Question about % and charging

[Debunker]

I plan to squeeze has many charge cycles as possible of my lunacycle 52v-24ah pack.

I hear that the golden rule is not to charge above 80% unless you plan a long ride or want to balance the pack, and not let them drop below 20%.

So here's the question, the readings show around 50.1v, Battery 52v, no problem... but the built in metter, despise showing the same voltage, marks the battery whit just 2 bars out ot 6 of the overall indicator... so.. is it already at 20% at 50.1v? or the indicator takes that in consideration and considers 20% left as no remaining bars? should I recharge it already or make a few more rides until drops around 47v? What is the exact 20% of 52v battery?

The other question is how frequent must I charge at 100% to balance the pack, 1 time every 2 months? every month? The use of the bike is not too intense, I doubt I need to recharge it more than 1 time per week at 80% or even less, because the 24ah and limiting the output whit a 3 speed electric gear gives me a lot of range.

Is the aging of the battery another issue?

 

[amberwolf]

The indicators are probably arbitrary, just voltage based, and which voltages depends on which meter they install in it. It's even possible to have the meter for a lower-voltage pack installed in a higher-voltage one, so it looks full even when it's empty. Or a meter for a higher voltage pack in a lower-voltage one, so it looks empty even when there's capacity left.

Even assuming the meter is the correct one for that pack, until you test it you won't know what each level represents in reference to that pack. You can use a voltmeter to check it as you charge it and watch each one light up. but that only tells you what voltage each one turns on at.

You'd have to test using a wattmeter to see what actual percentage of capacity (how many Wh) are either charged or discharged for each light in the meter, if you want to know exactly what percentage capacity each one represents.

 

[dogman dan]

First thing would be to ignore the bars.

To really know the % capacity you are using, at a very minimum you need an accurate voltmeter, and better still a watt meter.

FWIW, charging to 100% is not particularly harmful, but letting the pack sit that way is more harmful. So when you do balance it, go for a ride asap.

At some point, you have to balance out many things. How far you need to go each trip may mean you only need to charge to 80%, and discharge to 60%. Or it might be you need to go 90-10, to make your typical trip.

Personally, I just try not to discharge that last 10% each cycle, and charge to either 90% or 100% depending on the ride length. Its the last 10% in my experience that unbalances your pack, assuming no bad cells exist. So Id rather charge 100% when I need that exta mile, than discharge to 1%.

 

[kdog]

Idk the Luna pack so correct me if I'm wrong...I'm assuming its Li-ion
52v packs are usually 14s. 14x4.2 =58.8 (full charge)
90% is ~4.1V/cell = 57.4v
80% is ~4.0v/cell = 56v
50v/14= 3.57v/cell = nearly flat ( your bar meter is correct)

I'd say full charge every month or two for balance -leave it on for a few hours post green light. How are you going to monitor charging to correct voltage?

 

[Debunker]

Li-on make out of panasonic GA 18650 cells.

I got a smart charger, 2,5amp whit 80% 90% or 100% option.

So, to go for 1000+ cycles, I must recharge when the watt metter shows less than 50v, and never let it drop below 48v, is that?

 

[e-beach]

Unless something has changed in the last year or so, Justin Le was saying that the top end of the charge is what shortens the battery life. So going to the manufactures low voltage cutoff isn't a problem. Charging to the full manufacture charge voltage is what will shorten the battery life.

Find out what kind of cells you have in your pack. Charge to 90% of manufacture recommend full charge. Don't be afraid to run you pack to near low voltage cutoff. (don't get stuck pedaling without power) Periodically balance charge your pack.

Get a good watt meter to track your watt hours usage under the 90% charge scenario so you can gain high accuracy knowledge of your actual range under a 90% charge to your pack.

Gain access to your cells or BMS and learn to meter your individual cell groups to see how far they get out of balance on each ride. First meter them when fully charged and balanced. Write down the voltages. After you take the pack to near lvc, meter them again to see what the voltages of the cell groups are. Some groups might be lower then others. Once you charge to 90%, meter them again to see what groups take a charge and which don't charge as much. Ride to near lvc and meter them again. Keep writing all your findings down and repeat the process until you know the characteristics of you pack. Once you understand what is actually happening to your pack you can then know how often to balance charge.

 

[dogman dan]

To clarify what I was saying. you can go to the bottom without shortening the life. But the fact is, if you do that, then you need to balance. The deep discharges unbalance the pack, in my experience.

