Voc vs SOC winston cell

[Barba]

Hi there again can someone post a graphic of Voc vs Soc of a Winston cell?

[karrak]

I haven't come across any official graphs of Voc vs SOC for Winston Cells.

I have graphed SOC v Cell Voltage from two sources. The data for the blue line comes from here http://advrider.com/index.php?thread...#post-18206897 and the data for the yellow line comes from some tests I have performed recently.

My tests involved setting Bulk=Absorb=Float to the same voltage at the start of the day and taking an SOC reading when the charge current had dropped to around zero.
SOCvVoltage.jpg
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

[Barba]

What about the SOC vs under voltage vs C discharge ? Is there a graphic showing what would be the SOC based on the voltage vs C????
Thx in advance

[Sunking]

There is no good answer to your questions. 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.

What you want to do is set your Low Voltage Disconnect to 3.0 vpc. So if you have a 24 volt or 8S system, disconnect at 24 volts or if any cell sags to 3.0 volts. Limit charge voltage to 3.45 vpc and you are good to go.

[Barba]

How do u know? Did u use them?

[Sunking]

How do u know? Did u use them?

In the biz. Try finding a discharge curve for them You cannot do it or else you would not be here.

[PNjunction]

Sunking's right.

Barba, voltage is a poor indicator of SOC, especially under load. However, stopping at 3.0v per cell is *roughly* 5% SOC. You may want to stop a bit higher at 3.1 to 3.15v per cell *rested*, which is roughly 20% SOC.

In-between values higher than this are hard to predict with any accuracy under load, and most attempt to do coulomb-counting or other current-measuring techniques to predict SOC under load. Even that is not totally precise, but good enough for ballpark figures.

[Barba]

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

[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.

[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

[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

[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.

[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]

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.

[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.