Beginners Guide to Processing 18650 Cells | Cell Database


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ebike battery lithium alternatives.
#1
So I just moved to college.

Great! 

But I would like to bring my ebike. The problem is its a 1KWh battery built from old laptop cells. I currently live in an apartment. Lithium-ion is great and all when you have a garage to charge your battery. It's not so great when you are in college and if the battery explodes, I could be liable for literally millions of dollars of the apartment complex burns to the ground.

I don't need much capacity. 10AH should do just fine. It just needs to get me around campus. 

current battery specs:

42v 22.4AH. (12S10P)

All made from 96 samsung 28A cells. They get hot under load but I really don't care. It was about $20 to build. It would be dirt cheap to replace.

Bike draws 20-24 amps under full throttle.

Alternatives:

lifepo4 cells: These are very expensive. I can't go down to my local scrapyard and buy old lifepo4 cells by the pound, I have to buy them online. 

NIMH: An older but still very safe battery chemistry. Not nearly as dense as li-ion but it is an option.

Lead-acid: old chemistry, cheap new too, can put out lots of amps. But they sure don't last long. Very safe.

Any suggestions?
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#2
Just build some packs into some ammo boxes (repaint them, of course) and make sure everything is sealed. Then, if you want extra safety while charging, put them inside yet another type of metal box and seal them in while they charge.

But, if you wanted to change chemistry, I'd go with LiFePo4's if possible. They have almost as much capacity for the size and easy to adapt anything you already have over to. LA's are heavy and I think it may not be worth it. Unless your ride is so short you could get away with a large capacity lawn tractor battery (or even a motorcycle battery; though a little pricey for their size). You'd want to go with sealed LA's as i'm sure your bike won't stay in the up-right position 100% of the time. You don't need acid dripping out onto the floor
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#3
Lithium cells usually don't explode just so and, of course, you never charge them unattended in your room. If you use the right charger for the job and have that pack built to a certain standard then I would consider this very safe. Almost as safe as charging your laptop battery.

However, if you really want to change the chemistry, then it really depends. Do you really have a 42V system on your bike or is it a 36V system and you are just pushing it a bit and a 36V battery would be sufficient?

Lead Acid doesn't seem to be practical in this case. 3x12V or 7x6V in series would do the job, but that seems to be a bit bulky given their sizes and weight for a certain capacity. I have seen single cell Lead Acid, but they don't come in small capacity either, so you can't go straight for 18S or 21S.
NiMh would be a thing with a 30S or 35S setup, but appropriate NiMh cells in decent industrial quality are not really easy to source around where I live. If you can get them cheap, then yeah, would do the job. Can easily be assembled into a convenient shape, unlike Lead Acid.
LiFePo4: Totally yes, but as you said, easily the most expensive option.
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#4
(09-05-2017, 12:39 AM)Korishan Wrote: Just build some packs into some ammo boxes (repaint them, of course) and make sure everything is sealed. Then, if you want extra safety while charging, put them inside yet another type of metal box and seal them in while they charge.

But, if you wanted to change chemistry, I'd go with LiFePo4's if possible. They have almost as much capacity for the size and easy to adapt anything you already have over to. LA's are heavy and I think it may not be worth it. Unless your ride is so short you could get away with a large capacity lawn tractor battery (or even a motorcycle battery; though a little pricey for their size). You'd want to go with sealed LA's as i'm sure your bike won't stay in the up-right position 100% of the time. You don't need acid dripping out onto the floor

To cover the reason why I want to switch chemistry yeah, THIS is why:

https://endless-sphere.com/forums/viewto...=1&t=87975

This dude burned his house down charging what were perfectly good branded cells with a good charger. BMS and everything in his garage. The battery went up in flames and took the whole house with it. I just don't want to take that risk. 

Ammo box + another metal box + fire extinguisher nearby MIGHT work. But the only place to charge the battery is indoors.

also yes, my 42v system is really just a 36v system i'm running hard.
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#5
I think this says a lot here, at least he recognized what he did and was able to post it so others don't repeat his mistake.

