Reduce, Re-use and Recycle !

DeWalt, Makita, Ridgid, Milwaukee, only a few of the big name brands that now use Lithium cells !

Used battery packs, yeah, they can work !!...

Buying a brand new battery for your electric bike can be expensive, a quality 36v 10ah complete pack with built-in BMS and charger can run you 300 to 600$..

Some guys have built ebike packs using brand new power tool battery packs, this is certainly possible but not always the least expensive way to do it, however, if you can get " defective " packs for free, well, it starts to become an attractive option !!

WARNING WARNING

It will cost you some time and effort but if you have more time than money on your hands, Bonus !

You do need to understand the dangers and what to do and not to do while working with these things, batteries canot be turned off while you work on them, so being aware of the dangers involved is very important. Lithium cells pack alot of energy, even when almost discharged they can make things HOT in a hurry. Remove all jewelry ( metal rings for example ) work in a clean space free from metal parts, have an Exit plan in case of emergency, i have 2 fire extinguishers in my house for a reason !

WARNING WARNING

Ok, so now that we have " that " over with..

Going back a few years, just about all cordless power tools used Nicad, some went nimh for a while but all current generation quality cordless tools use lithium. Nicad has a proven track record, robust, reasonably safe, long lasting and all that but toxic..

If you have had the chance to use both NiCad and Li-Ion power tools, you know how much of a difference it makes, Lithium keeps it's charge while on standby, weighs alot less, much more usable capacity for a given size, no fade, and much more powerfull..

Below, notice the white recycle symbol, all power tool packs will have these, look for the " Li-Ion " mark, and if you see " Ni-Cd " like below you want to leave them there, resist the temptation to take them home, nicad is no good for ebike sized packs because you need more capacity than the typical 2.x Ah of a single string of cells.. Paralleling Nickel cells is a bad idea, ( Insert link to long version of why )

Most of them use " 18650 " cells that are commonly found in laptops, but with a chemical formula that allows for high rate discharge .... vs laptop cells that are formulated for high capacity with low discharge rates... Just like common AA or D cells, 18650 is a universal format and has been around for a long time..

There are 2 main cell sizes you will find in almost all lithium packs, most popular is the 18650, but Ridgid and DeWalt use 26650 on some of them.. Larger cells means more capacity and you need less of them to make a pack..

18650 cells = 18mm Wide x 65mm Long

26650 cells = 26mm Wide x 65mm Long

 

Getting your hands on these can be a challenge, most big box stores like Home Depot etc will not want to give them to you.. for " Legal/Safety " reasons.. however sometimes you can find them in a big rubbermaid bin at the service counter that people drop AA cells into for recycling, don't ask the clerks, most of them will refer you to their supervisor and he will not be interested in your projects unless you get really lucky... just take them..

Sometimes you can talk your way into a stash of these if you know authorized repair centres, or find them online via ebay or certain e-bike Discussion Forums *cough.. wink wink..

So, what do you need and how does this work ?

Let's say you get your hands on a dirty box of used and/or defective LITHIUM battery packs, first thing you need to do is sort them out.

These packs are being recycled for a reason, they don't work properly, either one or more cells are dead inside, or the electronics are shot, sometimes the casings are cracked from being dropped etc... The packs you want are the one's that have only a few cycles on them but have a failed single cell or it got discharged completely empty, left sitting for months and charger is refusing to recharge them..

- Completely Dead :

Using a volt meter set to DC Volts, probe the tabs of the pack that connect to the tool, if you get 0.0v or anything less than 3v, it's toast, don't even bother to waste your time trying, just put it back in the bin and return it to the recycle centre. I"ve tried to revive dead cells like this but it's generally hopeless, Lithium cells do not tolerate being left at 0v, they need to be kept at or above their LVC ( low voltage cutoff ).

I have had success reviving 0.0v cells that were very ver very slowly discharged below their LVC, but that had only been in this state for a few days, it can be dangerous to try and recharge cells like this as they get hot and can cause serious problems.... don't try it.. ( if you are that type of person, the pyrotechnic type, at least do it outside far away from your house or garage... )

Below, notice 4.8 mv ( notice the M before the V, ie : millivolt, ) this is 0.0048v ( 1v = 1000 mv )

----------------

- Possibly ok :

If you get 10v or more you likely have a few good cells in there...

Below, 3.119v , in a 5 cell pack ( 18v ), so there may be one good cell , or they are all ( 3.119 / 5 = 0.6v each ) so not much hope in a pack like this, if you have alot of packs to work with, put something like this asside for rainy days and experimentation ..

----------------

- Still good !

Most popular 18v tools have 5 series cells, completely discharged ( 2.5v + ) would be 12.5v, and fully charged ( 4.20v per cell ) 21v

Below, 8.0v from a 3 cell pack, so at least 2 good cells for sure, this is the good stuff !!!

