Charging efficiency LifePO4

[Sunking]

I would recommend that you get a Cellog8

Why would he waste his money doing that, he has a PL8 which can do everything the Cellog 8 can do plus a lot more like charge any battery on the face of the planet.

[createthis]

Why would he waste his money doing that, he has a PL8 which can do everything the Cellog 8 can do plus a lot more like charge any battery on the face of the planet.

Yeah, I've got a Celllog 8, but I really don't use it. You can't have anything monitoring the cells if you bottom balance or it will ruin the bottom balance.

[createthis]

If there is 1% tolerance there is not need to do anything, just middle balance and operate like a Pb battery. NASA, Lockhead Martin, and other DOD contractors are the only ones who can afford 1% tolerance cells. That is what they use in sattelites and spacecraft so they do not have to use any BMS or anything else that takes up weight and space.

You are3 using Chi-Com cells which are the lowest quality out there, and GBS lowest of the bunch. Tolerance is +/- 10%. That is why they are so inexpensive. If you were to buy quality cells would cost you 3 to 5 times what you paid. But even then no where close to 1%. That would be military and aerospace grade.

I think this is what I was missing. I didn't realize the tolerances were so dramatic.

[Sunking]

I don't understand how that is meaningless. It seems pretty damn meaningful as that's how I'll actually be using the thing.

I give up. You cannot get past voltages and current..Karrak has you so hung up on voltage you can't get past it. You have to find the Amp Hours before you give a damn about a charge voltage set point.

What SOC is 3.30 volts on a LFP?
What SOC is 3.31 volts on a LFP?
What SOC is 3.32 volts on a LFP?
What SOC is 3.33 volts on a LFP?
What SOC is 3.34 volts on a LFP?
What SOC is 3.35 volts on a LFP?
What SOC is 3.36 volts on a LFP?
What SOC is 3.37 volts on a LFP?
What SOC is 3.38 volts on a LFP?
What SOC is 3.39 volts on a LFP?
What SOC is 3.40 volts on a LFP?
What SOC is 3.41 volts on a LFP?
What SOC is 3.42 volts on a LFP?
What SOC is 3.43 volts on a LFP?
What SOC is 3.44 volts on a LFP?
What SOC is 3.45 volts on a LFP?
What SOC is 3.46 volts on a LFP?
What SOC is 3.47 volts on a LFP?
What SOC is 3.48 volts on a LFP?
What SOC is 3.49 volts on a LFP?
What SOC is 3.50 volts on a LFP?
What SOC is 3.51 volts on a LFP?

Come on tell me. I am waiting.

You cannot answer the question, no one can answer it. The only way you are going to be able to answer the question is fully charge each cell, measure each cell capacity, find the weak one to know what AH Capacity it is. Then Bottom Balance, charge the pack to 90% using AMP HOURS to terminate charge, not VOLTS. Allow it to rest disconnected, and then measure what the pack voltage is. The Voltage will be whatever it is.

[karrak]

Charge and float the battery at 13.6V till the current drops to less than C/50.
Tell us the voltages of each of the individual cells
Increase the voltage to 13.7V and wait till the current drops to less than C/50
Tell us the voltages of each of the individual cells
Increase the voltage to 13.8V and wait till the current drops to less than C/50
Tell us the voltages of each of the individual cells
If you use the PL8 to do this connect the balance port up to the individual cells to stop any individual cell going above 3.6 volts.
If you use the Classic, monitor the individual cell voltages to make sure they don't go above 3.6 volts.

Simon

[karrak]

That would be Top Balanced to get every cell 100%. I tried he does not get it.

As long as all the individual cells are above 3.4 volts when floated with the charging current less than C/50 you know that they are all above an SOC of 98%.

Simon

[karrak]

Yeah, I've got a Celllog 8, but I really don't use it. You can't have anything monitoring the cells if you bottom balance or it will ruin the bottom balance.

If the device monitoring the battery takes an equal amount of current from each cell in the battery it will not make the battery go out of balance.

I have measured the current draw from the Cellog8 and it is not the same from each cell but it is so small that it would take several years to make the battery go out of balance.

Simon

[createthis]

I give up. You cannot get past voltages and current..Karrak has you so hung up on voltage you can't get past it. You have to find the Amp Hours before you give a damn about a charge voltage set point.

