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using little aa lithiums for geo metro? why not?

20K views 26 replies 11 participants last post by  DJBecker 
#1 ·
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
 
#4 ·
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.
 
#3 ·
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.
 
#5 · (Edited)
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.
 
#7 ·
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.
 
#8 · (Edited)
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".
 
#9 ·
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.
 
#11 ·
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.
 
#12 ·
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.
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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