Solar panel setup questions

Barkuti · 2019-10-27T01:16:29.000Z

The above 26800 cells are made by a good chinese OEM this is nearly for sure as far as I know (it may as well be Heter, but God knows).

In order to get high cycle life out of li-ion certain life-prolonging practices are due. Check BU-808: How to Prolong Lithium-based Batteries @ Battery University. The article is somewhat old and, while still valid, it may not be required to restrict the maximum charge voltage as much. I say this because I get excellent cycle life out of my smartphone batteries, charging only up to ⅔ of max or ≈4V with minimum load according to 3C Battery Monitor Widget (yes, I give 'em thousands of cycles), and also from what I can fathom out of documents like this Samsung INR18650-35E datasheet from Orbtronic (check page 14/19 table, Electric Storage Systems/Uninterruptible Power Supplies). Could select 3.95/4.2V just to be safe, still 20+Wh out of each of the above 26800 cells.

Yes, you will have to solder cells for a while.

snakebite · 2019-10-28T16:22:05.000Z

whatever you calculate for panels just go ahead and double it.
or triple.
i have solar setup here and its not uncommon to get long stretches of low production.
upsizing the battery has its own set of issues one of which is cost.
i overpanel and find something to do with any overproduction.
like heat water.

volchyonok · 2019-11-14T16:41:26.000Z

I am also interested in these 26800. In this store, QB26800 can be bought much cheaper than asking for Liitokala 3.7 V 26800 7200mAh. However, QB promises 6800mAh against Liitokala, which promises 7200mAh. In appearance of the “positive” output, these are elements from one manufacturer and I think that Liitokala is simply lying about such a large capacity, because the QB26800 shows less results (when discharging a current of 10A to a cut-off voltage of 3 volts, the best batch reached 7000mAh, and The same ‘the big guy! @ Thunderheart Reviews’ with a similar discharge current of 10A received only 6568mAh). Where can there be 7200mAh from? Is this another fantasy from a famous liar named Liitokala?

QB26800 (price)

The_Fat_Controller · 2019-11-14T16:50:32.000Z

Well i ordered 3 as a sample, I cant do accurate test but i will certainly post what i get from my charger

(When they eventually arrive)
I think they are being shipped by sea turtle

volchyonok · 2019-11-14T18:03:23.000Z

The_Fat_Controller:

Well i ordered 3 as a sample, I cant do accurate test but i will certainly post what i get from my charger

It will be interesting if you do not have a simple household charger (with very low currents), but there is such a high-precision four-wire electronic load (discharge current up to 10A), with which, for example, the QB26800 test was performed on this forum QB 26800, 6800mah, 30A - Страница 3

When discharged with a current of 10A and before the cut-off 3v, this person received a maximum of 6900-7000mAh, but the results for other people were somewhat more modest, since his party with very fresh elements was the most successful QB 26800, 6800mah, 30A - Страница 4

Such a discharge device can also be purchased on ali-express 30.09€ 27% OFF|150W Konstante Strom Elektronische Last 60V 10A Batterie Tester Entladung Kapazität Tester meter 12V 24V 48V|discharge capacity|battery testerconstant current electronic load - AliExpress

Barkuti · 2019-11-14T22:15:48.000Z

volchyonok, be sure both QB26800 batteries (datasheet) and LiitoKala 7000/7200 (cough!) are manufactured by the same original equipment manufacturer. The OEM sells his cells to whoever can buy the MOQ (Minimum Order Quantity) which can be a few thousand pieces, but other than this it is a relatively simple thing to do for a business or society (like Vapcell or LiitoKala whoever it may be).

The effective capaciy for the 26800 cells may be a little bit higher when using BMS systems with lower than 3V cutoff; this is common and I really doubt it would in practice be really detrimental for the batteries.

P.S.: to be accurate any testing device needs some sort of calibration. I, for example, took the time to properly average all my Lii-500 channels and obtain channel correction indexes. In my experience Lii-500s tend to very slightly underestimate capacity, at least mine does.

volchyonok · 2019-11-15T07:59:04.000Z

Barkuti:

I, for example, took the time to properly average all my Lii-500 channels and obtain channel correction indexes. In my experience Lii-500s tend to very slightly underestimate capacity, at least mine does.

