Has anyone bought these K2 Energy cells off eBay? And other battery pack questions

[CONSIDERABLE SHOUTING]

https://www.ebay.com/itm/2941974475...aultOrganicWeb&_trksid=p2563228.c101113.m2108

I'm plotting a battery pack for a first all-custom machine and because of my space requirements, it seems like the 26650s are the best bet. In using a combination of the Battery Package Calculator app, and a battery configurator, I found that both the cheapest AND best-power LiFePO4 pack I can build will either be from these K2 cells, or A123 cells from servers. The pack will (arguably as you'll see) be a 20S6P with both packs easily maxing out a Grintech Frankenrunner controller (my baseline). My questions for ya'll are however:

• Has anyone bought these cells, and if yes can you tell me if they were in good shape or not? The price is simply too good not to try.

• I can only fit a 20S 6P pack by allocating 5mm of space between my cells and the bike frame. If I went for the A123s I could give far more side-space at the cost of going to a 20S5P; do you think 5MM is WAY too little space, especially as a newbie?

I am not 'married' to the battery used, and the A123 cells have serious discharge potential to the point where I could go even larger FOC controllers than what Grin sells at a cost of "only" having a 1kWh pack instead (versus my math saying these K2 Energy cells being close to 1.5kWh which I have NO need for lmao). I will likely use a copper-nickel sandwich method for the battery connections. Any opinions?

Stats calculated so far are:
ANR26650 M1B
• 2600mAh Per cell
• 8.25 Watt hours
• Max Continuous Charge 10A, Recommend 3A
• Max Continuous Discharge 50A
Can be bought as salvage from Battery Clearing House, though their shipping leaves something to be desired. If bought from them, estimates say the price of a 120 cell pack would be ~$160 at a price per 1Wh of 0.154.
BATTERY PACK CALC
Voltage 66v
Capacity 15.6 Ah
Energy 1.03 kWh
Max Con. Discharge Current 300Amps
Weight 10.5Kg
Cost (new from maker) $665
Price (New from maker) for 1Wh: 0.646

K2 Energy LFP26650E-3800-21-
• 3800mAh per cell
• 12.16 Watt hours
• Max continuous charge 3.8A (1C)
• Max Continuous discharge 12A (4C)
Bought from eBay reseller, which is sketchy and source/data sheets must be verified. Sold in what seems to be “lots” of 20 cells per package, so will need 6 packages for a total cost of ~$120 before shipping. Versus the ANR server cells, these trade absurd discharge current for more capacity to a pretty impressive degree; nearly 1.5kWh pack, and possibly even cheaper than buying used cells from Battery Clearing House. With using XT60 battery connectors, it may be prudent to use a pack that physically cannot discharge enough power to met the connectors...
BATTERY PACK CALC
Voltage: 64v
Capacity: 22.8Ah
Energy: 1.459 kWh
Max Con. Discharge Current: 72A
Weight: ~10.5Kg (Estimated, no weight on these known)
Cost: ~$125
Price for 1Wh: 0.086

 

[larsb]

Only lifepo4 then? And why would 26650s ? They’re not the cheapest cell size? You’d get molicel p42 21700 lithium cell for the same price, 4ah/30A continuous, top performer, brand cell.

 

[skeetab5780]

Id personally go with a newer 21700 cell they are only $4 each and they put out like 45a continuous now

and you'll get a higher voltage, higher top speed and less sag with 21700 li-ion

 

[CONSIDERABLE SHOUTING]

Only lifepo4 then? And why would 26650s ? They’re not the cheapest cell size? You’d get molicel p42 21700 lithium cell for the same price, 4ah/30A continuous, top performer, brand cell.

Id personally go with a newer 21700 cell they are only $4 each and they put out like 45a continuous now

and you'll get a higher voltage, higher top speed and less sag with 21700 li-ion

I'm feeling the Lithium-Irons for their long lifespan and safety; my hope is, by building the pack real well that their low voltage and capacity aren't such a hindrance. Because of that, I statted out using the configurator 18650s, 26650s and even the battery hookup 32650s (I haven't done 2170s because there's none I know of in the LiFePO4 chemistry) and found that with Irons, these 26650s were the best for both energy density and discharge with what is available right now though sites like 18650 Battery Store.

As for cost, where can you get Molicells for the same price? Including shipping, these K2s are basically a $1.20 per cell or so, and if they're good and basically unused, that's a $160 pack before BMS that'll have more than twice the lifespan of an equivalent Li-Ion pack.

 

[larsb]

It said 5.99usd on ebay for 1?

 

[CONSIDERABLE SHOUTING]

It said 5.99usd on ebay for 1?

Oh? Looking again at "2-lo, 3-lot" ect. it looks like you might be right. I thought it was a "lot" of the 20 cells in the box shown.

 

[TrotterBob]

Battery Hookup had those at just over $2 a cell and they were selling them in lots of 20 and *120. They're quite good as they were new cells for a military project that got cancelled. They were testing at or slightly above 3,800mah each.

