How to wire a second 4S BMS to my 12V system in parallel

[harbin1234]

Hi everyone. I need help.
I have what I believe to be a 4S2P 12V battery setup.
I have 8 cells setup the same as Wills video of 3 or 4 years ago shows, the compact version and I wired my 500 amp smart Daly BMS the way he showed.

The problem is I have cells that always read a 3.44 charge and the other 5 cells show a 3.37. Yes this worries me.
I tried the 8S Daly Smart Balancer but it only showed 4 cells of the 8 and not the other 4 cells the BMS was connected to.
So, I am here to ask someone to please show me how to connect another BMS.
I assumed that I would connect this bms to one parallel bank and the other to the next bank, But I'm not any good with this stuff.
Thank You

 

[Samsonite801]

Hi everyone. I need help.
I have what I believe to be a 4S2P 12V battery setup.
I have 8 cells setup the same as Wills video of 3 or 4 years ago shows, the compact version and I wired my 500 amp smart Daly BMS the way he showed.

The problem is I have cells that always read a 3.44 charge and the other 5 cells show a 3.37. Yes this worries me.
I tried the 8S Daly Smart Balancer but it only showed 4 cells of the 8 and not the other 4 cells the BMS was connected to.
So, I am here to ask someone to please show me how to connect another BMS.
I assumed that I would connect this bms to one parallel bank and the other to the next bank, But I'm not any good with this stuff.
Thank You

Daly does a poor job of cell balancing based on the work I've done on my friend's 16s Daly BMSs..

I have 6 of the Overkill 4s BMSs all running in parallel for six 12v batteries, and I love them, they always stay in sync as long as I set the packs to balance on charge and discharge in the Xiaoxiang app. All in all, I love these BMSs from Overkill, I use the 120a ones.

4 Cell BMS (12 Volt) – Overkill Solar

BMSs for 4 cell LiFePo4 battery assemblies.

overkillsolar.com

 

[harbin1234]

Daly does a poor job of cell balancing based on the work I've done on my friend's 16s Daly BMSs..

I have 6 of the Overkill 4s BMSs all running in parallel for six 12v batteries, and I love them, they always stay in sync as long as I set the packs to balance on charge and discharge in the Xiaoxiang app. All in all, I love these BMSs from Overkill, I use the 120a ones.

4 Cell BMS (12 Volt) – Overkill Solar

BMSs for 4 cell LiFePo4 battery assemblies.

overkillsolar.com

Thank you for the advice.
I use the 500 amp bms because I live pretty much off grid in my fifth wheel. It is a 30 amp unit and I use my A/C a lot here in AZ.
I have a 4000 (8000 peak) watt pure sine inverter.

The gentlemen at Overkill customer service infomed me I would need two 120 amp bms.
I don't care what BMS i use, I just need a picture of how to wire them.
Do I need to use the same brand of BMS on the other 4 batteries?

I really wish I knew why the Smart Balancer didn't recognize the 4 cells the daly bms was connected to?

 

[Samsonite801]

Thank you for the advice.
I use the 500 amp bms because I live pretty much off grid in my fifth wheel. It is a 30 amp unit and I use my A/C a lot here in AZ.
I have a 4000 (8000 peak) watt pure sine inverter.

The gentlemen at Overkill customer service infomed me I would need two 120 amp bms.
I don't care what BMS i use, I just need a picture of how to wire them.
Do I need to use the same brand of BMS on the other 4 batteries?

I really wish I knew why the Smart Balancer didn't recognize the 4 cells the daly bms was connected to?

I've heard of some random hit and miss issues as far as parallel BMSs behaving well when running side by side in parallel banks. I personally never understood the fundamental reason behind it (why some BMSs could care less about other BMS running along side another, but others' seemed to matter and didn't support it), I've heard some people here explain why it could happen in some instances, but for this reason, I know the OverKills didn't have this problem for sure (many here have confirmed this), so I tried them out and found it's true, the OverKill work fine side by side. Also FYI, OverKill are basically rebranded JBD BMSs, but they offer excellent USA support through OverKill.

I just rename the BMSs different in the app so I can tell which one is which (Like BMS-1, BMS-2, BMS-3, etc). I can't remember the last time I logged into them, they just work fine all the time. With six of them in parallel on my system, I get gobs of amps, I have a total of 24 of the 280Ah cells and they can run one of the roof AC units for around 8 or so hours without solar.

I also use a Victron BMV-712 as the master gateway to read SoC at single point, so that is my more goto gauge than looking at individual BMSs so much.

