Whole Laptop batteries transformed to ebike battery?

KennyS · Oct 19, 2016

I went to purchase some cheap laptop batteries on ebay to add to my collection to build an ebike battery with. I found a bunch for 4.99 each and bought all the last they had, just expecting mediocre around 1700 to say 2000mah 18650 china cheepo cells. I got 8/6cell units and when I go back to take a look, they are all going for $22 or so each, and I see they are not just Lenova cheap replacements, but OEM's. I could be mistaken but judging by the price difference, it appears the guy mistakenly put them up for 4.99 and they might be all quality cells. He did ship them and I will know more once I get them.

My point is I was going to just scavenge the batts and build a separate pack but if these are the quality I think, is it possible to leave them in their shells, wire them together somehow to equal something close to 48v? I could maybe add or subtract units if need be. Again, there are 8 units @11.1v each. I have never built one of these batteries and not only might this be an easier/cheaper way for me, but I'd just be interested in trying it this way.

There are a few if's involved of course, and one would be, do laptop batteries have a built in manager to keep them balanced? And is it possible to wire them all together, and charge them with a 48v charger of say 5 amps or so for that battery type, and charge them all at once? Or would I have to charge them separately? also could I get 18ahr out of the total 48 batteries and if not, how many? I'm terrible at math already and especially for this and again, I can add more to the 8 maybe..

Just trying to get a rough idea of if this is possible, and I think that's all I need to ask, but if you can think of any other problems that might be a deal breaker or that I need to get past, please let me know. thanks.

Lexel · Oct 19, 2016

You need a special balance charger to charge the battery packs.

The balance charger in the Laptop is usually not in the battery pack.
The battery has probably a PCB build in but get the battery working with its electronics is most likely not possible.

5A charging current might be too high depending which cells you got.

for building a battery pack you have to measure the cells and match em up
for example you have 3x6 cells from three laptop packs with 11.1V
first with 1800mAh x2 second with 2000mAh x2 and the last with 2200mAh x2

to get the maximum performance each 3.7V unit of the battery pack needs the same capacity
so you got 18 batteries if you want to build a 33.3V battery with 9x2 cells you have to match each for 4000mAh
So first 3 are 2000x2 and the other 6 1800+2200, overall is 4000mAh

the mAh of the whole battery is equal to the lowest 3.7V unit
so if you just put the 3 laptop batteries in row you end up with 3600mAh

Gauss163 · Oct 19, 2016

It is highly unlikely that you can reuse the laptop BMS - for various reasons. They are not designed for high-current apps such as ebikes. Nor are they designed to be assembled into larger packs. Further, they require special chargers that can speak the Smart Battery protocol.

Be aware that building large Li-ion battery packs (e.g. for ebikes) requires signficant expertise on Li-ion technology in order to design safe systems. Your questions seem to reveal that you have much to learn about such matters. Be very careful.

Overclocker · Oct 20, 2016

CPF is the wrong forum for this. try endless-sphere.com

gauss163 is right about the pack comm protocols. you don't really want to go there. that's why no one does what you're planning to do

i'm not going to go into the details but basically what you want to do is to crack open all those packs, perform a rigorous selection process to weed out the bad cells, then arrange the cells in a configuration of parallel groups that are wired together in series, in such a way that all your parallel groups are of the same capacity and internal resistance

but if you're lucky enough that ALL your cells have the same capacity and internal resistance then it becomes more straightforward

these were cells harvested from portable projector battery packs. all very healthy so it's just a matter of wiring them up in 17-series 6-parallel (17s6p config)

then you have to think about balancing and charging. i use this DC-DC boost module to "bulk" charge my packs:

you may also use a BMS battery management system but i'm not a fan of those things. i prefer to balance manually

do a ton of research before attempting any of this

Overclocker · Oct 20, 2016

here's a 13s4p pack i'm building now. brand-new sanyo GA cells. again no BMS. to be balanced via that 14-pin connector using that balancing device on the right

Dr. Mario · Oct 20, 2016

And I'd add that in order to design a battery pack with smart BMS, software programming experience is also a must. And, don't bother reusing the BMS board in the laptop, they could be encrypted - both in-situ communication (recent battery packs do that), and firmware flash / ID.

