LifePO4 batteries for use with Midnite Classic 150?

[Sunking]

Yes. That's what I just said.

I guess your memory is failing and cannot read what you wrote. You said and I quote:

The terms "bulk" "absorb" "float" have no meaning in LiFePO4 charging. There is constant current and constant voltage; that's it.

That is BS and I called you out on it. Every battery charger is Bulk Absorb aka Stage 1 & 2 or CC/CV. Want FLOAT with those fries, lower the voltage to the appropriate battery chemistry called the 3rd Stage.

[vast]

Sunking,
What value I must set for Rebulk on Midnite?

Thanks.

[karrak]

As someone whose whole professional career was in digital and instrumentation engineering I am somewhat puzzled by the vague and inexact terminology used when discussing battery charging.

What exactly does Absorb mean from a technical point of view? I can see that it might mean something with regards Lead Acid batteries where water has to be "absorbed" from the electrolyte into the lead oxide plate and sulphate and hydrogen ions have to be "absorbed" back into the electrolyte, am I right? All I do know is that the absorb process is slow and limits the speed that you can charge an LA battery when it is nearly full. It has no relevance when talking about charging lithium ion batteries which operate with a totally different chemical process than LA batteries.

Again I suppose that Bulk could mean majority of charge with regards to LA batteries but again is fairly meaningless with lithium ion charging where you can get greater than 98% of your charge before having to do any current limiting.

One of my pet hates is how bulk charging is called constant current (CC) charging when talking about charging from solar panels. The current coming from the solar panels is dependent on the solar power falling on the panels and their temperature, these are not constant!!! I think a much more useful term would be something current limited charging.

Even constant voltage (CV) charging as a term is not right if you can't guarantee the supply of enough current to keep the voltage constant which is definitely the case with solar power. Again a term like voltage limited charging would be more accurate.

Another pet hate is Sunshine Hours, but I won't go there.

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

[jflorey2]

I guess your memory is failing and cannot read what you wrote. You said and I quote:
That is BS and I called you out on it. Every battery charger is Bulk Absorb aka Stage 1 & 2 or CC/CV.

Which is what I said. When it comes to lithium chemistries there is constant voltage and constant current. Period. "Bulk" and "absorb" are specific to lead acid chemistries. You can, of course, call them whatever you want; call them "bulk" and "absorb" or "the fast part" and "the slow part" or "hard charging" and "soft charging." All are equally accurate, and most people will know what you are talking about. And all refer to the only two phases of charging a lithium ion chemistry - constant current and constant voltage.

[Sunking]

Which is what I said. When it comes to lithium chemistries there is constant voltage and constant current. Period. "Bulk" and "absorb" are specific to lead acid chemistries.

No Sir it is not specific to Pb. You didn't read any links now did you?. Manufactures chargers made for LFP uses the terms Bulk and Absorb.

[Sunking]

What exactly does Absorb mean from a technical point of view? I can see that it might mean something with regards Lead Acid batteries where water has to be "absorbed" from the electrolyte into the lead oxide plate and sulphate and hydrogen ions have to be "absorbed" back into the electrolyte, am I right? All I do know is that the absorb process is slow and limits the speed that you can charge an LA battery when it is nearly full. It has no relevance when talking about charging lithium ion batteries which operate with a totally different chemical process than LA batteries.

Finally a good question from you and fair enough. I can explain it in detail, but you have to have some math skills to understand. Does not make any difference what the battery chemistry is because it is a function of the battery Open Circuit Voltage (OCV) and the Battery Internal Resistance (Ri). A model example should do the trick. Take any 12 volt 100 AH battery you want, be it LFP or Pb and let's assume that the battery is fully discharge and reading 10.5 volts. Again it can be either chemistry you want 6S Pb or 4S LFP, makes absolutely no difference. We connect them to a 10 Amp battery charger, and set its voltage to 14.4 volts. 14.4 is what both battery chemistries use. The battery Ri = .01 Ohms. Initially when we connect the charger, charge current is limited to 10 amps by the charger. The voltage of the Charger by design of the current limiter will FOLD BACK the voltage of the charger to; OCV + (Ic * Ri), or 10.5 volts + (10 amps x .01 Ohms = 10.6 volts. It has to because if it did not charge current would be 14.4 volts - 10.5 volts / .01 Ohms = 1035 amps. Simple Ohms Law

