48v 25Ah pack cell selection help

[JIMMY_J]

Due to a charging problem with my Electric Motion 5.7 trials bike i left the battery discharged for a few months and the cells dropped down to around 2.0-2.4v over the course of several months. As these cells are no longer safe its time to build a new pack.

Original battery was 48v 24.5Ah lipo pack made with:
Kokam High power type SLPB82255140H cells 13S 0P
discharge of 196A (8c)
Peak discharge. 245A (10c)
With a cycle life of 90% DOD 1c/1c 6000 cycles 70% remaining capacity
Lower/upper limit 2.7-4.2v
https://kokam.com/skin/pc_en/img/cell_down/TDS_SLPB82255140H%20(24.5Ah)_EN.pdf

Controller is a Kelly KEB48601 24-48v 6kw BLDC
Cont. 130A
10sec. 350A
24-48V

Motor is 5KW BLDC stamped “HPM 5KW-15138” but i cant find any more info on it

Charger is 15A li ion/lipo 54.6v

I would like to end up with a pack similar in Ah and current draw as the old one. I would like to upgrade the BMS to either a spedict Neptune 20 because of its allowable current and display so I can monitor individual cells. or a similar BMS that one of you has had success with (please advise)

I am considering 14 cells in series and I have read this is good for pack longevity because each cell would have a lower peak charge voltage. using my 54.6v charger 13s = 4.2/cell and 14s = 3.9v/cell at full charge. Is this a good idea, Necessary ?

Seems like building with cylindrical cells and soldering/welding tabs on for connections is popular but would require more research tools and time to build a new pack. I’m ok with this if it is necessary but am mostly interested in lipo

I have looked at a few websites that sell RC LiPo packs but by the time I put enough together in series and parallel to achieve both 25Ah capacity (approx) and 48v the price is extremely high

These A123 NMC 26Ah lithium ion pouches would fit nice but I’m not sure what’s real or fake (especially on alibaba)
Here is one site with a good price but i cant find the constant and max Amp draw for these cells
https://a123batteries.com/a123-systems-3-7-volt-26ah-prismatic-pouch-cell-amp26-nmc/. $28.00 x 14 = $392

I’m located on Vancouver Island BC Canada if any locals out there know of Canadian distributors ?
Any info, suggestions or questions are much appreciated thanks.

 

[john61ct]

That is a good site for the A123 NMC cells.

also https://www.buya123products.com/goodsdetail.php?i=45

Should have no trouble at 10C but better burst than continuous, 3-5C if you want decent longevity, say 1000 cycles to 80% SoH.

The LFP variant less energy dense but IMO 10x longer lifespan.

Do not buy from Ali unless seller specifically recommended by a trusted member, and even then IMO only if they take CC or PayPal.

 

[JIMMY_J]

Thanks john61ct

I checked that site out but they have a 36 cell minimum order

“Should have no trouble at 10C but better burst than continuous, 3-5C if you want decent longevity, say 1000 cycles to 80% SoH.”

are you saying the higher the C rate of the pack the less amount of time it will last ? I’m basing my current draw needs on the specs of the OEM battery as i have nothing else to go on. 1C for a 24.5Ah pack is 24.5A so 3-5C for a 24.5Ah pack is 73.5 - 122.5A correct ? That would mean the OEM battery is capable of much more then what’s needed at 196A cont and 245A burst. ?

“The LFP variant less energy dense but IMO 10x longer lifespan.“

The Lifepo4 i have found have much lower c ratings like these:
https://www.electriccarpartscompany.com/Fortune-25Ah-Aluminum-Encased-Battery
Would love a longer lifespan but fist off they need to supply the correct load safely.
Are there versions of Lifepo4 that have higher C ratings?

 

[john61ct]

> Are there versions of Lifepo4 that have higher C ratings?

The A123 ones are top notch. The C rates I gave are but a small fraction of what they **can** do.

There are a half-dozen other quality makers, but mostly in much larger cell sizes, awkward for a performance bike, maybe OK for a 500# cargo rig. Hundreds of crap makers out there too of course.

are you saying the higher the C rate of the pack the less amount of time it will last ?

Absolutely, for a given cell model and chemistry. That is probably the #1 care factor, along with avg DoD, and how charging is done.

> I’m basing my current draw needs on the specs of the OEM battery as i have nothing else to go on.

Get a wattmeter to remedy that, getting a handle on what your rig wants to pull under various conditions will be key to longevity if the battery is the weak link.

> 1C for a 24.5Ah pack is 24.5A so 3-5C for a 24.5Ah pack is 73.5 - 122.5A correct ?

yes

> That would mean the OEM battery is capable of much more then what’s needed at 196A cont and 245A burst. ?

I thought you said you don't know what's actually needed?

Mfg C capacity ratings are very often grossly "optimistic". The actual true performance can only be determined by standardized testing IRL.

Many cells have been so tested by trusted forum members.

But then of course there is the problem of counterfeit cells.

BTW no way is that 6000 cycle rating real in a propulsion use case, I'm not familiar with Kokam but that's a big red flag there.

> The Lifepo4 i have found have much lower c ratings

lower than what?

The goal IMO should not be to identify the cells with the highest C-rate capacity, but to reduce the C rate required by getting a higher Ah pack.

Unless you are drag racing maybe? I don't know your use case, personally I stay at low speeds and look for many hours of range.

The NMC pouches will give you the ability to fit many more Ah in a given volume / weight factor than any LFP, if that is important to you forget LFP completely

just as impractical as lead for your use case.

Probably best to let others with actual biking-related experience chime in here, my more general "just battery" knowledge is likely to lead you astray

 

[JIMMY_J]

Thanks again for your reply

What are the half dozen quality makers ? I have only found A123


I have ordered a 200A watt meter that will give me accurate current draw at full load. I will report back in a few days with numbers to size the new pack off

The bike is a trials bike. Top speed of 55km/h (super rare) and weighs 70kg with battery. It’s a trail and rock climber I use 90% on my 5 acres

So the Depth of discharge or DoD is how low of a pack voltage I allow, recharge the battery when it gets down to 46v rather then down to 45.5v on 13S

And potentially adding a 14th cell if that’s a good idea and it will fit

I think the LiPo NMC pouches are going to be the choice over the Lifepo4 but ill let the Numbers decide what’s best