LifePO4 GBS Amp Hour Testing 2.5v to 3.6v per cell

[karrak]

Answer is simple, so you can pass that current along to undercharged cells to Equalize them and get them charged up. Thus with Lithium if you want to maintain 100% SOC every time you charge requires a VAMPIRE Board aka BMS or Bypass Circuit Board. So when the board senses 3.6 volts, it turn on and bypasses a predetermined amount of current around the cell to pass current onto the other cells still in need of a charge.

If you charge to 3.45V/cell at an end current of around C/20-C/50 you are going charge to >99%SOC. Under these conditions you do not need any balancing boards if you are prepared to do the balancing manually.I don't have any balance boards. The last time I did a manual balance was in February. Yesterday at the end of charge my highest cell voltage was 3.48V and lowest cell voltage was 3.43. This is on a battery in use 24 hours a day, 365 days of the year.

Simon

[Sunking]

Jesse here is what I am trying to lead you to discover, but Simon keeps clogging the works up with attacks. Remember that is the only reason Simon is here for. He sells cheap Chi-Com junk batteries and has vested interest. He calls himself an Electronics Importer. That is how he butters his bread. I can give you his web page if you want it.

You charge Pb and Li the exact same way. There is no difference in charging. The difference is how you Equalize the two.

As I stated and you performed the experiments, Li batteries have one unique characteristic no other battery has. In fact it works exactly opposite of all of the other batteries. As a lithum battery charges up, its Ri goes up. As it discharges, its resistance goes down. If you were to look at a graph of Resistance as the Vertical line, and SOC as the Horizontal line would look exactly like the charge graphs you made with your PL8. You would see a sharp knee bend lower at the 0% SOC, and a sharp rise when charged. Everything in the middle is pretty flat. That is very desirable in a battery. No other battery does that.

What the effect is, a Li battery is not capable of passing current when fully charged. Pb, NiCd can all pass current when fully charged because their resistance is at the lowest point. Why would you want to pass current through a fully charged battery?

Answer is simple, so you can pass that current along to undercharged cells to Equalize them and get them charged up. Thus with Lithium if you want to maintain 100% SOC every time you charge requires a VAMPIRE Board aka BMS or Bypass Circuit Board. So when the board senses 3.6 volts, it turn on and bypasses a predetermined amount of current around the cell to pass current onto the other cells still in need of a charge.

Those knees at the ends of a Li battery charge/discharge curve are your signals, red light signals you do not want to go past. Where do the knees occur? Take a look. Around 2.9 and 3.4 volts. Note I said AROUND not EXACTLY 2.9 and 3.4.

[Sunking]

You do not remove lead sulphate from the electrolyte and deposit it on the plates of the battery as crystals, you take sulphate ions from the electrolyte and combine them with lead and lead oxide from the plates to form lead sulphate. Lead sulphate is insoluble, it will not go into solution. If it were soluble a lead acid battery would not work. Want to learn more, try https://www.av8n.com/physics/lead-acid.htm for more information.

Shove it up you arse Simon. I have forgottemn more about batteries than you wil ever know. Geez you are a salesman of cheap Chi-Com junk. Stick with what you know. You cannot even comprehend what you are reading. I can take blame for not going into technical depth, and would if the audience could comprehend what was being said.

In Laymen terms, when you discharge the lead sulfate moves from the electrolyte and coats the plates in the form of soft crystals. During charge the crystals in Laymen terms are dissolved back into the electrolyte. Simon I know you are not aware of it but electrolyte is is acid, not water. Electrolyte (sulfuric acid) is diluted with water.

The process is the same with both Pb and Li. Both are metals, and both work by moving atomic particles called ions from cathode to anode and back again. Pb is chemical, and Li is electrical.

You do not change the polarity between the anode and cathode to move the lithium ions. The + terminal is always the plus terminal and the - terminal is always the - terminal. See http://www.nova.org.au/technology-fu...-ion-batteries for more information on lithium ion battery charging and discharging.