The charger pushes 10 amps into the battery constantly. As the battery charges the battery OCV starts to rise with SOC until it reaches 14.3 volts. At 14.3 volts by Ohm's law starts the ABSORB or SATURATION phase or stage. (Take your pick) . When the battery OCV reaches 14.35 volts charge current has Tapered down to 14.4 volts - 14.35 volts / .01 Ohms = 5 amps. Simple Ohs Law and has nothing to do with the chemistry. It is Physics, not chemistry. When the battery OCV voltage = 14.4 amps, or equal to the charger voltage, you have 0 AMPS and the battery has fully Absorbed aka Saturated. Makes no difference if charge is stored by moving Ions in an LFP battery or electrons in a Pb battery. Again it is Ohm's Law, not chemistry.

Again I suppose that Bulk could mean majority of charge with regards to LA batteries but again is fairly meaningless with lithium ion charging where you can get greater than 98% of your charge before having to do any current limiting.

Well you got it half right. Bulk is the majority of the charge, the rest is hogwash and chicken teeth. Bulk is as the name implies and provides the majority of the recharge as fast as possible. But to say a Lithium battery is 98% SOC when the Absorb stage is flat out FALSE under 99% of charge conditions. That statement is only true if you charge a LFP equal to or slower than C/20 or .05C the term you use. As you increase the charge rate say from C/20 to C/10 you arrive at Absorb at 70% SOC and now will take a much longer time to saturate, You hit a wall with LFP at C/2 charge rate and you arrive at absorb at 50% SOC, and will now have a 2-hour Absorb time. At 1C it will take you 3 hours from fully discharged to fully charged. Is that because of the chemistry? No Sir. Its Ohm's Law because Pb has the same speed limits regulated by the INTERNAL RESISTANCE. Do the math and use 100 amps from the above drill.

If you did that you will hit Absorb at 14.4 volts - (100 amps x .01 Ohms) = 13.4 volts instead of 14.3 volts

One of my pet hates is how bulk charging is called constant current (CC) charging when talking about charging from solar panels. The current coming from the solar panels is dependent on the solar power falling on the panels and their temperature, these are not constant!!! I think a much more useful term would be something current limited charging.

No technically it is called Constant Power, which is limited by the flaky and unreliable source of power; the sun and clouds. But it is still referred to as CC because the circuit is identical in operation. A Solar CC will deliver as much current as the variable Power can provide up to CURRENT LIMIT. AC chargers do not have this problem as power is unlimited with no time constraint. If you replaced your Solar Panel with a 18 volt DC Power supply, the Controller would work exactly like an AC charger as I described above.

[karrak]

Finally a good question from you and fair enough. I can explain it in detail, but you have to have some math skills to understand. Does not make any difference what the battery chemistry is because it is a function of the battery Open Circuit Voltage (OCV) and the Battery Internal Resistance (Ri). A model example should do the trick. Take any 12 volt 100 AH battery you want, be it LFP or Pb and let's assume that the battery is fully discharge and reading 10.5 volts. Again it can be either chemistry you want 6S Pb or 4S LFP, makes absolutely no difference. We connect them to a 10 Amp battery charger, and set its voltage to 14.4 volts. 14.4 is what both battery chemistries use. The battery Ri = .01 Ohms. Initially when we connect the charger, charge current is limited to 10 amps by the charger. The voltage of the Charger by design of the current limiter will FOLD BACK the voltage of the charger to; OCV + (Ic * Ri), or 10.5 volts + (10 amps x .01 Ohms = 10.6 volts. It has to because if it did not charge current would be 14.4 volts - 10.5 volts / .01 Ohms = 1035 amps. Simple Ohms Law

The charger pushes 10 amps into the battery constantly. As the battery charges the battery OCV starts to rise with SOC until it reaches 14.3 volts. At 14.3 volts by Ohm's law starts the ABSORB or SATURATION phase or stage. (Take your pick) . When the battery OCV reaches 14.35 volts charge current has Tapered down to 14.4 volts - 14.35 volts / .01 Ohms = 5 amps. Simple Ohs Law and has nothing to do with the chemistry. It is Physics, not chemistry. When the battery OCV voltage = 14.4 amps, or equal to the charger voltage, you have 0 AMPS and the battery has fully Absorbed aka Saturated. Makes no difference if charge is stored by moving Ions in an LFP battery or electrons in a Pb battery. Again it is Ohm's Law, not chemistry.

