what is the minimal safe voltage not to go under for good life span battery and storage voltage.

[want to build]

hello.
i build a prototype with used vtc4 2 years ago 13s 2p.
i bought a mini lunacycle charger with option 80% 90 % 100 % and 12345 amp

i read that charging at 1 amp is better for life span so that point is ok
if im not mistaken the life span is lesser if i charge the battery to 100% . it gives more cycle if charged until 90 pourcent and even better at 80 %.
1) is this info correct?

100 is 4.2 x13 so 54,6v
90 is 49.14 v
80 is 43.68.

i read somewhere not to go under 3.5v for good life span but that does not make sens since it is 45.5v hence more than 80 pourcent.

i feel confused about
2)what is the the voltage not to go under if i dont want to break the battery?
and 3) what is the voltage i should not go under if i want to have a good battery life span?

4 ) the fourth question is what is the ideal voltage to store a battery for long time?

5) for some reason when on 3amp charger and 80% the battery stays at 42v (it has been charged for one hour not moving) what does that mean since 80% of 54.6 is supposed to be 43.68v... would that mean that the max capacity charge of my battery is lower than 54.6 since the cells are used?
btw i tested 2 years ago all cells and chose those that were 4.16 and more.
tx

 

[john61ct]

Lifespan has nothing to do with the pack level voltage.

Use per-cell (1S) voltage for easy general discussion, then just multiply, say by 13 for a 13S pack.

Similarly, use C-rate for current, rather than absolute Amp numbers, 1C for a 3Ah cell is 3A, for a 12Ah pack is 12A.

You get best lifespan charging at 0.4C but only if your avg discharge rate is also moderate and other care factors are optimal too, e.g. avg LVC when discharging, see below.

In a propulsion context most people are happy charging at 1C or even higher when time is critical, and in hot ambient temperatures that should be fine.

When you have overnight, and a safe setup for unattended, then slower is fine, even 1A for a small pack.

For voltages, stopping at 4.05Vpc is a very gentle definition of full, better for longevity than 4.15Vpc.

Storage can be anywhere you like between 3.2Vpc and 3.8V, precision is not required

lower the better so long as self-discharge is never allowed to drop it below 3.0Vpc

and cooler the better, ideally in ziplocs in a fridge.

Never mind SoC% just use voltages, the correspondences between the two varies a lot with specific model / type / chemistry.

Now, when actively cycling, LVC voltage under load is a wildcard, calibrate against the RESTING voltage after isolated an hour.

For longevity, the AVERAGE over many cycles is what matters, and the higher the better.

3.4-3.5Vpc is good, 3.6-3.7Vpc is better

but it is a balancing act against capacity utilisation, IOW range.

 

[spinningmagnets]

When it comes to making the battery last as long as possible, the most important thing to do is limit the full charge voltage.

Since it is "possible" to charge these cells to 4.2V per cell, most chargers do this (13S x 4.2V = 54.6V). However, as soon as you use the battery for a minute or so, there is a sudden drop in the voltage and then the voltage flattens out and is fairly consistent. It then drops at a much slower rate. I point this out to show that if you charge to only 4.05V or 4.1V...you are not losing very much range. Maybe 1/20th of your range.

However, doing this can double the life of the entire pack. As far as the lowest voltage to limit the drain to...I don't know.

As far as the charge rate, it's not the amps of charge (you mentioned 1A). The problem is getting the pack hot when charging. What I mean is, a high-amp pack can be charged at 5A without getting warm. But, a small low-amp battery pack might get very hot at 3A. So...charge at any rate that doesn't get your battery hot. cool is good, warm is OK, hot increases the aging of the chemicals.

 

[Silvaticus]

High temperature and 100% charge damage the battery the most, especially if both factors are applied at the same time.
If you charge up to 100% then do not charge for future use. The best practice is to start using the battery as soon as it reaches 100% charge.

If the energy reserve in the battery allows you to charge up to 90%, and preferably up to 80% or even lower. Batteries in space are never charged more than 70%. However, remember that balancing is often not possible at these charge levels.

Discharge to 0% does not affect the battery life as much as high temperature and charge tending to 100%. Cycle 0-80% is preferred over 10-90%

The battery voltage during long-term storage should be about 40-50%. It is good practice to periodically check the voltage and return it to the optimum zone. Storing in the refrigerator, for example, also helps. A cooled battery should never be charged until it reaches the optimum temperature.