If you still want smart BMS, you'd be better off building one from scratch (ATMEL has a few application notes in how to use the microcontroller in a DIY BMS design), and test it on a scratch monkey (a few ultracapacitors) first. BMS design is an art to be followed and refined very strictly - there's very little room for mistakes. As in, don't try this at home, unless you have sufficient knowledge in electronics design. Lithium-ion batteries are dangerous when mishandled (although you knew that).

Lastly, since you have shown that you know very little, I'd recommend ditching BMS completely and use programmable balancing RC battery pack charger instead. Much safer that way.

Dr. Mario · Oct 21, 2016

And... Buy a RC battery alarm too, just in case.

Lexel · Oct 21, 2016

If he doesnt get a proper battery safety board for his battery pack its easy to kill the cells missing the alarm

it is possible to get a proper sized relay to cut off the battery pack
drive it with the voltage of the RC battery warner that normally let the alarm go off

all you need then is a good balance charger for the amount of cells in series there are ones like Imax B6 that are pretty common

Dr. Mario · Oct 21, 2016

That's correct, of course.

Overclocker · Oct 21, 2016

i've done the hobby charger route for a while and i'm telling you now that it's rather tedious to have to undo/redo all the connections every time you have to charge. these things usually do only 6-series. a typical "48v" ebike pack is 13-series. i'm basically done w/ those things

this charging system is so much easier to use. but also a lot more dangerous!

Gauss163 · Oct 21, 2016

Overclocker said:
i've done the hobby charger route for a while and i'm telling you now that it's rather tedious to have to undo/redo all the connections every time you have to charge. these things usually do only 6-series. a typical "48v" ebike pack is 13-series. i'm basically done w/ those things

this [generic CC / CV] charging system is so much easier to use. but also a lot more dangerous!

Yes, of course one can use general CC/CV buck regulators, but they lack balance charging capabilty. And there are RC / hobby chargers that go higher than 6S.

There are now nicer generic CC/CV chargers, e.g. the $35 RD DPS5015 50V/15A buck regulator discussed in this BLF thread on DIY bench power supplies. RD will be releasing a buck+boost version in the next couple weeks.

KennyS · Oct 22, 2016

CPF is the wrong forum for this. try endless-sphere.com

I don't know, y'all seem to be doing a pretty good job.

I have used ES a time or 2 and still may on this but with the knowledge I'm seeing here, might as well pick a few brains.

Thanks so much for all the replies/advice. Guess I'll can the idea of using the whole battery then, and move back building the pack. Even if it could be done, with my limited expertise on the subject, I'm really no the man to try it right now.;

I built my first two bikes over the last few months, both hybrids, a 3 wheel w/1000w front hub and Predator 6.5 HP, and a 2 wheel front hub and 49cc cheap ebay special (just finishing it up. The idea was to do without a car because I just don't have that much of a need for one so had to go with a trailer anyway to share between the bikes and that made it so I could use 4 heavy SLA batteries (nearly 50lbs between the 4) as I drag them behind me with the trailer. But of course I've been looking into the 18650 packs, if for no other reason I need to learn how to build them because after no having a project for years, I really enjoy this, and it is nice just to hop on our bikes and go...no trailer, and go far between charges.

So yeah, I'm rock dumb in this particular aspect of ebikes but do everything myself so will do what I must...research and what not to get through this. Up to now I'd purchased 4 or 5 laptop batteries and made out pretty well, and it's helped me a bit on figuring out what's going on. This is the first multiple battery pack buy I've made and though it's not the buy of the century I was hoping, looks good so far...I'm testing them now. I have 4 of the 8 Lt packs and the first had some leakage, and the next two I opened looked fine. No brand on them, but the first 4 tested great at all 2100 + and are marked as 2000mah. Specs very close or exactly the same as charging and discharging them, as well as beginning voltage readings.

I'll have some comments later after I've read and try to absorb all this info here, but for now a few questions. I've had this happen a few times..one in this first batch of these, when the battery wouldn't even register on the Lii-500, but when put it in the NC intelecharger, it recognizes it, charges a bit, and then shows up fine and seems to be fine when returned to the Lii-500 charger. What causes that? Why does it take the other charger to get the battery going?

