Battery cycles

[Hickbeard]

When we talk about optimum discharge /recharge cycles 80% to 40% is considered optimal correct?

Is this resting voltage or under load?

Say at rest my 14s pack is reading 51v (46%). If I open the throttle fully it may drop to say 48v (23%) and then start to creep up as acceleration tails off. Is this still considered in the optimal range or is this damaging the potential life of the battery by going too low? Coming off the throttle completely sees it back up to 51v ish.

Thank you muchly.

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[pwd]

For discharge, I cap it under load. The same way that most controllers would hit their low voltage cut-off and it prevents the cells from ever going over the "cliff".

 

[Hickbeard]

For discharge, I cap it under load. The same way that most controllers would hit their low voltage cut-off and it prevents the cells from ever going over the "cliff".

OK cool.

So as the battery gets lower ride it more conservatively I guess.

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[pwd]

Ya that is a good way to do it, then you can eek those last watt hours out of your pack without going under the low voltage limit. Some controllers will ramp down max power as you approach the low voltage cut off too.

 

[Hickbeard]

Yeah so fully charged I can pull 1700w, about now most is 1500w.

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[john61ct]

At the top end while charging, backing off by 0.05 to 0.10Vpc is conducive to optimal longevity but certainly not sacrificing that much range.

Besides the voltage setpoint, better to just Bulk / CV charge, stop at the setpoint or only holding Absorb / CV A few minutes

if your charger AHT is not adjustable, then lower the voltage setpoint a bit,

it really is the combination of charging V and endAmps that determines the ending SoC% and resting voltage.

or just use a HVC / contactor to terminate charge.

That allows use of dumb PSUs or DC-DC converters rather than paying more for proper chargers.

 

[john61ct]

At the bottom end, the more you leave in the pack the longer they last, so that is a judgment call, but 40% is a lot higher than most do.

Resting voltage can be roughly mapped to a precise SoC% for a given pack

and then guesstimate how that relates to V under load at various current rates / throttle / hills etc

calibrating your intuition over time as you gain experience, cross-referencing with your wattmeter / coulomb counter.

3.1V at rest would be a minimum definition of 0% SoC, LVC under load at 3.2-3.3% might be ballpark 70-85% DoD.

 

[Hickbeard]

Wow thanks John that's a lot of acronyms to Google. [emoji2357][emoji1317][emoji23][emoji3059]

So upper voltage isn't the problem. Low voltage is. So fully charging but only going down to higher voltages will result in extended life over going from full to lv cutoff.

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[john61ct]

Wow thanks John that's a lot of acronyms to Google

Let me know any that aren't readily found.

>So upper voltage isn't the problem.

Certainly it has an impact on longevity, charging to full vendor spec and then holding a long Absorb time will kill cycles off the back end.

But letting a pack sit at anywhere near Full for a long period even more so.

If you just meant "staying lower is easier to achieve" yes that is true.

There are many other longevity factors, if you are using very high C-rates for example, then you will get more limited gains from the two discussed here.