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14s2p Minicube w/ 21700 batteries

Posted: May 19 2019 11:23pm
by drbenjamin
I spotted this from UPP tonight:

https://www.ebay.com/itm/UPP-Portable-P ... 4227423546

It's a 52V 10AH battery based on the Samsung 50E 21700. Curious what people think - these batteries have a higher capacity but lower current rating than the Samsung 30Q cells used in a 6AH Minicube. I like these small form factors for my "errand bike" where I only ride 5-10 miles but need to climb a 500 foot steep hill to get home. Not sure this pack would be a good match -

D

Re: 14s2p Minicube w/ 21700 batteries

Posted: May 19 2019 11:39pm
by amberwolf
Less parallel cells means less current delivery ability (vs a pack of the same cells with more parallel cells).

If they're more energy dense, then they're also (generally) less power-dense, which usually means they are less capable of higher current discharge (or charge) than a similer more power-dense cell (which, as it's own compromise, would then be less energy-dense). It's a tradeoff. ;)

So anyway, the faster you draw current out of it, the harder it is on it (especially vs more parallel cells).


You'd have to look at the cell specs for that model cell, and double the currents given, to know what this pack would be capable of and if it would be appropriate for your system, especially for the high-load portion of the ride.


I could use a pretty small capacity pack for my SB Cruiser, as most days I don't even need 5-6Ah for my work commute... but a pack that size would have a lot of voltage sag trying to supply 100A+ during my accelerations from a stop in traffic, especially if I have a bunch of cargo (or a dog). :/

So I end up using a much bigger pack than I need (right now a 40Ah, minimum 20Ah), just to get more power (more current with less voltage sag) for quick accelerations. I also carry the bigger pack because I *do* sometimes need the range, and can't always predict the days I'll need it...and the trike uses a lot of capacity per mile (about 60wh/mile).

Re: 14s2p Minicube w/ 21700 batteries

Posted: May 21 2019 10:58pm
by Matador
The Samsung 50E are rated at a max discharge rate of 9.8A. The ad is misleading to the novice. Yes the BMS supports a discharge rate of 30A, but the battery only supports a discharge rate of 19.6A (2P) configuration, but I would not run it at more than 10A to expect any usefull lifespan out of it in terms of usefull cycle life...

Not the best for an eBike, unless you're running a low power 250W setup... Or if you parralel 2 packs togoether

matador

Re: 14s2p Minicube w/ 21700 batteries

Posted: May 22 2019 3:56pm
by drbenjamin
Thanks - that was what I was thinking. Hopefully there will be a high discharge 21700 cell in the future, I love the small size of the minicube but would also like a little more capacity. This battery is close, but not suitable for a hill climber.

Re: 14s2p Minicube w/ 21700 batteries

Posted: May 22 2019 11:29pm
by Matador
drbenjamin wrote:
May 22 2019 3:56pm
Thanks - that was what I was thinking. Hopefully there will be a high discharge 21700 cell in the future, I love the small size of the minicube but would also like a little more capacity. This battery is close, but not suitable for a hill climber.
Check out the Samsung 40T 21700 cells. Seems promizing. The cell is rated for 4000 mAh @ 0.8A (0.2C); 3900 mAh @ 10A (2.5C), but the most interesting thing is it is rated for a max continous discharge rate of 35A (8.75C) or 45A (11.25C) with 75 degree celcius temperature cutoff.

Pretty solide power density, while still very good (volumetric and gravimetric energy density).
But still a bit pricey!

Matador

Re: 14s2p Minicube w/ 21700 batteries

Posted: May 24 2019 12:48am
by Easy_Rider
Matador wrote:
May 21 2019 10:58pm
The Samsung 50E are rated at a max discharge rate of 9.8A. The ad is misleading to the novice. Yes the BMS supports a discharge rate of 30A, but the battery only supports a discharge rate of 19.6A (2P) configuration, but I would not run it at more than 10A to expect any usefull lifespan out of it in terms of usefull cycle life...

Not the best for an eBike, unless you're running a low power 250W setup... Or if you parralel 2 packs togoether

matador
:bigthumb: :bigthumb: :bigthumb:

...and in addition...if they use Nickel as welding material, the limitation is around 10A-12A on every parallel connection. Only with Copper you can conduct more current...but 2P with 50E? you might be able to boil eggs on the battery?! :roll: