Scavenging one nearly new battery to make another?

Safety? LFP is the one, by a very long shot.

But you can't override the laws of science.

How wide can you go?

mammonista said:

Okay, according to the 'book' Toll says, "NO" on RC Lipo and he's not a big fan of LiCoO2 either. Not the safest batteries out there?
And I realize no Lithium based battery is completely safe. But in 18650, NMC and NCRs are readily available.
So which is it? Which is the preferred of those two chemistries is most favored here.
AND I'M NOT DOING LIPO!!! AND THE BATTERY IS GOING IN THE TRIANGLE!

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Well seeing as you seem to have a better source of info..
Why dont you ask the "book" ?

..and have you even checked how many 18650 cells you can actually fit in the triangle.

PS..i would state that RC packs are safer than any amature assembled 18650 pack !

until they're not!

So after taking a few months off for other projects I finally got around to figuring out just how much space I have above the mid-drive Cyclone motor (mounted above the bottom bracket) in my Gravity fatty. I had ordered these two big, heavy 48v/20ah battery packs off Risun Motor in China for powering my fat tire bikes. I don't know why I assumed they were some configuration of 18650s. They're not! What they are, are 16 Lithium Ion pouch cells roughly 10"x7" stacked on top each other forming a 'brick'.
I put each brick in a rigid case/bag and strapped each on seat post racks on the bikes. While that works ok with my girlfriend's bike for cruising up and down the beach, it's no fun at all on my fatty for taking on the back trails through the dunes.
This thread began when I had the crazy idea of scavenging the 18650s that I assumed these 'bricks' were made up of and building my own custom pack to fit in the triangle of my Gravity.

I'm relatively adept at building stuff and a housing would seem to give me enough room for lots of 18650s in just about any configuration I want. So I went to the Russian battery building website and gave them the rough dimensions of the space available.
Remember I'm shooting for 72volts (that's what the Cyclone 3k can handle) and maybe 12ah? I could easily get 50% more cells in this space. So give me reasonable numbers here. Budget for the cells about $500 (less? )

This bike has a 3-speed IGH on the rear and I rarely go above 500 watts although I've pulled as much as 1,800 if the CA is to be believed. And I just like the idea of a full 3,000 watts for the rare times when I want to power straight up a hard-packed dune face. So assuming I find the right BMS, what are the appropriate 18650 'S' and 'P' numbers for something that can put 72 volts to the motor for maybe an occasional 30-sec hi load burst but more normally operate at loafing along speeds?
And what 18650 chemistry (make and model) is preferred these days?
as usual,
thanks in advance

okay, I'm a big dumb ass. Those big pouch batteries were LiFePO4 things that prolly were listed in the catalogue as scooter batteries and actually the thing isn't that big of a deal on a beach fatty. lots of weight but a fair amount of power for not a lot of money. But now I'm gonna build a proper custom 18650 battery so previous questions still apply?

Yes, that style is known as "prismatic", soft pouches internally, but shipped sealed up in a hard case with easy bolt terminals.

Can be one LFP cell per big block, so 3.3V nominal at say 40Ah up to thousands of Ah, obviously those need a forklift to install.

Huge advantage in only one or two series needed to get to target Ah capacity, fewer interconnects and can just use marine battery cabling with crimped ring terminals, super easy to break out the pack for maintenance cell testing / re-balancing, replacing faulty units etc.

But the larger size can make that style inconvenient to fit for many bikes.

mammonista said:

So assuming I find the right BMS, what are the appropriate 18650 'S' and 'P' numbers for something that can put 72 volts to the motor for maybe an occasional 30-sec hi load burst but more normally operate at loafing along speeds?

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If you want to stick with LFP, the best is A123, pretty sure K2 not nearly as good.

Nominal voltage is 3.2-3.3Vpc instead of Lipo 3.6-3.7?V.

So 24S used to get over 72V, maybe 23S at the lower end, goal is for Volts to stay in a narrow range no matter the power required, it is the Amps that vary to give you the Watts needed for acceleration and hills.

Then these 24S strings are put in parallel to get you Ah capacity, e.g. if each cell / string is 3200 mAh, you need 4 strings 14S4P to get over 12Ah.

LFP gives both good longevity and high discharge / low voltage sag.

But less energy density than Lipo, so more space and weight required to get to high Ah capacity.

Lipo is cheaper, higher discharge chemistries may give lower longevity at the same quality.

Going cheap will sacrifice both high discharge performance and longevity. Maybe sell off the prismatic packs?

Again, lipo is also a different voltage, so getting over 72V I think 20S is normal.

Note 26650 gives more Ah per cell than 18650, fewer strings required to build up Ah capacity, but higher cost.

Hope this helps.

I don't want LFP! (I don't think) I want 18650 form. According to the battery design site I could squeeze a custom made box in there that would accommodate 138 cells in a 23s6p configuration. I don't think I need 23 cells in series (23x3.7=85volts) to get 72volts and 6p sounds like lotsa amp hours. or do I have this all wrong?

That's fine to exclude LFP, but then why did you buy it before? Does come in 18650 you know, that's just a physical form factor spec, dozens of different chemistries come in that size.

Just FYI.

mammonista said:

I don't think I need 23 cells in series (23x3.7=85volts) to get 72volts and 6p sounds like lotsa amp hours. or do I have this all wrong?

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As I said, 20S is the norm for "nominal" 72V with non-LFP, as in NMC, LCO, LMN, NMA.

The more Ah the better, lower C-rate and DoD gives better longevity.

Balance against size, weight and cost of course.

I bought those big batteries because they were high capacity, cheap, and had long life. And I didn't know any better?