Also one pack I bought way back, I think I paid $11 supposedly new, had one dead cell and the other 8...all 2500 Samsung that tested to take that actual capacity or more. How can I tell if this was a used battery pack where one cell went out, or if it was like that off the shelf and the good batteries are actually new? I just don't wan to put batteries with half the life or whatever used up in with new batteries. I charged and discharged them twice and they all came back up to the same capacity each time, of course meaning they aren't fast dying but still not sure if that tells me enough.

It looks like I'm close to ready to get serious about doing this but need to know roughly how many batteries I'll need for a minimum of 18ah pack? I'd prefer at least a 22ah or so but just need an idea of how many more batteries I need. I think I'm at just under 75 total now but still have to figure out how to and to test them. I see some helpful mention of that on this thread.

Just to get more of an idea on what's going on here...is there a schematic/blueprint or good tutorial somewhere somewhere that I can just copy step by step for this build, or does it not quite work that way? If not, a few comments on why would probably be helpful to me.

As for the safety aspect, I've run into problems with them, nothing major, but enough to where I understand the dangers involved.

Thanks again for all the great input.

18650 · Oct 22, 2016

KennyS said:
CPF is the wrong forum for this. try endless-sphere.com

I don't know, y'all seem to be doing a pretty good job. I have used ES a time or 2 and still may on this but with the knowledge I'm seeing here, might as well pick a few brains.

Thanks so much for all the replies/advice. Guess I'll can the idea of using the whole battery then, and move back building the pack. Even if it could be done, with my limited expertise on the subject, I'm really no the man to try it right now.;

I built my first two bikes over the last few months, both hybrids, a 3 wheel w/1000w front hub and Predator 6.5 HP, and a 2 wheel front hub and 49cc cheap ebay special (just finishing it up. The idea was to do without a car because I just don't have that much of a need for one so had to go with a trailer anyway to share between the bikes and that made it so I could use 4 heavy SLA batteries (nearly 50lbs between the 4) as I drag them behind me with the trailer. But of course I've been looking into the 18650 packs, if for no other reason I need to learn how to build them because after no having a project for years, I really enjoy this, and it is nice just to hop on our bikes and go...no trailer, and go far between charges.

So yeah, I'm rock dumb in this particular aspect of ebikes but do everything myself so will do what I must...research and what not to get through this. Up to now I'd purchased 4 or 5 laptop batteries and made out pretty well, and it's helped me a bit on figuring out what's going on. This is the first multiple battery pack buy I've made and though it's not the buy of the century I was hoping, looks good so far...I'm testing them now. I have 4 of the 8 Lt packs and the first had some leakage, and the next two I opened looked fine. No brand on them, but the first 4 tested great at all 2100 + and are marked as 2000mah. Specs very close or exactly the same as charging and discharging them, as well as beginning voltage readings.

I'll have some comments later after I've read and try to absorb all this info here, but for now a few questions. I've had this happen a few times..one in this first batch of these, when the battery wouldn't even register on the Lii-500, but when put it in the NC intelecharger, it recognizes it, charges a bit, and then shows up fine and seems to be fine when returned to the Lii-500 charger. What causes that? Why does it take the other charger to get the battery going?

Also one pack I bought way back, I think I paid $11 supposedly new, had one dead cell and the other 8...all 2500 Samsung that tested to take that actual capacity or more. How can I tell if this was a used battery pack where one cell went out, or if it was like that off the shelf and the good batteries are actually new? I just don't wan to put batteries with half the life or whatever used up in with new batteries. I charged and discharged them twice and they all came back up to the same capacity each time, of course meaning they aren't fast dying but still not sure if that tells me enough.

It looks like I'm close to ready to get serious about doing this but need to know roughly how many batteries I'll need for a minimum of 18ah pack? I'd prefer at least a 22ah or so but just need an idea of how many more batteries I need. I think I'm at just under 75 total now but still have to figure out how to and to test them. I see some helpful mention of that on this thread.