A typical condescending reply with many factual errors. I should have been clearer, I was interested to know how the term Absorb came about, not what the process is.

Now to the glaring factual errors. The internal resistance of a battery or to be more correct the internal impedance, but lets keep it simple and stick to resistance is dependent on many factors some physical and some chemical. The simple physical factors that you are talking about are the bulk resistance of the conductors and the active materials in the battery and as you say are covered by Ohm's law and don't change much. They are only part of the total resistance, the resistance caused by the many chemical processes is variable and difficult to calculate. See powerstream.com/internal-resistance.htm or en.wikipedia.org/wiki/Internal_resistance for more details. The chemical processes are a large factor with lead acid batteries that limit extended large charge and discharge currents and result in the need for long absorb times.

Your statement "Makes no difference if charge is stored by moving Ions in an LFP battery or electrons in a Pb battery. Again it is Ohm's Law, not chemistry" just shows that you do not understand battery chemistry and how it impacts on the electrical characteristics of batteries. For starters, both LFP batteries and PB batteries have ions moving from the anode and cathode to and through the electrolyte and electrons moving from the anode and cathode through the external circuit to balance out the flow of ions. The chemical difference between the two battery types is that in LFP batteries lithium ions move from the electrodes into the electrolyte then move through the electrolyte to the opposite electrode and electrons moves through the circuit. With LA batteries a chemical reaction occurs at the electrodes which releases or consumes hydrogen ions, sulphate ions and water from the electrolyte.

As you increase the charge rate say from C/20 to C/10 you arrive at Absorb at 70% SOC and now will take a much longer time to saturate, You hit a wall with LFP at C/2 charge rate and you arrive at absorb at 50% SOC, and will now have a 2-hour Absorb time. At 1C it will take you 3 hours from fully discharged to fully charged. Is that because of the chemistry? No Sir. Its Ohm's Law because Pb has the same speed limits regulated by the INTERNAL RESISTANCE.

Where do you get your data? These two graphs are from charge tests I did on a four year old Winston LFP cell. Nothing like what you say.
AbsorbTimes3.45V.jpgAbsorbTimes3.6V.jpg

No technically it is called Constant Power, which is limited by the flaky and unreliable source of power; the sun and clouds. But it is still referred to as CC because the circuit is identical in operation. A Solar CC will deliver as much current as the variable Power can provide up to CURRENT LIMIT. AC chargers do not have this problem as power is unlimited with no time constraint. If you replaced your Solar Panel with a 18 volt DC Power supply, the Controller would work exactly like an AC charger as I described above.

Power = Voltage x Current, how can you have constant power if the current is variable when charging from solar?

For LFP batteries, charging from solar is not the same as charging from a constant current charger. With a constant current charger we can charge at say ~C/4 (0.25C) and terminate the charge at 3.45 volts and have a predictable ~90%SOC. With solar we could have anything from ~90%SOC to ~99%SOC due to the variable nature of the power coming from the solar panels. If you are bottom balancing with no BMS this could have disastrous consequences.

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

[Sunking]

Karrak you are proving you really do not get it. First Impedance has nothing to do with the discussion. it is pure DC resistance. That is just a diversion tactic you are trying to use. Impedance is used as a measurement for baseline reference for battery health, and modeling how a battery is going to perform on digital loads. DC resistance cannot be used on working systems without interruption in service, impedance can be used at any time.

Your temperature argument is just another diversion without merit. All batteries are affected by temps, the most sensitive is lithium, so significantly most of them cannot be charged when cold.

Your charts are pure rubbish. It is impossible for you to know what the SOC is at any given moment in time. To do that you would have to run a full capacity test to know what the actual capacity of a given cell is, start from a completely discharged battery at 2.5 volts, and graph Amp Hours vs voltage and current.

But I will use one of your own sources against you to demonstrate you are full of crap. You very own Power Stream tells you under Conventional C/1 charge current:

During the conventional lithium ion charging process, a conventional Li-ion Battery containing lithium iron phosphate (LiFePO4) needs two steps to be fully charged: step 1 uses constant current (CC) to reach about 60% State of Charge (SOC); step 2 takes place when charge voltage reaches 3.65V per cell, which is the upper limit of effective charging voltage. Turning from constant current (CC) to constant voltage (CV) means that the charge current is limited by what the battery will accept at that voltage, so the charging current tapers down asymptotically, just as a capacitor charged through a resistor will reach the final voltage asymptotically.