What SOC is 3.30 volts on a LFP?
What SOC is 3.31 volts on a LFP?
What SOC is 3.32 volts on a LFP?
What SOC is 3.33 volts on a LFP?
What SOC is 3.34 volts on a LFP?
What SOC is 3.35 volts on a LFP?
What SOC is 3.36 volts on a LFP?
What SOC is 3.37 volts on a LFP?
What SOC is 3.38 volts on a LFP?
What SOC is 3.39 volts on a LFP?
What SOC is 3.40 volts on a LFP?
What SOC is 3.41 volts on a LFP?
What SOC is 3.42 volts on a LFP?
What SOC is 3.43 volts on a LFP?
What SOC is 3.44 volts on a LFP?
What SOC is 3.45 volts on a LFP?
What SOC is 3.46 volts on a LFP?
What SOC is 3.47 volts on a LFP?
What SOC is 3.48 volts on a LFP?
What SOC is 3.49 volts on a LFP?
What SOC is 3.50 volts on a LFP?
What SOC is 3.51 volts on a LFP?

Come on tell me. I am waiting.

You cannot answer the question, no one can answer it. The only way you are going to be able to answer the question is fully charge each cell, measure each cell capacity, find the weak one to know what AH Capacity it is. Then Bottom Balance, charge the pack to 90% using AMP HOURS to terminate charge, not VOLTS. Allow it to rest disconnected, and then measure what the pack voltage is. The Voltage will be whatever it is.

I should be able to expect the same ah capacity with my cells wired in series between whatever my float voltage is and whatever my lvd cutoff is at a given load rate. That should be reproducible. I don't know what you're on about.

[Sunking]

I should be able to expect the same ah capacity with my cells wired in series between whatever my float voltage is and whatever my lvd cutoff is at a given load rate. That should be reproducible. I don't know what you're on about.

No you cannot. That only works if you TOP BALANCE. You are using BOTTOM BALANCE and referencing to the weakest cell in the pack. If you cannot understand that, you are heading into trouble.

When you Top Balance you are taking the cells to 100% SOC. When fully charged all the cell voltages are equal, but NOT AH CAPACITY. Your weakest cell can be as low as 90 AH and the highest 110 AH a 20 AH difference. That voltage floated is 13.6 volts. On the discharge side, the cell votage are not equal as they discharge. The weakest cell volate fall lower and faster than all the other stronger cell. When the weak cell has fully discharge its 90 AH will be at 2.5 volts and all the others will still be above 3 volts. They will eat the weak cell and destroy it. Point here is the only time Lithium Batteries voltage is equal in a Top Balanced system is at or near the TOP. If you Top Balance you can control SOC by lowering the Voltage from 13.6 to 13.4. But not a BB system

But guess what? Are you Top Balancing? Come on answer the question. You are NOT TOP BALANCING now are you? No Sir you are Bottom Balancing right? In a Bottom Balanced system voltage is only EQUAL at 0% SOC of 2.5 vpc. At the bottom all Cells have the exact SAME CAPACITY of 0 AMP HOURS. As you charge the cells, voltage is NOT BALANCED, but Capacity is EQUAL in all cells. As you charge up the weakest cell voltage will be higher than all others. As the weak cell approaches 100% the voltage will shoot up. When it is fully charged up at 3.65 volts will Stop all charge current from flowing. All the other cells will not be 100% capacity and have much lower voltage. However every cell will have the exact same AH CAPACITY. What pack voltage is that on a 4S system. You DO NOT KNOW what it is. It could very easily be 13.3 volts. If you used 13.4 on your charger all you know is the weak cell stopped charging when it reached 90 AH as all other cells, but the weak cell is at 3.65 volts and stopping current flow an di snow being stressed stopping charge current. Well Hells Bells if the weak cells is 3.65, and pack voltage is 13.4 volts what is the Voltage of the other cells?. Hell you only have 9.75 volts left for the 3 other stronger cells. For sake of argument say they split 9.75 volts equally because they are 110, 109, and 111 AH cells they are 3.25 volts.

Your method is highly likely to destroy your weakest cell if you just arbitrarily select 13.4 volts because it is limited to 90 AH when full. You defeated the purpose of Bottom Balancing using Top Balance mentality. Wake up silly. You are not Top Balancing, you are Bottom Balancing trying to use Top Balance logic.

