Victron SmartSolar Charge Controller MPPT 100/50 absorption time question

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
Personally I’d like to see top balancing start at the float voltage.
At the float voltage level, the charge curve for the cells is flat, nearly a straight horizontal line. There is no balancing to do because all the cells are essentially at the same voltage, even if the state of charge of each cell is different. It is not until the battery comes up in voltage and the cells are above 3.5 and up to 3.65 v point that the curve turns upward and the cell voltage variance can be detected and properly balanced.
 

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
465
Your float voltage is 3.40V per cell. You are balancing at 3.50V per cell. You are not balancing at the float voltage. As your solar controller chargers up the battery, it is blowing buy that float voltage with lots of current still being absorbed by the cells, no balancing is even occurring at the float voltage even if that is where you have it set to start. I fail to see any advantage of doing so.
 

Kemills1

New Member
Joined
Feb 18, 2022
Messages
42
Location
Spain
At the float voltage level, the charge curve for the cells is flat, nearly a straight horizontal line. There is no balancing to do because all the cells are essentially at the same voltage, even if the state of charge of each cell is different. It is not until the battery comes up in voltage and the cells are above 3.5 and up to 3.65 v point that the curve turns upward and the cell voltage variance can be detected and properly balanced.
If the cells are all at the same voltage when the SCC drops back to float then yes, there will be no balancing. It is when there is an imbalance and one cell is higher when the SCC drops back to float that the balancing occurs. I’ve arrived at the setting I have by observation and experiment and have found these values work for my system. As I said, it may not suit everyone.
 

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
If the cells are all at the same voltage when the SCC drops back to float then yes, there will be no balancing. It is when there is an imbalance and one cell is higher when the SCC drops back to float that the balancing occurs. I’ve arrived at the setting I have by observation and experiment and have found these values work for my system. As I said, it may not suit everyone.
Seems odd. Top balancing usually is carried out at the end of Bulk or Absorb phase of charging when the cells are at the high end of their charge cycles SOC or charge voltage. That's when the voltage difference between unbalanced cells can be detected and balanced (passive or active balancing) usually is performed. Once the cells discharge to a float charge voltage, they are more likely to have equal voltages, because the charging curve for LiFePO4 batteries is nearly a straight horizontal line at float voltage SOC (Not much difference in cell voltages, even if their individual SOC's (balance) are different).
Can you post the charging settings you have decided to use ?
 
Last edited:

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
465
Supposedly, the industry standard is to balance at 100% SOC. Would be an interesting test to see how balanced the cells were when they were drawn down to 5% after first balancing at something other than 100%. If you have really well matched cells, probably not an issue. If you don't, probably a bigger issue if one cell hits its lower voltage earlier than the others and turns off your battery prematurely.
 
Last edited:

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
Supposedly, the industry standard is to balance at 100% SOC. Would be an interesting test to see how balanced the cells were when they were drawn down to 5% after first balancing at something other than 100%. If you have really well matched cells, probably not an issue. If you don't, probably a bigger issue if one cell hits its lower voltage earlier than the others and turns off your battery prematurely.
 

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
465
I can't stand that guy... can you tell me what the summary was?

I just got my DIY battery going, I have 280AH Eve cells with a JBD 120A BMS. Right now I go with the default and balancing starts at 3.4V cell voltage which would be 13.6V if they were all equal. One cell is always a little higher than the other 3 but once a load is put on the battery, all 4 are pretty much perfectly aligned with each other. I haven't left it more than 24 hours to see if the passive balance brings that high cell down a bit but I am not worried about it at all. I did do a full discharge down to 10.5V and all the cells were perfectly aligned with each other all the way down to 0% SOC.
 

Attachments

  • PXL_20220531_032934797.jpg
    PXL_20220531_032934797.jpg
    135.5 KB · Views: 5
Last edited:

Sabre36

Solar Addict
Joined
Dec 13, 2019
Messages
108
You don't get a cell disconnect at 14.0V. You get a cell disconnect at a much higher voltage. You don't even get it at 14.6V!
You do if the cells become out of balance and one cell triggers a disconnect..
172727353.jpg
 

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
I can't stand that guy... can you tell me what the summary was?

I just got my DIY battery going, I have 280AH Eve cells with a JBD 120A BMS. Right now I go with the default and balancing starts at 3.4V cell voltage which would be 13.6V if they were all equal. One cell is always a little higher than the other 3 but once a load is put on the battery, all 4 are pretty much perfectly aligned with each other. I haven't left it more than 24 hours to see if the passive balance brings that high cell down a bit but I am not worried about it at all. I did do a full discharge down to 10.5V and all the cells were perfectly aligned with each other all the way down to 0% SOC.
Nice looking DYO LiFePo4.
What was the battery voltage at 0% SOC, 10.5v ?
I think the summery was, don't attempt to balance your cells until you get to a voltage at the upward knee of the charging curve, where there is a significant variance in voltage vs SOC between cells that are not balanced.
 
