Revolectrics

[sacharlie]

If it's set to 3.6 target. Pl8 will bypass the rest of the cells till the lower cell catches up. It does it to each cell in real time. till all r 3.6. If it's set to go to 3.6. Once there it holds it till term. Point.

So it charges forever instead of bringing all the other cells down to 3.5v?

[Burgerman]

Just like a BMS the balance charger like a PL8 reduces the cells charge by taking out power (proportionally up to 1 amp NOT ON/OFF like a BMS) and turning it to heat Iin a resistor to blow away with its fans.

As a cell reaches the point where it is at the chosen voltage a resistive brake is applied. It does this to every cell that reaches say 3.600V or maybe 3.5V if you set it to start balancing there instead. Since 3.5 and 3.6 are both full, it makes almost no difference. This is not a lipo! You gain nothing starting sooner other than around 3 seconds.

It does the same to EVERY cell in turn/together as it/they too reach the same exact charge voltage.
Since we are charging 40A across the whole 8S pack at once, as soon as this 1A (1000mA) brake (the balance current load) is exceeded then the voltage would rise above 3.600V. So the chargers power is instantly reduced to whatever power level is required in amps, to allow the cell to remain at exactly the 3.600V setting continually. As it sits at CV absorbing the last part of the charge. If this means that 5 or 6 cells are full, sitting at 3.600V (and the other have not yet reached this point) then the charger power May be at only 1 amp. That means the low cells are still charging. And the full ones are both charging at 1A and discharging at 1A at the same time. So they remain at 3.600V as long as required for the rest to catch up.

But normally because a well maintained and properly charged/balanced pack is easy to charge this only happens for a few minutes at the very end of the CV stage. And when all cells balanced, and total charge current reaches 450mA or whatever you set the charge ends.

A BMS on the other hand has a different approach. It CANNOT shut off the charger. It has a full (40A?) charge current, all the time. Limited only by chargers output voltage during its TOTAL CV which ideally will be 3.6V X 8 = 28.80V.

The problem is that if say 7 cells are at 3.5V (24.50V) that means the other one fed 40A and total 28.8V and so a high one will try and reach 4.3V. The BMS with its tiny drain current and no control over the charger has no choice but to disconnect the charger every time, then after its pulled the cell lower it connects it over and over! Rinse and repeat.

So as soon as the BMS (if its working CORRECTLY and many dont) sees a cell go above the balancer trigger point - say 3.5V since you cannot balance a pack below this figure (it actually unbalances it if attempted - and many BMS do that too) its feeble balancer ( that Utuber experts one was a miserable 80mA!) adds a pull down resistance to the high cell. Approx 3 seconds later its reached the desired 3.600V and it continues to climb very fast. The BMS allows this to go to its max allowed point, usually over 3.7V as it cannot just throttle the charger to a low current. This is its cell overvoltage trigger point. And at this point it chops off all power from the charger. And then tries to pull the overcharged cell down to 3.5V again. Once it has, it reconnects the chargers 40A again. Provided the charger hasnt turned off (no load). Which sends it back into orbit. So this almost instantly causes the cell to shoot up above 3.7V and cut off the chargers power again. This is frequently even higher at 3.8 or 3.9V. Over. And over. And over.

This can take days to balance if its a new pack, or if its been stored a week or in use if a cell is slightly higher impedance. Because that higher impedance cell wastes energy as heat in charge or discharge compared to the rest. This is why a balance circuit less than 1A is hopeless on a large pack.

So with a BMS balancing is a continual overcharge/discharge wave. Like a sawtooth. Its not possible for it to do it any other way. It cannot control the charger. And the next problem is the charger has no way to know when its actually balanced or when to stop.

[sacharlie]

anyone doing lithium now will benefit from the feedback on new hobby chargers and BMS details etc, - from my little bit of understanding with the BMS - we would like it to just balance - keep the cells at 3.6 at most during the process - and start the balance at 3.5v ? and hold it till all cells reach 3.6v ?

Is this the magic of the pl8?
When charging a group of cells like 4/12v or 8/24v if one cell only charges to 3.5v all the others are then brought down to 3.5v?

Asking again what does the pl8 do when one cell in the pack will only charge to 3.5v?

Still not answered!

[Burgerman]

I answered this in MASSIVE detail above.

[sacharlie]

I answered this in MASSIVE detail above.