To put a clock to the process, step 1 (60%SOC) needs about one hour and the step 2 (40%SOC) needs another two hours.

Resistance and Charge Rate is the Traffic Cop that limits any battery type charge type. Need more? Battery University will tell you the same thing. If you really wanted to know, it is super simple to find the information, I am not going to waste my time educating you.

Increasing the charge current does not hasten the full-charge state by much. Although the battery reaches the voltage peak quicker, the saturation charge will take longer accordingly. With higher current, Stage 1 is shorter but the saturation during Stage 2 will take longer.

Clear as day, so zip it up, you do not know what you are talking about. The same process is true for any battery because when you reach the CV phase is function of Charge Rate and the battery Internal Resistance. If you understood basic electric fundamentals you would understand starting with Ohm's Law.

Power = Voltage x Current, how can you have constant power if the current is variable when charging from solar?

For LFP batteries, charging from solar is not the same as charging from a constant current charger. With a constant current charger we can charge at say ~C/4 (0.25C) and terminate the charge at 3.45 volts and have a predictable ~90%SOC. With solar we could have anything from ~90%SOC to ~99%SOC due to the variable nature of the power coming from the solar panels. If you are bottom balancing with no BMS this could have disastrous consequences.

Are you really that stupid and cannot grasp Ohm's Law? Yes P = IE, which means I = P/E. In the charging process on solar P changes with sun conditions, and thus varies unlike a stiff source with unlimited Power of the grid and commercial AC charger. If Power Input changes, so does charge current. As power goes up, current follows, as power goes down, current follows. Very simple 5th grade math. So technically a Solar Charger is Constant Power in Stag 1, butz the circuitry is a Constant Current Source. It will convert all available power into current up to the point of the chargers current limit rating. It is not hard to get your brain wrapped around if you understand basic principals of Ohms Law, current and voltage sources. Apparently they do not teach that where you live.

This is one reason I hit you so hard. You are pretender which makes you a fraud. You do not know basic electrical fundamentals. You do not even understand day 1 course material Ohms Law. You further prove your ignorance with dangerous advice in which you have been banned twice for doing so. Why they let you come back baffles me.

[jflorey2]

No Sir it is not specific to Pb. You didn't read any links now did you?. Manufactures chargers made for LFP uses the terms Bulk and Absorb.

Yes they do, and everyone knows what they are talking about because people are familiar with those terms from working with lead acid batteries.

Pilots still refer to stick and rudder skills. Doesn't mean that most aircraft have control sticks. But everyone knows what they mean.
Carpenters still refer to Philips screws. Doesn't mean that the screws are actually Philips and not Pozidriv or Frearson. But everyone knows what they mean.

Same thing here.

[Sunking]

Yes they do, and everyone knows what they are talking about because people are familiar with those terms from working with lead acid batteries.

Pilots still refer to stick and rudder skills. Doesn't mean that most aircraft have control sticks. But everyone knows what they mean.
Carpenters still refer to Philips screws. Doesn't mean that the screws are actually Philips and not Pozidriv or Frearson. But everyone knows what they mean.

Same thing here.

Not from a general public and DIY POV. The public at general does not know that Bulk = Constant Current= Fast Charge, Boost Charge and the various terms used in the Industry. Ask John Doe and he will think each is different. So when they buy a Solar CC intended to be used on a Pb battery, may come away thinking it cannot be used on a Lithium battery which may or may not be true if the controllers voltage set points are fixed and not user settable. OTOH some controllers like Midnite Solar and Morningstar do have models the user can set voltages to what is required for Lithium. If the manufacture does that you can turn the Controller into what you want to call a CC/CV charger by setting Bulk = Absorb = Float. You and I know that, but the mass public does not know that. Karrak is a good example of not comprehending what is really going on. Any charger is DUMB and does not know what battery type it is connected to. The chemistry inside is irrelevant to the charger. The only difference is how you terminate the charge and what algorithm you use. With LFP cells used in 4S, 8S, 12S... are drop in replacements for Pb. If you buy say a 12 volt LFP battery (4S) replacement for your vehicle, no modifications are needed to the vehicle charging system. They will work with any alternator voltage from as low as 13.6 volts up to 14.6 volts.