Learn how to read, you change the ion charge polarity.Again you do not know what you are talking about and cannot comprehend what is being said. I never said the positive terminal changes polarity. Only an idiot like yourself would believe that. Again the lithium ions change polarity by gaining or loosing an electron. When Li ion give up an electron, it becomes charge positively charge and moves to the negative cathode electrode. When it gains an electron negatively charged and moves to the positive anode electrode. Opposites attract, basic chemistry and physics.

Sunking, you are really embarrassing yourself making these totally incorrect statements, they just show that you don't have a basic understanding of how Lead Acid batteries or Lithium batteries work.

Keep on dreaming Simon.

[karrak]

When you discharge a Lead Acid battery a chemical reaction takes place. You remove lead sulfate from the electrolyte and deposit it on the plates of the battery as crystals. That makes the specific gravity go down. So if you weighed the water it would be less weight, but that does not change the weight of the battery. All you have done is shifted it from the water to the plates. Once you charge the batteries reverses the process by dissoving the lead sulfate crystals back into the water.

You do not remove lead sulphate from the electrolyte and deposit it on the plates of the battery as crystals, you take sulphate ions from the electrolyte and combine them with lead and lead oxide from the plates to form lead sulphate. Lead sulphate is insoluble, it will not go into solution. If it were soluble a lead acid battery would not work. Want to learn more, try https://www.av8n.com/physics/lead-acid.htm for more information.

Lastly don't let yourself get confused about Ion in lithium vs Chemical reaction of a lead acid battery. There is no difference you need to know or be concerned with. In a Lithium battery you move ion particles from Cathode to Anode by changing its polarity. In a lead acid you move lead sulfate particles from solution to plates.

You do not change the polarity between the anode and cathode to move the lithium ions. The + terminal is always the plus terminal and the - terminal is always the - terminal. See http://www.nova.org.au/technology-fu...-ion-batteries for more information on lithium ion battery charging and discharging.

Physically different, but no difference to you or how to charge up a battery. Both Lead Acid and Lithium use the exact same chargers.

That is very different from your past statements that you need a special Lithium charger to charge Lithium Ion batteries properly.

Electrons do not know the difference as they are just passing through picking up hitchhikers on the way and dropping them off on the other side.

This is one of the biggest loads of rubbish that you have ever stated. Pure fantasy and totally wrong. Electrons flow through the wires, lithium ions and sulphate ions diffuse (travel) through the electrolyte.

Sunking, you are really embarrassing yourself making these totally incorrect statements, they just show that you don't have a basic understanding of how Lead Acid batteries or Lithium batteries work.

Simon

[karrak]

Huh. I remember reading batteries weigh more when fully charged, but doing some research now, it appears this is due to oxygen and CO2 venting, not electron movement: reddit.com/r/askscience/comments/1hj8k7/do_discharged_batteries_weigh_less_than_fully

If you look closely at that post you will see they are talking about zinc hearing aid batteries. You have to look very carefully at the detail, all batteries are different.

Regarding Lithium Ion based batteries, when they are being charged they will not loose or gain any weight by gaining or loosing atoms or electrons unless they are abused but they will gain weight because of that famous formula E=mC². One of your 100Ah 3.6V cells stores around 327Wh (100*3.27) which is the same as ~ 1,180,000 J (Joules) of energy. m=E/C² so a fully charged cell is ~.000000000013g (.00000000000046oz, 1,180,000/(300,000,000*300,000,000)) heavier than a fully discharged cell.

So, as I've been building my V3 portable solar generator, I've been thinking about this heat issue. I guess if you could adequately cool the battery you could charge at a higher rate, right? Prismatic cells are probably poor candidates for water cooling, but I guess this is another area where small cylindrical cells shine.

I actually agree with Sunking that at the sort of charge and discharge rates that your battery is likely to see you will not have any problems with heat. For long life you should limit the charge and discharge rates to C/2 and keep the charge voltage below 3.5V and float voltage below 3.4V . If you do this I can't see any reason your battery will not last 10+ years.

Simon

[Sunking]

Huh. I remember reading batteries weigh more when fully charged, but doing some research now, it appears this is due to oxygen and CO2 venting, not electron movement:

Nonsense, don't be silly. Where would that weight come from or go to?