 

[john61ct]

A123 are the best cylindrical LFP, by FAR.

Especially longevity, so price per Ah PER YEAR comes out lower, even if your up front investment is triple.

 

[CONSIDERABLE SHOUTING]

Battery Hookup had those at just over $2 a cell and they were selling them in lots of 20 and *120. They're quite good as they were new cells for a military project that got cancelled. They were testing at or slightly above 3,800mah each.

Key statement "had" :lol: Looks like the K2s are out just because of lack of quantitiy.

A123 are the best cylindrical LFP, by FAR.

Especially longevity, so price per Ah PER YEAR comes out lower, even if your up front investment is triple.

Yeah, by my math a 144-piece purchase from Battery Clearing House (if more than 80% are usable and the don't ship them like they did the wheels) would make a near 1kWh pack for less than $200, which is a hell of a steal. My fear tho, is that such a pack would be capable of shorting 300Amps; I'll use a good BMS thanks to researchers here, but that a LOT of amperage when I'm only trying to use a controller like a Frankenrunner and a leafbike motor. Do you think that's too imbalanced, too many amps for a controller like that? Or could good BMS's help keep everything "controlled"?

 

[john61ct]

Amps are only offered to the controller, not pushed out.

The controller only sipping from a big resevoir of power is exactly how it should be, no "balance" in that context is a great thing.

 

[amberwolf]

battery is water bottle, controller is valve, motor is paddlewheel driven by water falling on it to spin something connected to it's shaft.

Giant water bottle means that a big valve trying to feed a big paddlewheel with a lot of load on it doesn't immediately drain the bottle and cause it to collapse in on itself damaging the bottle and preventing it from being refilled.

Tiny water bottle would empty quickly and possibly be crushed in the process. Medium bottle would empty quickly and maybe wrinkle...

Etc. Just a (poor) analogy, but perhaps visual enough to make sense?

 

[CONSIDERABLE SHOUTING]

The controller only sipping from a big resevoir of power is exactly how it should be, no "balance" in that context is a great thing.

battery is water bottle, controller is valve, motor is paddlewheel driven by water falling on it to spin something connected to it's shaft.

Giant water bottle means that a big valve trying to feed a big paddlewheel with a lot of load on it doesn't immediately drain the bottle and cause it to collapse in on itself damaging the bottle and preventing it from being refilled.

Tiny water bottle would empty quickly and possibly be crushed in the process. Medium bottle would empty quickly and maybe wrinkle...

Etc. Just a (poor) analogy, but perhaps visual enough to make sense?

Thanks guys, that explains it perfectly!

 

[TrotterBob]

Key statement "had" :lol: Looks like the K2s are out just because of lack of quantitiy.

Yes I did say had. And now there are people on feebay who've obviously loaded up on these in anticipation of the day when Battery Hookup runs out. They did the exact same thing when Battery Hookup had the Navitas 25ah lifepo4 cells.

Yeah, by my math a 144-piece purchase from Battery Clearing House. (if more than 80% are usable and the don't ship them like they did the wheels)

So far, Battery Hookup has been accurate in stating the condition of the batteries they sell. I bought quite a few of those 26650s and just one arrived with a near zero voltage. Hardly worth the hassle of having them ship out a single $2 cell even though they would have if I'd asked. So by my count their cells are over 98% useable and even the one flat cell did ok after it was recharged but its not performing like new. The rest of the cells I bought were at 3.28 to 3.27v, meaning they were very close to 50% SOC, which is ideal for storage.

(if more than 80% are usable and the don't ship them like they did the wheels)

When did Battery Hookup sell wheels? I must have missed that sale.

would make a near 1kWh pack for less than $200, which is a hell of a steal. My fear tho, is that such a pack would be capable of shorting 300Amps; I'll use a good BMS thanks to researchers here, but that a LOT of amperage when I'm only trying to use a controller like a Frankenrunner and a leafbike motor. Do you think that's too imbalanced, too many amps for a controller like that? Or could good BMS's help keep everything "controlled"?

Any 12s or better ebike battery could produce over 300 amps in a dead short. Handle with care.

With LiFePO4 you'll need a BMS with a balancing function thats capable of keeping up with your charging rate so the cells dont go out of balance towards the end of the charging cycle. Unlike li-ion and LiPo cells, LiFePo4 voltages ramp up as they approach full and that can amplify any difference in the state of charge of each cell.

 

[CONSIDERABLE SHOUTING]

accurate in stating the condition of the batteries they sell. I bought quite a few of those 26650s and just one arrived with a near zero voltage. Hardly worth the hassle of having them ship out a single $2 cell even though they would have if I'd asked. So by my count their cells are over 98% useable and even the one flat cell did ok after it was recharged but its not performing like new. The rest of the cells I bought were at 3.28 to 3.27v, meaning they were very close to 50% SOC, which is ideal for storage.

Good to know, thanks!

When did Battery Hookup sell wheels? I must have missed that sale.

