Continuous Charge Amp vs Continuous Discharge Amp

[eMark]

Here's a sneak preview (undercover) look at my DIY 10S3P Samsung 30Q 141 that can be easily split (in less than 3 seconds) into two 5S3P packs for balance charging at .5C with my older UltraSport 2S-6S Balance Charger. P-groups are balanced within 4mV of each other (so far) after 150+ charge/discharge cycles :thumb:

Currently have 1,773.7 miles since August of 2019 (kept it inside from mid-November to mid-March). The DIY build was a winter project using a Vruzend V2.1 Kit. It took awhile before i settled on what i felt was the best build and the best solution for splitting the 10S3P into two 5S3P. Like most projects it seems simple enough, but your first DIY build is always more challenging and by all means safety, safety, safety is numero uno !

The other battery that I rotate with my 10S3P 30Q slides in underneath the Plano container. That HD Plano container is just one of several modifications ... don't we all love making modifications :thumb:

 

[eMark]

docware's "ageing tests" were a labor of love, very informative and worth revisiting from time to time ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=103092 :thumb:

Frustrated and tired by never ending unfruitful debate about cycle life of various Li-ion cells, I finaly decided to start some long term cycling to see the real results. Parameters was chosen in effort to imitate real utilization, but on the other hand to get some results in acceptable time. Important was to not use parameters like 100 % DOD, 0,5 C charging, 1 C discharging, as these are in my opinion too severe and unrealistic in the real life.

Here's an informative chart attachment (11th post down) by DogDigstick on "Standard Charge" and "Standard Discharge" posted on this Low Voltage.cutoff informative thread started by emike11 ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=107031 ... https://endless-sphere.com/forums/download/file.php?id=275794

This was my first DIY pack build. During first 50 cycles it would balance the ten p-groups to within 6-8mV of one another, but has settled into 9-12mV variance between p-groups. Am very satisfied with the Vruzend V2.1 kit. Easy to assemble and a great first time DIY learning experience and for experimenting. As a first time DIY build a 10S3P pack is a happy medium choice for most beginners. Will also be easy to disassemble and reuse when the life of this pack has diminished to only 60% capacity (or less ) if i decide to use a little longer as a backup reserve before disassembling.

Note: There were only a few times the p-groups were within 4mV so should have changed to 8-10mV. Have also noticed that the p-groups will be closer 4mV-6mV until the final balance charge from 4.0V to 4.1V when the variance increases to 8mV-10mV between the ten p-groups.

 

[eMark]

The thirty 30Q cells in my 10S3P are still reasonably balanced after discharge. Have never needed to balance the P-groups before Balance Charging. This time (for the first time) will discharge the pack at full throttle 75%-80% of riding time. Will see how well the cells are still balanced at low voltage cut off. Then am going to do a "regular charge" instead of balance charging and at 2.5A (.83C) instead of 1.5A (.5C). Will track how well the cells stay balanced from 3.4V to 4.1V.

Should also mention that i bought fifty 30Q 141 cells when they were on sale last November with plans to build a 10S5P pack. Then decided i needed a little more room for my rebar and U-post driver so downsized to 10S3P. As a retirement hobby (besides photography) i design, build and monitor 15 bluebird nest boxes (going on 5 years). My Bluebird Trail of nest boxes is spread out over 25 miles round trip. Recently purchased another Unitpackpower 10Ah battery so can check them all in one day. Suppose to check on them every week, but every 10 days is often enough.

Some more photos of my etrike modifications. Get many positive comments like "cool", "i like it", "nice" and "i should get one" from kids to seniors (even cool 8) dudes). Axman Surplus carries quite a selection of self-adhesive foam (used for top and sides) also the 12 ga silicone wire with copper strap for battery disconnect into two 5S3P packs for balance charging with 2S-6S Balancer ...

