Voc vs SOC winston cell

[Sunking]

You cannot even understand what Jeff is telling you. It is simple basic physics which you do not understand. You have no clue what is going on.

The coloumbic efficiency of a battery is defined as follows:

Where is the coloumbic efficiency (pu)
is the amount of charge that exits the battery during the discharge cycle (C) is the amount of charge that enters the battery during the charging cycle (C) Coloumbic efficiency is not 100% because of losses in charge, largely because of secondary reactions, such as the electrolysis of water or other redox reactions in the battery. The coulombic efficiency of a typical lead-acid battery is >95%.

Here is the source link.

You lost the argument and your credibility. Now get lost.

[karrak]

It is directly related coulomb efficiency and contributes significantly to Coulomb Efficiency.

Wrong yet again, with reference to my simple battery model drawing below the coulomb efficiency of the battery is dependent on the current i_lost. If i_lost is zero the battery has a coulomb efficiency of 100%. It is obvious from this diagram that R_i has absolutely no bearing on the amount of charge lost in the battery, any charge flowing through R_i also goes through the load. To draw a rough analogy between a battery and a water tank. If the water tank has a leak in it, this leak is equivalent to R_lost and lets water leak out, the loss of water is equivalent the the coulomb inefficiency. R_i can be likened to scale inside the pipes. It doesn't mean you loose any water, it just reduces the pressure of the water.

image_7459.jpg
I stated that the power efficiency of my battery is around 95%. This power efficiency is a combination of power lost due to the coulomb inefficiency and the thermodynamic losses mentioned in my last post. The coulomb efficiency of my battery is around 99.4%.

Then watch a video by Jeff Dahn who goes into deep detail of Coulomb Efficiency which is what his whole career and life is about. Closer you get to 100% charge efficiency, the longer the battery last. With each charge cycle, the efficiency goes down. Or as Jeff says "Moves To The Right". A cell with a coulomb efficiency of 99.99% is a 10,000 cycle battery

With each charge cycle the coulomb efficiency does not go down, it is the capacity that is going down, just listen to the video from 16:15 minutes from the start to around 20:00 minutes from the start. The coulomb efficiency actually goes up which is also shown in the graphs in the section of the video from 22:30 to about the 27:00 minute mark

Simon

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

[Sunking]

That is news to me, before now, never heard of Short Discharge Time.

Not surprised at all. You seem to know very little about performance and measurement metrics

Very useful information for EV users who put their batteries under heavy load but not so relevant for lightly loaded off-grid batteries. Please explain how it can tell me how long my battery will last in my off-grid application.

I have tried, but you cannot wrap your brain around it.

Ri does not determine the coulomb efficiency. It is part of the theoretical Thevenin equivalent model of a real battery and is there to represent the thermodynamic losses moving the electrons and lithium ions inside the battery, has nothing to do with coulomb efficiency.

It is directly related coulomb efficiency and contributes significantly to Coulomb Efficiency. You even went as far as to say what your measured efficiency is of 97%. I suggest what Coulomb Efficiency is. Because you are just making my case you really do not know what you are talking about. Then watch a video by Jeff Dahn who goes into deep detail of Coulomb Efficiency which is what his whole career and life is about. Closer you get to 100% charge efficiency, the longer the battery last. With each charge cycle, the efficiency goes down. Or as Jeff says "Moves To The Right". A cell with a coulomb efficiency of 99.99% is a 10,000 cycle battery

Why not 2.8 volts, means you can still run large loads at lower SOC. Charge and discharge Voltages for Winston are the same as CALB.

Because at 2.8 volts is well beyond the knee and has fallen off the cliff of the Discharge Curve. Calb and Winston Charge and Discharge voltages are no where near alike. Again is showing your ignorance. At 2.8 vpc you are just asking to destroy a cell and driving them into reverse polarity. CALB limits are 3.6/2.5 with 3.2 volts nominal. Winston is 4.0/2.8 with 3.4 volts nominal. They are no where near being the same. I suggest you read this White Paper written by Portuguese-Spanish Conference on Electrical Engineering. It details the Winston LFP cells. Pay real close attention to charge and discharge voltages and where not to go. Who knows you might actually learn something.

[karrak]

One graph I have tried to get you to look at and understand, with no luck at, is Short Discharge Time or SDT.

That is news to me, before now, never heard of Short Discharge Time.

It is a extremely good graph to judge how a battery will perform under load and how long it will last.

Very useful information for EV users who put their batteries under heavy load but not so relevant for lightly loaded off-grid batteries. Please explain how it can tell me how long my battery will last in my off-grid application.

