or 1500 lbs). This will honestly break the Metros back as its simply too much weight (this also assumes you can actually find a place to put 24 batteries in the car).

The alternative is to go with lithium batteries. They will allow you to get your 50 miles and highway speeds. However, the pack alone is going to cost you roughly 6X more. 45 3.2V (for 144V) 90ah lithium batteries will cost you $6075.
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Old 08-13-2010, 09:41 AM   #3 (permalink)
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Daox is right. To achieve that kind of range from a lead-acid EV, you simply need a bigger vehicle with more weight carrying capacity. 1500 lbs of batteries would even put my Jeep a couple hundred pounds over the GVWR of 5300 pounds (Jeep is about 4200 curb weight).
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Old 08-13-2010, 01:39 PM   #4 (permalink)
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ok, I can take a hint.... what range has been or is possible in the metro w/ lead batt.s? again on the budget thing, batteries aren't really included in that. I mean I have $1500 from selling my Saturn last week, and another $1000 saved for this project.... can I just get 4-8 batteries rgiht now and add more later? Yes i do believe this will affect my "range" goals, but it should just be temporary.but then i wouldn't have the total volts i'd like....son of a *****. you know they have the technology above and beyond Lithium batteries but the lobbyists of the oil company got a strong and tight lid on it? true story. I have yet to decide what voltage i want to run and for that matter what i CAN run. this week I'm gonna go out and hunt down some lifts (will those 'scissor lifts' work?) I'm gonna take some pics and see what, if anything, i can find.

how well do the home built controllers work? i mean are they as 'efficient' as Curtis 1231's? Can I build it to whatever voltage i need?
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Old 08-13-2010, 01:52 PM   #5 (permalink)
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One advantage of a controller that supports a range of voltage is that you CAN start with a few batteries, and add more later. For example, you could start with a 96V system, then add batteries to upgrade to 144V.

Just make sure that you have a charger that can later be set to a higher voltage, to match the future expanded battery pack. Otherwise, individual chargers can work. Just buy more in the future to go with the later batteries.

Homebuilt controllers can work great, give a great sense of pride that you did it yourself, and are reprogrammable and repairable.

The Solectria Force was a factory built electric Geo Metro which ran an AC system. Those used 13 group 27 batteries and could go about 40 miles. They also had regenerative brakes.
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Old 08-13-2010, 02:27 PM   #6 (permalink)
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Quote:
Originally Posted by bennelson View Post
The Solectria Force was a factory built electric Geo Metro which ran an AC system. Those used 13 group 27 batteries and could go about 40 miles. They also had regenerative brakes.
It would be interesting to see what speed that 40 mile range is quoted at. Some of the range gain is due to the efficiency gain with using an AC system vs DC. If you can lower your Wh/mile (effectively your electric mpg), you can go farther. The thing about electric vehicles (especially with regen) is Wh/mile is more proportional to speed than almost anything else. Theres no idling to harm low speed operation, plus with regen the start/stop isn't as big a penalty. That really only leaves rolling resistance and aerodynamic drag. Of those two, aero drag is a much larger energy hog, so aero mods will be key to reducing Wh/mile and therefore range at higher speeds.

If I were going to build a metro, I'd get the biggest capacity 12V batteries I could (group 31 batteries are usually just over 100Ah). I'd try to get up to 144V. This will give you 14,400 Wh capacity. Now, you should really only use half that (7,200), so the range will be ~24 miles. You'll get more range at lower speeds, and less at higher speeds.

At that point, you're already adding ~850lbs to the Metro and I don't know if I'd go much further than that. The only other way to increase range from the same size battery pack is to further increase the voltage. This reduces the current needed to accelerate and maintain the same speeds. The efficiency gain comes from reducing the Peukert effect. However, finding components (motors & controllers mainly) that handle higher voltages isn't the easiest thing while staying with DC motors.
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Old 08-13-2010, 02:34 PM   #7 (permalink)
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Quote:
Originally Posted by james.lafrance View Post
ok, I can take a hint.... what range has been or is possible in the metro w/ lead batt.s? again on the budget thing, batteries aren't really included in that. I mean I have $1500 from selling my Saturn last week, and another $1000 saved for this project.... can I just get 4-8 batteries rgiht now and add more later? Yes i do believe this will affect my "range" goals, but it should just be temporary.but then i wouldn't have the total volts i'd like....son of a *****. you know they have the technology above and beyond Lithium batteries but the lobbyists of the oil company got a strong and tight lid on it? true story. I have yet to decide what voltage i want to run and for that matter what i CAN run. this week I'm gonna go out and hunt down some lifts (will those 'scissor lifts' work?) I'm gonna take some pics and see what, if anything, i can find.

how well do the home built controllers work? i mean are they as 'efficient' as Curtis 1231's? Can I build it to whatever voltage i need?
Hi James.

You might want to consider going on Craigslist and seeing if you could trade the Metro straight-up for an S10 or other compact pickup (even one with a dead engine.) On a budget, battery weight is the name of the game for range. A pickup will have more room for batteries (and might be more practical for you as a plumber) and more carrying capacity. Since you're ripping out the ICE anyway, that means you can go for an older pre-injected pickup, which I regularly see on CL for $500 or less, and is lighter to boot. (A '91 S10 is 2,600 pounds with ICE--a little more than a Metro, but equivalent to a modern subcompact car, and older models are even lighter.)

A rule of thumb on the EVDL is that 500 pounds of lead is roughly equivalent to a gallon of gasoline. On an S10 that gets around 25 mpg, that's 1,500 pounds of batteries to get the range you're looking for without murdering the batteries.

On my '99 Metro, it took about 600 pounds (including driver and luggage) to reach GVWR. Even at 45 mpg, that's still 750+ pounds of batteries to get the range you want with some margin to keep the batteries alive--and that's before you add the weight of you, tools, passengers, etc.

EDIT: Another point: older pickups had manual steering as an option, which saves you more money and trouble.
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Old 08-13-2010, 02:34 PM   #8 (permalink)
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Hi James -

If you haven't yet, why not start a new thread and state your goal in the subject? It's info I'm sure others will be hunting for.

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Old 08-13-2010, 02:38 PM   #9 (permalink)
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One caveat to battery size is "does it fit or not?".

My car uses group 31 batteries, mostly because I got them REALLY cheap.

However, they are just a little too big to run longitudinally in the radiator space, whereas group 24 will fit there, and maybe even group 27.

Additionally, if you cut out where the gas tank was, you can fit 5 group 31 batteries in there (without cutting into important body/frame parts) but you can fit 7 group 24 batteries.

If I was using group 24 batteries, I would be able to fit 4 more batteries in essentially the same space. That would make the car a 120V system, without taking up any trunk space whatsoever!

I think it's possible to build a 144V Geo Metro that would look stock from the outside, by using the smaller size batteries.
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Old 08-13-2010, 03:01 PM   #10 (permalink)
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I moved these posts to give this topic its own attention.

Lets keep the discussion going, EVs are always fun to talk about.

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