So avoiding the last 10% is what I do to avoid having to balance. I don't hesitate to charge to full, if I will ride the bike immediately after it gets done. But as stated above, you usually need to leave the battery on the charger, or unplug, wait 15 min or so, then start charging again to get it to fully balance. The charger stops when one cell is over full, then the bms discharges that high charge cell back to 4.2v. Then the charger re starts. Or not, some chargers you have to unplug briefly to trigger a restart to red.

So if you want to charge to 4.1v most of the time, you have to keep er balanced. No high discharge rates, and less use of the last 10%. And ESPECIALLY, no high rate discharges of the last 10%, when internal resistance is high.

Watch your bottom end, and you can balance as little as once every 3 months. But do balance every time you do use 100%.

 

[Ykick]

Battery pack charging discussions and knowledge will always be a bit like Oil change recommendations. Someone will apply an exception that appears to be “legit” but applied by someone else at different time or place, things may not always turn out the same results.

There’s simply numerous factors at work which sometimes can and will influence any “practical” measurements/benefits about short-charging cells for increased longevity.

But IF you’re absolutely, positively, never, ever, gonna come close to needing full battery capacity perhaps regular 80% top charge might be of some measurable advantage? Personally, I don’t wanna take that risk. What if I forget my phone and double back? How about a strong headwind or unplanned detour? Those things can and will happen riding the roads on a regular basis.

The other problem about not charging to 100% every once in a while is that the pack BMS may never balance the cell groups. Of course, good cells, construction and sensible use should never really never require balancing but it’s not a perfect world and things can also change over time - so that may be another “thing” about short charging cells which may come back to haunt someone who just charges to 80% every cycle over a long period of time?

As I discovered from years of using Lithium chemistry coupled reading and watching lectures, sitting full SOC appears to be the most damaging condition. Yet it’s so very easy and simple to prevent.

If you’re already full SOC and realize that you won’t ride for several days, burn off a little charge. Or, perhaps you know you won’t be using the pack for several days simply charge to 80% and then it will only require a quick top charge to 100% when you’re ready to go again.

Merely bringing cell SOC down from 4.2V to 4V is much greater benefit than bringing cell SOC down from 4V to 3.8V. I consider this sort of technique “low hanging fruit” while it isn’t very hard to do and won’t do any harm.

 

[dogman dan]

That seems to be the most practical approach to charging to 100%, just ride around the block right away, if you don't plan to ride after all.

Just so simple. Don't let it sit around at 100% is all you really need.

I would not mind though, if you could easily swap in a bms that balances the pack at 90% charged. If 90% is not enough, then you need to up your battery size by about a third or so anyway.

With the three position switch charger, its pretty practical to just charge to 90% each cycle, and when you want to ride, put it on 100% about an hour before you take off. If not planning to use for a few days, I just charge to half full for the storage.

FWIW, I run my charger like that on no bms packs. I set it to 50%, 90% , and 95%. So I never actually charge to 100%. I balance the pack manually, using single cell charging to bring up any low cells, and balance at 4.15v. Then even when deep discharging, I still leave about 5% on the bottom. A typical ride never gets close to that deep, usually no lower than 3.7v when I get home, on cells that are empty at 3.4v.

If you add balance plugs to your pack, you can then charge to 80% or whatever, and sort of balance it there, manually. Even at 90%, balancing is kind of inaccurate, since they don't fully balance till 4.2v. Balancing lower as I do at 4.15v is only close enough balanced, not true top balanced. Since I leave some on the bottom too, its close enough.

 

[Matador]

I plan to squeeze has many charge cycles as possible of my lunacycle 52v-24ah pack.
I hear that the golden rule is not to charge above 80% unless you plan a long ride or want to balance the pack, and not let them drop below 20%.

The third golden rule is to let your pack at 50% state of charge (3.600 volts or 3.700 volts, depending on your chemistry) or less (30-50%) when you have to put in storage for long time periods. This reduces the effect of calendar aging (OF course, UPLUG THE BMS before long tem storage, or quiescent current drain of BMS could fully drain your battery beyon recoverable). See my thread for scientific explanation and publication :

https://endless-sphere.com/forums/viewtopic.php?f=14&t=86777&hilit=calendar+aging
This is hard data to relie on. Not just opinions.

