Charge equalizing 2 x 48v Lifepo batteries

[SallenB]

Hi,

If there's already a post of this please let me know where to find it.

1 x Sunpowergold 5000w all in one inverter
2 x Sunpowergold 5kw 48v lifepo battery
14 x Sunpowergold 200w pv panels

I have two sunpowergold 48v powerwall lifepo batteries connected in series to a sunpowergold 5000w all in one inverter.
My problem is this: I have set inverter parameters to cutoff charging at 95% capacity and cutoff discharge at 20%. The inverter takes a combined reading from both batteries connected via BMS communication to inverter. Example, battery 1 could read 50% on its BMS display and battery 2 could read 60%.....inverter reads combined capacity of battery bank as 55%. This begins to be a problem at the inverter charge/discharge cutoff points because one battery could be overcharged or underutilized at the inverter cutoff points.

I think the 1st battery in series is getting a stronger charge/discharge than the 2nd battery down the line.

To equalize battery charging/discharging so both batteries are closer in relative capacities after charging/discharging would a shunt block solve this problem?

Interver -----> breaker
Breaker -----> shunt block
Shunt block -----> battery 1
Shunt block -----> battery 2


Thanks in advance.

 

[sunshine_eggo]

I have two sunpowergold 48v powerwall lifepo batteries connected in series to a sunpowergold 5000w all in one inverter.

This is not possible. Two 48V batteries in series would yield 96V. They are in parallel.

Are they connected in accordance with best practices?

Are all connections of high quality and properly torqued?

I think the 1st battery in series parallel is getting a stronger charge/discharge than the 2nd battery down the line.

Then this suggests you have a connection problem.

New batteries generally require some level of top balancing, i.e., they need to be charged to true 100% SoC. Inverter communications often don't facilitate this.

Once you've confirmed you have no connection issues, the popular practice is to set the battery type to USE, disconnect communications, and specify a 3.45V/cell bulk/absorption voltage and a 3.40V/cell float with daily charges to full. The batteries will eventually equalize at 100%.

 

[SallenB]

This is not possible. Two 48V batteries in series would yield 96V. They are in parallel.

Are they connected in accordance with best practices?

Are all connections of high quality and properly torqued?




Then this suggests you have a connection problem.

New batteries generally require some level of top balancing, i.e., they need to be charged to true 100% SoC. Inverter communications often don't facilitate this.

Once you've confirmed you have no connection issues, the popular practice is to set the battery type to USE, disconnect communications, and specify a 3.45V/cell bulk/absorption voltage and a 3.40V/cell float with daily charges to full. The batteries will eventually equalize at 100%.

You're correct. Parallel not series, my mistake.

Good job, but beyond that sunshine_eggo, you sunshine_ass, you assume too much. Everything is not just slapped together haphazardly with shitty components.

You bring nothing to the table.
Read again, I'm asking about a shunt, you ****. Fill in the blank.

 

[Brucey]

My understanding is that the shunts in the BMS units aren't as precise as say a smartshunt, so if you have low discharge rates you could get quite a variation from BMS soc and true soc.

 

[sunshine_eggo]

You're correct. Parallel not series, my mistake.
Good job, but beyond that sunshine_eggo, you sunshine_ass, you assume too much. Everything is not just slapped together haphazardly with shitty components.

You inferred something here. This was not a criticism or implication. You haven't been around long enough to understand how common and easy simple mistakes are.

Bad connections

So lo and behold enven the Magnificient Daddy Tanuki can have issues gather round younglings and learn. So last week finished commissioning two new 400 aH banks to bring the total to 1300 aH or 70kWh depending upon your calculations. While wiring everything in I had to remove the cable from...

diysolarforum.com

You bring nothing to the table.

Not true. I usually bring an appetite!

Read again, I'm asking about a shunt, you ****. Fill in the blank.

**** = stud? Thanks! You humble me with your flattery.

A shunt is a specialized resistor used in current measurement.

I'm guessing you meant a bus bar?

I answered the question you needed to ask. When you only have two batteries, proper connections in accordance with best practices will result in acceptably equal current sharing. If you have more than two batteries, a bus bar starts to make more sense as an alternative to more complex wiring schemes.

 

[Partimewages]

You need to refer to post 2. It has the answers. A shunt is not going to fix your problems!

 

[Brucey]

Are the battery cables connected this way?

 

[42OhmsPA]

You're correct. Parallel not series, my mistake.

Good job, but beyond that sunshine_eggo, you sunshine_ass, you assume too much. Everything is not just slapped together haphazardly with shitty components.

You bring nothing to the table.
Read again, I'm asking about a shunt, you ****. Fill in the blank.

Post some photos of your setup.
I have an idea what's wrong, want to confirm.
A shunt won't fix your problems.
Be nice to Sunshine, he brings great things to the table.

 

[hwy17]

Take them up to full charge or empty and see what they do. I don't think they will behave how you're expecting. The battery with lower SOC will suck more charge to catch up as you near the upper leg.

I have two very mismatched batteries, 300ah and 100ah, wired completely lopsided, and I have not had either one get pushed out of the way at the top or bottom. They will get out of balance in the mid range but they top and bottom out together. Granted I only charge to a gentle 55v.

 

[sunshine_eggo]

Post some photos of your setup.
I have an idea what's wrong, want to confirm.
A shunt won't fix your problems.
Be nice to Sunshine,

Bah... I can take it!!!

he brings great things to the table.

Not always...

 

[Partimewages]

I think the problem is it's the wrong color blue!

 

[sunshine_eggo]

I think the problem is it's the wrong color blue!

Easy now... we need to turn down the temperature in here!