SDT is directly related to Internal Resistance or Ri. Ri determines the charge/discharge coulomb efficiency.

Ri does not determine the coulomb efficiency. It is part of the theoretical Thevenin equivalent model of a real battery and is there to represent the thermodynamic losses moving the electrons and lithium ions inside the battery, has nothing to do with coulomb efficiency.

You always squak about RE users primary objectives are not those of DIY EV's which is hog wash.

No, I say that the operating conditions are different. I couldn't express it any better than you have, so here is your quote.

Look you may not like it or agree, but Solar is a completely different set of parameters radically different than motive. Solar does not have the extremes unless you are talking RV where the engine alternator will do most of the heavy work. Max charge rate is on the order of C/10 to C/6 only for a few brief hours in a day. Batteries are in open air at room temps and not sealed up in a oven and coffin. Discharge rates typically C/20 and occasional burst of maybe 1C, but on average very slow discharge rates.

EV users want the most efficient, cost effective, highest Energy Density, and longest life possible that we can afford. . So you are saying none of that matters to you. Well OK, I don't care if you settle for less. Most would say BS, they would use a CALB or SINOPOLY because they perform better and cost less less. You choose poor performance and highest price. I am good with that. I am tickeled pink and happy for you.

I got the most cost effective battery which is also very efficient (logged overall power efficiency is around 95%), and can't see why it won't last at least ten years. When I bought my battery three years ago I only had the choice of Winston or CALB batteries and the Winston's were cheaper.

Bottom line for th eOP or anyone using LiFeP04 cells. Set LVD to 3.0 vpc, and Chargge no higher than 3.45 vpc except Winston the queer of the bunch is 3.6 to 4.0 vpc.

Why not 2.8 volts, means you can still run large loads at lower SOC. Charge and discharge Voltages for Winston are the same as CALB.

Simon

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

[Sunking]

The only graph in this thread that shows Voc versus SOC is my graph in the second post which does not tell you anything about internal resistance under load. If you mean the Winston graph, that is a set of discharge curves and shows battery voltage under various loads versus SOC. It has nothing to do with open circuit voltages.

I rest my case again. You hare showing the Discharge Cures from Winston. If you know how to read them they tell you exactly what the Internal Resistance is and exactly how they perform under load. If you understood it, you would know how poorly they operate. Of the Chi-Coms Sinopoly, Calb, Winston, GBS) all perform poorly. From best to worse in terms of performance is Sinopoly, CALB, Winston, and GBS. One graph I have tried to get you to look at and understand, with no luck at, is Short Discharge Time or SDT. It is a extremely good graph to judge how a battery will perform under load and how long it will last. SDT is directly related to Internal Resistance or Ri. Ri determines the charge/discharge coulomb efficiency. The closer you get to 0, the more cycles and calander life you have. So now look at the Graph and see where they fall. Chi-Coms fall dead last.

In terms of price per Watt Hour capacity from lowest to highest is CALB CA, Sinopoly, Winston, and GBS. Longest life from highest to lowest is GBS Winston, CALB CA, and Sinopoly. Based on that a informed consumer would choose Sinopoly or CALB CA. How about warranty? .

You always squak about RE users primary objectives are not those of DIY EV's which is hog wash. EV users want the most efficient, cost effective, highest Energy Density, and longest life possible that we can afford. . So you are saying none of that matters to you. Well OK, I don't care if you settle for less. Most would say BS, they would use a CALB or SINOPOLY because they perform better and cost less less. You choose poor performance and highest price. I am good with that. I am tickeled pink and happy for you.

As for me I learned from 35 years professional experience and the hard way loosing money. Today I do not use Chi-Coms. I use even a lower cost alternative you have to have patience to find and cash on hand when you find them. I am using a LiMn2O4 with LINIO2 cathode and graphite Anode aka Nisan Leaf battery from a 2 year old salvaged vehiclle, I paid $1000 USD for a 24 Kwh battery or $41/Kwh. I would do the exact thing if I was RE. In fact I am. My Ham Shack is not Lithium using Leaf batteries at 12 volts. Used th eleft over battery cells. Sold the rest an dhelped another person build his small 24 volt 120 AH solar system.

Bottom line for th eOP or anyone using LiFeP04 cells. Set LVD to 3.0 vpc, and Chargge no higher than 3.45 vpc except Winston the queer of the bunch is 3.6 to 4.0 vpc.

[karrak]

I rest my case. You do not even know common terms. vpc = volts per cell.