 

[Samsonite801]

I really wish I knew why the Smart Balancer didn't recognize the 4 cells the daly bms was connected to?

Also, on my friend's system with Dalys, he had a few he accidentally hooked up wrong and blew out some ports on the sense wires, and we were seeing some where cells were showing 0v (even after fixing the wiring order problem). Even had a couple of his BMSs we couldn't ever get to work at all. He had 8 of the Dalys total, and I think only like 4 of them wound up working somewhat at all by the time I got done helping him get the issues worked out.

And they still don't balance very well, because there is a small window of voltage where they balance at, and his system doesn't stay in that window very long. Then there is issue of their software. Half of their Daly BMSs work only using one software program, and half using the other software. The phone app doesn't let you change every possible setting to tweak balancing and such. But then using the usb-serial cable with laptop programs (which is supposed to allow more tweaking of params), I couldn't get either of the programs to let me change the params I had wanted to change. So he is just going to replace them all out with Overkill 120a at this point, and be done with the hassle.

Or you could put some JK active balancers on as well to help the Daly on that part.

 

[harbin1234]

WoW, Thanks again for the help.
I guess I'll have to buy two 120 amp Overkill BMS and just wire one 4S for each side.
Maybe you have a picture of how to wire the two together.
I suppose I can use the pos. and neg. post on the other side and wire to the cells that are not wired now.
I just don't know, that is why I need a picture. Thank You for repling.

 

[Samsonite801]

WoW, Thanks again for the help.
I guess I'll have to buy two 120 amp Overkill BMS and just wire one 4S for each side.
Maybe you have a picture of how to wire the two together.
I suppose I can use the pos. and neg. post on the other side and wire to the cells that are not wired now.
I just don't know, that is why I need a picture. Thank You for repling.

You are running 12v system, correct? IF you are actually running a 24v system, you would for sure want OverKill 8s BMS instead.

Think of a 4s BMS as a 4-cell (for 12v system operation), as a single battery (cell bus bars only connecting 4s together as one battery), so wiring two of them it is just 2 independent systems, then parallel them together onto the same common bus bars (on outside of BMSs). They won't have any correlation with each other, other than paralleling 'two' batteries in parallel, just balancing the common voltages across to each other, each BMS shouldn't care what the other is doing, outside of itself.

An 8s (24v), would be one battery, same concept. So just treat them like that. An 8s battery assumes cell bus bars connecting all 8s cells into one string to make one 24v battery.

EDIT:
And OverKill has diagrams and manuals you can download on their site which show good wiring schematics of all their BMS offerings...

 

[mikefitz]

4S2P 12V battery setup.
I have 8 cells setup the same as Wills video of 3 or 4 years ago shows, the compact version and I wired my 500 amp smart Daly BMS

I have a 4000 (8000 peak) watt pure sine inverter.

The gentlemen at Overkill customer service infomed me I would need two 120 amp bms.

All this seems very confused
At 12v a 4000 watt inverter needs 350 amps of current, two 120 amp BMS for two 12v batteries won't work.

A 4S2P cell setup needs two BMS , not a single 500 amp BMS.





A diagram or picture of the cell arrangement would help the discussion.

 

[Samsonite801]

All this seems very confused
At 12v a 4000 watt inverter needs 350 amps of current, two 120 amp BMS for two 12v batteries won't work.

A 4S2P cell setup needs two BMS , not a single 500 amp BMS.


A diagram or picture of the cell arrangement would help the discussion.

I have what I believe to be a 4S2P 12V battery setup.
I have 8 cells setup the same as Wills video of 3 or 4 years ago shows, the compact version and I wired my 500 amp smart Daly BMS the way he showed.

After reading all this again, I am thinking I had missed what he originally meant about his current configuration.

It seems to me he had maybe meant to describe the above setup he has as a 2p4s, wired through a single Daly 500a BMS. He did say he had a 5th wheel RV, so sounds like 12v for sure, so if that is the case then no 8s balancer or BMS would ever work here, which is why the 8s Daly Smart Balancer he tried could never work there (since they were configured as 4s on the cell bus bars).

My rule for myself is to never parallel up multiple cells onto one larger-amp BMS, like only use 1 cell per BMS, so any 12v (4s battery) I build only has 4 cells max. I'd rather spend a little more and build a bunch of smaller 12v batteries and parallel those together (each battery having their own BMS).

So he may not like my recommendation here (due to more cost involved), but if he needs more amps for his 4000w inverter, I'd buy more cells and BMSs, and make more smaller batteries, and parallel all those batteries together, to have your big enough bank. This also reduces single-point-of-failure, by having more BMSs, and makes troubleshooting the system easier when individual cells may have issues.