This is not a matter of calibration, but of the strength of the discharge currents, which are mandatory as an orientation for choosing the suitable elements, which then will have to work under high loads in the battery for electric vehicles. Given the estimated number of parallel cans in each cell (3P …. 5P, etc.), one should bear in mind the ability of each element to hold a load in the region of 10 amperes and know exactly what capacity it can give to the ‘common boiler’ (“Joint boiler”). Your household charger, even if it is treated with high-grade pure gold, does not work with discharge currents greater than 1 ampere, so its informational value in the case of selecting batteries for a powerful battery has no value. A discharge device is required with the ability to load an element with a current of at least 10 amperes, even if its main load is a current in the region of 5A.

The_Fat_Controller · 2019-11-15T11:06:05.000Z

The cells for a large solar battery bank do not have to be identical, they do however have to be protected & fused individually , it is inevitable that in a pack containing a few hundred cells some will fail over time and degrade at different rates so redundancy and protection has to be built in to accommodate it

This is why i ended up going with Tubular Gel, The costs involved even if you build your own Lion bank by the time you have factored in all of the extra bits you need to make it safe , the cost of the cells BMS fuses & protection boards etc you end up spending just as much money and life time of the pack is really no better, The real advantage for lithium in a solar system is that it accepts high charge rates , there is no tail off like there is with lead acid

volchyonok · 2019-11-15T15:22:41.000Z

For an additional guideline, whether the QB26800-6800 and LiitoKala-7200 are the same product, it is necessary to clarify their actual dimensions (diameter and length of the case), which should be measured with a fairly accurate meter. Yes, they look almost exactly the same “positive” contact, but this is just iron, which can also be ordered from a third manufacturer, which produces only component shells, but not the inside. If there is a difference in size, then QB and LiitoKala can easily be not the same OEM product, so their characteristics can also have a significant difference.

And here for some reason they go not like 7200 (mAh), but already as 7000 (mAh)
https://aliexpress.com/item/33048536823.html?spm=a2g0o.detail.1000014.7.34496ab7vrse35&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.146400.0&scm_id=1007.13338.146400.0&scm-url=1007.13338.146400.0&pvid=e560c318-4cb8-4c6d-b86b-76289663f3cc

The_Fat_Controller · 2019-11-15T18:57:30.000Z

volchyonok:

Page Not Found - Aliexpress.com

4. Actual capacity : 5500mah I will be most dis chuffed if the ones i ordered only make 5.5ah

cells

Barkuti · 2019-11-15T20:58:10.000Z

volchyonok:

…

This is not a matter of calibration, but of the strength of the discharge currents, which are mandatory as an orientation for choosing the suitable elements, which then will have to work under high loads in the battery for electric vehicles. …

I can perfectly understand what you mean, don't worry. My Lii-500 serves me well to obtain accurate capacity measurements at low discharge rates. With regards to power delivery or discharge rate estimates, I have what I need to obtain accurate DC internal resistance measurements with a hack of my own. With this data I can more or less easily estimate maximum discharge rates.

Discharge curves are an excellent asset which standard discharge testers do not support. Here are a couple devices from ZKE Tech which can do discharge curves with PC software:

https://www.aliexpress.com/item/32856429623.html EBD-M05, a small little marvel for up to 5A discharge which recently someone recommended.
https://www.aliexpress.com/item/32806617908.html EBD-A20H, a more professional device for up to 20A discharge rate.

Just taking a quick look at some standard discharge curves, 1A and 5A for example, lets me discern battery internal resistance and expected maximum discharge rate.

The_Fat_Controller:

… it is inevitable that in a pack containing a few hundred cells some will fail over time and degrade at different rates so redundancy and protection has to be built in to accommodate it

…

I can't completely agree with that, I think cell life can be largely extended and mishaps avoided.

In any case, affordable 1S BMSes can be obtained which, for a very large pack, could be installed for each pair or trio of cells:

https://www.aliexpress.com/item/33025760150.html I see a hundred pieces of these 6x 8205 BMSes for ≈€43.99 shipping included.

volchyonok:

For an additional guideline, whether the QB26800-6800 and LiitoKala-7200 are the same product, it is necessary to clarify their actual dimensions (diameter and length of the case), which should be measured with a fairly accurate meter. Yes, they look almost exactly the same “positive” contact, but this is just iron, which can also be ordered from a third manufacturer, which produces only component shells, but …

…

And here for some reason they go not like 7200 (mAh), but already as 7000 (mAh) :FACEPALM:
https://aliexpress.com/item/33048536823.html

Battery factories are not hot dog stands. They cost large sums of money and resources which only large corporations can afford, namely if they're geared for large volume scales.

