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Old 10-17-2008, 03:22 AM   #1 (permalink)
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Cordless drill lithium batteries

So, I see 24V lithium batteries with a capacity of 3Ahr on eBay for about $70 each. What's the typical requirements to power a small electric car conversion? If you put 5 of them in series to get a 120V pack, then wire 3 or 4 packs in parallel, what kind of range and speed can you expect? 15-20 of those batteries don't seem that expensive. Is my math totally off here?

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Old 10-17-2008, 08:36 AM   #2 (permalink)
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$1400 in batteries...hmmm. 120V is probably high, most work in the 48-84V range from what I've read..no matter. I don't think 20-3Ah is enough to get the car very far. Honestly, without knowing the motor draw, mass of the car, there is no easy way to shoot in the dark. I know a bicycle can use 3 of those in parallel and have a 20mile range at about 18-22mph, but that's 200lbs, not 2000lbs. So maybe taking that simple math, say 40 miles, upto 40mph? I have no real idea. Just firing blanks.
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Old 10-17-2008, 09:42 AM   #3 (permalink)
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about 250 watt hours per mile, 24v X 3AH is 72 watt hours.
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Old 10-17-2008, 02:00 PM   #4 (permalink)
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Hi Ryland. How does voltage factor into the watt hour per mile figure? So in my example, let's say you have 20 batteries to work with - a) 96V at 15 amp hours or b) 120V at 12 amp hours.

I did a bit of digging around and found out the Tesla's ESS is probably 324V and 151Ah, so that's a good place to start for comparison. So roughly speaking, to get 1/3rd the performance and 1/3 the range, I'll need 96 of these drill batteries (~$7000). Then there's something called a C rating to worry about.
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Old 10-17-2008, 06:21 PM   #5 (permalink)
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you are going to gain some efficentcy with a higher voltage, but mostly you are going to be able to drop wire size, my 1,400 pound commuti-car has number 2 wire (conductor little larger then a pencle), and it really should have 2/0 wire (conductor about the size of a sharpy marker) so it can run it's 6hp 48V motor, giving it a 40mph top speed... basically if I wanted to go faster I would have to up the voltage, as the wires in the motor wouldn't be able to easly handle the amps needed for that kind of power, just like if you want a table saw for cutting alot of hard wood the motor is going to last longer if it's 220V instead of 110V, less of that energy is going to turn to heat, how much I can't say off the top of my head, but enough that your big advantage is that your vehicle electronics are going to last longer, the draw back of it is suddenly you have high enough voltage to kill you, my 48V system I can feel the tingle of electrons, and can make a nasty spark of I am not careful, but death is not the first thing on my mind when working near my batteries.
My DeWalt 36V lithium batteries are rated for 120 amps for I think 10 seconds, and around 70 amps for the 3 minutes it would take to totally drain them, they work well for my electric bike but there are cheaper batteries for cars out there.

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