 

[goatman]

maybe write letters to Samsung, LG Chem, Sony/Murata, Panasonic and other manufacturers of 18650's telling them to remove Standard Charge and Standard Discharge from their 18650 datasheets as it's "arbitrary" :wink: ... just list maximum charge and maximum discharge ... but then that's also "arbitrary" :lol: :lol: :lol:

... moving on :thumb:

i understand what youre getting at and agree with you, Samsung just doesnt pull out of their butts the idea that 10 amps continuous will deliver 100% capacity and put it on the datasheet for a 30q,40t or 25r for no reason, not everything some members have said above holds up under testing.

ive only tested 3 batteries and each have to be treated differently

operating temperature is a huge factor when it comes to capacity.

take your 30q at 3p and discharge at 25 amps continuous with outside air temp at 25 celsius and youll get alot more capacity than at 5 celcius outside air temp. then try same test but 30q at 6p and youll get less capacity than the 3p test.

i also believe batteries need to be discharged the way they were designed to be discharged.

noone seems to be doing those tests or if they are, they are not sharing that info.

 

[eMark]

Samsung just doesnt pull out of their butts the idea that 10 amps continuous will deliver 100% capacity and put it on the datasheet for a 30q,40t or 25r for no reason, not everything some members have said above holds up under testing.

Your post does reflect a sentiment; especially that of RC Lipo Pylon Racing Top Guns ...
High Discharge C rating Lithium Polymer Battery
3.7V Prismatic Cell 10C 15C 20C 25C 30C 40C 60C ... https://www.lipolbattery.com/high%20rate%20discharge%20lithium%20polymer%20battery.html

One reason (besides cost) that ebiking Top Guns don't use those high discharge Lithium Polymer Prismatic Cells is because their DIY builds are for an entirely different ball park. A RC Pylon Racer getting up to speed to break 200mph only takes seconds at 50C-60C vs So Cal Mountain Bike ENDURO racers at what -- 5C with short bursts at 6C for what -- 1 hr

Then there's grandpa's Vruzend V2.1 10S3P 30Q etrike outings under 2C 80% of the time -- except for my recent Enduro :wink: experiment over 2C 80% of the time. Will post p-group cut off variance, charging data, etc later today

On the opposite side (you decide which side :wink: ) of the American Gold Eagle coin is a more conservative discharge used by medical instruments and docware's ageing tests (4.1-3.4 2.5/1A)...

Frustrated and tired by never ending unfruitful debate about cycle life of various Li-ion cells, I finaly decided to start some long term cycling to see the real results. Parameters was chosen in effort to imitate real utilization, but on the other hand to get some results in acceptable time. Important was to not use parameters like 100 % DOD, 0,5 C charging, 1 C discharging, as these are in my opinion too severe and unrealistic in the real life.

Really ... .5C charge and 1C discharge are too severe and unrealistic in real life?

i also believe batteries need to be discharged the way they were designed to be discharged. noone seems to be doing those tests or if they are, they are not sharing that info.

Maybe, because the (severe) charge/discharge cycle life longevity (cessation) doesn't come close to matching docware's extended cycle life longevity ageing tests

 

[eMark]

After my first test run yesterday at approx 80% full throttle and controller cut off at 32.25 volts with bounce back resting voltage only 33.3 volts after 45 minutes because i restarted three more times with four total cut offs. Then straight charge without balance charging to 40.7 volts at 1.3 amps (.5C = 1.5 amps). Then balance charging from 40.7 to 41.0 volts at 1.3 amps.

Decided to do a second (same) test run again today at approx 80% throttle with only two restarts and three controller cutoffs. Bounce back resting voltage after 45 minutes of 33.9 volts this time. Am about half way through using same charging procedure as yesterday. Only difference will be to balance charge top end at just 1.0 amp from 40.7 volts to 41.0 volts. Will explain reasoning tomorrow.

Basically the ten P-groups are within 8-9mV of each other at the top end after 150 cycles of balance charging from beginning to end at 1.5 amps. The first 25-50 cycles the P-groups were within 4-5mV of each other after balance charging. At the bottom discharge end (33.3 volts to 33.9 volts) the P-groups of the two test runs (yesterday and today) varied from 41mV to 45mV and settled in at 10mV to 12mV after 30 minutes with straight charging to 40.7 volts. The only balance charging on these two test runs is between 40.7 volts to 41.0 volts.

That's enough for now ... more to come

Because i usually carry a collapsible camping chair i needed to extend the right pedal for clearance. Also necessary when securing 4' rebar, 5' of conduit and 5' U-post for bluebird nest box support column. Critters can't climb/crawl up it to get at eggs or nestlings (unlike wood post) ...