-------------

Most of the battery packs come with " Security Screws " they are Torx with a dimple in the middle

They require security bits, you can order these online or find them at most automotive tool places like Princess Auto and Canadian Tire, etc.

You can also get them in allan key style, not as convenient, i prefer the bits on the left that you can fit in a drill for quick work of multiple packs.. easier on the fingers !

I like to arm myself with 2 drills, ( both of the mastercraft drills below used to have Nicad cells, i replaced the 6v one with 2 cells from a makita pack, and the 14.4v drill below is now an 18v 3ah makita cell powered tool !! )

The reaming bit is usefull for recessed screws that you canot reach with a hex bit..

And voila, now you can attack it with the regular bit ( not having to resort to the allen key style )

. otherwise it's a hack job... literally... I've tried hack saws and angle grinders etc but removing the screws properly is by far the best option, if the screw is full of crud hit them with compressed air to save your bits or you will wear them out quickly...

Once you split the cases, you have to yank the cells from the packs, and remove the circuits or BMS's.. I found wire cutters and a dremel tool with cutting disks come in handy for this job.

(* future place for video to show how this is done )

Using a volt meter, probe each cell and mark them, either X or Y, anything above 3.0v is good, anything below that is bad on all but DeWalt packs with 26650 cells ( 26mm x 65mm ) A123 cells that are LiFepo4 with a voltage range of 2.0v to 3.6v.

There are 2 basic voltage ranges to know, the majority of packs use Lithium Manganese or Lithium Cobalt = 3.0 to 4.2v

Dewalt 36v packs use Lithium Iron Phosphate = 2.0 to 3.6v

The dewalt 36v are no longer made as far as i know, they are still found in recycle centres but getting rare..

 

Do not remove the spot welded tabs from the cells, keep them on there, to seperate the cells just cut the tabs between the cells ( Carefully !!!.. ) with a dremel and cutting disks.

The tabs provide a good material for soldering, if you remove them you then have to solder directly to the cells and depending on the cell this is sometimes difficult and puts the heat directly to the terminals that you want to minimize as much as possible.

Spot welds, vs Soldering.

If you happen to have a battery tab spot welder on hand, this page is likely a waste of your time ( as you likely know all this already ) , and buying one for recycled cells is not worth the expense, some guys make their own with various cheap parts but this is over my skill level and involves components that can hurt you ( like.. very large capacitors.. )

A lenghty discussion about home made spot welders

So, since this is a " Use what you got " project, a soldering iron will get the job done if you do it right.

A while back i got myself a Hakko soldering station:

Prior to this i had a cheap 10$ radio shack 15/35 watt unit that was not up to the job, you need a powerfull enough iron to get the job done quickly, with cell tab clean and wiped down with solvent ( remove all finger prints and sticker residue before trying to solder anything.. ) you need to get the job done in under 3 to 5 seconds, if it's taking you longer than this your iron is not hot enough...

Above, notice the copper strip, i found " All Round " copper strap at canadian tire, nice thick stuff, almost too thick making it hard to solder ( soaks alot of heat from the iron.. ) but it works.. This is a 10S-2P pack ( 36v. 3ah )

See HERE ( dewalt 12v pack ) for another example of recycled cells at work..

-------------

Making a large capacity pack from these cells requires matching them up properly, do not mix cell brands together, and make strings of similar behaving cells to help keep the pack in ballance as much as possible..

What i do ( not the best, or the only way but it's how i've done it so far ) is fully charge the cells and let them sit overnight, then re-measure the resting voltages and group them up in matches..

For example, makita cells ( also called " Konion " cells made by Sony ), fully charged to 4.20v ( I use RC Chargers ) .. the good cells will retain their voltage to 4.17v + .. the bad or heavily worn one's will drift down to 4.16v or less, if any cell canot maintain 4.0v + overnight it's hopeless and should be recycled back to the bin..

Depending on the purpose of the pack, you need to use enough in parallel to supply the required amperage of your device or controller... each cell brand has varying specs, some are more capable than others.. the infamous " C " Rate.

When using large capacity cells, it's generally recommended to not parallel the cells at the cell level and use a BMS to monitor each individual cell in the pack, but when using smaller cells it's less expensive and easier to group X amount of cells in parallel first, then series them for the requried voltage...

All cells in a parallel group will be forced into having the same voltage all the time, so the weaker cells are helped by the stronger one's and it all works in harmony, but if you develop a bad cell ( with an internal short ) it can take the entire group along with it.... using recycled cells requires an attentive person and if you opt to not use a BMS with a pack like this you need to periodically check the pack for issues....

( This is not done, still working on it.. March 12 , 2011 ()

Back To Projects

HOME