Yep it was so massive I missed it.
I will try a longer question. If there is one cell in a battery pack that will charge to only 3.5v does the pl8 leave it there and charge the others to 3.6v OR does the pl8 bring the all the other cells down to 3.5v?

[Burgerman]

If there is one cell in a battery pack that will charge to only 3.5v does the pl8 leave it there and charge the others to 3.6v OR does the pl8 bring the all the other cells down to 3.5v?

The question makes no sense.

The PL8 and every cell balancing charger will if set to 3.5V will not charge the calls properly. 3.550 is the lowest voltage that gives a complete charge AND allows the pack to end up properly balanced. Where is 3.5V coming from?

The cell manufacturers say 3.65V because they are presuming a BMS which as no fixed balance point possible will be used. It bounces between 2 points. 3.5 and 3.7 normally to average wbout 3.6...

The PL8 charges all 8 cells to an exact figure. It doesent pull down any high cells from a high figure. It doesent let them get above what you choose in the first place.

Try and make a more sensible or better explained question. ALL chargers and BMS charge all 8 cells from a high voltage in series.

[Burgerman]

All charge all 8 cells in series. All cell balancing chargers. And all BMS.

Then both WATCH the cells. If any cell gets above an exact choosen figure (3.600V?) in the case of a good celL balancing charger it puts a resistor across that cell. Or cells. (in the case of the PL8 a propotional load. And so allows the rest to keep climbing to the same 3.600V. Once ALL cells are full, at 3.600 volt and current fallen to the termination point it stops charging.

I have no idea what pulling down cells to match your 3.5V one has to do with anything. A BMS does that over and over.

[Burgerman]

CELLS...

28.8V +CELL-+CELL-+CELL-+CELL-+CELL-+CELL-+CELL-+CELL- 0V

Between every cell (connected at each + and -) is a resistor and a mosfet. THIS IS WHAT CHARGES EVERYTHING.
28V and 40A goes in one end of the string. And exits at the opposite end. Every cell then sees EXACTLY the same current.

+CELL-
resistor

When ANY cell sees the correct voltage is reached it has its mosfet switched and so starts draining 1A through a fan assisted resistor (or about 80mA with a BMS)

So as to not exceed the 3.600V of the highest cell, the PL8 reduces charge amps. And its all accurate to 2mV.

Meanwhile the BMS is trying to discharge a high cell, whilst its stll being charged at 40A with an 80mA discharg rate!

[sacharlie]

I answered this in MASSIVE detail above.

Yep it was so massive I missed it.
I will try a longer question. If there is one cell in a battery pack that will charge to only 3.5v does the pl8 leave it there and charge the others to 3.6v OR does the pl8 bring the all the other cells down to 3.5v?

Well pardon me!

Just replace the 3.5v with 3.55v. Can you answer the question then?

[Burgerman]

It still makes no sense. Theres never any time a cell balancing charger does anything othr than charge UNLESS YOU ASK IT TO DO SOMETHING DIFFERENT.

If you choose 3.55, or 15v per cell, the answer is the same. It will BRAKE a cell as you charge so it does not exceed the voltage you choose.

The only time it will pull 7 cells down to match your 3.5V one is if you CHOOSE 3.5V as the charge voltage and somehow all the other cells are higher than this when you connected it. But that isnt really possible as the full battery resting voltage is 4.5xxV after a charge.

So the question makes no sense.

It just shows that you didnt grasp anything I posted in the last 5 posts. And still dont.

A BMS nessasarily HAS to keep on dragging the cells down lower than it target voltage as it has no other way to charge the rest of the cells. Because if it didnt do that as soon as it reconnects a full power charger the high cell will go over voltage all over again. So THAT DOES keep pulling any high cells lower than 3.6V over and over. It hasnt got any other options. It cannot throttle the charge rate.

[sacharlie]

OK so if one cell in the pack will not hold a charge as high as all the others the pl8 leaves the pack unbalanced.

[Burgerman]

No. It couldnt happen. If you are charging a cell its voltage rises. Unless its got an internal short and then it would be dead already and the charger will quite correctly refuse to start.

Even if you could trick it somehow, If it did start, (and it wont, because anything under 2.55V causes a low current 500mA afety charge state to prevent fires) it would still error as the voltage rise or cell gap would exceed safety limits. Because charging an internally shorted cell would cause a potential fire. So again even that couldnt happen.