 

[Balmorhea]

You’re gonna break that pedal off if you use it in earnest.

 

[eMark]

At the bottom discharge end (33.3 volts to 33.9 volts) the P-groups of the two test runs (yesterday and today) varied from 41mV to 45mV and settled in at 10mV to 12mV after 30 minutes [followed] with straight charging to 40.7 volts. The only balance charging on these two test runs is between 40.7 volts to 41.0 volts.

After a good night's rest Grandpa's brain saw the need to clarify so you guys don't think my own 76Q is agingly arbitrary (or is it aging arbitrarily). To be precise should've rearranged the bottom discharge variance to 45mV to 41mV (33.3 volts to 33.9 volts) for the two test runs. YES, i then bottom balanced for first 30 minutes before straight charging at 1.3 amps to 40.7 volts. followed by top balancing to 41.0 volts at 1.3 amps (.46C figuring 2800mAh cell capacity). Any guesses how long it will take to top balance charge from 40.7 to 41.0 volts at 1.00 amp rate (.36C figuring 2800mAh cell capacity charging from 34 to 41 volts).

You’re gonna break that pedal off if you use it in earnest.

Anyone's guess what/who will last longer. The steel forged crank, 1/2" x 6" hardened steel bolt, or grandpa's foot. Thanks for the T-shirt when pedaling with my teenage grandson (he goes faster)...

SENIOR LIVES MATTER

 

[goatman]

doesnt bottom balancing conflict with top balancing?

 

[john61ct]

So long as you don't try to balance at multiple spots in the V/SoC curve, the cells don't care.

Balanced at the bottom (just below stop-discharge point) you can use pack-level voltage as your guide

but then charging must be without balancing, just stop when the weak link cells hit your HVC.

The more common top-balancing means LVC must be based on per-cell voltage.

No difference in how much overall pack capacity is sacrificed by the imbalance.

Can even midpoint balance but then HVC and LV both must be based on the weakest link via per-cell measurements, requires a pretty advanced fully adjustable BMS if not just cycling manually.

 

[goatman]

thats something i think about, wouldnt it be better to bottom balance than top balance?

if you bottom balance the pack at 3.0v then just charge to about 4.15v.

if you have a 4s pack and bottom balance at 3.0v/12.0v

then charge to 16.6v it doesnt matter if the groups are at 4.16v, 4.15v,4.15v,4.14v because when you discharge they all should hit 3.0v at the sametime on the discharge.

on my 17s packs that charge to 4.1v they go out of top balance but stay the same after 2000km or 6months. i checked the 3 packs i use regularly last week. youll see the numbers are off but thats how they were 6 months ago. i dont use a bms, the 25r will see 12amps max. 4p/50amps. the 3p is a range extender of panasonic pd and it will see about 7amp max/3p/20amp.

i discharge my packs to 3.0v/group under full volt sag but really i discharge to about 3.2v

i just question wether trying to force balance to 4.2v is wise, if the pack is actually pretty happy being naturally out of top balance then why force balance it to 4.2v?

 

[Balmorhea]

then charge to 16.6v it doesnt matter if the groups are at 4.16v, 4.15v,4.15v,4.14v because when you discharge they all should hit 3.0v at the sametime on the discharge.

That presumes that the imbalances are due only to differences in capacity, as opposed to difference in self-discharge rates. You can presume that, but it would be a gamble.

 

[goatman]

yes, if you are going to be selling to consumers you need something idiot proof and its easy with the standard 4.2v top balance BMS.

does anyone make an automatic cell balancer that would automically balance a pack 30 minutes after being active at whatever voltage the pack happens to be at. instead of relying on a charger to balance the pack

 

[Balmorhea]

does anyone make an automatic cell balancer that would automically balance a pack 30 minutes after being active at whatever voltage the pack happens to be at. instead of relying on a charger to balance the pack

You can get "active balance" boards that keep all the cells at the same voltage, and do it with more than an amp of current instead of 20-30mA like a typical BMS. They don't care whether it's lithium ion, lithium ferrophosphate, or lithium titanate. They just keep all the cells at the same voltage, and nothing else.

