what min and max voltage YOU do with lipo?

[Hummina Shadeeba]

people seem to be all over the place as far as the minimum they will allow lipo to go. 3.15 seems a good max.

It'd be nice to find a graph showing batteries used with varying max/min and see what cycles they're getting to.

and is it worth "breaking them in" with mild discharge at first?

and will my batteries always perform longer if I keep the charge rate low or can I charge to the max specified by the manufacturer and get just as many cycles?

 

[dogman dan]

By lipo, you mean lithium cobalt? This comment refers to that, the cheap RC and drone packs.

I never heard anybody say batteries last longer when charged at their max rate. But on a good sized, say 10-20ah pack of RC cells, you need pretty big charger to even get close to charging at 1c, let alone the max.

Personally, I tend to charge to 4.1v a lot, charge to 4.15v when I need longer range, and balancing is always (but seldom needed) done at 4.2v.

On the other end, I really try to carry enough battery so that 90% of my rides end above 3.65v. This is how I need to balance so seldom. I really believe that less than 100% discharges help a battery stay balanced. But if I must do it to get home, or to a plug, I don't hesitate to drive em down to 3.3v or so. But below 3.5v, I'm creeping along just trying to make pedaling home easy, not expecting to run at 1000w.

Breaking in. Whether new or old, I have found the first cycle after a battery has been stored a month or more seems a bit low capacity. So I do a low DOD cycle to "break in" the pack, before balancing it if it needs it after that.

New packs get several low DOD cycles. but not to break them in. It's to evaluate them, and see if they do the ol, puff after 3 cycles trick. Or the ol, never stays in balance trick. Not a break in, so much as doing my own quality control before I put them into routine service.

 

[Ykick]

With a BMS I go 4.2V-2.8V.

Have a look:


It's important to realize this was "under load" - doing this "naked" is kinda guesswork to find the resting voltage which correlates to an empty cell. As you can see, it's a pretty narrow margin where a near empty cell drops off the cliff. Therefore, people who run naked avoid the extremes and often barely use 1/2-3/4 of the available pack capacity.

I did it that way for many years and it worked. However, now with BMS it's much safer and I often use a much smaller/lighter pack for the same range.

Longevity isn't affected by 4.2V top charge as long as it's not left sitting at that voltage for days on end, IMO. I generally short-term store them around 4V/cell. Long term, put them at the suggested 3.85V.

 

[friendly1uk]

Factories tend to specify capacity based around 2.75 - 4.2 volts.
I run 3 - 4.2v and if I got the full 160 cycles It would take me 1600 miles (based on my average speed and pack size)
I'm just over 1800 miles now, and getting close to the 20% capacity loss that will signify they are done. This 20% is also an industry spec.

I think I have about 500 miles left. Many more than the batteries said, because I offer some assistance myself. Making it hard to calculate. What I believe is I can buy RC lipo and take it through just as many deep cycles as it says I can on the box. This is useful to know. I could instead nanny my battery, but then I would have no idea how much life expectancy they have.

I like 3v lvc as if I conk out then leave the bike sat about for a few weeks it won't drain down below 2.75V and it's over discharge that looks to do the most damage. I don't mind charging to 4.2 each time as they don't stay fully charged for more than a day or two at worst.

I'm happy to use them to their full extent and just get the label life. I feel it gives me consistency.

 

[cal3thousand]

Personally, I prefer charging to 4.15 Max. I even have a large pack that I only charge to 4.0. That will greatly increase the mileage I get out of the pack. I will charge to 4.2V if going on a really long or unknown length trip, but that is really rare.

As for the bottom end, I generally like to stop at 3.5 VPC. At that point, sag can bring the cells down to 3.0 VPC and there isn't much left anyway.

I use a combination of Cycle Satiator, EMC bulk chargers, iCharger, and Meanwell CLG depending on my situation and needs.

 

[wesnewell]

I charge to 4.2V and have my LVC set to ~86V for my 10ah 24s pack, but normally don't ever run to LVC. When I have, I've had a 10% soc with ~3.7V per cell resting. I've got ~8K miles and almost 3 years on the pack. I don't keep track of charges, but I'd estimate maybe 100 per year. I didn't check original capacity, but I'd guess I still have ~90%. Kind of hard to say since I never run them empty.

 

[friendly1uk]

Be aware this topic only applies to people that don't have packs built to commercial standards. Most well built packs require you to reach over 4.2v per cell before any balancing will take place. Without which your just pissing in the wind.

This thread is mainly for people who charge a pile of cells with rc gear. Then wire them into a pack, use it and take it to pieces again.

 

[dogman dan]

Yes, I found I was pissing in the wind for some time with my Allcell pack. Not lipo, NMC or whatever they call it.

