LifePO4 batteries for use with Midnite Classic 150?

[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]

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.

[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.

[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.

[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

[vast]

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

Thanks.

[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.

[jflorey2]

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

Hogwash Jeff. Gotta call BS. That is exactly what it is, Every Battery Charge made for Pb and Lithium is a very simple CC/CV charger.

Yes. That's what I just said.

Karrak is a fraud and dangerous, and you know it. He has been banned two times for dangerous and fraudulent post. He came here for one purpose to his own admission, to only harass me. Back at him, the SOB got exactly what he asked and begged for.

Data talks, bull**** walks. You may hate his guts but he has the data to back up his assertions.

[Sunking]

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

Hogwash Jeff. Gotta call BS. That is exactly what it is, Every Battery Charge made for Pb and Lithium is a very simple CC/CV charger. Absolutely no difference between them except voltage set points and how you terminate the charge.

CC = Constant Current = Bulk
CV = Constant Voltage = Absorb and FLOAT

Nothing more than gimmick marketing names. Just like Pb batteries, there are only 3 types of SLI, Hybrid, and Deep Cycle. Hybrid is the gimmick market like Golf Cart, RV. Marine, Trolling Motor, Leisure, Floor Machine, Traction, Stationary and the list goes on. So stop the BS I know better.

During CC aka Bulk phase, the charger pumps in a fixed constant amount of current until the battery voltage reaches the set point. Say 14.4 volts for example on either Pb or LiFeP04

When the battery voltage reaches set point begins the CV stage in which nothing really happens electronically except that the battery voltage has reached a point to about equal of the charger voltage set point and the Charger holds 14.4 volts. As either battery saturates, aka Absorbs, charge current tapers off toward 0 amps. Both a Lithium battery and FLA are fully charged to 100% when charge current tapers to 3 to 5% of C.

The only difference is Termination. Typically a FLA charger if it has the 3rd stage will lower the set point voltage to 13.2 to 13.8 volts called a Float Charge which is a gimmick term for Constant Voltage. Typically for a Lithium Battery you terminate the charge, but not necessary because they can Floated just like a Pb by lowering the voltage to 13.4 to 13.6 volts. Absolutely no difference and completely compatible. You just tweak the voltage set points

In fact on a solar system you want to Float Charge a Lithium Battery and Never Ever Fully charge them staying away from the knees at either end of the charge/discharge curve. Many charge controllers can be set up to do this simply by setting Bulk = Absorb = Float = 13.4 to 13.6 volts. Multiply by 2 or 4 for 24 or 48 volt systems. Works great. Follow that up by setting your LVD to 12, 24, 0r 48 volts and you eliminate the knee at the discharge side which you want to avoid like the plague. There should never be be more than .1 volt spread at any point except at the extreme edges of the charge discharge cure which you want to stay far away from.

You can say what you want about Bulk, Absorb, and Float, they are just marketing gimmick names made up, but fact is any charger is a CC/CV charger no matter how you want to spin it. Bulk is CC, and Absorb/Float is CV period end of story. Designed and built to many of them to count. Today you can buy a hobby charger made for RC freaks like myself. They can charge any battery types made today and all in the future for one simple fact. EVERY CHARGER IS CC/CV. The Hobby Chargers trick is the processor built inside so you can set the voltage, current limits, current cut-off to anything you want. Just about everyone of them has an A123 Systems setting. It is exactly the same algorithm used for PB a standard 3-Stage Bulk > Absorb Float, On a 4S LFP 14.4 until current reaches 3% of C and Floats at 13.4 volts. Exactly what A123 Systems says to do for their batteries.

So I am calling BS on you.

Read Battery Tender 5-stage LFP Charger.Click on Algorithms Fundamentals and learn.

Stage 1 Qualification Charge: checks to determine if it is safe to charge or not.
Stage 2 Recovery Mode: If 12 volt battery is greater than 4 volts or less than 8 volts, trickle current is applied for up to 4 hours. If greater than 8 goes to BULK
Stage 3 Bulk Charge: Constant Current to Set Point which begins Absorb stage.
Stage 4 Absorb: Constant Voltage until current tapers to predetermined level then goes to stage 5
Stage 5 Float: Constant voltage until the cows come home or you turn it off.