If one cell failed WHILE you charged with a sudden short internally that one cell would never reach its taget voltage. Even if it did it would time out and never reach the termination current. Errors all the way. And still the other cells would be at target voltage. Not pulled lower to "match" a bad cell.

If you tried the same with a BMS it cant do anything about it and the charger would keep trying to charge it and you would end up with a possible fire. No BMS or Charger pulls cells down to match a faulty one. You have a fundamental misunderstanding of how any of this stuff works. As I said the question makes no sense.

[sacharlie]

No. It couldnt happen. If you are charging a cell its voltage rises. Unless its got an internal short and then it would be dead already and the charger will quite corectly refuse to start.

Even if you could trick it somehow, If it did start, (and it wont because anything under 2.55V causes a low current 500mA state to prevent fires) it would still error as the voltage rise or cell gap would exceed safety limits. Because charging an internally shorted cell would cause a potential fire.

If one cell failed WHILE you charged with a sudden short internally that one cell would never reach its taget voltage. Even if it did it would time out and never reach the termination current. Errors all the way. And still the other cells would be at target voltage. Not pulled lower to "match" a bad cell.

If you tried the same with a BMS it cant do anything about it and the charger would keep trying to charge it and you would end up with a possible fire. No BMS or Charger pulls cell down to match a faulty one. You have a fundamental misunderstanding of how any of this stuff works. As I said the question makes no sense.

You seem to be saying that each cell holds the exact same amount of energy and can be charged to that same amount as all the others. I don't believe that is true. There old cells, new cells, A grade and B grade cells.

[Burgerman]

Of course I am not!
Do you have learning disabilities or something?

I can parallel charge a 4S lithium polymer pack with a 8S one. And do so all the time. Totally different capacities and the PL8 charges and balances every cell to exactly 4.200V. Why would it do any different???

I honestly do not know what you are talking about. And neither do you.

Are you confusing voltages with capacity or something? Totally got no clue what you are thinking. You MUST have a basic understanding of how stuff works, what volts/amps and oghms law is. Or its like trying to teach my dog physics.

[Burgerman]

You seem to be saying that each cell holds the exact same amount of energy

No EVERY CELL IS DIFFERENT!!! I never said any such thing. Why do you think they need to be balanced???

and can be charged to that same amount as all the others.

What do you mean charged to the same amount? You are mixing up voltages and state of charge with capacity.
A 2Ah cell is full when its charged to 3.600V and current is low.
A 2000Ah cell is also full when it reaches 3.600V and its current is low.

You can charge any lifepo4 cell at any voltage from 3.45V to 4.5V if you want. Its just that those figures will either not allow balance to be performed or will severely damage the cells. Non of that has anything to do with old/new/A or B grade.

What the hell does voltage have to do with the amount of stored energy??? And why would you think you cant charge an old cell above 3.5V?

I don't believe that is true. There old cells, new cells, A grade and B grade cells.

And every one of them is charged fully at the exact same voltage.

[shirley_hkg]

Asking again what does the pl8 do when one cell in the pack will only charge to 3.5v?

Again , if one cell is 3.5 and the rest are 3.55/3.60, PL8 will drain all input to them, so that only the 3.5 one is still gaining . Eventually it will catch up to 3.55/3.60 .

PL8 can do it @1,000mA max, while most BMS can do 60/80 mA.

[Burgerman]

And just in case, if you have a really old and knackered cell thats only half its original capacity. Its STILL FULLY CHARGED at 3.6V. And theres nothing limiting it to going even higher like 3.8V either.

[shirley_hkg]

This one is balancing @4,500mA now .

[terry2]

You are welcome to your views. Wrong regarding BMS but welcome to it anyway.

A question for you.
How does your BMS know the battery balance has completed, and that the battery charge has completed?
I can tell you the answer, it doesent, But more importantly even if it did it has no way to tell the charger this. Which in turn has no idea what the BMS is doing... They cannot talk to each other.

Because good BMS these days are programable.(pages and pages of options)
Either on a PC or Mobile via bluetooth.

You can tell it when to start when to finish, amp\volts ECT. for each cell.
A good 2021 BMS even has a temperature cut off. For when the cells are to hot or to cold during charging.

A good BMS Program is open source and has a github\forum.
The list for 2021 BMS are long.

[terry2]

Well I certainly won't be using a Failly (oops sorry Daly) BMS... https://diysolarforum.com/threads/daly- ... nce.27086/

Looks like a POC to me.