Anyway, I never got the full 13 ah from this pack. (actual spec is 12.8 ah) I read something Justin commented on about needing to charge to 4.2 for these bms equipped packs.

I had been charging to 4.2v, 54.6v. Never felt the bms warm. Tweaked my charger up to 54.8, and bam. Warm bms, balancing that pack. Next ride, discharged 12.8 ah to bms trip, as the spec sheet said.

Clearly the problem, was a combination of a very slightly off charger, and a very slightly off voltmeter I used to set the charger. Harbor freight cheapie.

What a difference! After 4 months of not getting balanced, my capacity was way off, and I just thought, "yeah, it's cold".

Anyway, balance them, when you balance, to 4.2v. That's my opinion. Then discharge them soon, don't store them at 4.2v, especially in a hot garage! I see little harm in a full charge that is discharged again soon. I keep reading it's time and temp, at 4.2. Not just ever going to 4.2.

Now back to the lipo. I usually charge to less than 4.2v with them, because I charge then bare back, no bms, on a bulk charger. So I undercharge to keep from burning my house down.

 

[athletic91]

Charge to 4.1, discharge never below 3.7, never had to balance.

 

[Hummina Shadeeba]

Charge to 4.1, discharge never below 3.7, never had to balance.

How many amphours u get compared to the batteries stated capacity doing that?

 

[Ykick]

Majority RC Lipo users don’t really know what every cell voltage happens to be but they “assume” by way of “averaging” the pack voltage divided by # of cells in the pack.

Some of you know I’ve been playing with the old tried and true CellLog 8S, CA, power supplies, resistive (toaster oven) load, performing cycle tests, etc. Here’s a pic from logging an 8S section of my 20C 5Ah Turnigy hardcase 6S pack using roughly 1C discharge/charge rates. About 5A.

This would be considered “top-balanced” as all the cells are pretty close to equal voltage at the beginning of the load measurement test. Everything drops very linear from about 4.2V until the steep knee about 3.65V. No surprise that’s the commonly quoted per cell LVC.

Trouble is, all we do when we set a LVC in a controller or CA is "assume" we have evenly matched cells at the same SOC. That usually works pretty good, until it doesn’t.

But assuming we go that route, for the pack in my example here, if I were “deciding” on a controller/CA pack voltage LVC, I’d probably choose 3.3V/cell or 40V if using these cells in a 12S1P configuration. However, this doesn’t leave much room for error so if you plot the graph based on 3.65V/cell (44V pack LVC 12S) it’s obvious there’s less likelihood of taking any cell too low.

But, cells change over use and time so unless you’re actively monitoring each cell group under discharge you will really have no idea if/when 1 cell is possibly close to 0V while 11 others are still chugging away @ 3.65V.

This is the reason and good judgement to use a BMS for both charging and discharging. Otherwise, you’re really just hoping and "assuming" Controller/CA LVC is actually covering all the cells. And of course since most charging takes place indoors, going over max cell voltage during charge is potentially even more dangerous and expensive.

 

[Hummina Shadeeba]

thanks for that.
i'll likely be babying my cells and balance charging them often if not every time because I'll have two packs I'll be swapping in and out and I'll be in no rush.
I'll be top balancing with my icharger..which it turns out I didn't burn up with my last foray into this. So I'll be up on the cell's state of charge and I'll figure how to find the resistance of each cell as well hopefully(?). I feel I'll have my eyes on the cells. (if you have any good advice on better doing this please tell me). so assuming the cells are balance-able and balanced...what would be the best low voltage cut off of an individual lipo cell? I get that its a trade off at some point between the battery's longevity or delivering more ah but...if discharging within the c rating as well..where's a graph showing how many cycles can be gotten based on their repeated charge and discharge voltage? I feel I'm in the dark as far as how much battery longevity will suffer if I were to discharge all the way to 3volts or something.
I'd like to set my esc cut off and my low voltage alarm on my watt meter as well. And I'd like to have huge range and batteries that last forever :wink:

 

[Ykick]

Ya know, there’s a lot of “stuff” out there about the best HVC/LVC for individual cells and I used to have some “creative” ideas myself. However, now that I’ve dealt with some professional battery pack manufacturers I realize they have a pretty good read on this.

If you use a BMS/PCM which can control it tightly, as my discharge graph demonstrates, 2.8V is an accepted industry standard for Li-ion, Lipoly. And same goes for 4.2V top charge. And as long as you have cell level monitor controlling the battery pack input/output, I see no reason not to follow those established values.

However, I wouldn’t leave a pack sit around 4.2/cell for more than a day or two. Even the “holy” 4.15V/cell value doesn’t do much for longevity if you leave it sit at that SOC for long periods of time.