Now the electrolyte specific gravity changes in a FLA battery as it charges and discharges. Perhaps that is how you or whoever told you that made that silly conclusion. However that does not change the mass. When you discharge a Lead Acid battery a chemical reaction takes place. You remove lead sulfate from the electrolyte and deposit it on the plates of the battery as crystals. That makes the specific gravity go down. So if you weighed the water it would be less weight, but that does not change the weight of the battery. All you have done is shifted it from the water to the plates. Once you charge the batteries reverses the process by dissoving the lead sulfate crystals back into the water.

Now you can electrolise the water out of the battery charging at 2.4 vpc or higher which changes water into Hydrogen and Oxygen. But as soon as you replace the water you are back to specified weight of the battery.

So, as I've been building my V3 portable solar generator, I've been thinking about this heat issue. I guess if you could adequately cool the battery you could charge at a higher rate, right? Prismatic cells are probably poor candidates for water cooling, but I guess this is another area where small cylindrical cells shine.

In theory yes, in practice not so much. But you are making mountains out of molehills. Just where in the world are you going to get a charger that can generate 100 amps or more of current? It can be done, but you will never do it. You are talking 1500 watts of power on a 12 volt battery. Your PL8 is only capable of 55 amps max or C/2 on your batteries. At 12 volts is 700 watts.

Do some math. What is the Ri of your battery? 2.5 milli-ohms ring a bell? So at 55 amps ho wmuch power is being converted to heat?

Current x Current x Resistance = Watts.

55 amps x 55 amp x .0025 = 7.5 watts of heating from 150 watts input. Will the cell get warm? Yes it will, but not hot. It would have to go to 70 degree C or 160 degree F to be a real problem. If th ecell started at room temps, would still be cool to the touch at 7 watts in such a large area of the cell.

Look at the specs of your cell and not recommended charge rate. What does it say? C/2 right? What is max? 1C right? You wil never get close to 1C charge rate. Even if you do is no problem if th ebatteries are at room temp with ventilation. Heat issues are not a concern with solar or stationary applications. That is only a problem with EV's where the batteries are in a insulated box and heat cannot escape easily.

Lastly don't let yourself get confused about Ion in lithium vs Chemical reaction of a lead acid battery. There is no difference you need to know or be concerned with. In a Lithium battery you move ion particles from Cathode to Anode by changing its polarity. In a lead acid you move lead sulfate particles from solution to plates. Physically different, but no difference to you or how to charge up a battery. Both Lead Acid and Lithium use the exact same chargers. Electrons do not know the difference as they are just passing through picking up hitchhikers on the way and dropping them off on the other side.

[Sunking]

407 amps, which exceeds the 3C (300 amp) max charge rate for this battery according to the specs page: http://www.batteryspace.com/lifepo4-...-2vx4-dgr.aspx
Interesting. This means you could damage a LifePO4 battery by attempting to jump a low voltage LifePO4 battery from a fully charged LifePO4 battery, correct?

In theory yes, in practice no. What is throwing you is assume that current is going to be flowing for a significant period of time, when in real world just a fraction of a second. Your battery is also rated for 10 C for 30 seconds, and 3C contnious

Ri limits current on the high knee. Super interesting.

OK try this, Charge your cells to 4.0 volts and let them saturate. Don't be scared you can take LFP to 4.2 volts. Then check the Ri and see how high it goes up. You could not push 1 amp through with a Truck. Your battery Ri will be well above 1 ohm

But if you change that voltage to 13.4v or 3.35vpc, you'll only charge the battery 40-60%. I proved that by measuring the AH in at that voltage using the PL8.

OK like I have said over 100 times you have to find the voltage. Go to 13.5, then 13.6 until you find the voltage that correlates with 90% SOC. FWIW it will be around 3.45/cell.

Those knee bumps are the signal you are looking for. You want to charge until the voltage starts that upward fast turn. That happens at around 3.4 volts. As soon as it starts up you are 90%. SOC STOP!

[createthis]

Your analogy is wrong, when you are charging a battery you are not putting extra electrons (air in your analogy) into the battery you are just shifting Lithium Ions from a lower energy state in the cathode to a higher energy state in the anode, when you discharge the battery you are shifting the Lithium Ions back to a lower energy state in the cathode. To use the analogy of two ponds, a waterfall and a pump the top pond is the anode, water running down the waterfall is current being discharged from the anode into the bottom pond(the cathode) and the pump is recharging the water into the anode again.