In a Solar Application 13.6, 27.2, and 54.4 is the sweat spot. It yields up to 95% SOC capacity when fully saturated (100% Absorbed and charge current STOPS), and will double the cycle life of the battery by not going to 100%SOC of 3.6 volts. again using Karraks own source against him this graph from Power Stream demonstrates clearly where users want to operate. There is little to be gained above 3.4 volts SATURATED aka Floated, CV, ABSORB or whatever you want to call it. Set your charger to 3.4 vpc and you are good. No risk or worries or meaningful capacity loss. Power stream even goes on the say:

Commentary: It looks like the magic number is around 3.3 volts. Below that you don't have significant charging, above that you do. A lithium iron phosphate battery doesn't care if it is never fully charged, so if all you have available is 3.3 volts and you don't mind the loss in capacity you could use the 3.3 volts. This opens up new possibility for a simple but very long life backup battery

At 3.4 volts any BMS is just a waste of money and would never be used. In short if you operate between 3.0 to 3.4 Volts life is easy with no worries. Completely compatible with Pb. On a 4S LFP is 12 to 13.6 volts. Set your charger to 13/6 volts, and your Inverter LVD to 12 volts and relax. Ohm's Law and common sense will take car of the rest. The load equipment and charger only know Ohm's Law of voltage. current, and resistance and it makes no difference what battery chemistry is used. They all charge the exact same way from the outside looking in. The electrons flowing don't care if they are moving Ions or chemical reactions around from one polarity to another. It is still current measured in AMPS either way. The formula for Amp Hours and Ohms Law does not change. For some reason Karrak thinks the Laws of Physics change.



Anyway Jeff if this was a Professional Forum, I would agree with you. But his is DIY forum and terminology has to be explained out in great detail so people like Karrak can understand. Even then they may not get it.

[karrak]

Karrak you are proving you really do not get it. First Impedance has nothing to do with the discussion. it is pure DC resistance. That is just a diversion tactic you are trying to use. Impedance is used as a measurement for baseline reference for battery health, and modeling how a battery is going to perform on digital loads. DC resistance cannot be used on working systems without interruption in service, impedance can be used at any time.

If you want to reduce this more accurate simplified battery model to this less accurate one
that is fine by me.

Your temperature argument is just another diversion without merit. All batteries are affected by temps, the most sensitive is lithium, so significantly most of them cannot be charged when cold.

Where did I mention temperature?

Your charts are pure rubbish. It is impossible for you to know what the SOC is at any given moment in time. To do that you would have to run a full capacity test to know what the actual capacity of a given cell is, start from a completely discharged battery at 2.5 volts, and graph Amp Hours vs voltage and current.

Well if I can't do it then no one else can. Yes, I did do full capacity tests, actually I did several at each charge/discharge rate to make sure that the results were consistent. Interestingly the total capacity of the four year old 90Ah Winston cell that I tested was still ~90Ah. So much for your ranting that Winston batteries are a pile of **** and are only likely to last 2.5 to 5 years.

But I will use one of your own sources against you to demonstrate you are full of crap. You very own Power Stream tells you under Conventional C/1 charge current:

Sorry Sunking, that data agrees with my graphs, my graphs are at much lower charge rates (0.4C to 0.05C). If you look at my 3.45V graph you see that at 0.4C the absorb phase started at 78%. If you pushed the charge current up to 1C the absorb start point would be far lower than 78%, 60% seems very plausable.

Resistance and Charge Rate is the Traffic Cop that limits any battery type charge type. Need more? Battery University will tell you the same thing. If you really wanted to know, it is super simple to find the information, I am not going to waste my time educating you.

Clear as day, so zip it up, you do not know what you are talking about. The same process is true for any battery because when you reach the CV phase is function of Charge Rate and the battery Internal Resistance. If you understood basic electric fundamentals you would understand starting with Ohm's Law.

I agree with you that the current going into the battery is dependent on the resistance of the battery, problem is that a portion of the resistance of the battery is caused by the chemical processes that are going on inside the battery. I am fairly sure that this resistance if nearly constant over the whole charging range of LFP batteries which gives the nice flat curve. It is not the case for LA batteries.

