Li-Ion: Should I top off the battery cells to 4.2v?

[neptronix]

Do your own research, i have given you the links, and you can use your googler and find out if what i am saying is correct instead of knee jerking and trying to prove me wrong by using different metrics every time i say something.

As funny as it is to me, i think you would be better for the wear by educating yourself. Please do it, for the better of yourself and for the better of the poor newb who has to read these posts 8)

 

[DrkAngel]

As funny as it is to me, i think you would be better for the wear by educating yourself. Please do it, for the better of yourself and for the better of the poor newb who has to read these posts 8)

I research my posts!
Still looking for your link to evidence that 4.1v causes battery to last twice as long as 4.2v?

 

[neptronix]

As funny as it is to me, i think you would be better for the wear by educating yourself. Please do it, for the better of yourself and for the better of the poor newb who has to read these posts 8)

I research my posts!
Still looking for your link to evidence that 4.1v causes battery to last twice as long as 4.2v?

Where are the links for your research?

If you see earlier in this thread..

Here is a great thread on ES.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=15552

Shallower discharges seem to extend cycle life a lot. By how much... seems to depend on the chemistry.
That being said i am charging my lipos to 4.1 instead of 4.15 now. I am shooting for 1000 cycles.

I admit, the 50% cycle life by charging to 4.1 instead of 4.2 claim is one of the better case scenarios and it does apply to lipo primarily. From what i have seen, it applies to some non-polymer li-mn and lico chemistries too.
RC lipo and lithium titanate

Your cells may not have such an extreme effect.

I still think it's smart to charge to 4.1v/cell. It gives you headroom against disbalance, and will extend your cycle life to some degree with every chemistry.

Also it is agreed upon that storing batteries closer to their middle charge voltage will extend their calendar life greatly.
This is why EV battery packs are designed to charge a bit lower than the max voltage for said chemistry. The Nissan Leaf charges to around 90%, The Volt is in the 60% range ( it has lipo ), The Tesla charges to about 90-95% but has an option on to charge to 3.9v or so to extend the battery's lifespan.

Here is an interesting post from Tesla motors, remember that the Tesla is using lico laptop cells. Please read it, drkangel. if anyone knows about EV use of laptop cells, it's them.

http://www.teslamotors.com/blog/bit-about-batteries

 

[DrkAngel]

Well I wasted a lot of time reading your links.
There was nothing to support your claim that 4.1v vs 4.2v doubles cycle life!

I did find that reduced 4.15v charge decreases usable energy by 5%.
Most everyone, in the "thread" supported that cycle life is reduced by deeply discharging, or by charging above 4.2v, exactly as I claimed ...
Didn't learn anything new!
Just found, more support, reinforced, my position.

Makes me wonder how you can read the same articles, but still think differently!

 

[neptronix]

You don't have to listen to me, any people on the forum, or any of the links i provided, whether they be academic, from companies whose business is selling EVs, or what.

The problem is that we don't know the chemistry of tuxman's battery pack, it could be a lithium polymer ( lico ), lithium titanate, or lithium magnesium ( polymer or not ) so it is safer to say keep the original voltage that the pack is designed for, in fact it would be better to reduce the voltage.

Of course charging to only 4.17v will prolong lifespan, percentage unknown.
The question should be, "How important is an extra 4% range, to you?"

You claimed that charging to a higher voltage will prolong the lifespan of a battery, and that's what started this.
You claimed that the difference was 4% and i proved that it was less, and it really depends on which battery chemistry we're talking about.

So do me a favor, and if you don't agree with me, suspend judgement and find out on your own whether or not this is true. In the meantime, don't go telling people whose battery chemistry you are not aware of, that they should charge to, or keep their batteries charged at the max voltage.

 

[DrkAngel]

Of course charging to only 4.17v will prolong lifespan, percentage unknown.
The question should be, "How important is an extra 4% range, to you?"

You claimed that charging to a higher voltage will prolong the lifespan of a battery, and that's what started this.
You claimed that the difference was 4% and i proved that it was less, and it really depends on which battery chemistry we're talking about.

Learn to read!


I clearly stated that charging to 4.17v will prolong lifespan, compared to, the full charge 4.2v.
That would be at an estimated 4% loss of energy storage capacity.