Huh. I remember reading batteries weigh more when fully charged, but doing some research now, it appears this is due to oxygen and CO2 venting, not electron movement: https://www.reddit.com/r/askscience/...ss_than_fully/ Good to know. I like the two pond analogy.

The problem with too much current is that due to the internal resistance of the battery that it heats up, the heat produced is proportional to the Current squared (Amps*Amps). Heat is bad for the battery because it causes unwanted side reactions. With high charge currents this heat can also get concentrated in hot spots which amplifies the problem.

So, as I've been building my V3 portable solar generator, I've been thinking about this heat issue. I guess if you could adequately cool the battery you could charge at a higher rate, right? Prismatic cells are probably poor candidates for water cooling, but I guess this is another area where small cylindrical cells shine.

[createthis]

The current = 3.6 volts - 3.0 volts / 2.7 milli-ohms = 222 amps. In this case the battery Ri limited charge current and yours would be just fine with it. ou would only see 222 amps for a few seconds, then the current will quickly taper off as the battery voltage riss to meet the charger. Despite the 2C charge rate, it will still take at least 600 to 90 minutes for the battery to saturate and be fully charged up. Now tell me what the current would be if the cell voltage was at 2.5 volts, and 3.2 volts?

407 amps, which exceeds the 3C (300 amp) max charge rate for this battery according to the specs page: http://www.batteryspace.com/lifepo4-...-2vx4-dgr.aspx
Interesting. This means you could damage a LifePO4 battery by attempting to jump a low voltage LifePO4 battery from a fully charged LifePO4 battery, correct?

Ri limits current on the high knee. Super interesting.

Now if I want slow and gentle all I would need is 1-Stage. Set the charger to 13.6 volts and walk away. Both batteries are still going to get 100% charged up, it will just take a little longer until the batteries saturate to 13.6 volts.

But if you change that voltage to 13.4v or 3.35vpc, you'll only charge the battery 40-60%. I proved that by measuring the AH in at that voltage using the PL8.

[karrak]

Hmm. ok. I wasn't aware it was possible to put too much current into the battery. I thought it would simply accept what it would accept and that was the end of it. I thought that was why the current tapered off at the end of a charge. What is doing the squeezing in this analogy? voltage or amperage?

Current is flow of electrons, like flow of water from a tap.The squeezing is the voltage. If you squeeze a sponge a certain amount you will first get a large flow and then this flow will taper off to nothing, squeeze a bit harder and you will get another flow that will taper off.

I guess I always thought of LifePO4 batteries like a standup paddle board being pumped up. The voltage is like the pressure of the pump. If you set the pump to 12 PSI, the paddleboard "charge" will complete and the paddleboard will be full of air and usable, but it can still accept more air. If you set the pump to 15 PSI, that's like using 3.6v on a LifePO4 cell. It's the max the cell or paddle board can safely handle. You can increase the voltage or air pressure beyond that, but you'll risk damaging the paddle board / battery from over pressure.

The amperage in this case would be the size of the air tube or maybe the capacity of the pump for each throw of the handle. Toward the end of the charge, it becomes more difficult to move the handle up and down because you're resisting all that air pressure in the paddle board.

Your analogy is wrong, when you are charging a battery you are not putting extra electrons (air in your analogy) into the battery you are just shifting Lithium Ions from a lower energy state in the cathode to a higher energy state in the anode, when you discharge the battery you are shifting the Lithium Ions back to a lower energy state in the cathode. To use the analogy of two ponds, a waterfall and a pump the top pond is the anode, water running down the waterfall is current being discharged from the anode into the bottom pond(the cathode) and the pump is recharging the water into the anode again.

But I guess this analogy isn't perfect. I'm hearing from you and sunking that too much amperage can overcharge too. I need to go back to re-read his post. Clearly I'm still a little fuzzy on that.

The problem with too much current is that due to the internal resistance of the battery that it heats up, the heat produced is proportional to the Current squared (Amps*Amps). Heat is bad for the battery because it causes unwanted side reactions. With high charge currents this heat can also get concentrated in hot spots which amplifies the problem.