 

[john61ct]

Yes high temperatures hurt longevity, ambients as a long term factor.

But most especially internally generated, any rise detectable from the outside caused by high currents, charging or discharging.

Of course, the use case may require such "abuse" in which case the owner just accepts frequent replacement of the pack as inevitable. Some racing flyers only get say 40 cycles.

In which case charging to 4.2Vpc won't have much impact might as well get the extra 3sec of range.

But **definitely** true that sitting anywhere near Full for a long time, is more harmful than just charging to 4.2Vpc and then start discharging within the hour.

Again, maybe the user has no choice, but at least be aware of these factors and make informed decisions.

 

[john61ct]

Discharging to 0% will very quickly murder even a top quality pack, every LI chemistry with LTO as the sole exception.

Certainly if you define 0% as dead flat.

The **average** DoD% over the battery's life has a huge impact on cycle lifespan, a much stronger factor than the charge-termination voltage.

(Using at-rest isolated voltages here, those under load are meaningless. Also assuming other care factors well-coddled.)

If you are using the maker data sheet minimum voltage, say 2.5V as your 0%, just going up to 3.0V can double or triple lifetime.

And 3.4V or 3.6V double or triple again.

And just like avoiding the top voltage shoulder, the sacrifice of capacity utilisation is not significant.

 

[john61ct]

Batteries in space are never charged more than 70%. However, remember that balancing is often not possible at these charge levels.

Balancing can be done at any point in the voltage/SoC curve, if you have the gear to do so.

The fact that 99.9% of balancing circuits do it at the top, end of the charge cycle, is because that type of circuitry is cheap, not because top balancing is better for the cells.

 

[john61ct]

Cycle 0-80% is preferred over 10-90%

No, or rather can depend on how you define 0%, see above.

The absolute ideal for longevity, is lower capacity utilisation, centered around the midpoint.

(at rest isolated, other factors coddled, cool temps etc)

So assuming midpoint is 3.6V,

continuous cycling between 3.55V and 3.65V lifespan is likely to be 10000 cycles or more.

Calendar life issues may end up being the limiting factor rather than cycle count.

Cycling between 3.4V and 3.8V might be "only" 3000 cycles.

 

[john61ct]

i bought a mini lunacycle charger with option 80% 90 % 100 % and 12345 amp

Just realize that Luna putting those SoC% labels on the charger, does not mean they are accurate.

Would be better to just work with Voltages

> since 80% of 54.6 is supposed to be 43.68v

You CANNOT use % with voltage directly like that

Yes, 54.6V is 100% Full, but 43.68V is lower than you should go, call it maybe 10% SoC

the curve / table of resting voltage vs SoC% varies depending on the specific chemistry used in the battery, from one model cell to the next, even in variations between production runs for cheap cells.

100 is 4.2 x13 so 54,6v
90 is 49.14 v
80 is 43.68

Those last two numbers cannot be right, maybe measure again?

> 3.5v for good life span but that does not make sens since it is 45.5v

Yes that does make sense, well below the 50% midpoint when isolated and at rest.


> what is the the voltage not to go under if i dont want to break the battery?

in theory, the minimum listed on the maker datasheet, say 2.5Vpc

but I would use 3.1V isolated and at rest as my lowest definition of 0%

> what is the voltage i should not go under if i want to have a good battery life span?

up to you, see above, but somewhere between 3.4V and 3.7V isolated and at rest. How much Ah capacity and actual range sacrificed will depend on that battery's chemistry. Experiment and see.

...

Never let a pack sit for long when not being used with a BMS attached; disconnect it so the cells are fully isolated.

Or frequently check the voltage level and top up to your desired storage V



> for some reason when on 3amp charger and 80% the battery stays at 42v (it has been charged for one hour not moving) what does that mean?

Your pack has likely reached EoL and needs to be replaced or rebuilt with new cells.

 

[MoneyPit]

I put these charge charts together some time ago as a reference. 36v - 72v. They're just that: A benchmark. Different cells and different chemistries all have differing discharge curves, so a mathematical generic chart is imperfect, but you have to start somewhere.

https://talesontwowheels.com/2019/10/02/li-ion-ebike-battery-charge-charts/

As noted, Depth of Discharge is as bad or worse than 100% storage charging, or heat. You don't hear about it on the typical "how to" blog posts because, I think, so many people need a basic education on li ion longevity. The 80% bit is considered low hanging fruit. Drilling that into people's skulls will at least get them somewhere positive if it sinks in. Its hard enough getting a mainstream, casual ebike owner to accept an 80% limitation, but if you add to that telling them that around 40% should be the floor, you'll lose them. Especially with how small mainstream packs tend to be.