The 26800 cell is a new entry in this market, and I really doubt there is another OEM manufacturing such cells right now, i.e. all 26800s with the “QB26800” triple leg/lobe top pole shape come from same brand factories.

Source: https://www.thunderheartreviews.com/2019/01/queen-battery-qb26800-6800mah-20a-big.html

Fri, 11/15/2019 - 20:26

volchyonok · 2019-11-15T20:36:58.000Z

Barkuti:

all 26800s come from same brand factories.

There are different ones, and not only 26800 with another ‘plus’ output, but even 26700 26700-26800 — Yandex Disk

Barkuti · 2019-11-15T20:58:05.000Z

Mmmkay volchyonok, you convinced me to correct myself. Edited my above post.

Barkuti · 2019-11-15T21:12:27.000Z

The_Fat_Controller:

…

4. Actual capacity : 5500mah :| I will be most dis chuffed if the ones i ordered only make 5.5ah

cells

Your cells are expected to clock around 7000mAh at a low discharge rate. In the advertisement from the shop where you bought them with tabs, 7200mAh can be read as Nominal Capacity in Specifications:

I was told somewhere that is what matters, so test your bunch and file a dispute if they fail to meet ≈7Ah with very high consistency.

volchyonok · 2019-11-16T05:28:50.000Z

Barkuti:

The 26800 cell is a new…

For about a year now I have had this very information that you are showing. And I have long been looking for more recent research about these QB26800 from any other sources. In principle, according to the discharge schedule, I understand a lot. Especially the fact that the optimal load on these elements is within 1C, that is, it should not exceed 7 amperes, or better, if at all, 5 A. Otherwise, the discharge characteristic curve takes on a form that is disadvantageous for the longevity of this 26800. In short, when creating a battery, it is better to immediately count on the maximum current between 5A and 10A, that is, about 7A (1C), based on each individual item QB26800

:exclamation: However, it’s not yet clear to me what this guy means by the parameter that he calls “Charge cut-off current: 340mA (0.05C)” ?

Barkuti · 2019-11-16T06:45:18.000Z

volchyonok:

…

:exclamation: However, it’s not yet clear to me what this guy means by the parameter that he calls “Charge cut-off current: 340mA (0.05C)” ?

Here is a small quote from the cell specifications in the review:

…

Standard charge current: 6.8A (1C) (i charged at 5A, which is the max charge current of my tester)
Maximum charge current: 13.6A (2C)
Charge cut-off current: 340mA (0.05C)
Charge end voltage: 4.20V

The cell looks to be specified for a standard 1C charge current, 6.8A, and a 0.05C (1C/20) cut-off current which is 340mA.

The cut-off current is the current flow level at which the charge is stopped at the end of the Constant Voltage phase.

In my opinion, the 3C maximum continuous discharge rate is about right. It is a maximum, there is no need to say better cycle life will be obtained out of the batteries at slower discharge rates. Similarly, the specified charge currents are certainly steep (high). The discharge cut-off voltage is also too high at 3 volts, I'd use a more standard 2.8/2.75V cut-off (or even lower) and I'm sure the cell would do fine. You do not always let a battery completely discharge, after all.

Needless to say the cell will live better if kept within ½ the specified charge rates and (√2/2) times the specified maximum discharge rate (which cuts down in half dissipated power and maximum heat generation when discharging).

volchyonok · 2019-11-17T07:21:00.000Z

Barkuti:

The cell looks to be specified for a standard 1C charge current, 6.8A, and a 0.05C (1C/20) cut-off current which is 340mA.

The cut-off current is the current flow level at which the charge is stopped at the end of the Constant Voltage phase.

I honestly tell you that I still didn’t understand what is this “cut-off current”, especially since in his other videos about various other elements this same parameter is also mentioned. And if you yourself can explain what it is and in as much detail as possible, then this will become very useful for all of us.

Barkuti:

In my opinion, the 3C maximum continuous discharge rate is about right. It is a maximum, there is no need to say better cycle life will be obtained out of the batteries at slower discharge rates. Similarly, the specified charge currents are certainly steep (high).

