Old laptop cells, ebike battery build

mnplus1556

10 W
Joined
Sep 6, 2010
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69
Location
Hoffman Estates, Illinois
hello. i have sla batteries right now and they are starting to crap out. i've filled the batteries with water multiple times but they just don't get the job done that great anymore to get me to school and back. about a 7 mile trip. anyone know of anyway i can use these old laptop cells to build me up a 36 volt battery for my ebike? they are all 18650 and i'm assuming they are all different ah ratings. any kinda bms i can get to do this? please let me know of any ideas! thanks!

http://www.flickr.com/photos/17573019@N05/8227243557/in/photostream
 
I think you would need a crap load to get the power you need.
Most of new laptop batteries (assembled) are between 11v-20v and 3000mah to 6000mah.
They are meant to be discharged at 0.5c-1c.
Most ebike controller will be rated at 20A; so you would need like 20000mah of power if you want them to last couple ride.
It would be a 2 series 4 parrallel setup for +-24v controller depending of batteries used.
Also charging different type of cells is really a pain in the a**.

Bottom line; you need WAY more laptop batteries to get anywhere.
 
Look for postings from Drkangel. He has built tons of packs from those cells and has given detailed info on them. He generally posts on EZip threads.

Bob
 
I run laptop batteries on mine. Its a 15s24p pack, so 360 cells! You have to go with lots of parallel cells to get enough amps out.

It's a very time consuming process. You need to try and use cells that are as similar as possible in capacity. I charged all my cells and let them sit for a couple of weeks. Any that self discharged more than 0.1-0.2v were rejected.

I ended up building modular packs of 3s8p as most of my laptop batteries were 3s2p packs, so I stacked four on top of each other, parallelled each cell group together with nickel strips and added main power leads and balance leads. Big job!

It was worth it for me as the cells were all free, but I certainly wouldn't bother if I was buying them. Another consideration is weight. My pack is 15kg. It's not even that much overkill as I draw 40A out of it and I don't think it would cope with less parallel cells. As for the cells in your photo's well they might get you a couple of hundred metres up the road...once...

As for charging, I can charge each pack as a 3s pack on my lipo charger but rarely bother. Most of the time I bulk charge the whole pack with a mean well to 62v. It seems to stay pretty well balanced so that's good.
 
I built my first ebike battery using laptop 18650 cell.
It's a 12s6p pack (72 cells). Total weight is less 8 lbs. You can see the battery/bike performance here:
http://endless-sphere.com/forums/viewtopic.php?f=4&t=29356
That ebike is still running and now has over 1,000 miles on it.

Since then I have built many other ebikes and many other battery packs using 18650 Laptop (LiCo) cells. A 21s10p (210 cells, 22 lbs) pack is sufficient to push my dual 9C 2807 hub motors bike to 40mph (just for fun, I ride much slower). I tried a BMS once and hated it, so no BMS for me. My pack is balanced after each charge.

DrkAngel did a great job on instructions for building 18650 LiCo battery.
http://endless-sphere.com/forums/viewtopic.php?f=3&t=26383
Read that thread and post questions if you have any.

Have fun building your pack. It's time consuming but also rewarding.
 
That's a good result with your packs there, SamTexas. I built mine big as I didn't want to push the cells past 1C discharge, so 24p for me is around 48A (most of my cells are 2200mah). Hopefully the pack will last longer. They also don't sag too much which indicates that I'm not overly stressing them. I did a 30km ride recently and used less than a quarter of my capacity....
 
Spicerack said:
That's a good result with your packs there, SamTexas. I built mine big as I didn't want to push the cells past 1C discharge,
Thanks. If you look at the performance numbers I posted, you'll see that I average below 0.5C whether I pedal or not.
 
Aaah, I see. I have a monster of a bike compared to you- very heavy downhiller and heavy rider- but I also want to push the pack a little when I have a play. I've got a 9C 8x8 which I want to try out and see what she can do at 20S or more... I have a box full of deboxed laptop cells so just need to make 5S booster pack for playtime. Must say I'm quite impressed with my laptop cells- a year in and they're going well.
 
I made a pack 2s23p for increasing the voltage and hence the maximum speed of my 48V scooter.
I feel a little embarrased because the pack is not nicelyassembled. BUT it worked for about one year. The initial capacity was about 25 Ah. The last time I used it, the capacity was reduced to 16 Ah. The scooter draws about 40A, full throttle.

laptop2s23p_(800_x_600).jpg

laptop2s23pb_(800_x_600).jpg
 
It takes a steady hand and soldering skills for sure.

I like laptop cell packs for extender packs and A123 26650 cells for the main pack.

That way the laptop cell pack can be smaller like 10s 4p.

Longer trip ? Hook up 2 extender packs.

I don't like larger packs because I like to use matched cells and it was hard to find a large number of used cells that match.

The better they are matched the easier they are to charge.

Do it and join the recycled laptop cell ebike battery pack builders club ! :)
 
I have been making batteries from old laptop batteries from last 3 years , and it works , but as mentioned before , 0.5C should be max for discharge as they have already been EOL cells. So good discharge should be 1A continuous. For example for 36v 20A load, 10S20p battery will be good enough. But make sure to measure internal resistance, in my experience each parallel group should have similar capacity, and every cell should have less than 60mOhm IR, I use YR1035 meter for IR. voltage drop test is also very important.
In short - if you have a lot of free time , then use old cells.
As mentioned earlier. These old cells can also be used as range extender when paralleled with high drain new cell smaller pack. Or can be used as load divider. For example new high drain pack gives you 20A continuous but you need 25-30A , just add old cell battery in parallel and it will cover extra load.
To handle peak load at starting bike. Super capacitor bank is great but I haven’t tried it yet.
I have made, used and sold a lot of batteries , (yes I have sold batteries made with old cells 😂). Batteries making from old cells has it’s own fun and addiction.

For more knowledge and expertise, join Facebook groups. My favorite are:
DIY powerwalls
Jehu’s diy powerwalls
DIY battery

And good luck
 
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