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Old 12-28-2009, 04:26 PM   #1 (permalink)
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Poor man's lithium

Inspired by MetroMPG and a thread elsewhere, I am beginning to think about using Lithium to power E-Sandra. Here's my logic: a Tesla uses 6,831 of the 18650 laptop batteries to go 200 miles (according to some dude, I haven't bothered to check, and 6,798 according to MetroMPG). So, since I need 2 miles, I can use 68 of them, right?
Yes, I'm kidding, but not totally. I mean, I'm certainly not going Tesla speeds and laptop batteries are not crazy expensive: I can get 2 of them NEW (wow, something NEW in my car) for $4. So a decent pack shouldn't be TOO crazy expensive. The biggest drawback will be BMS. Tesla has all kinds of safety stuff I won't have. Then there's charging: I can picture me taking my batteries out every night and hooking up 20 or so power supplies. So my "pack" would need to be taken apart every day for charging......
Any comments appreciated.....

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Old 12-28-2009, 05:09 PM   #2 (permalink)
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They hypermiled that Tesla for that mileage, so don't expect your numbers to be that good. I do see where you're going with it though. I don't know about charging individually though, that will probably get old FAST!
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Old 12-28-2009, 06:54 PM   #3 (permalink)
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I'd sure like to know where you get 2 new lithium laptop battery packs for $4.

My understanding is that the single most expensive component of the Tesla is the lithium battery pack.
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Old 12-28-2009, 08:01 PM   #4 (permalink)
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You guys realize that "lithium batteries" are about as specific as a "fuel driven car" right?!

Laptop batteries may be what comprises the building blocks to the battery pack in the Tesla roadster... But what makes it work in a EV with quite different demands than a laptop is the smart little chips surrounding it...

Trying to charge a pack of that many cells without BMS is asking for trouble... And charging separately is a PITA...

If you really can get them new for $4 you could probably spend the money to get the most basic BMS (or DIY one) and charge them as 12V/24V/48V blocks at least... Then you'd only need a few chargers or PS's to plug in... Still a hassle, but of a different magnitude...
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Old 12-28-2009, 09:11 PM   #5 (permalink)
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PbH2SO4 is the poor man's lithium. Either that or junkyard NiMH.
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Old 12-28-2009, 09:35 PM   #6 (permalink)
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I think the Tesla uses cells from A123 which are not quite the same as the batteries that you find in your laptop.

The big difference is that the A123 cells can tolerate extreme rates of charge and discharge, far in excess of what a laptop battery can take.

The A123 battery does have lithium in it.

If you are dying for these cells the new DeWalt 36V batteries have them. If 2miles is your goal might I suggest a good pair of feet?

Failing that this is well well within the technical limit of good old lead acid.
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Old 12-28-2009, 11:48 PM   #7 (permalink)
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how many watt hours per mile do you need?
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Old 12-29-2009, 01:39 AM   #8 (permalink)
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Well rough estimate 15hp gets you 60mph so 2 min would do it.

15hp goes to 12.5kw x .05hrs give about 0.625 kwh. That would be 10 laptop packs (bearing in mind that won't work).
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Old 12-29-2009, 12:16 PM   #9 (permalink)
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Most batteries can not handle the kind of electrical draw that is needed to power a car, my 1,400 pound car draws as much as 25,000 watts when starting from a dead stop, 600 amps for a second or more at 48 volts, most if you try to draw that out of a laptop battery, or even 10 laptop batteries they will melt, start on fire, or produce some other thermo event.
Dewalt packs are A123 batteries, they have better specs then lap top batteries but still if I remember correctly 75 amps out of a single 33 volt (labeled as 36 volt) pack can be drawn for a second or more, of course the BMS does not allow that kind of discharge, it's limited at around 15-20 amps, I could see having a few deep cycle lead acid starting batteries and a lithium battery that keeps them charged, so the lead acid would act as a buffer, that could work.
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Old 12-29-2009, 01:27 PM   #10 (permalink)
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I still have not made up my mind what to do with my City-EL. Lithium batteries has been tried in the UK about 2 years ago then it was mysteriously sold. Story ended right there- no plusses, no minuses- nothing.

Out of about 60 C-ELs sent to Sacramento in 1992-1993; I have one of about 5 operating. I have seen 4, but only 1 has lithium batteries (as of Oct. I think) instead of the 4 lead-acid deep cell batteries. Not enough "trial and error" for me to know for sure if I should go that route.

With a primary, secondary, and that computer circuit charging circuit, deciding which batteries has always been a problem- several times I have charged all 4 batteries one by one (that got VERY old VERY fast!) then I just lost patience and left those computer power sources 'on' along and used an external charger at the same time- takes about 6 hours. I think I will get 4 lead-acid batteries from Costco- even that price is terrible: $280.+ but the ones in it were $1300.+. Lithium batteries are very expensive.

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