Solar assistant charging to100%. Only want 80

[sjordan0228]

Hopefully my last “newb” question.

Eg4 3000 inverter
Lifepower4 battery

I have SA hooked up to the battery and inverter. I have the eg4 3000 set to USE as the battery type. All of this is working in SA. I have no utility hooked up. I do have the option but only want to use it as a last resort.

My issue is I cannot figure out how to get this setup to stop charging the battery once it hits 80%. Right now it’s charging to a 100%, but from what I have read this is not good.

Is there a trick to get it set this way?

 

[Adam De Lay]

The maximum charge value would be set in your inverter. While SA might be able to change the inverter setting for you, it’s only a monitoring tool.

 

[sjordan0228]

The maximum charge value would be set in your inverter. While SA might be able to change the inverter setting for you, it’s only a monitoring tool.

I figured this would be true but can’t seem to figure out what setting that is. Maybe it’s called something else?

 

[42OhmsPA]

Reduce your bulk and float charging voltages.
The issue with doing this is you may lose cell balance over time.

 

[Supervstech]

To keep the battery from reaching 100% all the time, set the float voltage down below 3.4V/cell 80% is going to be difficult to reach regularly, due to the hugh spread in capacity at that level.
Over time, the bms will be running constantly trying to balance the cells.

 

[Lt.Dan]

No need to stop at 80%. This is a myth that I've read too many times.

 

[Supervstech]

Hopefully my last “newb” question.

Eg4 3000 inverter
Lifepower4 battery

I have SA hooked up to the battery and inverter. I have the eg4 3000 set to USE as the battery type. All of this is working in SA. I have no utility hooked up. I do have the option but only want to use it as a last resort.

My issue is I cannot figure out how to get this setup to stop charging the battery once it hits 80%. Right now it’s charging to a 100%, but from what I have read this is not good.

Is there a trick to get it set this way?

While it is true that STORING a battery at 100% or keeping it fully charged will lead to rapid degradation, a battery that is used daily has a specific total kWh of use, and it won’t matter if you charge 0-100-0-100 every day, or 20-80-20-80 every day…

The TOTAL kWh of use doesn’t change. You will reduce the # of cycles the battery can output, but you will get the same kWh from the cell.

 

[GXMnow]

No need to stop at 80%. This is a myth that I've read too many times.

It does depend a bit on the type of cells being used.

Most home energy storage batteries are LiFePO4 cells. From what I have read, I agree, you would want to charge them into their upper knee voltage range to ensure all the cells are getting charged to an equal high state. How much you need to go above 3.4 volts per cell will depend on the way the cell balancing works. If the cells are well matched and balanced, going up to just 3.45 volts for an hour of bulk charge each day could be enough to keep the cells well balanced. The cell life benefit of not charging to 3.65 volts is still there, but it does not seem as drastic as it is on other cell types. A common full charge voltage used on LFP cells is about 3.55 volts per cell for a good balance of reducing cell stress and still getting a solid top balance. Below 3.4 volts, LFP cells hardly change voltage at all with state of charge. So even a perfect voltage balance at 3.95 volts could have cells that are more than 30% different on state of charge. Balancing the cell voltages at 3.55 volts per cell should bring their state of charge within less than 5%

If you don't have a good top balance, trying to chare to the true 100% charge state on a "48 volt" 16 cell LFP battery bank can be nearly impossible. As the cells approach full charge, the voltage of the highest state cells begin to run away. In a perfect world with a perfectly balanced pack, full bulk voltage would be 58.4 volts. That is 3.65 volts x 16 cells. As the battery bank charges up, If just one cells goes into the upper knee, it could start to run and hit 3.65 volts while the rest of the cells are at just 3.4 volts. This could cause the BMS to shut off charging as early as 54.65 volts with just one out of balance cell. The better the top balance is, the higher you can charge without this error happening.

I am using Li NMC cells. These act very different when compared to LFP cells. The cell voltage changes fairly linear across the entire state of charge range. This allows them to be "Top Balanced" at whatever top voltage you choose to run. While the cells are considered full when they hit 4.2 volts, that voltage is putting higher stress on the cells and will reduce their capacity over time. Limiting the full charge voltage to just 4.0 volts, is close to 80% and puts a lot less stress on the cells. And cell balancing at 4.0 volts works just fine to keep them top balanced within a few percent.

 

[sjordan0228]

While it is true that STORING a battery at 100% or keeping it fully charged will lead to rapid degradation, a battery that is used daily has a specific total kWh of use, and it won’t matter if you charge 0-100-0-100 every day, or 20-80-20-80 every day…

The TOTAL kWh of use doesn’t change. You will reduce the # of cycles the battery can output, but you will get the same kWh from the cell.

Well that helps a lot. I do plan to use at least 40% a day at a minimum. Right now is the low end use because the weather is very mild. Once it gets cold the heat pump will start using a lot more (same in the summer with ac)