Real world, it sorta depends on “when” you intend to use the pack again. If plan to use the next day, I simply charge to 4.2V and don’t worry about it. If I know it’ll sit for a couple days I often leave it uncharged around 3.85V. If I’m not sure if I’ll use it the next day, I often charge around 4V and wait and see. If I charged it the day before and decide not to use it I whip out the old "toaster oven" load and burn some charge off. Maybe reheat lunch?

Funny thing, I’ve been getting such good life and thus value from RC Lipo for so many years I don’t even worry about longevity anymore. My current Turnigy 20C 5Ah 16S1P packs cost all of $116 for the bricks shipped and they’ve been lasting well over a year with little sign of degradation.

Hell, that’s what I used to pay for comparable (9Ah) capacity HR SLA which was practically junk after about 3 months daily use.

Once you have a BMS and charger setup for RC Lipo, it’s merely about replacing bricks as they die off. Thus primary reason why I like something very common (Turnigy 4S hardcase) which will likely be available year after year after year. Plus, they’re a great cell count package for various system voltages - 12S, 16S, 20S. Lastly, if a brick develops a bad cell, it’s only 1qty $25 brick to replace.

 

[Hummina Shadeeba]

wow Id have thought maybe 3.7 volts would be a minimum voltage but you're almost a whole volt under that. That's lower than anyone says. I still wish there was a study done and a graph to look at. I'm sure some people would say "never under 3" and here you are confidently saying otherwise. I'm just stewing on it because they still haven't arrived but I'm surprised at the ambiguity. I imagine letting a battery sink that low when not even under load it must hit much less than even that with a load. You're the only one I've come across with such a low number

 

[Ykick]

Using BMS/PCM cells only touch extreme LVC for a moment and I don't think it's enough to damage anything. Obviously, BMS/PCM manufacturers chose these values for a reason and they have a little more experience with battery packs than me or practically anybody else around here.

My example's executed with tightly controlled cell monitoring and ability to cut-off the load when any cell is depleted to minimum low voltage. When people are running naked they're merely "hoping" all the cells are depleted at the same point in time. That can work with a conservative LVC if/when every cell is new and practically identical but unfortunately with an older Hobby pack operated over many cycles, things can and do change for the worse.

 

[DrkAngel]

"Discharging deeply" to get full rated capacity(?) is "damaging"!
Every cycle "damages" (reduces cycle life and capacity) to a degree.

The question is:
At what voltage does discharging return minimal current for the damage inflicted.
Obviously, IMO, discharging beyond the top of the "cliff".
Before the cliff, a 1/10V discharge might supply 500mAh
After the "cliff", a 1/10V discharge might supply <50mAh
There is some indication that each 1/10V discharge causes an equal amount of deterioration.
So, stay above the "cliff" for most efficient battery life!

Each 1/10th V of reduced charge voltage is reputed to double cycle life.
E.G.:
4.20V supplies 100% capacity for a 500 usable cycle life
4.10V supplies 90% capacity for a 1000 usable cycle life

I map the current density and try to restrict charge-discharge cycles to the voltage regions of greatest capacity.
(Every cell type differs in optimal voltages 1 Lipo type had good capacity down to 3.50V, another not below 3.70V)
One type of LiPo not discharged below 3.7V (rest voltage) and charged to only 4.12V (Estimated ~180% cycle life)
Another LiPo discharged to near 3.50V and charged to 3.87V supplied 70%+ of rated ... but with 800% cycle life!!!

See - Capacity Mapping (Optimal Charge-Discharge Voltages)

Sorry, not allowed to post graphs here ...

See also -Optimal Charge Voltage - (LiCo)

 

[IdleMind]

Ykick, Interesting. I have come to the same conclusion about Turnigy hard case batteries. This is my discharge test of 12 bricks ranging from 6 to 18 months old. After riding, I use a 208b icharger and balance/storage charge to 2.85v at 340 watts. Then before riding I balance charge to 4.1v. I don't use a bms.

I have been working on ways to make a pack from 18650 cells just to see if I like them, but I think in the end it won't serve my needs as well as these bricks.

My bike has a Q100 328rpm motor in a 20 inch wheel so top speed is 16/17 mph and on the flats I draw close to the 4 amps like my test. I easily go over 50 miles with this pack for about $350.

