# using little aa lithiums for geo metro? why not?



## amynalbuq (Jan 21, 2012)

I'd like to convert my geo metro hatchback. From what I've read while it is a light car it is not necessarily ideal since it can not hold as much battery weight. I've read that the tesla uses 6000 or so aa similar lithium batteries. Why can't I use 1000 -1500 or so little AA lithium batteries? A 50 mile range is plenty for me and 45 mph is also plenty fast. It looks like with the little batteries it would be easier to store and work with placement and securing the batteries. 

Thoughts?

BTW. This would be a permanent car for me. I also intend to take the backseat out and use this as a commuter car/mini truck. Also intend to add a solar panel to the roof for some constant minimal charging. I live in super sunny New Mexico so a little goes a long way!

Thanks in advance. Amy N Albuquerque


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## rwaudio (May 22, 2008)

amynalbuq said:


> I'd like to convert my geo metro hatchback. From what I've read while it is a light car it is not necessarily ideal since it can not hold as much battery weight. I've read that the tesla uses 6000 or so aa similar lithium batteries. Why can't I use 1000 -1500 or so little AA lithium batteries? A 50 mile range is plenty for me and 45 mph is also plenty fast. It looks like with the little batteries it would be easier to store and work with placement and securing the batteries.
> 
> Thoughts?
> 
> ...


I believe cruisin on here built his pack using 18650 size cells, which is similar but slightly larger than an AA cell. If you get enough of the correct cells and get a CD welder to attach them then you are set.


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## dtbaker (Jan 5, 2008)

amynalbuq said:


> I'd like to convert my geo metro hatchback. From what I've read while it is a light car it is not necessarily ideal since it can not hold as much battery weight. I've read that the tesla uses 6000 or so aa similar lithium batteries. Why can't I use 1000 -1500 or so little AA lithium batteries?


this would be a nightmare to assemble and balance. you can EASILY get 50 mile max range into a Metro with a 120v (38 x 100ah) prismatic cells and end up at stock weight.... come visit my site linked below.

If you intend to regularly need 40+ miles or need longer highway miles, I would suggest a 144v x 100ah system which would fit without giving up any cargo space, OR you could go more if you really need more and are willing to give up cargo space.

forget the PV on the car, and put it on your house.

I am in santa fe if you want to some see a converted Metro/Swift in person.


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## cruisin (Jun 3, 2009)

rwaudio said:


> I believe cruisin on here built his pack using 18650 size cells, which is similar but slightly larger than an AA cell. If you get enough of the correct cells and get a CD welder to attach them then you are set.


Using individual 18650 cells can be a nightmare if you want a decent ah rating and a resonable voltage. If one intends to do it anyway (not recommended) I would suggest you use the cells that have the attached tabs like I did, makes it a little easier.


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## Coulomb (Apr 22, 2009)

amynalbuq said:


> Why can't I use 1000 -1500 or so little AA lithium batteries?


I don't think that lithium cells come in AA size; perhaps you are thinking if Nickel Metal Hydride rechargeable cells, or 18650 size lithium (but not lithium iron phosphate) cells (as used in the Tesla, I believe).

Tesla have a lot of technology in their packs; it's not something you can easily replicate at home. Other OEMs license the technology from Tesla, rather than go through the cost of re-learning the technology from scratch.


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## madmike8 (Jun 16, 2011)

lithiums come in 14500 size which is approximately AA size.


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## Coulomb (Apr 22, 2009)

madmike8 said:


> lithiums come in 14500 size which is approximately AA size.


I stand corrected; thanks for pointing that out.

The prices I saw were a fair bit higher than the ~$1.15/Ah for larger prismatic LiFePO4.

Are they available at reasonable prices?

Are there higher discharge rate models available? (you really need at least 3C for EVs)

I suspect it will always be more economical to build a small number of larger cells. The Tesla pack however is a conspicuous exception.


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## DJBecker (Nov 3, 2010)

Tesla didn't have a choice. When they designed their prototype, the 18650 laptop cells were the only type they could buy.