Steve

Plenty of Overkill 2021 programable BMS happy people there

[Fred005]

Hi.

Many time you, BurgerMan, wrote BMS is in the wrong place.
You wrote AND affirmed.
So, where do you think the right place is ?

With 2 very bad 110ah LiFePo4 and 2 very ''not in the right place'' BMS, I made this hike yesterday and back home, without fire or any else probleme. (I agree, not the best LiFePo4).
25km, D+1040m, Total moving time 8h25
Less than 3km/h.
30kg load for a friend shepherd
You may can understand how difficult was my hike for my X8 F+.

I can imagine with a sweet PL8 charger how many hours I could hike ... Much more ! Lol.

[Fred005]

Because good BMS these days are programable.(pages and pages of options)
Either on a PC or Mobile via bluetooth.

You can tell it when to start when to finish, amp\volts ECT. for each cell.
A good 2021 BMS even has a temperature cut off. For when the cells are to hot or to cold during charging.

A good BMS Program is open source and has a github\forum.
The list for 2021 BMS are long.

Exactely. We are in 2021 not 10 even 5 years earlier.

[biscuit]

Because good BMS these days are programable.(pages and pages of options)
Either on a PC or Mobile via bluetooth.

You can tell it when to start when to finish, amp\volts ECT. for each cell.
A good 2021 BMS even has a temperature cut off. For when the cells are to hot or to cold during charging.

A good BMS Program is open source and has a github\forum.
The list for 2021 BMS are long.

Are you saying these new BMSs do all the thinking and you could just plug your battery into a power supply and the BMS will do all current and voltage setting according to the user's requirements? If that's the case, it sounds like perhaps we need more technical expertise on BMSs. Like how to know we aren't sitting on a bomb when they fail and what they do with the current coming in from the dumb charger when they do not fail.
That would be technical enough for me

To be sure, we have technical people on here besides Burgerman who have tested quite a few and found them wanting, but none of these techno whizz kids have gone into any in depth explanations of where they succeeded and where they failed. It never mattered much to PL8 users.

[shirley_hkg]

Balance ability is the bottleneck. It is exceptionally critical if Aliexpress is your only battery source .
People are free to run at 48V/72V/120V. Double the volt will half the Ah .
We are the ethic minority that are stuck with the damn 24v application . My 300Ah pack needs balance power equivalent to that of a 100kw Tesla. How would it be available to wheelchair user ?

[biscuit]

mhm... we have what we have! Can't change the entire industry.

So even those brilliant new BMSs will not balance cells of a 24V battery, because the current is too high?

Will it work to put in 300Ah and use the battery with no balance if we take only 40Ah from it?
Do we need to balance the battery in any case when it gets out of balance?
(a job for when we aren't using the battery!)

[steves1977uk]

This one looks interesting... https://github.com/Green-bms/SmartBMS

Terry, what's the balancing current on the OverkillSolar BMS?

Steve

[Burgerman]

You need to balance the pack every charge. Unless you KNOW it was in good balance already and DO NOT fully charge it. And only do that a few times max.

Terry, what's the balancing current on the OverkillSolar BMS?

Steve

Only a tiny 80mA according to shirley, and only then if its a long way above the correct voltage. So its useless on a big pack. Esp if less than perfect/new. And already balanced by something else first. Hence he big list of warnings. But its got BT and nice graphics!

[steves1977uk]

So it's basically useless without a proper charger that can do 1A+ balance current? In other words, it'd take DAYS/WEEKS to balance a 210Ah pack which defeats it's purpose on a new build.

Steve

[Burgerman]

All those like terry2 or fred005 who remain completely clueless are welcome to use their BMS. They work in EXACTLY the same way, and cannot be improved no matter how many add on adjustments and fancy graphics they pile on. And the fact that you are incapable of understanding that shows your ignorance. But I am trying to educate not stop you. I couldnt care less about your battery oryour risk if you dont.

80mA balance! Same as my laptop.

Its like trying to teach physics to my dog.

[steves1977uk]

Let them live in their fantasy world BM, sooner or later it will bite them in the .

I know better not to use a BMS, no matter how good it "claims" to be. And 80mA balance is just a joke, how can anyone expect their cells to be balanced properly with such a tiny current? Mind boggles at some inept people to understand this. Even the ole Hyperion chargers had nearly 4x the balancing current than these 2021 BMS's.

Steve