# 250+ used Li-ion battery cells - Ebike pack or EV supplement?



## Watts-the-matter (Jul 18, 2009)

Hello, I'm new to EV building and the EV community. I was hoping to get some feedback on possible uses for a very large cache of lithium ion cells salvaged from used laptop batteries. The batteries in question were used for 3 years, but in reality they were lightly cycled, plugged in about 90% of the time and cycled occasionally. They were 6 cell packs, 11.1 volts, 53 Watt-hours. Each cell is a standard 18650, 3.7 volts and probably 2.2+ amp-hours.

I was considering buying a AC/DC Bantam BC8 charger to charge/discharge and balance all the cells, and get a computer readout to sort them by capacity. Does anybody know of a similar charger that would do more than 8 cells? Alternatively, if (safely) I link all the batteries up in a huge pack, how might I go about (safely) charging it?

My original purpose for the packs was to use them in an Ebike, but with the seemingly unending supply of batteries (I may be getting 50 more packs shortly) would it be possible to stash the lithium cells in the smaller gaps of a car for extra power in my upcoming EV build?

I would greatly appreciate any feedback you battery experts could give me.

Thanks in advance,
-Watts


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## rillip3 (Jun 19, 2009)

The Tesla uses thousands of batteries stuffed between the car and the exterior. It is possible, but the cabling will be a royal PITA when you first set it up with so many terminals all over the place.

My other concern is that you're saying they're laptop batteries. This most likely means Lithium Cobalt, which is the same kind of battery that Sony and Hitatchi had huge recalls on, because they would short circuit and catch fire under certain usages. In effect, because of the construction of the battery, sometimes the cell can "run away," essentially a chain reaction inside the battery where all control is lost and the battery starts to put out as fast as possible, in turn over heating and catching fire. I'm not sure if the conditions are well enough understood that I would really feel safe putting a high voltage pack together with these.

I sometimes see people critique all lithium ion batteries in this way, but everything I've seen indicates new batteries like lithium polymer and lithium iron phosphate batteries do not have this issue. I'm not saying you can't or shouldn't do it. You definitely can do it. But I'd want to research that issue a lot more than what I'm providing here so you can be sure the vehicle will be safe.


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## Watts-the-matter (Jul 18, 2009)

Thanks for the word of caution. I've been trying to baby these cells as much as possible, being used and inherently unsafe is really making me think this through carefully. I just can't stop thinking that someone's gonna knock my boxtop filled with nice neat rows of batteries on the floor and somehow light the house on fire. Or maybe someone will spill a glass of water on it...

Ideally I'd try to rig up a holder that would hook up 8 cells with drops for a balancer in the appropriate spots if I can't find a better charger, and then try to run a hybrid pack with some good old fashioned lead-acids. I haven't a clue how to lump-charge them, though.

EDIT: The batteries are Dells, probably made in China.


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## Madmac (Mar 14, 2008)

If you intend to use the packs as they are one thing to consider is the internal protection electronics. Should over current, temperature or excess voltage during charging the protection circuit will disconnect that pack. The electronics to do this are only designed to switch the pack voltage not the voltage from multiple packs in series. Using the packs in this way is likely to let lots of black smoke out from the protection PCB.

If you remove the cells from the packs and wire into series / parallel blocks to build a bigger battery pack then you will need to drive an AC system. These batteries will not supply high current surges. Some of the lower cost manufacturers spec max at 2C while the better ones are 4C. With careful choice of pack capacity they can fully power an AC system

Usually these cells are powering portable PC's where the manufacturer wants long on time so they are cycled to the maximum. By limiting the range of charge, ie terminate at 4 volts instead of 4.2 and cutting off at a higher voltage 3.2 in stead of 2.6 then number of cycles will increase hugely.

The advantage of using 18650's is that they are the highest energy density at the moment, around double that of Lifo cells. In the thread

http://www.diyelectriccar.com/forums/showthread.php/which-better-31527.html 

you can see the difference between a block of 18650's and a cardboard mock up of a Lifo battery of the same amp hour capacity.

Modern cells are proving to be quite safe in terms of internal shorts. If there is a fire (most cause of EV fires are cable faults) Lifo will burn as well as Li-ion. If you use them design the pack to be safe.


madmac


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## Watts-the-matter (Jul 18, 2009)

I've actually already stripped the 30-some packs I have so far (my dad want's some good quality thermistors and used 3 year old packs have low resale value) but I won't get the other "fifty packs in the storage room" until Monday. From preliminary testing I've found that almost all the cells are quite functional, but they're reading at 4.2 v. I get the feeling that even if I get another 50 packs, (I'm thinking 20's more likely) and 90% yield out of the packs' cells, AND I balance them all, they're either going to discharge unevenly and/or shallow. I keep hearing about the trick of freezer, warm up, power cycle, freezer, warm up, power cycle to fix shallow discharges, is this black magic or just a short term fix?

My dad's coworker has a spot welder, I think that's probably the safest way for someone to make me packs after I sort them with the Bantam/better charger. I was thinking of keeping the old tabs but a few were slicing through the protective sleeve and threatening to cause a short.

If I have to buy more cells to get my desired 40 mile range on a Metro/S10/Porche, would they play nice with the old ones or totally skew my readings on charge/discharge?