Are you really that stupid and cannot grasp Ohm's Law? Yes P = IE, which means I = P/E. In the charging process on solar P changes with sun conditions, and thus varies unlike a stiff source with unlimited Power of the grid and commercial AC charger. If Power Input changes, so does charge current. As power goes up, current follows, as power goes down, current follows. Very simple 5th grade math. So technically a Solar Charger is Constant Power in Stag 1, butz the circuitry is a Constant Current Source. It will convert all available power into current up to the point of the chargers current limit rating. It is not hard to get your brain wrapped around if you understand basic principals of Ohms Law, current and voltage sources. Apparently they do not teach that where you live.

Are you just trying to baffle everyone with this drivel. How can power go up and down and still be constant? sounds like newspeak to me. When I went to University a Constant Current Source was an idealised device that provides a constant current into a load (in this case a battery) regardless of the voltage across the load. I have even designed circuits with constant current sources in them. Surely a Constant Power Source provides constant power into a load regardless of the voltage across the load and current going into the load.

[karrak]

In a Solar Application 13.6, 27.2, and 54.4 is the sweat spot. It yields up to 95% SOC capacity when fully saturated (100% Absorbed and charge current STOPS), and will double the cycle life of the battery by not going to 100%SOC of 3.6 volts. again using Karraks own source against him this graph from.
...
There is little to be gained above 3.4 volts SATURATED aka Floated, CV, ABSORB or whatever you want to call it. Set your charger to 3.4 vpc and you are good. No risk or worries or meaningful capacity loss.

The following is from the Powerstream website powerstream.com/lithium-phosphate-charge-voltage.htm.

Method 1. I used a 26650 cells from four different manufacturers. This shows that there is some variation in the chemistry of LiFePO4 cells, but the gross features are the same. 2. Charging was done with a lab power supply, the voltage was set and the power supply current was limited to 1.6 amps. The battery would start out at 1.6 amps and when the voltage rose to the set limit, the current would drop. In most cases I waited until the current dropped to below 30mA. This is a classic constant current-constant voltage charge. 3. The battery was discharged at 2.5A rate, approximately 1C to 2.6 volts termination voltage.

Summary of tests, see discharge curves below Charge voltage Capacity at 3.65V 3.0V 3.1V 3.2V 3.3V 3.4V 3.5V 3.6V 3.7V 4.2V K Series 2249 mAH 48 mAH 93 174 691 2222 2232 2249 2249 2249 mAH Percentage of 3.65V capacity 2% 4% 8% 31% 99% 99% 100% 100% 100% G Series 2310 mAH 47 mAH 126 168 703 2257 2293 2309 2310 2324 mAH 2% 5% 7% 30% 98% 99% 100% 100% 101% A Series 2136 mAH 57 mAH 101 173 543 2044 2127 2128 2136 2186 mAH 3% 5% 8% 25% 96% 100% 100% 100% 103% H Series 2236 mAH 0 mAH 19 60 440 2153 2175 2196 2236 2238 mAH 0% 1% 3% 20% 96% 97% 98% 100% 100%

As you can see the K series cells are at 99%SOC when charged to 3.4V, the G Series 98%, the A series 96% and the H series 96%, my Winston cells would be around ~99%SOC if floated at 3.4V.

Try charging an LFP cell at 3.4V and you start limiting the current at <80%SOC due to the internal resistance of the cell, leave it charging long enough and it will get to around 99% full. Charge at 3.45V, reduce the charge voltage at a current of C/20-C/50 to 3.35V and you end up with the same 98%-99%SOC in a shorter time. Using a float voltage of 3.35V rather than 3.4V should result in longer life for the cell.

At 3.4 volts any BMS is just a waste of money and would never be used. In short if you operate between 3.0 to 3.4 Volts life is easy with no worries.

Again from the Powerstream website

3. Self balance
Unlike the lead-acid battery, a number of LiFePO4 cells in a battery pack in series connection cannot balance each other during charging process. This is because the charge current stops flowing when the cell is full. This is why the LiFEPO4 packs need management boards.

The load equipment and charger only know Ohm's Law of voltage. current, and resistance and it makes no difference what battery chemistry is used. They all charge the exact same way from the outside looking in. The electrons flowing don't care if they are moving Ions or chemical reactions around from one polarity to another. It is still current measured in AMPS either way. The formula for Amp Hours and Ohms Law does not change. For some reason Karrak thinks the Laws of Physics change.