Its worth pointing out: these limits are good for your battery, but if they aren't good for you, don't do them. Enjoy / use the bike. Charge the hell out of it and ride it into the ground if thats what makes you happy, or what you need to do your job. Just know the consequences and plan accordingly.

 

[john61ct]

The 80% number is a gross exaggeration.

The stored energy actually available for discharge

between even 4.05V and 4.2V is nowhere near 20%

of the actual working capacity of the cell.

With most chemistries used these days probably not even 10%

And same with that 40% number.

Measuring V at rest isolated, the stored energy actually available for discharge

between say 3.5V and 3.0V is usually well below 20%.

So a care regime giving really good longevity might "sacrifice" 30% of **theoretical** max capacity.

Comparing to one based on maker nameplate specs that either is a complete lie, or results in under 50 cycles to me is unrealistic.

And of course IRL actual working capacity is always falling over the cell lifespan anyway, and that needs to be realistically taken into account in the planning / design stage.

As I stated in my first post, best to just use objective Voltage in such discussions, SoC% really is too nebulous.

 

[Silvaticus]

But most especially internally generated, any rise detectable from the outside caused by high currents, charging or discharging

You are certainly right, but the terms you describe may never or almost never apply to a user's battery use. This largely depends on proper design so that it is as close as possible to the nominal current value during use.
At the same time, the negative factor I described can arise with each charge cycle. Naturally, in the most negative scenario.

Discharging to 0% will very quickly murder even a top quality pack, every LI chemistry with LTO as the sole exception.

Certainly if you define 0% as dead flat.

The **average** DoD% over the battery's life has a huge impact on cycle lifespan, a much stronger factor than the charge-termination voltage.

Naturally, to what I have in mind DoD 0%. Needless to say, this cell voltage differs slightly from manufacturer to manufacturer and depending on the cell chemistry used.

There are certain cells that allow them to be discharged down to 2.5 volts. In truth, most often this does not make any practical sense, since the remaining energy beyond the 3.1 volt threshold is infinitely small. But it can make a difference on some long journey, when by reducing the power of the controller, you can get an additional good few miles to the place to stay overnight or charge.

We came to this conclusion at our national forum analyzing the recommendations in the datasheet from Samsung. Perhaps these conclusions are somewhat erroneous. It would be great if we could refine these findings. If necessary, I bring corrections to our forum. I will add pictures in the following posts.

Balancing can be done at any point in the voltage/SoC curve, if you have the gear to do so.

This is obvious, as well as the fact that for the vast majority of users there is no way to install such equipment.

Never let a pack sit for long when not being used with a BMS attached; disconnect it so the cells are fully isolated.

Or frequently check the voltage level and top up to your desired storage V

This is a very important remark. Since the connected BMS will sooner or later suck out all the juices and can permanently kill the cells.

 

[want to build]

tx everyone, after having put it to charge100 pourcent a 1 , 24 hour for some reason it came down to 40 volt. i have absolutely no clue why it would decreance like that

since the original cell where not optimal i plan on using what is still in there so using the 2.5 v theshcold so i would stop using it at 13x 2.5 =32.5v using a voltmeter.
iwonder how many km i could do from 40 v to 32.5v. 13s2p.

 

[john61ct]

Again, your pack has likely reached EoL and needs to be replaced or rebuilt with new cells.

To check, put it on another known-god charger.

If this is the case do NOT continue to use it, fire danger!

 

[want to build]

MOTOR NOT MOVING!

https://imgur.com/gP2jlqd
the 2 pin white is the only thing that is left unused .What does it serves for? is the reason why nothing works?
here is what i can see.

https://imgur.com/HZalhvO

https://imgur.com/NxdDt1u

https://imgur.com/PKE39SG

https://imgur.com/Tnx2mjH

https://imgur.com/zPp8VAv
https://imgur.com/YET1qK7
https://imgur.com/FqZjlC8

what to conclude from those info? sorry some are repetitive but not all

 

[john61ct]

Completely new topic, probably worth a new thread to get more eyeballs.

IMGUR is great, but does allow a single link to a gallery.