What is the cell count in your pack madmac? I don't really understand how you're pairing them up to get 355 V...

Lastly, how do I charge all of my cell packs, and should I plan for the spot welder to add in leads for more reliable monitoring, as I am using used cells?


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## Madmac (Mar 14, 2008)

The pack is organised as 8 boxes each with a full BMS linked by a serial data bus and a few other control lines. Inside each box are 12 blocks of 52 parallel cells (like the single one in the photo).

The 52 cells will be 2.4 AHr giving a total of 124.8 AHr. Each box is 12 x 3.6 volts = 43.2 volts. With 8 boxes the total pack voltage is 12 x 43.2 = 345 volts nominal. Capacity is then 129.6 x 345 = 43 KWHrs

If I were using used cells I would split them up so that they ran at full required pack voltage. If I then needed more capacity I would run a set of new batteries in parallel to the used ones. At a later point the old used ones could be swapped out and replaced by more new ones.

Spot welding is the way to go on assembling a pack. You may need to put in some work to clean the existing tabs off and provide a surface suitable to spot weld to. When you design the metall contact assembly to link the batteries together you need to make sure it will not interfere with the operation of the cell vent valve and also arrange for it to act as a fuse should a single cell start to sink power.

When you build the battery pack the BMS will need to monitor each parallel block of cells to make sure they stay within spec. For this reason each parallel group of old and new cells will need to be linked together. Remember that the cells need to be thermally managed. Under max current draw about 2KW will be dissapated, although not for very long.

Not sure what commercial chargers are available other than Brusa that will handle this voltage pack. I plan on using the motor inverter in reverse.

There are a few more details in posts 236 / 237

http://www.diyelectriccar.com/forums/showthread.php/diy-ac-bldc-controller-28541p24.html

madmac


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## Watts-the-matter (Jul 18, 2009)

Hmm 5000 cells seems a bit out of my league, considering I don't even have 500 yet. I would buy a few hundred more if I could add them with the used comfortably and get the desired range. Otherwise I'll stick to cheap lead acids. I just want a commuter that I could get to school and back and wow some passengers as needed.

What is your expected range with the 5000 cells, and where might I be able to buy some without using my entire budget?


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## Madmac (Mar 14, 2008)

You could try and track down recycling companies. Outfits like Dell must have an arrangement to collect and recycle batteries, the same as PC stores who arrange to dispose of used packs. You might be able to do an arrangement to grab packs and remove the good cells. One advantage of packs out of portable PC's is that the safety circuit will kill the pack as soon as any cell goes below the cutoff voltage. Most will not recover when connected to a charger. This means that most of the cells can be OK.


My aim is a range of 120 miles. The pack capacity divided by this gives approx 350watt hours to do a mile. My simulations show I should get this at 60 MPH. If I take the worst case figures this drops to around 50MPH. Hopefully it will be more towards the best case figures and be higher than 60 MPH but until built and tested who knows.

madmac


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## Watts-the-matter (Jul 18, 2009)

Hmm so even if I get said "50 packs" I still won't get more than 20 miles... unless I hypermile.

Guess I'm gonna have to scrounge and bargain hunt if I even want to consider using lithium...

Are you counting regen breaking in that estimate or not?


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## Watts-the-matter (Jul 18, 2009)

Good news! I got another 44 packs (total of 87) of lightly used 6 cell packs!
Bad news! 4500 watt hours (very optimistic) isn't gonna cut it for an EV, I don't want to spend another grand for the most powerful and difficult cells for my first EV, and I'm not gonna fit 450-475 cells on a bike XD.

I may just run em through a nice Bantam charger/balancer and sell/trade the good cells on the cheap to anyone who's interested. All proceeds go toward my EV conversion!!


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## Madmac (Mar 14, 2008)

Those figures do not take regen into account. The range calculation is for motorway driving which is not stop and go.


Best of luck finding more cells, with the number made each year it must be possible to find a source of partly used ones.

The price of new cells jumped about 18 months ago due to shortages but they have not come back down yet.... for what ever reason.

madmac


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## Watts-the-matter (Jul 18, 2009)

What parts did you rig up for a BMS? Is there any kind of mass-18650 holder or do you just spot weld them with strips and box them up?

I think I may just make a monster Ebike and sell the rest of my cells. Little cells seem way too tricky for my first build, but the thought of all my future projects using lead-acids makes me sad...


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## aeroscott (Jan 5, 2008)

Madmac said:


> If you intend to use the packs as they are one thing to consider is the internal protection electronics. Should over current, temperature or excess voltage during charging the protection circuit will disconnect that pack. The electronics to do this are only designed to switch the pack voltage not the voltage from multiple packs in series. Using the packs in this way is likely to let lots of black smoke out from the protection PCB.
> 
> If you remove the cells from the packs and wire into series / parallel blocks to build a bigger battery pack then you will need to drive an AC system. These batteries will not supply high current surges. Some of the lower cost manufacturers spec max at 2C while the better ones are 4C. With careful choice of pack capacity they can fully power an AC system
> 
> ...


 I'm wondering if the bms can be used to signal higher voltage components to bypass the offending stack


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