Need Help / Off Grid Battery Balancing

[LightZone]

I have an off grid 48 v solar system. The 2 batteries are Big Battery Rhinos and have been in service for about 2 years. Right now, our batteries max out at 54v. I would like to increase that to at least 56 or 57 volts. I feel like we are not fully using the storage capacity of our batteries.
I recently saw a video from Will with suggested settings for 48 v batteries. He suggests charging each battery independently to 100% to assure correct balancing. Our batteries are balanced within 2/10 of a volt.
Since we rely on our batteries for all of our power, I am trying to figure out to bring the capacity to the suggested 58 volts (currently at 54 volts) without losing power to our house. Will says each battery should be charged to 100% and then introduced to the system. I just don't have a way to effectively get both batteries to 100% at the same time.

Our SCC (Schneider Electric Mppt 60/150) is set to Custom Battery Mode with an absorbtion of 58 v and Float 54.4. With the float at this setting, getting the batteries to the upper range of "full" seems impossible. IF I were to INCREASE the float setting to a higher setting, it would seem to allow more energy to flow to the cells thereby increasing the maximum storage of the batteries. I just don't know if increasing the float could potentially cause damage to the cells.
I'm sure this post is exposing my lack of knowledge but heck, if you don't ask questions you'll never learn.
Thank you for any feedback.

 

[Aridom82]

Are you sure that the Big Battery Rhino doesnt include a bms with an active balancer?
It says in the user manual that there is an active balancing option (top of page 6)
https://bigbattery.com/wp-content/u...3ZvNeZXjVzgq1APrOAc8V-zu4zcRZIWtn7gMS9vRPZNk9
If set up correctly it could balance the cells automatically.
With lifepo4 cells, at the upper limit the voltage difference represents little extra capacity. So if the cells are properly balanced, floating to 58v doesnt really gives that much extra energy storage. But if you decide to do it it should be ok, the bms should protect the cells from overcharging.

 

[MakeMePower]

uh you have your absorption set to 58v, uh that's 3.62, thats as close to max as possible. most people are below that. Float is not going to gain you anything, float simply keeps you from holding the the battery at maximum voltage, there is very little amps to push if your absorb is at 58.

your done. get more batteries if you need more capacity, should be using a shunt to see how many AH your using.

 

[LightZone]

Are you sure that the Big Battery Rhino doesnt include a bms with an active balancer?
It says in the user manual that there is an active balancing option (top of page 6)
https://bigbattery.com/wp-content/u...3ZvNeZXjVzgq1APrOAc8V-zu4zcRZIWtn7gMS9vRPZNk9
If set up correctly it could balance the cells automatically.
With lifepo4 cells, at the upper limit the voltage difference represents little extra capacity. So if the cells are properly balanced, floating to 58v doesnt really gives that much extra energy storage. But if you decide to do it it should be ok, the bms should protect the cells from overcharging.
View attachment 322177

uh you have your absorption set to 58v, uh that's 3.62, thats as close to max as possible. most people are below that. Float is not going to gain you anything, float simply keeps you from holding the the battery at maximum voltage, there is very little amps to push if your absorb is at 58.

your done. get more batteries if you need more capacity, should be using a shunt to see how many AH your using.

uh you have your absorption set to 58v, uh that's 3.62, thats as close to max as possible. most people are below that. Float is not going to gain you anything, float simply keeps you from holding the the battery at maximum voltage, there is very little amps to push if your absorb is at 58.

your done. get more batteries if you need more capacity, should be using a shunt to see how many AH your using.

For the first 2 years of service I had my absorbtion set to 54. Then when I ran across Will's video with suggested absorbtion to be set at 58 it got me to thinking of the potential storage capacity that is not being used. My float continues to be set at 54 ( Will's suggested settings is 54.4 which I figured is close enough. So as you've said, we're done. For 90% of the year we are never even thinking about the battery capacity. We've just gone through an extremely long hot spell in southern Arizona and running the a/c till 9pm was really stressing out our battery capacity.

 

[timselectric]

You don't need to float as high as 58v (although you can).
But you do need to get above 55.2v, to balance and get full capacity.
Assuming that they are 16s batteries.

