diy solar

diy solar

How to Parallel Balancing. (YEP 99% of us is doing it wrong)(PART#1)

I thought Winters in Alaska had very little Sun?? I was in Anchorage one time and YES it was very COLD but we literally had 45 minutes of daylight ... well maybe a few minutes more ... but we all know what you are saying ... The colder it is the more amps the panels cranks out ...

Here in Finland (63 degrees North, higher up than Anchorage) we only get up to 4 hours max of sunlight in dead of Winter on a cold clear day, however taking the reflection on the snow in mind and the higher performance for solar panels in cold temperatures, this amounts to quite a bit of power.
 
Here in Finland (63 degrees North, higher up than Anchorage) we only get up to 4 hours max of sunlight in dead of Winter on a cold clear day, however taking the reflection on the snow in mind and the higher performance for solar panels in cold temperatures, this amounts to quite a bit of power.

and in the summers you get 24 hours to make up for it .. LOL .. I did my EE internship working for a SWEDISH power company in the summer -- Thank god for blackout curtains .. it was just weird to always have sunlight ...
 
and in the summers you get 24 hours to make up for it .. LOL .. I did my EE internship working for a SWEDISH power company in the summer -- Thank god for blackout curtains .. it was just weird to always have sunlight ...
go in the winter you want dark :)
 
While I see what is being claimed, then why did I see, (on Will's video) that my 16S bank should be set to run between a top of 53V and a low of 50V for the longest life? That is between 3.125 low and 3.3125 high. What does the higher voltage do to the optimal life span?
 
While I see what is being claimed, then why did I see, (on Will's video) that my 16S bank should be set to run between a top of 53V and a low of 50V for the longest life? That is between 3.125 low and 3.3125 high. What does the higher voltage do to the optimal life span?
Higher voltage is needed to push the charge into the battery at a reasonable rate, so the charge time can be reasonably short. "reasonable" depends on each person and application. What's reasonable to one is ridiculous to another.
 
Higher voltage is needed to push the charge into the battery at a reasonable rate, so the charge time can be reasonably short. "reasonable" depends on each person and application. What's reasonable to one is ridiculous to another.

If a cell is rated for 100ah and its max voltage is 3.6 volts and I only charge it to 3.5 volts I will never get the full charge into the battery, confirm?
 
If a cell is rated for 100ah and its max voltage is 3.6 volts and I only charge it to 3.5 volts I will never get the full charge into the battery, confirm?
Not true at all.
Read the specs for charge, it states voltage and termination current. Those 2 values are related and you can adjust both in either direction and still get 100% charge. Battery is not charged by voltage, it's charged by Coulombs , or Amps over time. Voltage simply facilitates the flow of Amps and the rate of that flow, which determines time factor.
 
Not true at all.
Read the specs for charge, it states voltage and termination current. Those 2 values are related and you can adjust both in either direction and still get 100% charge. Battery is not charged by voltage, it's charged by Coulombs , or Amps over time. Voltage simply facilitates the flow of Amps and the rate of that flow, which determines time factor.

Cool so I can fully charge a a lifepo4 cell @2.6 volts it will just take a very long time to charge and a very long time to discharge.
Can you provide a link for the specs that you suggest I read?
Please and thanks.
 
What does the higher voltage do to the optimal life span?
The relationship is very very non-linear, meaning that a small step away from the max limit has most effect. Another step further away has much lesser effect, etc etc. You have to see what is practical for you, so the battery serves your needs, while being at least a tiny bit below max spec voltage.
Also consider that voltage is not even the most important factor. The temperature is.
 
Cool so I can fully charge a a lifepo4 cell @2.6 volts it will just take a very long time to charge and a very long time to discharge.
Can you provide a link for the specs that you suggest I read?
Please and thanks.
not at 2.6V , you need at least 3.4V for LFP chemistry to eventually reach full charge, even if it takes days at this minimum voltage.
 
Here's an interesting experiment with LiFePo4 cells charged with 0.72 C up to 3.40 Volts, with a 0.013 C termination current (30 mA for 2200 mAh capacity).
All cells charged to 96% ... 99% of nameplate capacity, when tested with a 1 C discharge down to 2.6 V
It's unfortunate that the author does not mention the charging duration...


