What's the best charge voltage cutoff with today's cells?

[Ethanator10000]

I purposely got a larger pack than I needed so that I can go easy on the charge/discharge of the cells, with the intention of using the "80%" rule of thumb. But what does this actually correspond to in terms of cell voltages?

I see a bunch of different values, like in this chart, which would suggest 80% of my 48v pack is 51.5v (~3.96v per cell), and this thread, which suggests values between 4.05v to 4.1v per cell. Am I giving up extra range for zero benefit (or using the same range but running the battery closer to LVC) by only going to 3.96v per cell instead of 4.05 or something? Or if 3.96v is working well for me, should I just stick with that?

 

[Chalo]

Am I giving up extra range for zero benefit (or using the same range but running the battery closer to LVC) by only going to 3.96v per cell instead of 4.05 or something? Or if 3.96v is working well for me, should I just stick with that?

If you get the range you need at the lower voltage, and almost always have plenty of capacity left when you recharge, then no problem. But discharging to LVC is even worse for your cells than charging to HVC, and it tends to unbalance your pack. So if charging a little higher means you discharge a little less deeply on the other end, then that's a win.

Your battery would love to stay in the 25% to 75% range all the time, but it's there to do a job that may come into conflict with optimum archival conditions.

 

[neptronix]

Look up the cell's spec sheet, it will tell you what the maximum voltage is and reduce that as far as you can get away with for maximum life.

 

[Ethanator10000]

If you get the range you need at the lower voltage, and almost always have plenty of capacity left when you recharge, then no problem. But discharging to LVC is even worse for your cells than charging to HVC, and it tends to unbalance your pack. So if charging a little higher means you discharge a little less deeply on the other end, then that's a win.

Your battery would love to stay in the 25% to 75% range all the time, but it's there to do a job that may come into conflict with optimum archival conditions.

Currently I never go below 42v (~3.23v per cell), usually trying to stop around 44v (3.38v per cell) to charge. Is it better to slide this range up or keep as is?

 

[Ethanator10000]

Look up the cell's spec sheet, it will tell you what the maximum voltage is and reduce that as far as you can get away with for maximum life.

Samsung 50e, max of 4.2v and LVC of 2.5v, seems like it's pretty typical for Lithium cells.

 

[BlueSwordM]

Let's just say we're talking about an NMC811 or high Ni cathode cells in general with just graphite anodes.

You want to avoid the max charging voltage with those as internal resistance rises fastest at 4.20V. You need to only reduce the charging voltage down to 4.15V to avoid most of the parasitic reactions (oxygen generation and electrode degradation) which greatly boosts usable cycle and calendar life.

The next step down is 4.06V where degradation is kept to a minimum both in terms of usable capacity and internal resistance.
4.04V is where cells become practically immortal.

For the minimum voltage, anything around 3V is fine for high Ni cells. For cells containing some form of silicon in tyhe anode, the activation region for silicon is around 3.4V so if you can avoid that, you'll never touch the silicon. Of course, you should choose another cell type if you're never going below 3.4V, so just go down to around 2.8-3.0V if you need close to max capacity for Si-C/Si anode cells.

 

[Ethanator10000]

Let's just say we're talking about an NMC811 or high Ni cathode cells in general with just graphite anodes.

You want to avoid the max charging voltage with those as internal resistance rises fastest at 4.20V. You need to only reduce the charging voltage down to 4.15V to avoid most of the parasitic reactions (oxygen generation and electrode degradation) which greatly boosts usable cycle and calendar life.

The next step down is 4.06V where degradation is kept to a minimum both in terms of usable capacity and internal resistance.
4.04V is where cells become practically immortal.

For the minimum voltage, anything around 3V is fine for high Ni cells. For cells containing some form of silicon in tyhe anode, the activation region for silicon is around 3.4V so if you can avoid that, you'll never touch the silicon. Of course, you should choose another cell type if you're never going below 3.4V, so just go down to around 2.8-3.0V if you need close to max capacity for Si-C/Si anode cells.

How can I tell if the 50E cells I have fit this description?

 

[BlueSwordM]

The Samsung 50Es (or EVE 21700 50Es) are NCA cells with High Ni content using a Si-C anode (Si-Graphite specifically):

Cycle Tests on the Influence of Different Charging Currents—A Case Study on Different Commercial, Cylindrical Lithium Ion Cells

On the way to a Precise Battery, the generation of measurement results and findings based on them play an important role. Although cycle life tests are time-consuming and expensive, they can provide support and important information. Especially in the current topic of accelerating the charging...

www.mdpi.com

That means the 3.0-3.4V to 4.15V pareto-optimal rule applies

 

[Ethanator10000]

The Samsung 50Es (or EVE 21700 50Es) are NCA cells with High Ni content using a Si-C anode (Si-Graphite specifically):

Cycle Tests on the Influence of Different Charging Currents—A Case Study on Different Commercial, Cylindrical Lithium Ion Cells

On the way to a Precise Battery, the generation of measurement results and findings based on them play an important role. Although cycle life tests are time-consuming and expensive, they can provide support and important information. Especially in the current topic of accelerating the charging...

www.mdpi.com

That means the 3.0-3.4V to 4.15V pareto-optimal rule applies

Sweet.. Most days I can easily get away with 4.04 to 3.2-3.4 so that's going to be my daily charge. Thanks!!