I agree that the load or charger will blindly follow Ohm's law. The voltage that the current is drawn from or supplied to the battery at is dependent on the chemical processes that are going on inside the battery and the bulk resistance of the different components of the battery. It is not the electrons that move ions or chemical reactions around, it is the voltage that causes the ions to flow or the chemical reactions to occur. The electrons flow is a result not a cause.

Simon

[Sunking]

1. I used a 26650 cells from four different manufacturers. This shows that there is some variation in the chemistry of LiFePO4 cells, but the gross features are the same.

2. Charging was done with a lab power supply, the voltage was set and the power supply current was limited to 1.6 amps. The battery would start out at 1.6 amps and when the voltage. This is a classic constant current-constant voltage charge.

3. The battery was discharged at 2.5A rate, approximately 1C to 2.6 volts termination voltage.[/TD]


As you can see the K series cells are at 99%SOC when charged to 3.4V, the G Series 98%, the A series 96% and the H series 96%, my Winston cells would be around ~99%SOC if floated at 3.4V.

Karrak your reading comprhension flat out suks, and you do not know what your own terms mean. He did 9 charge/discharge test at 9 voltages. He started 3.0 volts and applied charge until the battery was SATURATED or fully Absorbed at 30 ma or C/73 . I know you do not know what that means, but it means until current all but stopped flowing and the battery floated at 3.0 volts. He then discharged it to measure the SOC.

He repeated this step all the way up to 4.2 volts. Here is what your thick head cannot get wrapped around. You do not understand what Absorb phase is or when it starts. It is a PURE FUNCTION of OHMS LAW and nothing else. The voltage of a Charging Battery = OCV + [Ri x I]. So when charging at the Constant Current, and your battery voltage reaches 3.4 volts, the OCV is less than 3.4 volts. The battery OCV will not be 3.4 volts until charge current tapers down to 0 amps. Get your thick head wrapped around that On the 3.4, 3.5, and 3.6 volt test when he reached those voltages, the battery was only @ 60% SOC OCV. It took another 2 to 3 hours hours for the current to taper down from 1.6 amps to .030 amps to get the last 40% in. Has nothing to do with the battery chemistry. It has only to do with the battery Internal Resistance and Ohm's Law.

It would be great if Solar Charge Controllers Absorb Phase could be controlled by current to switch from Absorb to Float. Fact is most are timed events. If they could be triggered by current you can stop charging at any SOC value you want for both LFP and Pb. If you want 100% SOC, it make no freaking difference if the battery is Pb or LFP, the parameters are the exact same. On a 4S LFP or 6S Pb set the Bulk/Absorb voltage to 14.4 volts, and switch to Float when Charge Current tapers down to 3 to 5% C.

Since that is not possible, you have to use another algorithm on LFP batteries. You set Bulk = Absorb = Float for LFP batteries, and on a 4S LFP is going to be 13.6 to 13.8 volts. If your panel wattage is correct to provide a charge current of C/5 to C/2, your batteries will have time to SATURATE aka fully ABSORB to 3.4 vpc by the time the sun sets. If it doe snot fully saturate is not a problem because there is no requirement to fully charge LFP batteries like Pb.

The fault with most any BMS is they are designed to charge LFP batteries to 100% SOC, and that is the last thing on earth you want to do. Extremely easy to do away with the BMS and get out of the Pb mentality thou must charge to 100% SOC to obtain the highest cycle life possible. Lithium is exact opposite where charging to 100% minimize cycle life. For LFP you want to operate between the knees of the charge/discharge curve, and that range is 3.0 and 3.4 volts per cell. On 4S is 12 to 13.6 volts.

[Mike90250]

.....Now to the glaring factual errors. The internal resistance of a battery or to be more correct the internal impedance,...

Ah, so you are charging your magic batteries with AC, and that's where the problem of you vs world comes to a head. Impedance or Impudence ?

[Sunking]

Ah, so you are charging your magic batteries with AC, and that's where the problem of you vs world comes to a head. Impedance or Impudence ?

Yeah I caught that to. Just proves Karrak is a fraud and dangerous. . Any damn fool knows batteries are charged with DC, and Resistance is the only factor. AC Impedance only comes into ply on digital or PWM switching Loads.

Mostly Impedance is used by manufactures and users to determine battery health because it can be measured on an operational system where DC resistance cannot. When Impedance rises 50% from new condtion tells you your battery capacity has reached end of life. The impedance goes up as a result of the DC Resistance going up.