I'm pretty sure that that was made crystal clear in it's original context!

Sadly, I must conclude that you tend to see, only what you want to see.
The alternative is that you are illiterate?
Possibly dyslexic?

 

[neptronix]

Me:
By the way, your batteries charge to 4.17v per cell for a reason.
There is very little energy above 4.1v per cell in the first place.
Don't bother charging it above 4.17v, that is just reducing their lifespan even more.

You:
I charge to 4.2v, and get 8 miles before my pack drops to 4.1v.
Of course charging to only 4.17v will prolong lifespan, percentage unknown.
The question should be, "How important is an extra 4% range, to you?"

There's the context.
You did not directly tell the original poster to charge to 4.2v per cell, but you did insinuate that the only difference is 4% of the extra range.

And it does sound like you are saying 4.17v will prolong the lifespan.. since the original poster's pack is already charging at 4.17v per cell, it sounds like you are suggesting that this is good for the lifespan, when in fact, for a handful of chemistries that have a nominal voltage of 3.7/3.8v, the exact opposite is true.

 

[DrkAngel]

Sorry ... I guess I'll have to give up on you.
I can only recommend that you take some remedial English classes ...

 

[neptronix]

The feeling is mutual.

 

[stanz]

WOW, you guys are serious!

To beat a dead horse, we still don't know tuxman's battery chemistry so we can't really tell him what's the safe top charge level.

His original question involved whether or not he should "top off" his cells. I did a BUNCH of reading on the Internet and found that one type of chemistry does like to be topped off, I don't recall which one but I know it's not Lico. (That's the type I'll be using and topping off will lessen capacity.)

I have only found one site that makes a specific claim as to how to double the life cycles of Li-ion batteries and it's for Lithium Cobalt.

"-3.92V/cell is the best upper voltage threshold for cobalt-based lithium-ion. Charging batteries to this voltage level has been shown to double cycle life. Lithium-ion systems for defense applications make use of the lower voltage threshold. The negative is a much lower capacity."

The flip side to this is some of the data collected by NASA on the Mars rovers. They abused the batteries and they have exceeded their original design specifications. For instance: the solar panels became covered during a sand storm and it took a while for them to clear. In the meantime they discharged the batteries far below optimum levels and it didn't seem to effect future capacity. I realize that NASA may not be the best reference point because they do tend to over-design their systems but they do keep accurate data on each charge/discharge cycle.

So, to summarize, without knowing the battery chemistry we can't give an accurate answer.

 

[tuxman]

Still, no word back from the manufacture. Depending on the type of Lithium; Can I gain charge cycles by sacrificing capacity?

I don't need 12ah, 10ah (85%) would be fine, which allows 8ah usable capacity, factoring in 2ah (20%) left unused. I calculated that I am using 4ah during my commute each way and can charge at work.

From what I've learned so far is that topping off at 4.2v or higher may decrease the life of the battery. Thank you again for your replies.

 

[DrkAngel]

Still, no word back from the manufacture. Depending on the type of Lithium; Can I gain charge cycles by sacrificing capacity?

I don't need 12ah, 10ah (85%) would be fine, which allows 8ah usable capacity, factoring in 2ah (20%) left unused. I calculated that I am using 4ah during my commute each way and can charge at work.

From what I've learned so far is that topping off at 4.2v or higher may decrease the life of the battery. Thank you again for your replies.

If you presently charge to 4.17v, then 4.2v would increase your range a mere 4%, and would decrease your usable "cycles" by, probably, that percentage or higher.

More important is how deeply you discharge your batteries, most protection circuits cut off at 3v, or lower. For best "life" do not let your battery discharge below 3.5v, never let "sag" below 3v, even while under heavy drain.

 

[neptronix]

^--- very important, but it is also proven that leaving batteries charged at their maximum voltage will degrade their cycle life.
If you are going to reduce the range of the charge, you are best cutting the voltage from the top. Your BMS is programmed to prevent over-discharge already, so don't worry about the low charge so much.

Unfortunately there may be no way to adjust the top of your charger's voltage.

So the best you can do is, if you are letting the pack sit around for over a few days, leave it charged to around 33%-66%.
Your battery's chemistry may have a major cycle life benefit from charging to a higher voltage, but we don't know. The easiest way to find out is to find who manufactures those cells, find the spec sheet, and hope that they provide said information.