 

[dnmun]

2.85V is too low for a storage voltage.

the facts are: 2.7V is fully discharged resting voltage and 4.2V is fully charged resting voltage. some manufacturers recommend never discharging to a resting voltage below 3V.

as i understand, the metal oxide cathodic matrix shrinks in volume as you drop the resting voltage below 3.5V resting voltage.

someone else may have more information but if you do not have actually verifiable information pleas do not fill other people with you own opinion about what is or is not 'safe'.

also the hysteria about fire and explosions is another issue which collects a lotta idiots.

it is called 'thermal runaway' and is not an explosion. lipo will go into thermal runaway when it is overheated by overcharging or by other heat sources up to the critical temperature where the exothermic reaction that results from the newly exposed carbon reacting with the fully charged electrolyte. the carbon is at 0V electro potential and the electrolyte can be above 4.5V which along with the heat of the exothermic reaction will promote even more of the carbon to be exposed as the SEI continues to flake off under the heating.

you can watch the utube video which explains at what temperature the exothermic reaction is initiated under adiabatic conditions:

https://www.youtube.com/watch?v=iieB3ePZGdQ&feature=youtu.be

 

[Ykick]

Thanks for sharing that IdleMind. Like many here ‘enjoy tinkering and fascinated with Battery cell characteristics. Particularly, light, cheap and powerful variety.

Comparing both our discharge graphs It’s interesting to notice the similar “dip” or “shoulder” around 4V/cell? It then levels out pretty evenly until the empty cliff. Probably doesn’t really mean much but an interesting characteristic to see captured by different logging gear.

Did I read correctly, you store @ 2.85V/cell? Perhaps you meant 3.85V resting? I’ve observed if discharge terminates @ 2.8V good cells usually float up little above 3V resting so someone would need to be fairly rough on some cells to store them @ 2.85V…

 

[spinningmagnets]

I am not currently using LiPo/LiCo, but...when I did: Pretty much what Dogman Dan does (you would be well advised to do that also). I charged to 4.1V per cell, and put a power timer on the charger cord so after X amount of hours the power was cut.

I had developed the opinion that a low C-rate battery that was also fairly small with its Ah size would sag more (even using the infamous LiPo/LiCo) so when it comes to the LVC (or low voltage alarm?) you could set it a little lower, because the resting voltage was what needed to be kept from getting too low. I never rode a long enough distance between charges to find out if that was a good idea.

If you have a high C-rate pack that is also very large (20-Ah/etc), there will be very little sag (if only drawing a common 25A load), so when the LVC is set to 3.5V...the battery will actually be very close to 3.5V per cell when the LVC shuts it down). I "think" this is why average LiPo/LiCo packs use a 3.0V LVC (which sounds too low), because when it sags to 3.0V, the resting voltage is actually closer to 3.5V per cell. I have no solid evidence of this, just a thought that occurred to me...

 

[IdleMind]

2.85V is too low for a storage voltage.

Excuse me--I meant 3.85v. I simply use the charger's storage program. I have LVC set to 29v (3.625/cell) but have enough capacity that I never reach it.

 

[dnmun]

if you do not monitor the individual cell voltages you do not know if you have discharged below 2.8V. it should be obvious from his well balanced pack that there can be large variations in the voltages of the individual cells during discharge and assuming that each cell is discharged to the same average voltage is the reason so many of these lipo packs end up puffed up and ruined.

 

[markz]

Well this thread cleared up a lot of my misunderstandings.

I was at first freaked out with my batteries charging/balancing to 16.8V (4S - 4.2V). Paranoid I guess.
So on a couple of them I just stopped charging or balancing them at 16.6V = 4.15V.
Which is wrong, because 4.2V is where the balancing takes place; is what I learned here.
Its good to know I can go up to that level, look at the cells with cell log, and discharge. Which I do immediately.

Perhaps I should let them sit for 6 to 12 hours fully charged. And cell log them again, then discharge them, let them sit, cell log. Repeat. I think the key is to first balance charge them. Or maybe the key is to always balance charge them, especially at first when the battery pack is not assembled. And you recieved them from the store or mail.

All I do now is I pick out a battery that has been shipped to me, and has been sitting around for some time, while I build my ebike, now I got time to look at my batteries, so I do one battery at a time. I balance charge, discharge, charge, discharge. Inbetween looking at voltages, no rest. Or I will Balance, dis, balance, dis, charge. I am quite random, no set sequence yet. Just getting a feel. I think I should let them sit or rest, which complicates things abit, because I need to set aside hours a day to do a set of batteries.

Between the imax b8 plus and the cell log there is a slight difference 0.01V.

 

[DrkAngel]

iMax B6 and B8 have Lipo and Lion settings.
Lipo setting charges and balances at 4.20V (somewhat lower with my iMaxes ~ 4.17V)
Lion setting charges and balances at 4.10V (somewhat lower with my iMaxes ~ 4.07V)
Confirmed with Fluke multi-meter.

Balance function does vary with manufacturer and type of balance charger or BMS.
(Some standalone balance devices bleed down all banks to equal, regardless of voltage)
Check specs, manual or search reviews for method used by your device?

 

[Ykick]

In the beginning it's useful to let them sit fully charged for a day or two looking for "leakers" which slowly drain on their own. Anything that drops significantly and continues to drop voltage over time should be suspect and culled out.