Much of the early engineering went into figuring out how to connect, package, cool and monitor thousands of individual cells.

That's a whole bunch of extra work and packaging expense that you can avoid just by getting off-the-shelf large cells.

Imagine that you have 6000 hens and a vial of horse semen. You want to build a transportation product to sell by the end of the year. The answer is learn how to sew chicken harnesses, not to talk about how great a horse would be.

Now you have a choice of copying their chicken harness design, or buying a horse. A surprising number of people would say "they used chickens, so that must be the right choice".


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## frodus (Apr 12, 2008)

DJBecker said:


> Imagine that you have 6000 hens and a vial of horse semen. You want to build a transportation product to sell by the end of the year. The answer is learn how to sew chicken harnesses, not to talk about how great a horse would be.
> 
> Now you have a choice of copying their chicken harness design, or buying a horse. A surprising number of people would say "they used chickens, so that must be the right choice".


I about spit my coffee out.....

great analogy.


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## madmike8 (Jun 16, 2011)

DJBecker, That's funny!


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## dougingraham (Jul 26, 2011)

The Panasonic 18650 laptop batteries that the Tesla Roadster uses are severely current limited. Not even 2C. I believe they are restricted to 4A. If you want to pull 500 amps that means you need to parallel 125 cells.

It is astounding to me that they went to the effort to build a pack like this with all the problems of using the little cells. You need to keep them within a certain temperature range and you need to be careful not to overcharge or over discharge them.

I haven't found a decent place to buy them either. I guess if you buy them in millions quantities you can get a good price.

An OEM can deal with all the problems/limitations of these cells. Save yourself a lot of effort and go with 100AH LiFePo4 prismatic cells.


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## cruisin (Jun 3, 2009)

dougingraham said:


> The Panasonic 18650 laptop batteries that the Tesla Roadster uses are severely current limited. Not even 2C. I believe they are restricted to 4A. If you want to pull 500 amps that means you need to parallel 125 cells.
> 
> It is astounding to me that they went to the effort to build a pack like this with all the problems of using the little cells. You need to keep them within a certain temperature range and you need to be careful not to overcharge or over discharge them.
> 
> ...


Your information regarding the 18650 cells is inaccrate. Also, if you look in classifieds you will find the 18650 2.7ah cells for $2 with tabs. You cant beat that price anywhere.


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## icec0o1 (Sep 3, 2009)

frodus said:


> I about spit my coffee out.....
> 
> great analogy.


Funny, but incorrect analogy. The more accurate one would be a harness for 8000 tiny camels which go slow (relatively, since the model S has 0-60 in 4.4s) but for a great distance or a carriage with 8 horses that can gallop for a bit.


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## frodus (Apr 12, 2008)

icec0o1 said:


> Funny, but incorrect analogy. The more accurate one would be a harness for 8000 tiny camels which go slow (relatively, since the model S has 0-60 in 4.4s) but for a great distance or a carriage with 8 horses that can gallop for a bit.


His analogy was funny, and correct. Tesla designed around what they had at the time (small cells), not what could be (larger higher power cells). But now, we can either design how they did at the time, or design around current technology.

Yours was neither funny nor was it a great analogy. Try again.


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## icec0o1 (Sep 3, 2009)

frodus said:


> His analogy was funny, and correct. Tesla designed around what they had at the time (small cells), not what could be (larger higher power cells). But now, we can either design how they did at the time, or design around current technology.
> 
> Yours was neither funny nor was it a great analogy. Try again.


There is no more current technology than the Panasonic 3.4Ah 18650. Are you really arguing that if there was a better techonology/battery out there, Tesla wouldn't use it?


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## dougingraham (Jul 26, 2011)

cruisin said:


> Your information regarding the 18650 cells is inaccrate. Also, if you look in classifieds you will find the 18650 2.7ah cells for $2 with tabs. You cant beat that price anywhere.


Thanks for pointing that out. I was going from memory. I poured over the datasheets and it looks like 2C is the max recommended. And on some of the models they seem a little strained at that current. In the case of the 2.75AH (NCR18650 is typical 2.9AH cell) cell this is 5.5 amps. 