Read it for yourself and argue with yourself. When you get tired of that go read Battery University. If you really want to dig deep into every kind of battery I suggest you purchase the Battery Bible and learn something. The book title is Linden's Handbook of Batteries, 4th Addition. I will make it real easy for you and you can thank me later because you can download the 3rd addition for free here. Dave Linden and I worked on IEEE Battery Committee for 8 years and wrote the standards and practices still used today with a few dozen other pros. Be sure to read all 1500 pages. Way more than you have ever done for me.

Karrak is a fraud and dangerous, and you know it. He has been banned two times for dangerous and fraudulent post. He came here for one purpose to his own admission, to only harass me. Back at him, the SOB got exactly what he asked and begged for.

[jflorey2]

Cheese-n-Rice I cannot believe you are that ignorant to say something so STUPID. LFP cell charge discharge are extremely flat, and a difference of .16 volts is in excess of 50% of the batteries capacity.

Nope, he's right. Charge curves of LiFePO4 are very flat - except near 100% charge and 100% discharge. That's why the voltages start to diverge so much as he approaches 100% SOC. Look at a .2C charge curve for a typical LiFePO4; a .16 volt difference might mean the difference between 25% and 75% of capacity , but also means the difference between 85% and 95% of capacity. That's because the curve isn't linear. Any difference in cell capacity is thus amplified at the extremes of charge - and where they are worst depends on whether you top or bottom balance.

Lastly any cell in Absorb phase the voltage does not change. If you are seeing that large of voltage difference in a top balanced system, your cells are shot. Hell even in a Bottom Balanced system they would be Toast.

The terms "bulk" "absorb" "float" have no meaning in LiFePO4 charging. There is constant current and constant voltage; that's it. When you get close to 100% charge you are going to see a lot more voltage difference than when you are at 50% charge, due to the nonlinear relationship between SOC and cell voltage.

[Sunking]

Lithium Iron Phosphate is where it is at. Lithium 101-Check out EWT. eBay and thought you might like it! Check it out now! LIFEPO4 12V 100AH LITHIUM PHOSPHATE DEEP CYCLE BATTERY FOR SOLAR WIND SLA Repl

Sun Eagle this is clearly PURE Chi-Com SPAM. Why leave it up and not ban the user?

[Sunking]

I think it is difficult to say how out of balance the SOC is from just looking at the total difference in cell voltages. Two extreme scenarios with a 16 cell 48V LFP battery with a difference of 0.16V

Cheese-n-Rice I cannot believe you are that ignorant to say something so STUPID. LFP cell charge discharge are extremely flat, and a difference of .16 volts is in excess of 50% of the batteries capacity. Lastly any cell in Absorb phase the voltage does not change. If you are seeing that large of voltage difference in a top balanced system, your cells are shot. Hell even in a Bottom Balanced system they would be Toast.

[karrak]

This gives some information on the SKP function http://midniteftp.com/forum/index.ph...32365#msg32365

runs through the Charge menu. The Limits are to do with temperature compensation. This should be disabled by setting the temperature compensation to 0.0mV/degree/cell

runs through the Aux menu options.

[vast]

I need help with different values in menu settings - see manual map:

1. CHARGE MENU
- Advanced -> SKP (Skip) = Days ?
- Limits -> Mint-Comp = Volts ?
- Limits -> Max = Volts?

2. AUX MENU
- I need all values for Aux 1



Thank you for help.

[karrak]

I think it is difficult to say how out of balance the SOC is from just looking at the total difference in cell voltages. Two extreme scenarios with a 16 cell 48V LFP battery with a difference of 0.16V between the cells at a charge voltage of 55.2V (3.45V/cell) and charge current of 0.5C are:

1. Fifteen cells at a voltage of 3.44V/cell and one at 3.6V/cell. From the charge/discharge graph I posted earlier 3.6V/cell gives an SOC of ~99.5%, 3.44V/cell gives an SOC of ~98%. The difference being 1.5%SOC.
2. Fifteen cells at a voltage of 3.46V/cell and one at 3.3V/cell. From the charge/discharge graph I posted earlier 3.6V/cell gives an SOC of ~98.1%, 3.3V/cell gives an SOC of ~22%. The difference being 76.1%SOC!

The actual data from my friends system shows that at a charge current of C/20 (0.05C) the charge voltage was 55.06, the lowest cell was 3.427V which from the charge/discharge graph gives an SOC of ~97% and the highest cell was 3.459V which gives an SOC of ~98%.

I thought I would re-graph the absorb information from my friend's battery in a different format showing the voltage difference and the battery SOC. Any comments?


GeoffAbsorbVdiffSOC.jpg
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