 
Not true at all.
Read the specs for charge, it states voltage and termination current. Those 2 values are related and you can adjust both in either direction and still get 100% charge. Battery is not charged by voltage, it's charged by Coulombs , or Amps over time. Voltage simply facilitates the flow of Amps and the rate of that flow, which determines time factor.

Can you explain? From my understanding you can achieve 100% charge at a specified voltage, but not necessarily 100% of the cell. Example:
  • Set a bench charger to 3.4v of constant voltage, the current would drop to zero when that voltage is achieved.
  • Adjust it to 3.5v and the cycle would commence again.
  • and onward to 3.65v...
Diminishing returns aside, you could only achieve true capacity of the cell if you took it to 3.65v or higher as noted in the article linked above.
 
Can you explain? From my understanding you can achieve 100% charge at a specified voltage, but not necessarily 100% of the cell. Example:
  • Set a bench charger to 3.4v of constant voltage, the current would drop to zero when that voltage is achieved.
  • Adjust it to 3.5v and the cycle would commence again.
  • and onward to 3.65v...
Diminishing returns aside, you could only achieve true capacity of the cell if you took it to 3.65v or higher as noted in the article linked above.
There is no such thing as "true capacity". The cell is labeled by factory based on specific measured test with specific parameters. So, a 100AH cell might be labeled as 102AH at those specific test parameters. If you change parameters you end up with 103AH or 101AH or 100AH, so which one is true?
Electrochemistry is like Einstein's relativity theory, everything is relative.
In your example, step from 3.4V to 3.5V will likely add 0.1%-0.5% of total rated capacity.
Step from 3.5V to 3.65V will add 0.01%-0.05%, exponentially less than step before.
Each one of these changes will affect cycle life if done every time for the life of the cell.
So, what is 100% charge? It's what you decide to pick on the exponential curve of possibilities, where datasheet represents only one data point at which factory engineers decided to test it, based on their best goal to balance cycle life with decent AH rating, all at room temperature by the way.
 
I interpret the true (or initial/expected) capacity of the cell to align to what's printed on the label.
If it's 150ah, I expect to see that AH rating at 3.65v at room temperature.
It could be more which is great. If less, not so much.

You said to SmoothJoey that you can lower charge voltage and still achieve 100% capacity of the cell, implying that I could charge to 3.4-3.5v and receive the same capacity as 3.65 but over a longer charge period - you can't.
 
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Diminishing returns aside, you could only achieve true capacity of the cell if you took it to 3.65v or higher as noted in the article linked above.

In that article he says he terminated charge when current dropped to 30mA, which most cc/cv charges will do. But if he continued the charge, coulombs would continue to climb very slowly until full capacity is reached. The battery will reach full capacity (in AH) at 3.4v, it will just take a lot longer. My take anyway.
 
I interpret the true (or initial/expected) capacity of the cell to align to what's printed on the label.
If it's 150ah, I expect to see that AH rating at 3.65v at room temperature.
It could be more which is great. If less, not so much.

You said to SmoothJoey that you can lower charge voltage and still achieve 100% capacity of the cell, implying that I could charge to 3.4-3.5v and receive the same capacity as 3.65 but over a longer charge period - you can't.
Technically you can, we are still splitting hairs on what 100% really means. I can argue that charge to 3.65V until the current is zero is actually slightly overcharging the cell, so you are getting maybe 100.5% or 101% of charge compared to 3.4V to zero which is really 100%.
You know that proper charge termination is not just voltage, but also terminating current, which is often not stated in datasheets, but implied.
So, your examples above only first is proper charge termination to 100%, while 2nd and 3rd is slight overcharge.
This is one of a few reasons people step down from max voltage, so you don't have to bother with termination current as much.
 
Charge to 3.4V and terminate when current drops below 30 mA.
Or charge to 3.65V and terminate when current drops below 100 mA.
These could, theoretically, put the same amount of charge in the cell.
The second method would be FASTER.

Then there's the discharge termination criteria...also something you have to pick as a compromise between cycle life vs. energy per cycle...
 
This is nonsense. You certainly can and should just set your supply at 3.6V and walk away. There is no reason to split up in steps, unless your power supply is not current limited and would shutdown. If you have a good CC/CV supply you can certainly do the balance in one step.
Agreed.
 
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