Not knowing a specific term does not mean I am an idiot or that I do not know what I am talking about, just as the mistake you made by saying that a set of discharge curves is a plot of Voc versus SOC does not mean you are an idiot or don't know what you are talking about.

None of us knows everything, and we all make mistakes.
Simon

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

[karrak]

Like I said, you do not know what you are doing or saying. The graph tells you what th eInternal Resistance is and exactly what is does under load.

You could care less what the impedance is, it is internal resistance that counts, and it is right on the graph if you know what you are looking at. You do not have a clue what you are looking at. Give you a hint: Delta Voltage and Delta Current.

The only graph in this thread that shows Voc versus SOC is my graph in the second post which does not tell you anything about internal resistance under load. If you mean the Winston graph, that is a set of discharge curves and shows battery voltage under various loads versus SOC. It has nothing to do with open circuit voltages.

For those that are interested, here is a link to an article on Discharge Curves, and other things about battery performance. http://www.mpoweruk.com/performance.htm

Simon

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

[Sunking]

What does "vpc" mean? The winston graphs tell me to disconnect at 2.8 volts.

I rest my case. You do not even know common terms. vpc = volts per cell.

[Sunking]

Please tell me how I can tell how poor the performance is by looking at the Voc (Battery open circuit voltage). That doesn't give any idea what the battery impedance is and how the battery will work under load.

Like I said, you do not know what you are doing or saying. The graph tells you what th eInternal Resistance is and exactly what is does under load.

You could care less what the impedance is, it is internal resistance that counts, and it is right on the graph if you know what you are looking at. You do not have a clue what you are looking at. Give you a hint: Delta Voltage and Delta Current.

[karrak]

Because they are failed Thundersky with the same poor performance.

Performance of Winston and other cheaper LFP batteries may not be any good for doing burnouts in a golf buggy as you found to your cost but are excellent for off-grid and grid connect systems. These cheaper LFP batteries give you a cost of round 30 to 50 cents per kWh cycled through them and you can draw current up to C/2 on a regular basis and up to 3C intermittently with any inverter that will work with Lead Acid batteries. There are also very few charging requirements, just keep the charge current below C/2 and charge voltage below 3.5 volts for long life. How does that compare with other batteries in the marketplace?

If you look at the Voc graph and know what you are looking at, you can see how poor the performance is.

Please tell me how I can tell how poor the performance is by looking at the Voc (Battery open circuit voltage). That doesn't give any idea what the battery impedance is and how the battery will work under load.

From the graph you choose 3.0 vpc disconnect.

What does "vpc" mean? The winston graphs tell me to disconnect at 2.8 volts.

Simon

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

[Sunking]

Thx karrak for the info that is exactly what I was looking for. Personally I don't understand why sunking is so negative about Winston...

Because they are failed Thundersky with the same poor performance. If you listened to PNJunction and I you got the answer you were looking for. Disconnect at 3.0 vpc and charge to 3.6 vpc. If you look at the Voc graph and know what you are looking at, you can see how poor the performance is. From the graph you choose 3.0 vpc disconnect.

[Barba]

Thx karrak for the info that is exactly what I was looking for. Personally I don't understand why sunking is so negative about Winston... My previous pack cycled thousands of times more than 500 cycles at 80% DOD and more than 15000 cycles with more than 5% DOD and still today after 6 years the pack has the same capacity as new. I always cycled at 0,5C but I am about to go as far as 2C for few minutes a day as my power demand as increased due to new toys in the house.
Now playing with 100 kW instant power......
Little scared to go there but I have no choice....
Thx again to everybody for the interest in this post

[karrak]

Winston does not publish discharge rates. It would be too embarrassing if they did. Of the Chi-Com lithium batteries, Winston scores next to last place. Last place belongs to GBS. Winston and BGS Internal Resistance are very high is very high for the Chi-Coms. That means Voltage Sag under load will be much higher than expected. That is why Winston and GBS will not publish discharge curves.

Wrong again, see http://en.winston-battery.com/index....ategory_id=176

[Sunking]

Sunking please answer my specific question.
Is your answer going to be yes or no?

There is no answer to your question, only recommendations. You cannot use SOC voltage on either charge or discharge. It means nothing. Winston cells run at slightly higher voltages than most LFP cells. All you can do is make sure you stay away from the knees at either end of the scale. Do not go below 3.0 vpc on discharge, or go above 3.7 on charge. (FWIW Winston specs are no lower than 2.7 or above 4.0. Don't go there). You want to run your cells between 10 and 90% SOC read at Open Circuit Voltages, not operating voltages.

[Barba]

Sunking please answer my specific question.
Is your answer going to be yes or no?