They point out that each cell incorporates a PTC device but dont show its characteristics. I assume it goes to high resistance in the event the cell temp exceeds some threshold.

The Tesla Roadster appears to have a 215kw drive system which draws its power from a 99S69P pack of cells. This gives a full power current of around 600 amps. 600A/69Cells = 8.7A per cell which is right at 3C on a 2.9AH cell.

$2 is a good price.


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## dougingraham (Jul 26, 2011)

icec0o1 said:


> There is no more current technology than the Panasonic 3.4Ah 18650. Are you really arguing that if there was a better techonology/battery out there, Tesla wouldn't use it?


You use what you know. They might still use them even if there was something better. At the moment it looks like the complete package is still superior in wh/kg to other solutions. However it requires a large pack to get the performance they wanted for the roadster. The side effect of that large pack was decent range. You can build a lot smaller pack that would provide the voltage and current used in the roadster with Headway's or A123 20AH pouches. And smaller still using the Haiyin cells. You could replace the Roadster pack with a 99S2P pack of the Haiyin cells and have a pack where the cells weigh something near 33.66kg (74 lbs). With all the interconnects and box to hold it together it would probably end up at 42kg (92 lbs). This would be a savings of 408 kg (897 lbs) although at a considerable reduction in range (56kwh down to 4.3kwh). I would estimate the range would be reduced to around 17 miles. But I bet the 0-60 time would go down considerably as would the 1/4 mile time.


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## frodus (Apr 12, 2008)

icec0o1 said:


> There is no more current technology than the Panasonic 3.4Ah 18650. Are you really arguing that if there was a better techonology/battery out there, Tesla wouldn't use it?


Why Tesla uses these 3.4's is for economy of scale. The more you buy of a commodity item like a laptop battery, the better price you get it for and the more profit..... it's not because it's the best battery out there. These Panasonics are far from the most dense and powerful battery. 

BACK TO THE OP's question, which is what this is really about.

Building a pack of 18650's is time consuming, just ask Al Bullock (cruisin). He hand soldered a ton of them. Made a great pack, but it took a while. There are considerations with a pack like that, that's all we're saying. There are other high power batteries that would make pack building much easier..... but I agree with Al, if you get 18650's, get one's with tabs soldered.


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## icec0o1 (Sep 3, 2009)

dougingraham said:


> You use what you know. They might still use them even if there was something better. At the moment it looks like the complete package is still superior in wh/kg to other solutions. However it requires a large pack to get the performance they wanted for the roadster. The side effect of that large pack was decent range. You can build a lot smaller pack that would provide the voltage and current used in the roadster with Headway's or A123 20AH pouches. And smaller still using the Haiyin cells. You could replace the Roadster pack with a 99S2P pack of the Haiyin cells and have a pack where the cells weigh something near 33.66kg (74 lbs). With all the interconnects and box to hold it together it would probably end up at 42kg (92 lbs). This would be a savings of 408 kg (897 lbs) although at a considerable reduction in range (56kwh down to 4.3kwh). I would estimate the range would be reduced to around 17 miles. But I bet the 0-60 time would go down considerably as would the 1/4 mile time.


Speed was always of secondary concern to Tesla. And if it's your primary (17 mile car is unusable), you might as well go with LiPoly 45C cells. 

If you look at the 9000 or so reservations for the Model S, 60-70% of them are for the 300 mile range model, even though it's $20k more. 



frodus said:


> These Panasonics are far from the most dense and powerful battery.


Which batteries are more energy dense? Maybe I missed something.

P.S. 
I'm not arguing for the OP to build his pack from these. They could potentially be unsafe if you don't know what you're doing (as can any battery) and they are more difficult to make into a pack. I just didn't like that analogy which compared Tesla to companies like GM or Chrysler, forever stuck in the past. If a more dense battery came about, they would throw away the 18650's faster than you could say wh/kg. Elon didn't replace NASA by getting stuck with economies of scale.