As for this, I have long had a different opinion, especially since no one realizes that when it comes to the possibility of loading batteries with currents exceeding 1C, by default the manufacturer means not a stabilized current, but a pulsed one, which can have medium time and even very large gaps (pauses) for resting and cooling the batteries, which dramatically reduces their heating even at high amperage. And with an increase in the discharge current above 1C, the pauses in the PWM-currents should also be increased in time, and the pulse loads, on the contrary, should become shorter. That is, the element should be more able to rest and cool, thus not overloading too much. Look carefully and rely on discharge graphs with the temperatures shown at different loads, because you can not heat Li-Ion more than 45-50 degrees Celsius, especially in tightly sealed batteries, that is, without air, which have very poor cooling inside. And amateurs who imagine themselves to be professionals can load elements at their discretion, because it is their own money, time to replace overheated elements, and also their right to risk their own property and skin.

Barkuti:

The discharge cut-off voltage is also too high at 3 volts, I’d use a more standard 2.8/2.75V cut-off (or even lower) and I’m sure the cell would do fine.

I have never been opposed to a more complete discharge (Li-Ion up to 2.5 or even sometimes up to 2.2v), but we cannot always adjust this threshold, which the manufacturer sets on any of his products by default. So, for example, the controller of my bike automatically turns off the battery when unloading 3v for each element. And this cannot be reconfigured, because this firmware was made at the factory for the sake of more universal compatibility with Li-Po batteries, which cannot be discharged lower than to the threshold of 3.0-3.3v. And this model of the controller does not have the ability to reflash it in the usual accessible ways, which you can use without risk, so that later you simply do not throw this controller into the bin. Therefore, from the very beginning, I focus on batteries for which the manufacturer himself declares a discharge threshold of 3.0v. And when I first met these QB26800 with such a parameter threshold discharge characteristics, they obviously immediately aroused my interest.

Kame_Sennin · 2020-02-04T19:55:38.000Z

The_Fat_Controller:

Actual capacity : 5500mah I will be most dis chuffed if the ones i ordered only make 5.5ah

Did you get the batteries ? I am eager to know how many Ah they are !

Kame_Sennin · 2020-02-04T20:38:10.000Z

The_Fat_Controller:

Things to be aware of with cheap controllers , Many sellers lie about them being MPPT most are in fact PWM there are many fake Mppt modules there are also some good cheap controllers which really are MPPT here is one example Real budget MPPT

I have this controller and while i have not tested it for long yet i already have a few comments about it :

When opening the cardboard box there was a noise inside the controller : After opening the controller i found a loose metal screw. Thanks i heard it before powering on because it might have shorted something !
one of the TO220 components is thinner than the others and because its thermal pad is the same thickness there is a gap between the pad and the thermal drain (= not good!)
beside that : neat and clean pcb with what looks like good quality components
There is obviously a real buck converter that convert some of the spare voltage at the input into more current for the battery but the tracking seem to be either very slow or requires the input power to disapear totally for a new "tracking" cycle to occur
While the specifications claim a "no load current" < 10mA i measure something that vary randomly betwwen 45mA and 65mA. From what i can see on youtube reviews other people have the same problem with a russian guy even measuring 130mA.

This last point is very bad news for me because with my low power pannel (20W) 45 to 65mA * 24h mean that i need more than one full charge hour each day just to compensate for the controller consumption plus the seemingly random variation is not very reassuring

Barkuti · 2020-02-04T22:47:09.000Z

volchyonok:

Barkuti:

The cell looks to be specified for a standard 1C charge current, 6.8A, and a 0.05C (1C/20) cut-off current which is 340mA.

The cut-off current is the current flow level at which the charge is stopped at the end of the Constant Voltage phase.

I honestly tell you that I still didn’t understand what is this “cut-off current”, especially since in his other videos about various other elements this same parameter is also mentioned. And if you yourself can explain what it is and in as much detail as possible, then this will become very useful for all of us.

…

Wellp, back in the day this somehow got lost but, exercising my english grammar, here's a definifion I've come up with:

Definition of charging cut-off current.-

Given that li-ion batteries are meant to be charged at a constant current rate, with a given maximum charging voltage (usually between 4.1 and 4.4 V, with 4.2 V typical for most cylindrical cells), this is done by progressively increasing the output voltage of the charging device to maintain a constant current rate to the battery while its voltage increases as it is filled, and monitoring and limiting the maximum voltage at the output of the charging device or at the battery terminals. Once the maximum battery voltage is reached and set (charging enters the Constant Voltage phase), current flow to the battery starts tapering off gradually but never reaches 0, like an inverse growth function (see the right graph below). What this means is that for current flow to stop the charging device must stop providing voltage to the battery at some point, at some minimum current flow rate which is the cut-off current.

https://www.sparknotes.com/math/calcab/logs/section4/

If some native english speaker thinks the above definition could be somehow enhanced, say so. Thanks.