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Only2Jakes
29 December 2010, 2106
Just a heads up!

Anyone looked into laptop batteries??
I'm seriously considering them.

I took apart two laptop batteries today. Look like some pretty good cells, all very balanced.
Am going to try them out tomorrow or sometime.

Pics sooon. I have 2 packs of 3s2p for 11.1v nominal.

Charging them up with a tiny little charger/power supply thing. :D

If discharge rates are alright I might look into some more second hand ones to make a small pack for the ebike. No BMS.
Just lvc and HVC.

Cheers

lugnut
29 December 2010, 2129
Anyone looked into laptop batteries?

Worked for Tesla. Using 6800 cells of the type used in laptops.

BaldBruce
29 December 2010, 2135
Except that the 18650 Li-ion batteries that dominate the laptop market are not that high in capacity and are also not optimised for high C rates. Worked in a manufacturing plant that made thousands of these. They then sorted them by capacity in 200mAH bins around the 2000mAH mark. Cheapo ones were less than 1800 and the most expensive were over 2400mAh. These are tested at C/6 or C/10 rates for capacity. Fast testing for extremes is at 1C. We even beat up a few at 6C to check for a grape trimmer aplication, but they failed very quickly. I abuse the heck out of a set at 4C in my RC Hummer. (and they won't last many cycles at that high a rate, but I don't run it that ofton anyway.) Sooo, just depends what kind of current you are designing for, but you will need a whole bunch in parrallel to get any voltage supported current.

Now, there are 18650 cells optimized for higher C rates being used in power tools out there, so they do exist. Capacity goes down slightly in those designs, but up to 5C can be done without too much design change.

Only2Jakes
30 December 2010, 0037
If I can get some cheap I might give them a go, just for a boost pack maybe, when battery runs low.
Or just for fun, or it can power lighting or something.
Here's the pics:
http://img17.imageshack.us/img17/6711/dscf8058l.jpg
http://img135.imageshack.us/img135/8043/dscf8059.jpg

Not sure what types they are. But they do have green ends?

Warren
30 December 2010, 0938
lugnut,

> Worked for Tesla. Using 6800 cells of the type used in laptops.

It will be interesting to see which, if any, strategy works for EV's in the new economy.

http://electric-vehicles-cars-bikes.blogspot.com/2010/12/tesla-says-electric-car-battery-plan.html

People will probably be using laptops, and cell phones until it starts raining frogs. Whether sufficient numbers will be able to afford to switch to EV's, and make any of the EV makers profitable, is the question.

Warren

chef
30 December 2010, 1515
Worked for Tesla. Using 6800 cells of the type used in laptops.Has that been confirmed? I mean, has anyone torn down a Tesla battery pack?

What I've heard from an industry insider is that Tesla's CEO wanted to use a bazllion small batteries scattered throughout the body. The engineering team realized it wasn't going to work with all those small cells and many left. Tesla had to start over with a new team which eventually came up with the unified large pack that sits behind the seats. That debacle delayed the Roadster years. Mind you, this is 2nd-hand info so take it for what it's worth. Maybe one day we'll get an accurate historical accounting of what happened.

DaveAK
30 December 2010, 1550
Has that been confirmed? I mean, has anyone torn down a Tesla battery pack?

What I've heard from an industry insider is that Tesla's CEO wanted to use a bazllion small batteries scattered throughout the body. The engineering team realized it wasn't going to work with all those small cells and many left. Tesla had to start over with a new team which eventually came up with the unified large pack that sits behind the seats. That debacle delayed the Roadster years. Mind you, this is 2nd-hand info so take it for what it's worth. Maybe one day we'll get an accurate historical accounting of what happened.
Never heard that story but I do think batteries lend themselves to being distributed to some extent. I always envisioned a GT40 like setup with the batteries in the sills, or whatever it is you Americans call them. In an EV you could also put a pack in the transmission tunnel.

chef
30 December 2010, 1609
Did some more digging and found discussion thread about the Roadster's battery pack. Looks like it really does use gobs of 6831 cells. But what really caught my eye was them trying to figure out how Tesla is getting the capacity and discharge rates out of commodity 6831 cells. One guy speculates they may be using a mixed chemistry strategy, mixing strings of high-C and strings of high capacity cells.

http://www.teslamotorsclub.com/showthread.php/102-Roadster-battery-pack-specs?p=577&viewfull=1#post577

DaveAK
30 December 2010, 1620
Did some more digging and found discussion thread about the Roadster's battery pack. Looks like it really does use gobs of 6831 cells. But what really caught my eye was them trying to figure out how Tesla is getting the capacity and discharge rates out of commodity 6831 cells. One guy speculates they may be using a mixed chemistry strategy, mixing strings of high-C and strings of high capacity cells.

http://www.teslamotorsclub.com/showthread.php/102-Roadster-battery-pack-specs?p=577&viewfull=1#post577
Hey! I know a guy who suggested doing that on another thread. :D I think 6831 is the quantity of cells though, not the type. At least I've always heard it quoted that way.

chef
30 December 2010, 1831
you're right *slaps forehead* meant to write 18650. Really :)

BaldBruce
30 December 2010, 2209
Haven't taken a battery pack apart, but it really is ~6800 laptop cells. 375 nominal, so there are roughly 100s68p in the 57kWh pack. Means they are asking each cell to provide less than 3C if my math is correct:D
See link to PDF if you want to read a report from TESLA on their pack configuration for the roadster. http://webarchive.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf