Battery life cycle over 40 amps

[Funkonabike]

hello everyone

I'm looking to build a 1500w leafmotor kit with this battery, 52v 28ah and requested a 50amp bms

https://a.aliexpress.com/_mKPNNC3

Perhaps the 52v 20ah 50a bms battery since its half the price, but I don't believe it uses the Samsung cells.

Question I have is will the Samsung 35E cells in the 28ah pack have any life cycle issues at 40 to 45 amps continuous power?

If im not mistaken thats the power range I need for what I'm looking to do, I'm just having trouble finding appropriate 18650 solutions since em3ev doesn't have an over 40amp bms and luna is out of stock on the higher ah packs. Absolutely no idea how lipo set ups work, and not sure if drawing this much power out of the upp pack is going to shorten its life.

I like the extra range of 28ah but also the price for anything in that size from anyone other than upp starts to get a little crazy for what it seems to offer in terms of power delivery.

Thanks everyone!

 

[Balmorhea]

The faster you drain a battery, the shorter the life.

The deeper you drain a battery, the shorter the life.

The higher you charge a battery, the shorter the life.

The longer you leave your battery fully charged, the shorter the life.

The hotter you store your battery, the shorter the life.

These are the rules. There are no thresholds to these rules where harm doesn't occur.

Lucky for us, we live in a time when batteries are getting better more quickly that they're getting more expensive. So if that trend holds, you don't need your battery to last for years and years-- you only need your battery to last until you can get a better one for a lower price.

 

[john61ct]

The faster you drain a battery, the shorter the life.

The deeper you drain a battery, the shorter the life.

The higher you charge a battery, the shorter the life.

The longer you leave your battery fully charged, the shorter the life.

The hotter you store your battery, the shorter the life.

Mostly

> There are no thresholds to these rules where harm doesn't occur.

False.

Ballpark for each of the above, respectively:

0.6-0.8C at warm temps

40-50%

4.05V

10-20min

 

[Balmorhea]

The faster you drain a battery, the shorter the life.

The deeper you drain a battery, the shorter the life.

The higher you charge a battery, the shorter the life.

The longer you leave your battery fully charged, the shorter the life.

The hotter you store your battery, the shorter the life.

Mostly

> There are no thresholds to these rules where harm doesn't occur.

False.

Ballpark for each of the above, respectively:

0.6-0.8C at warm temps

40-50%

4.05V

10-20min

Those aren't thresholds; they're compromises that many of us find acceptable. Battery life keeps getting longer as you make conditions easier. But you'll need more and more battery to do the same job.

I'm sure there's a point where the cycle life meets the maximum calendar life, and it would be fair to call that a threshold value.



There's just a point at which long enough is long enough, and the battery exists to do work, so you do it.

 

[john61ct]

I meant the thresholds where that factor is not reducing cycle lifespan.

Obviously many use cases do require such "damage", and yes then it's just a matter of balancing priorities, like lower C-rates vs too much weight if for a mobile context.

The 3.6-3.7V LI chemistries currently used for most propulsion uses will last many decades, if calendar life only no cycling and well maintained.

LFP and LTO are the only ones that can be cycled daily and still last that long.

 

[eMark]

Question I have is will the Samsung 35E cells in the 28ah pack have any life cycle issues at 40 to 45 amps continuous power?

What is your primary cycle life use price advantage compared to this ... https://www.amazon.com/Hitachi-RB24EAP-Handheld-Lightweight-Commercial/dp/B003VYC31Q ? (weighs less)

Guys, just a little "leaf" motor hubba hubba blowing in the wind gist. The joy is riding an ebike that can keep up with a gust of fall leaves blowing in the wind going 25-30 mph pulling 40 to 45 amps continuous. :thumb:

The deeper you drain a battery, the shorter the life.

Table 4: comparisons ... "https://endless-sphere.com/forums/download/file.php?id=279432" ... 100% DoD cut-off voltage for 35E is 2.65V

A 60% decrease in DoD (Table 2 ... https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries) is needed to double number of discharge cycles; whereas only a 10% to 15% reduction in SoC (capacity) will double the number of discharge cycles. Is 3.3-3.4V the optimal cut-off voltage for most all 18650 cells ?

• Table 2:
  100% DoD ~ 300 - 600 discharge cycles
  80% DoD ~ 400 - 900 discharge cycles
  60% DoD ~ 600 ~ 1,500 discharge cycles
  40% DoD ~ 1,000 ~ 3,000 discharge cycles

• Table 4:
  4.20V SoC at 100% ~ 300-500 discharge cycles
  4.15V at 90–95% ~ 400-700 discharge cycles (BMS' that top balance are s-l-o-w and not accurate)
  4.10V at 85–90% ~ 600-1000 discharge cycles
  4.05V at 80–85% ~ 850-1,500 discharge cycles
  4.00V at 70–75% ~ 1,200-2,000 discharge cycles

"In terms of longevity, the optimal charge voltage is 3.92V/cell. Battery experts believe that this threshold eliminates all voltage-related stresses" (Battery University).

An optimal discharge voltage cut-off of 3.3-3.4V rather than 2.50-2.65V will increase discharge cycle life. Both Table 2 and Table 4 are about discharge cycle life. What would be the DoD percentage for 3.3-3.4V in Table 2: ?

 

[Balmorhea]

There's not a lot of juice left to squeeze out below 3.3V/cell. My own preference is to charge up to 4.05V and discharge no lower than 3.3V. I occasionally charge up to 4.2V to exercise the balance function of my BMS, or to ensure maximum range for a long round trip.

 

[john61ct]

Battery University is a decent intro 101 level orientation, but lots of inaccuracies and over-generalisations not a good source for detailed specifics.

The mapping of voltage to SoC needs a resting pack isolated for a long time, and even then is not precise on its own, varies with chemistry and weal level.