I put one on my newest battery pack. But now it's up to me to keep the maximum charge voltage and the minimum resting voltage within spec. In this case, my "charger" (Meanwell power supply) and my controller's LVC should back me up if I falter.

 

[eMark]

doesnt bottom balancing conflict with top balancing?

Why would you think so? Balancing is balancing so explain why would bottom balancing conflict with top balancing?

My sole reason for top balancing at only 1 amp from 4.07 volts to 4.10 volts was to see if I could get the ten P-group variance below 8-9mV. And the answer was NO. Apparently after +150 cycles 8-9mV is the best P-group balance possible for my 10S3P 30Q 141 pack. When new could balance charge P-groups within 4mV at 1.5A (.5C) balance charging the entire charge cycle. Now the best is 8-9mV during the entire balancing charge cycle (which ain't too shabby)

As far as whether it's best to bottom balance, middle balance or top balance (if not balance charging the entire charge cycle) the bottom line is bottom balance. Think about it ... ... IF, as with my two test runs at 80% full throttle, the variance between the ten P-groups was 45mV and 41mV at Controller cut off (33.3 volts and 33.9 volts) then the rationale is to first bottom balance the P-groups at .5C before a straight charge at .5C or 1C.

If (for whatever reason) you were going to do just one of the three (bottom, middle, top) you would want to bottom balance for say at least 30 minutes before continuing with a straight charge. So, spinningmagnets was right-on the money when he suggested bottom balancing a few months back as the best of the three choices ... if (for whatever reason) you weren't going to do a complete balancing charge cycle.

 

[goatman]

i just think top balance at 4.2v will kill the packs lifecycle.

i use salvaged cells from packs that went bad and when i was learning about salvaged cells it was recommended to do bottom balance

ill have to look into the cell balancers mentioned. it makes no sense to me to try charging a pack with current going in just to be getting burnt off by a bms and some of the groups going over 4.2v all the time. the cell balancer sounds good to me, you dont need a charger to balance the pack, it will always try to balance the pack at any voltage?

 

[john61ct]

i just question wether trying to force balance to 4.2v is wise, if the pack is actually pretty happy being naturally out of top balance then why force balance it to 4.2v?

exactly

i just think top balance at 4.2v will kill the packs lifecycle.

Well going there for any reason does reduce lifespan, but if just for a couple minutes probably not that significantly.

Letting the cells sit at such high SoC is what hurts a lot more even if isolated at rest.

But continuing to feed a "Float" even at near zero current for a long time even more so.

So "top balancing" as such, is not the problem. It is the fact that cheap / poorly designed BMSs do so at super slow current rates, using "resistive burning off" methods and often do not even let you choose the start-balance voltage

that is so stupidly destructive, forcing those with badly unbalanced packs to sit at Full for hours even days.

 

[john61ct]

ill have to look into the cell balancers mentioned
…
it will always try to balance the pack at any voltage?

There are dozens of models now out there.

I would look for:

easy compatibility with all the cell/group counts I would ever need (some are sold as single modules, need to buy seven for 7S etc)

either "whatever voltage they are at", or fully adjustable start-balance voltage

high current rate, certainly over an amp, some go to 5A or higher

active circuitry, so the **actual** transfer amps is near constant and close to the rated current
(IOW does not depend on the delta between cells)

ideally shows "live" the cell-level voltages, highlighting the two extremes and maybe even calculating the biggest delta, the average or whatever

 

[john61ct]

if (for whatever reason) you weren't going to do a complete balancing charge cycle.

There is no such thing.

You have to choose a specific "ending" SoC/voltage to balance at.

If you do at more than one point you are totally wasting your time and putting unnecessary wear & tear on your gear and cells*

The only point of a "starting" voltage setpoint as opposed to the finish point

is when balancing is being done (usually with that stupid resistive burning methodology) in conjunction with pack-level charging.

does anyone make an automatic cell balancer that would automically balance a pack 30 minutes after being active at whatever voltage the pack happens to be at?

* See now why you would not want this?

"pick a lane!"

With good cells, you should not need to balance more often than annually, or maybe quarterly as they wear. . .