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## frodus (Apr 12, 2008)

Can we get back to the OP's question


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## dougingraham (Jul 26, 2011)

icec0o1 said:


> Which batteries are more energy dense? Maybe I missed something.


I would like to know also. I show the 3.4AH Panasonics as 266wh/kg and 691wh/liter. The follow up product which is supposed to have 4ah has a slightly lower voltage and an increased weight and calculates out to 252wh/kg and a staggering 768wh/liter. I don't see anything else even close to these. The closest cell I can find is a Dow/Kokam SLPB125255255H which is a 75A pouch cell and has a 160wh/kg and 346wh/liter. I think this is the cell John Wayland is using in his Silver Streak project.

Note: The wh/liter number is a little high on cylindrical cells because there is lots of wasted space between them when you start assembling packs. I should probably change the calculation on my spreadsheet to account for this.


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## frodus (Apr 12, 2008)

icec0o1 said:


> P.S.
> I'm not arguing for the OP to build his pack from these. They could potentially be unsafe if you don't know what you're doing (as can any battery) and they are more difficult to make into a pack. I just didn't like that analogy which compared Tesla to companies like GM or Chrysler, forever stuck in the past. If a more dense battery came about, they would throw away the 18650's faster than you could say wh/kg. Elon didn't replace NASA by getting stuck with economies of scale.


You really read it out of context....no one said that. It could have been compared to ANY company and their previous packs. I mean Zero used Molicel batteries, now what do they use? Nano-tech lipo.

What he was saying is that Tesla ORIGINALLY (as in 5,6,7 years ago) designed their packs with 6500 18650 cells in a pack, because it was there and viable and available, they didn't design it around what "could" be.

But now, there are many other options available to not just manufacturers, but also us enthusiasts. So just because Tesla built a pack of 18650's, doesn't mean it's the best thing to do. Other batteries that would be just fine for a vehicle like this, exist, where they didn't before.

It wasn't a NOW analogy, it was a "past" compared to "present" analogy.


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## icec0o1 (Sep 3, 2009)

I think all of us would recommend for him not to use them, especially the smaller 14500 ones. So whether he uses the CALB cells or the 20AH A123 ones depends on his ability and options to make a pack out of them. (And whether he can still buy them for ~$20 a cell)


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## frodus (Apr 12, 2008)

Exactly. All boils down to ability and time to put a pack of lots of tiny cells, and where the point of diminishing returns occurs.


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## DJBecker (Nov 3, 2010)

icec0o1 said:


> There is no more current technology than the Panasonic 3.4Ah 18650. Are you really arguing that if there was a better techonology/battery out there, Tesla wouldn't use it?


Telsa is on a tightrope. They don't have a lot of freedom to redesign right now.

They have a giant factory with their name in huge letters on the side, paid with federal stimulus money. It is located on I880 just a few minutes from the giant Solyndra factories that front I880. The Solyndra that famously closed with no warning, losing over a half billion of federal investment.

They stopped building roadsters quite a while ago, late spring or early summer 2011 (depending on how. Their focus is getting the new sedan ready for factory production, expected in May. That's a scary gap in having something to sell, and a huge risk. They aren't going to multiply that risk by changing any part of the design that doesn't absolutely need to change.


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## tomofreno (Mar 3, 2009)

DJBecker said:


> Telsa is on a tightrope. They don't have a lot of freedom to redesign right now.
> 
> They have a giant factory with their name in huge letters on the side, paid with federal stimulus money...


 They only bought part of the old NUMMI plant. Most is still owned by Toyota.


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## DJBecker (Nov 3, 2010)

tomofreno said:


> They only bought part of the old NUMMI plant. Most is still owned by Toyota.


That's a minor detail of the financing. Most commercial real estate has a complicated own/lease/shell-corp structure. No doubt they got an advantageous deal on a freshly empty factory that had no other potential users. Telsa has their name in giant letters on the building, and they are the only company using it. 

It doesn't change their situation. They have to get into production, swim or drown. They don't have the redesign flexibility that they might have had as a smaller company with lower profile and overhead.


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