You need to know what the weakest cell capacity is. That means you need to fully charge every cell to 100% SOC, and then fully discharge each cell to find the lowest capacity cell. Say it is 90 AH. You only want to charge the weakest cell to 90% Capacity, not 100%. Wake Up. 90% of 90 AH is 81 AH. Once you determine that, then Bottom Balance the cells. Reassemble in series. Pump 82 to 83 Amp Hours in and Stop. Disconnect the pack and let the cells rest for a few hours. Then measure the pack voltage. The weak cell will be very close to 3.4 volts or slightly lower. All other cells will be much lower voltage than the weakest cell.

You that piece of meat between your ears. If the weakest cell is 3.4 volts at 90% SOC and all 3 cells are less than 3.4 volts, WHAT IS THE PACK VOLTAGE SMART GUY? You don't effin know. It is not 13.4 volts is all you can say, It would have to be something less. You have to find that voltage, not just pick it out of the air based on Top Balanced mentality

If you want to pick 13.4 volts my Friend, you need to TOP BALANCE and forget all about Bottom Balance. You use that logic on a BB pack, you will destroy a cell. Perhaps you need to do that to learn a lesson. No better teacher than loosing money. In a BB system you have to find the charged voltage, not pick it. That only works in a Top Balanced system.

[createthis]

I'm getting really tired of this, Sunking. I'm following the charging procedure you gave me in the Midnite Classic thread. Now you're telling me it's garbage? Make up your mind.

link to post in question where you tell me to charge at 13.6v for bulk, absorb, and float:

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/lithium-ion/302025-lifepo4-batteries-for-use-with-midnite-classic-150?p=303053#post303053

[createthis]

This is the post where you told me to use 13.6v for bulk, absorb, and float: https://www.solarpaneltalk.com/forum...053#post303053

[Sunking]

Are you wanting to limit to 90% or not?

Try it your way. If the cells are reasonable equal in capacity it will work. Watch for any cell voltages going high. Shut down if 1 cell goes above 3.4 volts.

The big issue is GBS cells. They are the lowest quality of the Chi-Coms. My set and just about everyone I know who owns them had significant capacity differences. 100 AH cells ranged 85 to 115 AH for a 100 AH rated cell. If you have a wide spread is trouble.

Like I said if you could get 1% tolerance, you can Balance anywhere, Top, Bottom, or in the Middle and have no use for monitors or BMS. If you are going to Bottom Balance you need to protect the weak cell and know which one it is. Find it. If you have Bottom Balanced correct, it is the one with the highest voltage when at or near full charged.

I don't care if you are getting tired. It is not your time getting wasted. Not my fault if you do not understand the information being presented even after explaining it in detail 6 times. You are on your own.

[createthis]

Are you wanting to limit to 90% or not?

Try it your way. If the cells are reasonable equal in capacity it will work. Watch for any cell voltages going high. Shut down if 1 cell goes above 3.4 volts.

I'm not trying it my way. I'm following your instructions.

So, from this exchange, I take it that setting my bulk, absorb, and float to 13.6v, as you directed, Sunking, will not limit SOC to 90%. Correct?

Given that my charge controller is incapable of counting ah, how would I limit my SOC to 90%, given my existing hardware, without shutting off my charge controller manually every night?

[Sunking]

I'm not trying it my way. I'm following your instructions.

So, from this exchange, I take it that setting my bulk, absorb, and float to 13.6v, as you directed, Sunking, will not limit SOC to 90%. Correct?

Given that my charge controller is incapable of counting ah, how would I limit my SOC to 90%, given my existing hardware, without shutting off my charge controller manually every night?

Geez you are dense. Use your PL8 or your Victron AH meter to pump in 90% Amp Hours. Disconnect, let it rest. Then measure OCV and record it. Now set you MNS to whatever voltage you recorded. Its a one time test. After that you are set. It maybe 13.35 or 13.45, or somewhere between like a perfect 13.4. It is whatever it is. It will be around 13.4

[createthis]

Geez you are dense. Use your PL8 or your Victron AH meter to pump in 90% Amp Hours. Disconnect, let it rest. Then measure OCV and record it. Now set you MNS to whatever voltage you recorded. Its a one time test. After that you are set. It maybe 13.35 or 13.45, or somewhere between like a perfect 13.4. It is whatever it is. It will be around 13.4

Ok. I will do that. Until I do that, I've disconnected my charge controller.

Before I disconnected the charge controller (bulk = 13.8v, absorb = 13.8v, float = 13.7v), I took some measurements:

Victron reads 13.86v.
Fluke 87 at battery terminals reads 13.87v.
Cell 1 reads 3.5v.
Cell 2 reads 3.376v.
Cell 3 reads 3.42v.
Cell 4 reads 3.57v.