Just to get more of an idea on what's going on here...is there a schematic/blueprint or good tutorial somewhere somewhere that I can just copy step by step for this build, or does it not quite work that way? If not, a few comments on why would probably be helpful to me.

As for the safety aspect, I've run into problems with them, nothing major, but enough to where I understand the dangers involved.

Thanks again for all the great input.

One of the first responses suggested laptop pulls aren't the appropriate cell to be used in your application.

Overclocker · Oct 22, 2016

Gauss163 said:
Yes, of course one can use general CC/CV buck regulators, but they lack balance charging capabilty. And there are RC / hobby chargers that go higher than 6S.

There are now nicer generic CC/CV chargers, e.g. the $35 RD DPS5015 50V/15A buck regulator discussed in this BLF thread on DIY bench power supplies. RD will be releasing a buck+boost version in the next couple weeks.

yeah i've seen those before. too bad there are no higher voltage versions. my 13s pack is 54.6v. while the 17s is 71.4v

a boost module allows you to buy an off-the-shelf power supply like meanwells in the common voltages like 36v or 48v.

you don't have to balance charge everytime. in fact i could go for months without balancing. the manufacturing processes for these quality 18650's are pretty consistent so the cells are all pretty much identical, so if you build the pack right it doesn't get unbalanced

Gauss163 · Oct 22, 2016

Overclocker said:
you don't have to balance charge everytime. in fact i could go for months without balancing. the manufacturing processes for these quality 18650's are pretty consistent so the cells are all pretty much identical, so if you build the pack right it doesn't get unbalanced

It will eventually get unbalanced. Just how frequently it is wise to balance will depend on many factors. For example, cells in the pack that are closer to heat sources will age differently than those that are in cooler locations. Further cells may not be from the same batch so may have manufactruing variances that cause divergence over time. And the longer you put off balancing, the more wear and tear you put on the cells that are at extreme voltages, which gradually causes them to have different capacity, IR, etc, making it more difficult to keep them balanced. Only empirical testing can tell for sure what will work best in any given situation.

Dr. Mario · Oct 22, 2016

It will go unbalanced, due to minute variation in the "jelly roll" cell sandwich themselves. No cell is perfect, just like us.

So, it's wise to balance them every time you charge the battery pack if you beat the pack up (*beyond 5 Amps per parallel strings = 1 cell x 5 A) as they can be unpredictable under load.

* Of course, the effect varies depending on maximum current capability of the particular batteries used herein, and effect may not be immediately obvious. So, check your battery pack with digital multimeter just to be absolutely sure.

Lexel · Oct 22, 2016

You could look for a dead Bike battery where the Balance charger is ok
and just give it a load of fresh cells

found this here.
http://www.ebay.de/itm/14S-48V-Lith...hash=item33bff9a05d:m:mXJcv6WWEGQ-qOeNUcxNp9w

KennyS · Oct 22, 2016

18650 said:
One of the first responses suggested laptop pulls aren't the appropriate cell to be used in your application.[/

That considered, and the fact I've already accumulated around 75 18650's from LT batteries, what would you suggest I do?

KennyS · Oct 22, 2016

Overclocker said:
yeah i've seen those before. too bad there are no higher voltage versions. my 13s pack is 54.6v. while the 17s is 71.4v

a boost module allows you to buy an off-the-shelf power supply like meanwells in the common voltages like 36v or 48v.

you don't have to balance charge everytime. in fact i could go for months without balancing. the manufacturing processes for these quality 18650's are pretty consistent so the cells are all pretty much identical, so if you build the pack right it doesn't get unbalanced

Interesting.

With the 48 of the same brand (whatever the brand is?) I'm testing now, all seems very consistent. Only a pack with Samsung were as consistent as these, so with the right batteries, that would make perfect sense.

What constitutes unbalanced? Or how close should the battery to battery specs be?

KennyS · Oct 22, 2016

Dr. Mario said:
* Of course, the effect varies depending on maximum current capability of the particular batteries used herein, and effect may not be immediately obvious. So, check your battery pack with digital multimeter just to be absolutely sure.

A periodic check of individual batteries in the pack is advisable?

Whole Laptop batteries transformed to ebike battery?

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