 

[MakeMePower]

You don't need to float as high as 58v (although you can).
But you do need to get above 55.2v, to balance and get full capacity.
Assuming that they are 16s batteries.

why 55.5? most bms are 3.4 for balance no? which puts you around 54.4, prolly why will suggested it

 

[LightZone]

You don't need to float as high as 58v (although you can).
But you do need to get above 55.2v, to balance and get full capacity.
Assuming that they are 16s batteries.

Thank you for your help. The batteries do balance when charging but with my current foat of 54 I am only able to get the individual cells to 3400. I'm not sure what you mean by 16s batteries.

 

[MakeMePower]

Thank you for your help. The batteries do balance when charging but with my current foat of 54 I am only able to get the individual cells to 3400. I'm not sure what you mean by 16s batteries.

your cells are getting to 3.62 during absorption. His comment about 16 is some crappy companies market a 15s as 48V, which changes the charge voltages if that's the case

 

[LightZone]

your cells are getting to 3.62 during absorption. His comment about 16 is some crappy companies market a 15s as 48V, which changes the charge voltages if that's the case

Got it. Thanks for the clarification.

 

[Aridom82]

some crappy companies market a 15s as 48V

lol what a rip-off

 

[Brucey]

For the first 2 years of service I had my absorbtion set to 54. Then when I ran across Will's video with suggested absorbtion to be set at 58 it got me to thinking of the potential storage capacity that is not being used. My float continues to be set at 54 ( Will's suggested settings is 54.4 which I figured is close enough. So as you've said, we're done. For 90% of the year we are never even thinking about the battery capacity. We've just gone through an extremely long hot spell in southern Arizona and running the a/c till 9pm was really stressing out our battery capacity.

Maybe few percent if that at the higher voltage. And less cycles. At 54.4V its possible to fully charge given enough time.

 

[timselectric]

why 55.5? most bms are 3.4 for balance no? which puts you around 54.4, prolly why will suggested it

55.2v
3.45v per cell
Some do 3.4v, but that's barely in the upper knee.
Personally I balance to 0.003v delta, at 3.5v per cell.
But that makes some people nervous.

 

[timselectric]

Thank you for your help. The batteries do balance when charging but with my current foat of 54 I am only able to get the individual cells to 3400. I'm not sure what you mean by 16s batteries.

16s is a 16 cell battery. (As opposed to the 15 cell scams)
Take it to 55.2v, and see how much out of balance they are.

 

[LightZone]

Maybe few percent if that at the higher voltage. And less cycles. At 54.4V its possible to fully charge given enough time.

I've found that at 54.4 with minimal load but during the peak of summer that AC has got to get turned on or my wife will have a fit. Luckily in SE. Arizona we typically have great solar conditions.

 

[LightZone]

16s is a 16 cell battery. (As opposed to the 15 cell scams)
Take it to 55.2v, and see how much out of balance they are.

Just made the change and we'll see how things pan out tomorrow.

 

[LightZone]

Just made the change and we'll see how things pan out tomorrow.

So after a day of having my float set to 55.2, the results so a positive trend. There was no BMS intervention, no codes were thrown, and the overall amount of available battery at 17:00 (5pm) was 1 volt higher that I typically experience under similar circumstances. The individual cells were reading 3400 instead of the typical 3300. So now I will monitor the progress over the coming days to see if this positive trend continues.

 

[MakeMePower]

well yea? but how much usable did it actually gain you, do you have a shunt to see if you actually got more then say 10ah? i find once you hit the knee, not a lot more left there.

 

[DougL]

Our batteries are balanced within 2/10 of a volt.

balanced to .200V is not very well balanced since most expect and do get cells less than .020V( 20mV ) difference and often below .010V(10mV).
one tenth of a volt is lots of capacity in LFP batteries( ie the difference between 3.200V and 3.300V ).