Then maybe not actually LFP, landed costs here are usually over $500/kWh for anything decent.

You're just 'f'ing' with me, huh?

Again, I'm confused. I understand that 18650 size batteries come in a variety of different chemistries from a variety of manufacturers. MicahToll's book lists: Lithium Manganese Oxide, Lithium Cobalt Oxide, Lithium Nickel Manganese Cobalt Oxide, and Lithium Nickel Cobalt Aluminum Oxide. One of you just referenced NMC, LCO, LMN, NMA. I'm assuming some are the same? I know Lithium Nickel Manganese Cobalt Oxide is 'NMC', but the rest?
And what are the preferred chemistries these days? Regardless of cost? If cost is a consideration?
And part of my confusion stems from the fact that I thought that besides volts and capacity (3.7 & 2200mah) there were no other parameters on 18650s. That's obviously wrong. So what does 20amps refer to on one of these things?

Amps on a battery generally refers to the capacity, either stored or deliverable to the controller/motor. Take the amp hours, multiply it by the battery voltage and you have how many watt hours your pack is. You use that number to compare with how many watts you are using during your rides. You can then discern how long you battery will last before you need to charge it again.

How many amps a battery can deliver is used to determine how you can safely use the cells. As an example, a cell like the Pansonic PF 18650 is rated 3.6v Nominal voltage, 2900 mAh (aka 2.9 amps) and 10A maximum continuous discharge.

(teach yourself how to read battery datasheets)

So what does one do with this information?

It goes like this: If you want a 72v battery pack, then take the 72v and divide it by 3.6v (72/3.6= 20 cells) However since these cells charge to 4.2v when totally charged you will need a battery charger that can charge to 84v if you want to fully charge these cells. (20x4.2=84)

Ok, so as stated above, 20 3.6v 18650 cells is normal for 72v. But each of these PF cells has a limit of how many amps it can deliver. It happens to be 10A continuous according to the specs. So if you have a 20s 1p pack (a total of 20 cells) then you could run at 72v but no more then 10A or you might over heat the cells and cause a fire. So say you want to run a 30A controller, then you have to go with a 3p arrangement which would be 60 cells. (20s x 3p = 60) So now you have a pack that can take 30 amps continuous according to the manufacture. However there is no room for error. So say you want to build in a little bigger battery so you are not fully taxing your cells when you are at maximum amp draw and you go with a 20s 4p arrangement. So now you have a pack with 80 cells. Because it uses batteries that are rated at 10A and you have 4 in parallel, this pack could handle 40 amps draw continuously according to the manufacture. But since you are only going to draw 30 amps, the cells are not over taxed.

And as for watts, (volts x amps = watts) you would have about 835 watt hours to use. Or, 2.9A per cell x 4 cells in parallel = 11.6 ah usable. 11.6Ah x 72v = 835.2 watt hours usable. As a rule of thumb around here people use 25 watts per miles of range. Your mileage will very.

Okay, so that clears up some stuff. But here's an add from Ebay for 100 batteries. What's the 20amps they are they referring to in the hilighted area?

What it sound likes is a scarce eBay description.
However you didn't give the eBay link, so I will go with this:

It is back to the datasheet concept. On eBay they are selling Samsung 25R 18650's. And if authentic, they will match the Samsung 25R datasheet.

There usually a lot of links or datasheets, I happened to use this link because it was convenient.
https://www.18650batterystore.com/v/files/samsung_25r_data_sheet.pdf

This snip-it is to give an example:


This part of the data sheet says that cell can discharge 20amps continuously which is what the eBay seller is probably referencing.

But remember: “The flame that burns Twice as bright burns half as long.” Lao Tzu

The same holds for lithium batteries. The high C rated cells usually don't last as long as lower C rate batteries. (there are some exceptions.)

It usually comes down to a cost / weight / size / speed ratio that fits your budget and needs.

And since I happen to be on the subject, there is one more thing.....

Pop Quiz!

A) You have a motor rated to 3k. (which you have said your motor is)
B) You have decided to use Samsung 25R 18650 cells.
C) You want to run at 72 volts.

So:
What is the maximum amperage used by a 3k 72v motor?
How many cells do you need to run your 3k motor at 72v at maximum amperage?
What is the ?P?S configuration would you need to run it at maximum amperage?
What is your charging voltage?
What is your cut-off voltage?

And NO kibitzing anybody!!! :lol:

Okay then here's another ebay ad...

and I failed the quiz! my dad was 'senior electro-optical research engineer' at a large defense contractor in socal when I was a kid. wish he were here to help me out!

So I'm guessing the Panazonic batteries have much to low a 'maximum continues discharge' to be of any good in an ebike with a big thirsty motor?

mammonista said:

and I failed the quiz!...

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Sorry to hear it, but you need to be able to pass the quiz before you can effectively determine how to build you battery.
All the info you need to pass the quiz is in this thread. 8)

As for a low C discharge battery, what it means is you need more of them to handle a large amp hour draw from your controller.
Can you calculate how many of the of those 18650B cells you would need for your 3k motor to run at full capacity?

All the info you need to figure it out is in this thread. :thumb:

Otherwise it's

mammonista said:

You're just 'f'ing' with me, huh?

Click to expand...

Nope, no idea what you mean

mammonista said:

here's an add from Ebay for 100 batteries

Click to expand...

Makers exaggerate like crazy, aka flat out lie

Then sellers also toss SEO keywords into titles too, might not have much to do with reality.

It's 80-90% scammers out there, Ali even more so.

Get reco's here on trusted sources.

And nbd really, but your avatar's creeping me out, clowns are nightmare fuel. . .