Every chemistry is a bit different so i can only give you generalized information.

And if you want total control over your battery's parameters, the best way is to roll your own pack.
As for this one.. rock it 'till the wheels fall off, i say 8)

 

[tuxman]

The HP8204L3 charger is adjustable. More info on the 4.2v subject here http://endless-sphere.com/forums/viewtopic.php?f=14&t=16800

 

[neptronix]

Sweet!
Try out 4.10v and see if it works for you.
4.0v is best but i think it would reduce your capacity a bit too much. Best to leave a buffer in.
If you have a LVC on your infineon controller, set it about a volt higher if you have the programming cable.

Both of the changes should get your DOD closer to 90%.

 

[RVD]

if you charge up to 4.1 and discharge down to 3.7, how many mah do you generally get out of the battery? from some of the graphs that i've seen, it looks like you would still be getting a good 4000-4500mah out of a 5000 mah pack right?

today i went for a test ride. ride was mostly flat and i pedaled somewhat. i used a 12s3p pack. all data is according to my CycleAnalyst (shunt value set to 4.0mOhm). voltage started at around 49.2v. i went 9.893 miles and ended at 46.6v. 4.136ah used. 195.05 watt-hrs. 19.8 wh/mi. Amax 41.83. Vmin 45.1. max speed 26.4, avg speed 14.0. 42 minutes 16 seconds.

since i was in 3p, i should have 15ah full capacity right? since i'm not running at full voltage on the high end and plan to stop riding before it gets too low, i'm still guessing that i should have around 12ah or actual use.

however, it looks like my packs drained from 49.2 to 46.6 so 2.6 volts dropped. since i'm planning ride down to 3.7v, that would be 44.4v. my plan is to ride until the CA says 44.4v at the lowest in terms of range. i haven't actually tried this yet since i'm still tweaking my bike and i don't want to get stranded somewhere. however, since i used up 4.136ah and voltage dropped 2.6v, if the drop is similar for the next 2.6v (linear), that would be ~8.3ah used? another 2.6v drop would take me down to 44 which is lower than capacity.

so my question is...how much range should i actually get out of my batteries? my commute is 17 miles. will my 12s3p pack get me there? will a 12s2p pack get me there?

for a 12s pack, am i approaching this correctly when i say that i plan to ride until my CA reads 44.4v? i'm also assuming that 44.4v at steady (not wot because of voltage sag).

 

[neptronix]

RVD, if we are talking about lipo here, i posted my lipo graph earlier, so check that out.

lico ( 4.2v max ) curves are similar. Some have their middle voltage at 3.7v. Lipo's middle voltage is 3.8.

I wouldn't discharge further than 3.5v/cell ( resting ) for either chemistry, unless your pack is very well balanced, which would be a rarity for hobbyking lipo or say, recycled laptop battery packs.

 

[RVD]

Hi neptronix, I actually got my data from your graphs. If I interpreted correctly, it really looks like going 4.2 to 3.7 in lipo (good quality turnigy) 5000mah should get around 4500mah or at least 4300mah. But it just didnt seem that way from my ride today. I could easily be misinterpreting your graphs though.

 

[neptronix]

You will get a definitive answer from your balancing charger. It will tell you how many mAH it put back into the pack when you stick it on. My guess is, low 4000's figure. Some energy will be wasted via balancing, so do a non-balanced charge to get this number.

Different formulations have different discharge curves though. The best number is the figure you get from your instruments
Having a turnigy watt meter, or correctly calibrated cycle analyst helps a lot. Those will work too, to provide you the number you're looking for.

 

[tuxman]

This was a great read: Battery usable capacity vs Max charging voltage https://endless-sphere.com/forums/viewtopic.php?f=16&t=9268

Quote:
Cycle life vs charging voltage:
The cell phone industry did a study looking at the effects of ending
charge voltage on cycle life.
Under laboratory conditions, and with an 80% depth of discharge,
terminating the charge

at 4.1 volts, you get over 2000 cycles.
at 4.2 volts, you get roughly 500 cycles.
at 4.3 volts, you get under 100 cycles.
at 4.4 volts, you get less than 5 cycles.