Quote:perhaps I had the bike parked in a shitty place. Real shitty. In the corner of the very overstuffed garage, where on a peg above the bike, hangs, oh,, about 4 or 5 nylon coats. Couple wind shells, one ski parka, and my ballistic nylon armored motorcycle riding jacket. Hmm,,, I suppose I coulda just hung a gas soaked towel over the bike. Then, the cherry on top,, almost touching the bike, my Yamaha 400 cc scooter. Which I had just filled with 3.5 gallons of gas the day before. Soooo,, dumass,,, lets charge the battery within inches of three gallons of gasoline, and enough plastic to burn the house down

What I would do in this type of situation where it is possible to leave it and worry that something 'might' happen, is put the charger on a timer. Set it for 1 hour and just keep resetting it. Not much can happen in 1 hour time as you probably won't be resetting it right at the second. So the cell can have time to cool down and slowly discharge.
My guess is that the BMS failed. I didn't read the whole article, so I don't know what BMS he is using. However, it is clear that it definitely didn't have enough safety bells built into it. It probably only had "overcharge", and not temperature and maybe even current issues.

On the next page:
Quote:No idea what bms was in it,, except it surely was the cheapest they could source
There's his second mistake. First one was buying from that guy in the first place; which he also mentioned.

Quote:by cwah » Sat May 06, 2017 7:12 am

I'd say the worst combination would be:
- no continuous pack voltage visibility
- no continuous pack serie voltage sag and voltage difference visibility
- usage of no name batteries...
- poor 18650 assemblage without necessary precaution against vibrations. The ready made 18650 pack are often soldered (damage on cells) without chaffing protection
- no name cheap bms that may or may not be working properly
This is what I was thinking, too.

Quote:That day though,, both packs were run till the bms popped, for my spring capacity test. Each spring I do this, so I can plan a very long summer ride based on current capacity. I think perhaps the bms did allow one cell group to go below spec voltage. Then when it got full charging, a damaged cell went runaway.

The other just as likely cause, the bms or the charger or both allowed an overcharge of a normal cell. No way to tell which happened, there was no trace of the bms left after the fire. The bms was in a plastic case/ box, did this cause the bms to overheat and fail? who knows, the plastic box never got scorched or melted deformed. Never should have gotten that hot, even when in balance mode. But I do wonder if the balancers were still, or even ever, working. I had not checked individual cell group voltages since it was new, you had to open the box to get at the bms plug.

So there was a LOT going on here. There were setups for failure all over the place. And I'd say he got too comfortable with everything and complacent with the fact that the BMS would shut anything down if something went wrong. But he even mentions he wondered about it.

In conclusion to this, I personally don't think you'd have anything to worry about. However, it's your bike, batteries, place of residence and your neck/life on the line here. First and foremost, don't use a cheap bms, and don't use questionable cells, either.
Altho, I'm glad he & the others got out alive with most of the house in tact (tho, if the garage is what burned, not sure why 90% of the house would need to be redone???)

You asked for input, and we are here to oblige Smile
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#6
One thing to note with Lead Acid is it is HEAVY!!!
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#7
(09-05-2017, 03:34 AM)Korishan Wrote: I think this says a lot here, at least he recognized what he did and was able to post it so others don't repeat his mistake.

Quote:perhaps I had the bike parked in a shitty place. Real shitty. In the corner of the very overstuffed garage, where on a peg above the bike, hangs, oh,, about 4 or 5 nylon coats. Couple wind shells, one ski parka, and my ballistic nylon armored motorcycle riding jacket. Hmm,,, I suppose I coulda just hung a gas soaked towel over the bike. Then, the cherry on top,, almost touching the bike, my Yamaha 400 cc scooter. Which I had just filled with 3.5 gallons of gas the day before. Soooo,, dumass,,, lets charge the battery within inches of three gallons of gasoline, and enough plastic to burn the house down

What I would do in this type of situation where it is possible to leave it and worry that something 'might'  happen, is put the charger on a timer. Set it for 1 hour and just keep resetting it. Not much can  happen in 1 hour time as you probably won't be resetting it right at the second. So the cell can have time to cool down and slowly discharge.
My guess is that the BMS failed. I didn't read the whole article, so I don't know what BMS he is using. However, it is clear that it definitely didn't have enough safety bells built into it. It probably only had "overcharge", and not temperature and maybe even current issues.

On the next page:
Quote:No idea what bms was in it,, except it surely was the cheapest they could source
There's his second mistake. First one was buying from that guy in the first place; which he also mentioned.

