Cell Value & Life?

Batteries, Chargers, and Battery Management Systems.
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Skirmish   100 µW

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Cell Value & Life?

Post by Skirmish » Apr 07 2021 4:26am

Is there data on battery cell value over the long term?
Someone mentioned cost per Ah per year in another thread, that seems like a pretty good metric.
Number of useful also cycles seems like a useful thing to know.
The LG MJ1 has been recommended a couple of times from what I can see, are there better options in terms of cycles or cost per Ah per year?

I'm planning on a tsdz2 build, commuting ~30k per day & I need to be able to remove the battery when I'm parked if that affects anything.
Also Is it possible to set the BMS to charge up to only ~%80 overnight and then stop to increase battery life?

Thanks!

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flippy   10 MW

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Re: Cell Value & Life?

Post by flippy » Apr 07 2021 4:58am

first: the bms does not control the charge level. the charger does.
using a bms for charge control is like crashing a car into a wall, leave it in gear with the engine running and walk away.

second: its hard to beat the smasung 29E. they are by far the cheapest and robust cell out there.

third: "useful cycles" is not a thing. the lifespan is not rated by cycles but how its used. it perfectly possible to kill a cell in under 100 cycles but at the same time i can make one survive 5000 cycles.
Lithium beats liquid dinosaurs.

Skirmish   100 µW

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Re: Cell Value & Life?

Post by Skirmish » Apr 07 2021 5:28pm

flippy wrote:
Apr 07 2021 4:58am
first: the bms does not control the charge level. the charger does.
Thanks! I wasn't sure if the charger would supply power to the BMS for charging, or directly charge the cells itself.
Do chargers then allow charging up to ~%80 as a setting?
flippy wrote:
Apr 07 2021 4:58am
third: "useful cycles" is not a thing. the lifespan is not rated by cycles but how its used. it perfectly possible to kill a cell in under 100 cycles but at the same time i can make one survive 5000 cycles.
Definitely. I think it'd be useful to get the number of useful cycles under the same circumstances.

I don't know enough about the technology to say what would be considered treating the battery well while still being useful as a source of power for a commuter ebike, if you'd like to suggest some ideas on the specifics we could use that as the basis for our understanding of what a useful cycle is :thumb:

99t4   100 W

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Re: Cell Value & Life?

Post by 99t4 » Apr 07 2021 8:00pm

Skirmish wrote:
Apr 07 2021 5:28pm
Do chargers then allow charging up to ~%80 as a setting?
https://ebikes.ca/product-info/grin-pro ... iator.html
"With the cycle satiator, you can program your primary profile to give an 80% charge..."

eMark   1 kW

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Re: Cell Value & Life?

Post by eMark » Apr 07 2021 8:13pm

Skirmish wrote:
Apr 07 2021 5:28pm
Definitely. I think it'd be useful to get the number of useful cycles under the same circumstances.
Here's one comparative example (assuming you can find a reputable MJ1 supplier) ...

Samsung M29E (2850mAh, 2.75A rating) 14S7P at $2.98ea = $292 (98 cells)
LG Chem MJ1 (3500mAh, 10.00A rating) 14S5P at $4.50ea = $315 (70 cells)
( which of the above do you figure is a better solution for your commuting? )

You need be more specific as to your commuting requirements (e.g Mostly level or hilly; One way distance assuming you recharge battery before returning home; Average desired speed; Average applied pedal watt power during transit; practical number of cells and BMS that will fit in bike frame enclosure safely.

There are just too many variables to get the number of useful cycles as the meaning of "useful cycles" can vary depending on usage ... raw performance vs TLC (even TLC can mean different things to different ebikers.

Skirmish   100 µW

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Re: Cell Value & Life?

Post by Skirmish » Apr 07 2021 10:09pm

eMark wrote:
Apr 07 2021 8:13pm

Samsung M29E (2850mAh, 2.75A rating) 14S7P at $2.98ea = $292 (98 cells)
LG Chem MJ1 (3500mAh, 10.00A rating) 14S5P at $4.50ea = $315 (70 cells)
( which of the above do you figure is a better solution for your commuting? )
I'm still working out the finer details of a few things, 98 cells could be a tricky fit with some cases.
98 x 2850 mAh = 279.3 Ah
70x 3500 mAh = 245 Ah
So it looks like M29E provides more initial capacity for price. How the M29E's usable lifetime compares to the MJ1s given the same power usage is what I don't know.
eMark wrote:
Apr 07 2021 8:13pm

You need be more specific as to your commuting requirements (e.g Mostly level or hilly; One way distance assuming you recharge battery before returning home; Average desired speed; Average applied pedal watt power during transit; practical number of cells and BMS that will fit in bike frame enclosure safely.

There are just too many variables to get the number of useful cycles as the meaning of "useful cycles" can vary depending on usage ... raw performance vs TLC (even TLC can mean different things to different ebikers.
Good point. I feel like it might be productive to take a step back here: I'm not sure I can objectively define all of those parameters. If you feel it's helpful we can set a goal of keeping the charge level above 20% and if necessary below 80%. Let's say charging isn't possible mid-ride. Number of cells practical not currently known. I'm not expecting regular, massive hills. 25kph-ish cruising speed. Pedalling below the level of breaking a sweat would be preferred.

Is there an existing comparison or a way to compare the number of expected cycles before the cell is considered to be end of life, given the same or similar usage, eg. the above scenario?

fatty   1 kW

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Re: Cell Value & Life?

Post by fatty » Apr 07 2021 11:38pm

flippy wrote:
Apr 07 2021 4:58am
first: the bms does not control the charge level. the charger does.
using a bms for charge control is like crashing a car into a wall, leave it in gear with the engine running and walk away.
Agreed
flippy wrote:
Apr 07 2021 4:58am
third: "useful cycles" is not a thing. the lifespan is not rated by cycles but how its used. it perfectly possible to kill a cell in under 100 cycles but at the same time i can make one survive 5000 cycles.
Cycle life is most certainly a thing -- it's right in every datasheet. Of course you can modify the charge/discharge characteristics to change the spec, but that doesn't make the underlying spec any less valid.
Don't take advice from:
there is no difference between a mean well CC/CV power supply and a device sold as a charger. they operate in EXACTLY the same way
Testing has demonstrated that ordinary rim brakes thermally outperformed all but the best disc brakes...You'll always add weight and cost, while not equalling the capabilities of comparable rim brakes, if you use discs

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