Simon

[Sunking]

Hmm. ok. I wasn't aware it was possible to put too much current into the battery. I thought it would simply accept what it would accept and that was the end of it. I thought that was why the current tapered off at the end of a charge.

Charge current is determined by one of two factors; The chargers Current Limit, or the battery Ri. Example lets say we take one of your cells, it is at 3 volts, and we have an Infinite Current Charger set to 3.6 volts. What is the initial Charge Current? You should be able to answer this since you know each cell Ri. .

The current = 3.6 volts - 3.0 volts / 2.7 milli-ohms = 222 amps. In this case the battery Ri limited charge current and yours would be just fine with it. ou would only see 222 amps for a few seconds, then the current will quickly taper off as the battery voltage riss to meet the charger. Despite the 2C charge rate, it will still take at least 600 to 90 minutes for the battery to saturate and be fully charged up. Now tell me what the current would be if the cell voltage was at 2.5 volts, and 3.2 volts?

Now use a 10 amp charger. What is limiting the current? The charge now limits the current until your battery reaches 3.6 volts - [10 amps x 2.7 milli-ohms) = 3.573 volts.

What is doing the squeezing in this analogy? voltage or amperage?

Voltage is always the pressure. Look it does not matter what type of battery we are talking about, with the exception of Nickel based batteries, all batteries charge the exact same way. Ohm's Law does not change between battery types.

To charge a battery we need to be able to do at least two things. Regulate both Voltage and Current. In other words build a plain ole fashion DC power supply that we can set the voltage and limit current. Nothing more is needed.

Now if we want to charge fast, we need two more things. The ability to measure current,, and change voltage based on the current. We call that a 2-Stage Charger. In Stage we we crank up the voltage, say to 14.4 volts on a 12 volt system. We apply the voltage until the charge current tapers down to 3 amps on a 100 AH battery. Then when the current reaches 3 amps, we lower the voltage to 13.6 volts and FLOAT. All charge current stops, the battery is at 100% SOC and our charger will supply all power for the loads until we turn it off. What kind of battery did we just charge up?

From the voltage and current profile I just went through it has to be either LiFeP04, or a Lead Acid battery. Charger does not care, nor would the batteries as they have the exact same charge profile.

Now if I want slow and gentle all I would need is 1-Stage. Set the charger to 13.6 volts and walk away. Both batteries are still going to get 100% charged up, it will just take a little longer until the batteries saturate to 13.6 volts.

[createthis]

You make good videos!

Thanks! I try (sometimes).

If you mean the flat spot on the voltage graph, that is where the charger has gone into CV mode and is keeping the voltage constant by decreasing the current until it decreases to 1 amp at which point the charger terminates the charge. This decreasing of the current reduces the rate at which the battery is being filled up so the SOC graph on the right hand side flattens off. It has nothing to do with overcharging.

What does overcharging mean? It could mean putting too high a current into the battery at any stage of the charge cycle or it could mean going above a certain charge voltage or a combination of both of these. The voltage and current are not fixed or rigid numbers, they should be chosen depending on the battery specifications and the circumstances that the battery is being used in.

Hmm. ok. I wasn't aware it was possible to put too much current into the battery. I thought it would simply accept what it would accept and that was the end of it. I thought that was why the current tapered off at the end of a charge.

Lithium batteries are not like a bottle that we fill up and it overflows if we overfill/overcharge it. They contain a cathode and an anode. When the battery is empty the cathode is full of lithium ions and the anode is empty. When the battery is full the anode is full and the cathode is empty.

If we represent the anode and cathode as two sponges and the lithium ions as water, an empty battery is where the cathode sponge is full of water and the anode sponge is empty. Putting a voltage across the battery to charge it is like squeezing the cathode sponge, the harder we squeeze it the faster the flow of water/current out of the cathode sponge. When the battery is nearly full it gets harder and harder to squeeze the water out of the cathode sponge. We have to increase the voltage/squeeze harder to get more lithium ions/water out. We can't get all the lithium ions/water out of the cathode sponge, there will always be some lithium ions/water left in the cathode sponge, the amount left depends on the voltage that we charge the battery too/how hard we squeeze the sponge.