Quote:by cwah » Sat May 06, 2017 7:12 am

I'd say the worst combination would be:
- no continuous pack voltage visibility
- no continuous pack serie voltage sag and voltage difference visibility
- usage of no name batteries...
- poor 18650 assemblage without necessary precaution against vibrations. The ready made 18650 pack are often soldered (damage on cells) without chaffing protection
- no name cheap bms that may or may not be working properly
This is what I was thinking, too.

Quote:That day though,, both packs were run till the bms popped, for my spring capacity test. Each spring I do this, so I can plan a very long summer ride based on current capacity. I think perhaps the bms did allow one cell group to go below spec voltage. Then when it got full charging, a damaged cell went runaway.

The other just as likely cause, the bms or the charger or both allowed an overcharge of a normal cell. No way to tell which happened, there was no trace of the bms left after the fire. The bms was in a plastic case/ box, did this cause the bms to overheat and fail? who knows, the plastic box never got scorched or melted deformed. Never should have gotten that hot, even when in balance mode. But I do wonder if the balancers were still, or even ever, working. I had not checked individual cell group voltages since it was new, you had to open the box to get at the bms plug.

So there was a LOT going on here. There were setups for failure all over the place. And I'd say he got too comfortable with everything and complacent with the fact that the BMS would shut anything down if something went wrong. But he even mentions he wondered about it.

In conclusion to this, I personally don't think you'd have anything to worry about. However, it's your bike, batteries, place of residence and your neck/life on the line here. First and foremost, don't use a cheap bms, and don't use questionable cells, either.
Altho, I'm glad he & the others got out alive with most of the house in tact (tho, if the garage is what burned, not sure why 90% of the house would need to be redone???)

You asked for input, and we are here to oblige  Smile

Here's my thoughts...

Lithiums can go bad - if you stress them. The guy who's house burnt down seems to do everything he could to stress the batteries that day AND then put them in a situation where a fire would cause maximum damage.

So my recommendation would be:
- make sure you have a good BMS and/or add an external monitor so that you can see how the batteries are doing.
- never ride the battery down to the bottom (don't stress the batteries).
- never charge the batteries fully (don't stress the batteries). Find (or make) a charger that only charges to 90% full.

If you do those you'll be greatly reducing the chances of any problem.

Almost every lithium battery fire story I've read has involved the user overcharging. It's best to avoid charging all the way up to 100% on cheap BMS systems.

Cheers, Paul
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#8
Yeah, I think so too. The guy totally acknowledges all his mistakes, which is good, but they were mistakes nevertheless and I wouldn't take this as a prime example of lithium cells being dangerous. They can be, but this case is something different. Basically he built a nice incendiary composition there. By the sounds of it he never needed an actual fire to set this off, anything getting hot as part of its normal operation would have been sufficient.

As for overcharging, look at this: https://www.nkon.nl/sk/k/hg2.pdf
Second to last page. This sheet clearly could use some further explanation, but it looks very promising. Using proper cells will help in these cases.
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#9
(09-05-2017, 08:33 PM)DarkRaven Wrote: Yeah, I think so too. The guy totally acknowledges all his mistakes, which is good, but they were mistakes nevertheless and I wouldn't take this as a prime example of lithium cells being dangerous. They can be, but this case is something different. Basically he built a nice incendiary composition there. By the sounds of it he never needed an actual fire to set this off, anything getting hot as part of its normal operation would have been sufficient.

As for overcharging, look at this: https://www.nkon.nl/sk/k/hg2.pdf
Second to last page. This sheet clearly could use some further explanation, but it looks very promising. Using proper cells will help in these cases.

OK, so I know this thread is old, but I have some stuff to add. 

My pack is soldered together with 12AWG copper busbar, the pack has a fuse on the end. The pack has No BMS at all. I have been running it without one ever since I built it. 

I use the ming-he B900W to charge the battery and 6S battery pack balancers to bleed down each parallel group to keep the cells in check. I have found this system to work much better than having a BMS. Previously I used to charge the battery pack in my garage, but now I live in a tiny dorm room surrounded by drywall and carpet. The battery is 22.4AH and I charge it at a whopping 3 amps, so the charge rate is always very light. If I want to, I can fast-charge the battery pack all the way up to 15 amps (I have done it this high before). 

I can also choose to charge it with an RC lipo charger, but that usually takes forever. Although it may be fine to use just as a top-up because I may only use something like 2-3AH during the day, so even a 1A charge rate is fine overnight.
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#10
Well, ok, but what is your point exactly? As long as you don't build a setup that is basically made to go up in flames like this guy then you will be fine.
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