You should find some capacity by getting your battery cells balanced to under 30mV instead of 200mV

 

[LightZone]

The batteries balance varies depending on the time of day and the amount of electricity being used. This is actually one of the issues I have with the Big Battery Rhino batteries. I have two in parallel and find that they discharge very differently. For example, overnight the tendency is for one of the 2 batteries to carry load while the other remains idle. This means than in the morning I can see as much as a 1-1.5v difference between the 2. I contacted Big Battery and they told me that in order for the BMS to "activate" the second battery, a minimum load of 8 amps is required. I found that strange and looked through the manual and nowhere did I find that mentioned, but they continue to say that because our overnight power load is under this 8amp threshold only one battery will be active at a time while the second battery remains idle. Because as I mentioned in the original post we are 100% off grid, we try to be mindful of our overnight power usage. 3 ceiling fans, full size fridge, small separate freezer and perhaps a box fan in the window will be around 6 amps. I even went through the house seeing what else could we have on overnight to reach this magical 8 amps. Frankly, nothing short of the Mitsubishi mini split. Short story long, the 2 batteries will balance themselves out relatively quickly during the charging phase, often times reaching identical loads. QUESTION: Does this information about the required 8 amps minimum sound correct or am I being fed a line of bull? This was the main reason I was looking to maximize my battery usage. 2 weeks ago we actually had a power outage at 2am. I went out to the batteries to find one battery shut down at the 20% of capacity level while the second battery was at about 70% but, according to Big Battery because our power draw was under 8 amps, the BMS did not "active" or wake up the second battery to help carry the load.

 

[MakeMePower]

are you using a communication cable between everything?

 

[LightZone]

are you using a communication cable between everything?

Yes, com line are in place.

 

[MakeMePower]

Yes, com line are in place.

then i can't answer that, they may shut off the discharge port. i don't know how their protocol works, but seems like a bad decision if its true

 

[LightZone]

I told Big Battery that had that very little but important piece of information been on either their website or in the owners manual ( which it is not cause I have looked..... repeatedly, I would have chosen another product. Now I just have to figure out a way to make it work.

 

[DougL]

The batteries balance varies depending on the time of day and the amount of electricity being used. This is actually one of the issues I have with the Big Battery Rhino batteries. I have two in parallel and find that they discharge very differently. For example, overnight the tendency is for one of the 2 batteries to carry load while the other remains idle. This means than in the morning I can see as much as a 1-1.5v difference between the 2. I contacted Big Battery and they told me that in order for the BMS to "activate" the second battery, a minimum load of 8 amps is required. I found that strange and looked through the manual and nowhere did I find that mentioned, but they continue to say that because our overnight power load is under this 8amp threshold only one battery will be active at a time while the second battery remains idle. Because as I mentioned in the original post we are 100% off grid, we try to be mindful of our overnight power usage. 3 ceiling fans, full size fridge, small separate freezer and perhaps a box fan in the window will be around 6 amps. I even went through the house seeing what else could we have on overnight to reach this magical 8 amps. Frankly, nothing short of the Mitsubishi mini split. Short story long, the 2 batteries will balance themselves out relatively quickly during the charging phase, often times reaching identical loads. QUESTION: Does this information about the required 8 amps minimum sound correct or am I being fed a line of bull? This was the main reason I was looking to maximize my battery usage. 2 weeks ago we actually had a power outage at 2am. I went out to the batteries to find one battery shut down at the 20% of capacity level while the second battery was at about 70% but, according to Big Battery because our power draw was under 8 amps, the BMS did not "active" or wake up the second battery to help carry the load.

So you were talking about the "balance" of the 2 48V batteries relative to each other. I've you're read other forums on batteries you'll know we are talking about the 16 battery cells INSIDE of each of your 48V batteries. i recommend you look at what others have done with DIY batteries using LFP cells to make 48V batteries. You should have a much better understanding of what to expect of your batteries and know when you'll start seeing wearing.
Overall capacity is not going to be affected by the battery packs discharging at different rates.

 

[LightZone]

So you were talking about the "balance" of the 2 48V batteries relative to each other. I've you're read other forums on batteries you'll know we are talking about the 16 battery cells INSIDE of each of your 48V batteries. i recommend you look at what others have done with DIY batteries using LFP cells to make 48V batteries. You should have a much better understanding of what to expect of your batteries and know when you'll start seeing wearing.
Overall capacity is not going to be affected by the battery packs discharging at different rates.

I appreciate the information. I guess the core issue or question is, is it normal for 2-48v batteries in parallel to discharge in the manner I described at the end of my previous post? And is it normal for 2 48 volt batteries to require a minimum power draw of, (as in my case 8 amps) for the 2 batteries to remain operational or remain awake ( through the BMS)? I am the first to admit I have a lot to learn and I am hoping that members of this forum will cut a less knowledgeable member a little slack. Thank you for for your advice!