I suspect more text details needed?

 

[want to build]

Completely new topic, probably worth a new thread to get more eyeballs.

IMGUR is great, but does allow a single link to a gallery.

I suspect more text details needed?

good idea.
do you know how to join the links into only one?

 

[john61ct]

Branched to here
https://endless-sphere.com/forums/viewtopic.php?t=113146

 

[tmho]

As far as the charge rate, it's not the amps of charge (you mentioned 1A). The problem is getting the pack hot when charging. What I mean is, a high-amp pack can be charged at 5A without getting warm. But, a small low-amp battery pack might get very hot at 3A. So...charge at any rate that doesn't get your battery hot. cool is good, warm is OK, hot increases the aging of the chemicals.

What temperature do you suggest for "warm" and "hot"?

 

[ZeroEm]

Try This:
Motor Temperature

by tmho » Aug 30 2021 2:33am

spinningmagnets wrote: ↑Aug 23 2021 8:46pm
As far as the charge rate, it's not the amps of charge (you mentioned 1A). The problem is getting the pack hot when charging. What I mean is, a high-amp pack can be charged at 5A without getting warm. But, a small low-amp battery pack might get very hot at 3A. So...charge at any rate that doesn't get your battery hot. cool is good, warm is OK, hot increases the aging of the chemicals.
What temperature do you suggest for "warm" and "hot"?

 

[spinningmagnets]

Id recommend keeping the battery, controller, and motor under 140F / 60C, but of course, many builders have run their motors up to 200F / 93C

If you are running your motor up to 200F / 93C and the motor is surviving, that's great, but...you are converting a LOT of battery watts into waste-heat instead of acceleration...

 

[eMark]

1) is this info correct?

100 is 4.2 x13 so 54,6v
90 is 49.14 v
80 is 43.68.

100% is correct (54.6v) but not the rest. If Controller cut-off was 41.6v (3.2v/cell) then the following are the voltage percentages ...

100% (13 x 4.2v = 54.6v)
90% (13 x 4.1v = 53.3v)
80% (13 x 4.0v = 52.0v)
50% (13 x 3.7v = 48.1v)
30% (13 x 3.5v = 45.5v)
10% (13 x 3.3v = 42.9v)
my 10s controller cut-off is 32.0v (3.2v/cell). If your controller cut-off were 3.2v/cell the cut-off would be 41.6v.

Setting your Controller cut-off for your 13s2p at 3.3v/cell (42.9v) will significantly increase cycle life longevity versus discharging to 2.5v (32.5v). The way you'd figure with a 13s controller cut-off at 32.5v is 4.2v - 2.5v = 1.7v x 10% = 0.17v ... 4.2v - 0.17v = 4.03v x 13 = 52.39v (90%) and 4.2v - 0.34v = 3.86v x 13 = 50.18v (80%).

i read somewhere not to go under 3.5v for good life span but that does not make sens since it is 45.5v hence more than 80 pourcent.

30% as shown above is 45.5v; 80% as shown above is 52.0v ... figuring Controller cut-off voltage of 3.2v per cell or 41.6v for your 13s2p Sony | Murata \ VTC4 battery pack.

i feel confused about
2)what is the the voltage not to go under if i dont want to break the battery?

VTC4 datasheet cut-off is 2.5v (32.5v), but that should be avoided. Build at least a 13s3p battery pack next time.

and 3) what is the voltage i should not go under if i want to have a good battery life span?

3.2v (41.6v) being you have limited capacity (2p). 3.4v (44.2v) would be even better ... SO THINK ABOUT BUILDING a 13s3p if enuf room is available.

4 ) the fourth question is what is the ideal voltage to store a battery for long time?

3.75v - 3.85v meaning you may need to periodically recharge depending on amout of self-discharge.

5) for some reason when on 3amp charger and 80% the battery stays at 42v (it has been charged for one hour not moving) what does that mean since 80% of 54.6 is supposed to be 43.68v... would that mean that the max capacity charge of my battery is lower than 54.6 since the cells are used?

You have to decide your cut-off voltage (e.g. 3.4V) before you can calculate 80% ...

4.2v - 3.4v = 0.8v x 20% = 0.16v ... 4.2v - 0.16v = 4.04v x 13 = 52.52v (80%) versus 52.00v (80%) with cut-off at 3.2v/cell versus 50.18v (80%) with cut-off at 2.5v/cell.