Last edited:

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
465
Nice looking DYO LiFePo4.
What was the battery voltage at 0% SOC, 10.5v ?
I think the summery was, don't attempt to balance your cells until you get to a voltage at the upward knee of the charging curve, where there is a significant variance in voltage vs SOC between cells that are not balanced.
I had my cutoff at 2.5V/cell so not sure what it exactly got down to becuase it rose up to 10.5 to 10.9V after the shutoff.

I was pretty happy with the 281AH of capacity though. My discharger could only discharge at 11A so not quite the 20 hour rate but close.
 

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
I had my cutoff at 2.5V/cell so not sure what it exactly got down to becuase it rose up to 10.5 to 10.9V after the shutoff.

I was pretty happy with the 281AH of capacity though. My discharger could only discharge at 11A so not quite the 20 hour rate but close.
I do believe that the battery voltage at any state of Charge is different under load (discharge) as compared to no-load conditions. That's what I see in all the battery voltage vs. state of charge data that I have found.
 

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
I had my cutoff at 2.5V/cell so not sure what it exactly got down to becuase it rose up to 10.5 to 10.9V after the shutoff.

I was pretty happy with the 281AH of capacity though. My discharger could only discharge at 11A so not quite the 20 hour rate but close.
Where did you buy your 280 AH EV cells from ? Did you get the data sheets for the cells from the company that sold them to you ? Is there a tracking data stamp engraved into each cell ?
Do you think you bought automotive grade LiFePO4 cells ?
 

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
465
Where did you buy your 280 AH EV cells from ? Did you get the data sheets for the cells from the company that sold them to you ? Is there a tracking data stamp engraved into each cell ?
Do you think you bought automotive grade LiFePO4 cells ?
Been awhile. I will have to check. One thing I made sure I did was get 8mm studs.

Exliporc New Energy (Shenzhen) Co., Ltd

Not near the batteries at the moment. I bought ten and I tested all ten multiple times and they all tested to 280 or 281. Advertised as Grade A.
 

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
Been awhile. I will have to check. One thing I made sure I did was get 8mm studs.

Exliporc New Energy (Shenzhen) Co., Ltd

Not near the batteries at the moment. I bought ten and I tested all ten multiple times and they all tested to 280 or 281. Advertised as Grade A.
Yes, I understand, advertised as Grade A. All EV batteries sold thru the Chinese Gray Market are Grade B cells usually advertised as Grade A. This does not mean that they are not good DYO Solar RV batteries, it just means that they are not Automotive Grade LiFePO4 batteries in my honest opinion.
 
Last edited:

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
465
Yes, I understand, advertised as Grade A. All EV batteries sold thru the Chinese Gray Market are Grade B cells usually advertised as Grade A. This does not mean that they are not good DYI Solar RV batteries, it just means that they are not Automotive Grade LiFePO4 batteries.
LOL

And you are an expert on this how?

How many DIY batteries have you made?
 

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
LOL

And you are an expert on this how?

How many DIY batteries have you made?
I am not an expert on anything. I should have included 'in my honest opinion' in my opinion. Edited that into my original comment now.
I have not built any DYO LiFePO4 cell batteries. And for good reason, I was not able to determine if any LiFePO4 cell I might buy was an Automotive Grade battery or not. Now I can make that determination because of current battery sales practices and available cell data sheets from EV Prismatic cells available from a few vendors. But the cost of that Automotive Grade cell is to high, so I would still buy a BattleBorn battery instead of buying individual prismatic automotive EV cells and building my own battery. YMMV.
 
Last edited:

brb58

Solar Addict
Joined
Mar 17, 2021
Messages
465
I am not an expert on anything. I should have included 'in my honest opinion' in my opinion. Edited that into my original comment now.
I have not built any DYO LiFePO4 cell batteries. And for good reason, I was not able to determine if any LiFePO4 cell I might buy was an Automotive Grade battery or not. Now I can make that determination because of current battery sales practices and available cell data sheets from EV Prismatic cells available from a few vendors. But the cost of that Automotive Grade cell is to high, so I would still buy a BattleBorn battery instead of buying individual prismatic automotive EV cells and building my own battery. YMMV.
I did my due diligence on the company before I bought and found them to be trustworthy.

Yes...I suggest you stick with BattleBorn.
 
Last edited:

RandyP

Solar Addict
Joined
Sep 21, 2019
Messages
653
I did my due diligence on the company before I bought and found them to be trustworthy.

Yes...I suggest you stick with BattleBorn.
I have no need to replace my BattleBorn batteries with individual LiFePO4 Cell DIY battery builds. The BattleBorns are meeting or exceeding my needs. The Automotive Grade EV Prismatic cells are extremely expensive. Yes. I will 'stick with BattleBorn' as you have suggested. Thank you for that suggestion.
 
Top