What is doing the squeezing in this analogy? voltage or amperage?

I guess I always thought of LifePO4 batteries like a standup paddle board being pumped up. The voltage is like the pressure of the pump. If you set the pump to 12 PSI, the paddleboard "charge" will complete and the paddleboard will be full of air and usable, but it can still accept more air. If you set the pump to 15 PSI, that's like using 3.6v on a LifePO4 cell. It's the max the cell or paddle board can safely handle. You can increase the voltage or air pressure beyond that, but you'll risk damaging the paddle board / battery from over pressure.

The amperage in this case would be the size of the air tube or maybe the capacity of the pump for each throw of the handle. Toward the end of the charge, it becomes more difficult to move the handle up and down because you're resisting all that air pressure in the paddle board.

But I guess this analogy isn't perfect. I'm hearing from you and sunking that too much amperage can overcharge too. I need to go back to re-read his post. Clearly I'm still a little fuzzy on that.

[karrak]

You make good videos!

I think this explains the flat spot on the high knee in my charge graphs. Thanks. I was thinking that was overcharge, but I wasn't sure why.

If you mean the flat spot on the voltage graph, that is where the charger has gone into CV mode and is keeping the voltage constant by decreasing the current until it decreases to 1 amp at which point the charger terminates the charge. This decreasing of the current reduces the rate at which the battery is being filled up so the SOC graph on the right hand side flattens off. It has nothing to do with overcharging.

What does overcharging mean? It could mean putting too high a current into the battery at any stage of the charge cycle or it could mean going above a certain charge voltage or a combination of both of these. The voltage and current are not fixed or rigid numbers, they should be chosen depending on the battery specifications and the circumstances that the battery is being used in.

Lithium batteries are not like a bottle that we fill up and it overflows if we overfill/overcharge it. They contain a cathode and an anode. When the battery is empty the cathode is full of lithium ions and the anode is empty. When the battery is full the anode is full and the cathode is empty.

If we represent the anode and cathode as two sponges and the lithium ions as water, an empty battery is where the cathode sponge is full of water and the anode sponge is empty. Putting a voltage across the battery to charge it is like squeezing the cathode sponge, the harder we squeeze it the faster the flow of water/current out of the cathode sponge. When the battery is nearly full it gets harder and harder to squeeze the water out of the cathode sponge. We have to increase the voltage/squeeze harder to get more lithium ions/water out. We can't get all the lithium ions/water out of the cathode sponge, there will always be some lithium ions/water left in the cathode sponge, the amount left depends on the voltage that we charge the battery too/how hard we squeeze the sponge.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[createthis]

DID YOU MAKE A BALANCE PLUG?

I have a balance plug pigtail for the PL8. Just a matter of solder for extra cable length and crimping on ring terminals. This will be my next step either way as the pl8 won't charge the pack as a whole without a balance plug wired up.

[Sunking]

I was all wired in parallel (yeah, I said I wouldn't, but the voltages were more divergent this time around) and ready to rewire in series, charge, and forget about it. However, I think I might make a video about this procedure instead.

Super easy to do. No more than 2 minutes to test all 4 batteries.

The numbers are usefull as it is a Battery Health Monitor or Age Meter. They are new, thus a refference point in time or standard to measure against. It is one of the most significant parameters. It is directly related to capacity, age, and performance. Very easy to read and interpet. The readings you take today are perfect 100% Healthy batteries. As they age, become damaged, loose capacity the resistance is going to go up and up to useless.

You should measure 2 to 5 milli-ohms on each cell. Your PL8 showed 13 to 15 right? Ignore it. If you measure 10 to 15 this way you gotta problem. Anyway when you see the resistance going up, you know the end is near.

There is just one catch, the TEST conditions must be met to be valid: SOC in the middle, rested cells, room temp cells and room. and same exact test setup and equipment. Making very small measurements requires attention to details. To be more accurate 10 times more accurate instead of using 1 and 10 amps, use 10 and 100 amps. For the high current test you could use an Inverter with a large load. When you test just record both Voltage and Current. Say 10 amps with the PL8 and 63.5 amps using a blow dryer on Inverter. You would need a way to measure the current.

DID YOU MAKE A BALANCE PLUG?