The RC people have seen similar results, and one test that is ongoing
is at roughly 800 cycles with a charge termination of 4.15 volts. This
seems to be the sweet spot for performance and cycle life.

In normal use, you can extend the life of your battery by limiting the
maximum charge to below 4.2 volts, and limiting the depth of
discharge.

 

[Spacey]

I'm charging my 15S4P 5.8Ah Turnigy Lipo to no more than 4.15volts......usually to just over 4.12V and I try to not discharge past 3.75V

 

[neptronix]

I'm charging my 15S4P 5.8Ah Turnigy Lipo to no more than 4.15volts......usually to just over 4.12V and I try to not discharge past 3.75V

3.75v.. damn.. that's because you have the funky cell packs isn't it

 

[RVD]

You will get a definitive answer from your balancing charger. It will tell you how many mAH it put back into the pack when you stick it on. My guess is, low 4000's figure. Some energy will be wasted via balancing, so do a non-balanced charge to get this number.

Different formulations have different discharge curves though. The best number is the figure you get from your instruments
Having a turnigy watt meter, or correctly calibrated cycle analyst helps a lot. Those will work too, to provide you the number you're looking for.

I ran a test today.

Last night I charged up to 85% TCS. All cells were 4.11-4.12 balanced. My setup is 12s3p.

When I started riding, voltage read 49.2v. Voltage sag when pulling the throttle was around .2-.4v. Speed switch setting was "2" (out of 3) most of the time which results in a top speed of around 22mph.

16.22 miles traveled. 6.027ah used. Ending voltage 45.8v.

After I got home, I charged again to 85% TCS and the Hyperion 1420i reported 6030mah charged.

Questions:

1) Does this mean that I could have done this trip with 12s2p pretty easily? (since I only used 6ah and I would have had 10ah (minus ~1-2ah from your graph since I'm going from 4.1->3.6 or so)).

2) Does this mean that I could have easily doubled this trip (done it again) with my 12s3p setup? (since I only used 6ah and I have 15ah (minus ~1-2ah from your graph since I'm going from 4.1->3.6 or so)).

It seems like my CA is calibrated pretty close to accurate since the CA reported 6027mah used and I charged up 6030mah. I would have expected the CA to report a little more because of loss so it's a little inaccurate but close enough for me I think.

 

[neptronix]

49.2v / 12 = 4.1v/cell, so that means your cells settled a little bit lower after the charge. You may want to try more like 90% to get an extra buffer.

45.8v / 12 = 3.8v, so on hobbyking lipo ( not nanotech ), that is about half way drained.

Yes, you could do this on 10ah.

Yes, you could probably double the distance on 15ah. You may need to drain down to 3.5/cell average though, which is not harmful really. That's a safe place to stop.

 

[RVD]

Awesome. I'll probably run a few more tests before I move completely to 10ah (e.g. run at 10ah but carry 2 extra lipo packs just "in case" I run out, etc.) But the little bit of weight that I save will be great.

I haven't weighed my bike yet but I wanted something that is somewhat do-able to pedal. I haven't tried a test where I load up the battery and just pedal 100% but maybe I'll try that next to get a decent workout + see what kind of range if my batteries die.

I actually need to work on the drivetrain a bit since I haven't been shifting gears. The one time I did shift gears, the chain popped out so it's probably not so good. If I did pedal, I would have to shift gears a lot more and will need to run on much lower gears that I'm used to with the motor.

Anyway, thanks for all of the help. I don't really need the extra range by going up to 4.15 and the data from this thread seems to indicate that going to 4.1 is better in the long run for batteries anyway. I am just running normal turnigy 6s 20c/25c lipos (not nano-techs).

Also, I have been taking it easy somewhat with this setup as to not fry the motor or controller. So I will go WOT and draw around 10-15 amps for maybe 30 seconds and then letting it coast to cool down, etc. Is it pretty safe for the batteries to just draw a constant 15amps or even 40 amps? Of course this is to avoid a lipo mishaps while riding....seems like it should be more than safe since with a 6s 5000mah 20c, we can draw 100 amps right (so batteries should be safe) but the motor probably can't handle that kind of watts so I try to keep it at around 10-15 amps and 1000 watts. Am I being way too cautious here with the batteries, controller, motor?