Sorry, it was from Battery Clearing House which sells the A123 cells and sold those wheel and motors! It was from the fail of Jumpbike; they were selling a package deal of 2 350w Bafang Hub motors and 2 Sturmey-Archer IGH 3-speeds in rims with tires for a total around ~$100. Both I and Amberwolf ordered them, and they still have some available for order- we both were missing parts and the box arrived for me, nearly falling apart. I think amber had a wheel bent; I can't find the thread offhand but I can link it later on a different machine if you'd like.

Any 12s or better ebike battery could produce over 300 amps in a dead short. Handle with care.

With LiFePO4 you'll need a BMS with a balancing function thats capable of keeping up with your charging rate so the cells dont go out of balance towards the end of the charging cycle. Unlike li-ion and LiPo cells, LiFePo4 voltages ramp up as they approach full and that can amplify any difference in the state of charge of each cell.

Yep! And I'm very scared of attempting that, because a 64v/300a dead short will kill me fast. I'm not in a super-rush to make this, so I'm going to make a few battery packs beforehand to get the skills and I'm gonna look for safety methods to make best practices before undertaking it. I think i'll likely get something like, sheets of ABS plastic or a similar isolator to "drape" across the terminals as I'm working to keep from touching anything I'm not actively welding. Definitely open to other methods tho.
As for the BMS- I'll be using either ANT or LTT Power (whom I believe Battery Hookup sells) as forum members here have tested their electronics and found them to be very high quality. Both have LiFePO4 options.

Also, my original question hasn't been answered- I can only fit a 20S 6P pack by allocating 5mm of space between my cells and the bike's frame. Do you think 5MM is WAY too little space?

 

[john61ct]

Maybe not using a strong high density board like G10 FR4

 

[nbtesh]

https://www.ebay.com/itm/2941974475...aultOrganicWeb&_trksid=p2563228.c101113.m2108

I'm plotting a battery pack for a first all-custom machine and because of my space requirements, it seems like the 26650s are the best bet. In using a combination of the Battery Package Calculator app, and a battery configurator, I found that both the cheapest AND best-power LiFePO4 pack I can build will either be from these K2 cells, or A123 cells from servers. The pack will (arguably as you'll see) be a 20S6P with both packs easily maxing out a Grintech Frankenrunner controller (my baseline). My questions for ya'll are however:

• Has anyone bought these cells, and if yes can you tell me if they were in good shape or not? The price is simply too good not to try.

• I can only fit a 20S 6P pack by allocating 5mm of space between my cells and the bike frame. If I went for the A123s I could give far more side-space at the cost of going to a 20S5P; do you think 5MM is WAY too little space, especially as a newbie?

I am not 'married' to the battery used, and the A123 cells have serious discharge potential to the point where I could go even larger FOC controllers than what Grin sells at a cost of "only" having a 1kWh pack instead (versus my math saying these K2 Energy cells being close to 1.5kWh which I have NO need for lmao). I will likely use a copper-nickel sandwich method for the battery connections. Any opinions?

Stats calculated so far are:
ANR26650 M1B
• 2600mAh Per cell
• 8.25 Watt hours
• Max Continuous Charge 10A, Recommend 3A
• Max Continuous Discharge 50A
Can be bought as salvage from Battery Clearing House, though their shipping leaves something to be desired. If bought from them, estimates say the price of a 120 cell pack would be ~$160 at a price per 1Wh of 0.154.
BATTERY PACK CALC
Voltage 66v
Capacity 15.6 Ah
Energy 1.03 kWh
Max Con. Discharge Current 300Amps
Weight 10.5Kg
Cost (new from maker) $665
Price (New from maker) for 1Wh: 0.646

K2 Energy LFP26650E-3800-21-
• 3800mAh per cell
• 12.16 Watt hours
• Max continuous charge 3.8A (1C)
• Max Continuous discharge 12A (4C)
Bought from eBay reseller, which is sketchy and source/data sheets must be verified. Sold in what seems to be “lots” of 20 cells per package, so will need 6 packages for a total cost of ~$120 before shipping. Versus the ANR server cells, these trade absurd discharge current for more capacity to a pretty impressive degree; nearly 1.5kWh pack, and possibly even cheaper than buying used cells from Battery Clearing House. With using XT60 battery connectors, it may be prudent to use a pack that physically cannot discharge enough power to met the connectors...
BATTERY PACK CALC
Voltage: 64v
Capacity: 22.8Ah
Energy: 1.459 kWh
Max Con. Discharge Current: 72A
Weight: ~10.5Kg (Estimated, no weight on these known)
Cost: ~$125
Price for 1Wh: 0.086

Hello, do you mind sharing your "Battery Package Calculator app, and a battery configurator"

 

[CONSIDERABLE SHOUTING]

Hello, do you mind sharing your "Battery Package Calculator app, and a battery configurator"

Hell yeah

Battery pack shape configurator: https://e4bike.ru/page/battery-shape-configurator

The battery pack app is called "Battery Package Calculator"- it's app icon has a little green and red cell on it, you can download it off the Google Pay Store. You have to physically enter most cell details, but it'll tell you the total energy, weight, and max continuous amperage.