 

[john61ct]

There is no inherent advantage to bottom vs top (or middle) balancing

unless you want to use pack-level voltage to trigger stopping at "that end"

so top balancing allows for pack-level charging

and bottom allows for discharge cutoff based on a pack-level LVC

None of this post necessarily involving "a BMS", these three functions can be done by known-good reliable OTS industrial controls, or even manually (human "BMS")

 

[eMark]

I've learned to just ignore his comments as they're often skewed with disinformation. Some of his statements makes one wonder if he's all theory and no practical experience. When has he ever posted a photo of his modified or custom built ebike or inovative DIY pack. All i've ever seen him post (infrequently) are hand drawn wiring schematics. His arbitrary theory is just that ... guess that's why they call it theory :wink:

He was told by an administrator months ago to stop with his low balling mission to black ball me. It all started in November 2019, when i pointed out an error in his thinking and ever since then he's had it out for me. He can't stand to have someone tell him he's wrong, even when he realizes he was wrong. The result being to post disinformation that he knows is skewed. I don't even give him the satisfaction of replying to his posts anymore. Am posting this to caution those reading his posts on this thread that his motives are unbalanced when replying to any of my posts.

Otherwise, he's knowledgeable enuf and usually helpful as long as you don't ever tell him he's wrong, even if he later realizes he was wrong.

 

[eMark]

i just think top balance at 4.2v will kill the packs lifecycle.

What do you think a BMS is doing at the top end. Just one reason why i decided not to incorporate a BMS which one member has referred to as a "Battery Murdering System". I wouldn't go that far unless all one can afford is the cheapest Chinese BMS. The best way to tell the health of my pack is to use a reliable voltmeter and a decent balance charger. The $60 dual 2S-6S charger i bought a few months ago turned out not to be as reliable as my older balance charger, but even it's voltage readouts aren't as accurate as a good reliable multimeter for more accurate voltage readings of each P-group.

i use salvaged cells from packs that went bad and when i was learning about salvaged cells it was recommended to do bottom balance

By all means bottom balance. You may only need to do it for 30-45 minutes at .5C if the P-groups variance is say only 30-60mV, but every pack is different depending on it's number of P-groups and number of cells in each P-group, number of charge/discharge cycles, remaining capacity percentage, any abuse, etc.

ill have to look into the cell balancers mentioned. it makes no sense to me to try charging a pack with current going in just to be getting burnt off by a bms and some of the groups going over 4.2v all the time. the cell balancer sounds good to me, you dont need a charger to balance the pack, it will always try to balance the pack at any voltage?

That's one reason why bottom balancing is the way to go if for whatever reasons you only want to balance for 30-45 minutes to achieve minimum P-group variance and then regular .5C or 1C with your bulk charger. I charge to 41V (10S). What inexpensive BMS' does any balancing of my 41V (10S) pack unless one or two of the P-groups are already at 4.2 volts and perhaps one or two of the other P-groups are as low as 3.9V. That's why it's even more important to at least do a bottom balancing with a pack/powerwall of salvaged/recycled cells :thumb:

 

[john61ct]

Paranoid man, I wasn't even sure you were the same guy as that "meandering strings" thread, but now you've confirmed, thanks I appreciate it.

I have no "motives" other than conveying the truth as I know it.

Your post #40 contains so much misinformation it is clear you do not understand the fundamental concepts and purpose of balancing.

It would be very useful for your learning if you were open to taking advantage of the opportunity to correct that situation, but I infer that that's not the case, so in the interest of reducing potentia conflict I'll just let it go, so long as it doesn't threaten to mislead other members.

But for other members, feel free to ask me detailed questions on any statements I've made that you think need clarifying.

 

[eMark]

IGNORE!

moving on ...

 

[goatman]

last comment on the subject battery murder system correct :thumb:

id just like something as described like a cell balancer with bluetooth and an on/off switch independent of the pos/neg battery leads that way i can turn it on, look at the voltages and if alls fine then turn it off.

anyways, i like your trike with the front motor, if your front loses traction on a gravelly hill, start pedalling and its a 4x4. built one for my boys to haul their fishing gear and coolers to the river