As people said previously and also Justin, it's charging close to 100% that's shortening battery life.

On the other hand, when discharging very low, cells are more likely to become unbalanced... DC internal resistance increases exponentially at this end of the spectrum (see graph below).... So one cell at 5.00% State of charge (eg: 3.201 V) might have a very much different internal resistance value that one cell at 5.01% State of Charge (eg: 3.204 V). No system is perfect in practice. Very small voltage differences between cells exist within a pack.... So when the pack is close to fully discharged, this resistance heterogeneity is aggravated and non uniform cell internal resistance promotes unbalanced cells with deep-discharge cycling...

 

[fechter]

What I do now is charge to about 80% after a ride and let it sit at that level, then charge to 100% immediately before going for a ride. The last 20% takes less than 1 hour. If you plan to store the pack for a long time, 50% may be ideal, but the BMS will tend to slowly drain things so I will still charge to 80%.

 

[Debunker]

Thanks for all the advises, I get it more or less... but, even If I give the best treatment, the pack eventually gonna waste itsef as time pass because of the aging effect? Thats sad...

When that happens, I hope we have portable nuclear reactors like the ones in fallout 4 that fits in power armors.

 

[amberwolf]

Unless something has changed in the last year or so, Justin Le was saying that the top end of the charge is what shortens the battery life.

AFAICR, Liveforphysics (a battery expert) said that higher voltages on the electrolyte degrades it (worse the higher the temperature is). Specifically:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=27263&p=229809
https://endless-sphere.com/forums/viewtopic.php?f=3&t=55269&p=823432
https://endless-sphere.com/forums/viewtopic.php?f=14&t=11171&p=171405

Another post where he acknowledged this
https://endless-sphere.com/forums/viewtopic.php?f=14&t=45357&p=661432

Probably more stuff out there by others, too, but I only did the one search.




I don't know any of the specifics or mechanisms myself, and am just speculating, but this is probably why the lower voltage chemistries like LiTO and LiFePO4 have a longer shelf life, vs ones like regular LiCo and LiMN, etc., and why charging cells to lower voltages than their max increases their lifespan--more time spent at higher voltages means faster degradation of electrolyte.



I don't know if the same mechanism occurs at extremely low (dead) voltages; I suspect it's a different issue.

 

[spinningmagnets]

Those "bars" on the battery status readout are LEDs. They all run off of the same voltage, so....each one has a different resistor in-line with it. Dropping the pack voltage from 48V down to running a bar-read-out probably is fairly inaccurate. If there are four bars, does each one represent 25% ?

Here's a discharge graph from a fairly common lithium 18650 cell. If the 4-bar LEDs read zero volts when the pack is at 3.3V per cell, then for the majority of the ride, the actual cell voltage is fairly flat (one of the benefits of lithium over other chemistries). Also notice there is a sharp downturn right at the beginning of the ride. By only charging to 90%, you are not losing 10% of your range, you are only losing 1/17th of the range.

Having a pack status readout of four LEDs is useful, but wildly inaccurate.

I agree with fechter. If you "must" recharge right after a ride, recharge to 80% (if your changer has that option). Then charge to 90%-100% just before the ride. With a big 24-Ah pack, you may never need to charge to more than 80%. I ride on the week-ends, mostly...and I used to recharge to 100% after every ride, but...no more. When I was doing that, my pack is sitting at 100% for 6-1/2 days a week. This information has been out there for quite a while, but its only been recently that I have found it, and took the time to read it.

https://www.electricbike.com/how-to-make-lithium-battery-last/

 

[Matador]

Thanks for all the advises, I get it more or less... but, even If I give the best treatment, the pack eventually gonna waste itsef as time pass because of the aging effect? Thats sad...

When that happens, I hope we have portable nuclear reactors like the ones in fallout 4 that fits in power armors.

unfortéunatly, there are limits to miniaturisation of nuclear reactor. The limiting factor is not the reactor... it's the shielding agains the nasty radiation...
Precaution on nuclear are not optionnal. Just look at Pripyat, lake Karashay, fukushima, goiania, etc... contaminated forever

 

[dogman dan]

Id settle for a dramatic increase in solar cell efficiency. if a 2x2 square could put out 100w of 48v, man, that would be a dream. Right now that would take about 2x 16 foot of panel.

Even just doubling the current efficiency would be pretty nice, even if you still had to tow a trailer, or have a roof, 8 feet long.