I had wanted lots of amps for my system, so I built 6 batteries, and paralleled all those together. On my system, I only need max 350a, but I have 1680Ah of battery there, so no single battery gets pegged for drawing too hard.

 

[harbin1234]

Thank you both for your kind and thoughtful replies.
@Samsonite801 I just don't have the money for more batteries, Not with Bidenmonics and the cost of food and diesel.
@mikefizt, you are correct, it is a 2P4S, my mistake, I call it Old Age Brain Farts. (78 years old)
I have (D) in your picture above.

Why do I need a 500 amp BMS? I guess it is because my son gave it to me for my last B-D.
Why a 4000 Watt inverter? I will have the ac, microwave, electric coffee pot on as I vacuum in the morning everything is on and my batteries drop from 13.4 to 12.9 and when I turn of the microwave and vacuum they go back to 13.2.

I can run my ac non low output for 2 or 3 hours and the drop is to 12.7.
But with my 400 watts of solar panels out in the Arizona sun, my batteries quickly recover.

I am very sorry for the long reply.
My question is do I need another bms and what terminals do I wire it to.
Thank You

 

[MisterSandals]

It seems to me he had maybe meant to describe the above setup he has as a 2p4s, wired through a single Daly 500a BMS.

There are quite a few of us who have multiple cells in parallel first. I have a 2P4S battery in my RV and its been rock solid for over 3 years. It does require a little effort in making your pairs (or parallel groups of 3 or 4 or...) equal in total capacity.
To do this pairing, its pretty easy for 2P as you simply pair strongest cell (highest capacity) with weakest cell (lowest capacity). Then pair second strongest with second weakest. Then 3rd strongest with third weakest.

Since it sounds like you have everything to give this a go, and a huuuuge BMS.

Regarding YOUR cell pairing,

The problem is I have cells that always read a 3.44 charge and the other 5 cells show a 3.37.

I would pair a 3.44V cell with a 3.37 cell for your first 3 pairs. These are all 100% full if measured after settling and at rest. This is a great sign.


Not mine but just like my buried setup:


And don't look too closely at this wiring, there are multiple wires to a couple pairs for some reason (maybe balancer and BMS?).
You have a 5 wire BMS:
Black pin 1 to cell 1 negative.
Red pin 2 to cell 1 positive.
Pin 3 to cell 2 positive.
Pin 4 to cell 3 positive.
Pin 5 to cell 4 positive.

 

[mikefitz]

The problem is I have cells that always read a 3.44 charge and the other 5 cells show a 3.37. Yes this worries me.

This is odd. Since the cells are in parallel pairs you cannot have an odd number of cells with diferent voltages.

The differential is not excessive , 7mv, perhaps within the resolution or error of the BMS. I would not worry about this.

My question is do I need another bms and what terminals do I wire it to.

The BMS is wired as shown in diagram D, must be able to handle 400 amps.
Why do you need a new BMS? If the current set up meets your power needs then why change.
The voltage difference on the cells is not huge and passive balancing in the BMS should help over time.
You may have cell to buss bar interconnections that are causing volt drops or volt drops in other parts of the system. A 4000 watt inverter on a 12v system requires high quality cables and conections. DC breakers can be an issue due to volt drops.

You have not indicated charging methods or charge voltages. This could influence how sucessfuly the battery is charged and if the charge peramerters are suitable to allow cell balance to take place. Details of chargers could help.

Mike

 

[Samsonite801]

Thank you both for your kind and thoughtful replies.
@Samsonite801 I just don't have the money for more batteries, Not with Bidenmonics and the cost of food and diesel.
@mikefizt, you are correct, it is a 2P4S, my mistake, I call it Old Age Brain Farts. (78 years old)
I have (D) in your picture above.

Why do I need a 500 amp BMS? I guess it is because my son gave it to me for my last B-D.
Why a 4000 Watt inverter? I will have the ac, microwave, electric coffee pot on as I vacuum in the morning everything is on and my batteries drop from 13.4 to 12.9 and when I turn of the microwave and vacuum they go back to 13.2.

I can run my ac non low output for 2 or 3 hours and the drop is to 12.7.
But with my 400 watts of solar panels out in the Arizona sun, my batteries quickly recover.

I am very sorry for the long reply.
My question is do I need another bms and what terminals do I wire it to.
Thank You

Well, MrSandals is correct, there are plenty of people who don't mind having multiple cells paralleled and use single BMS, perfectly fine. Since budget is of prime concern first, I would first try just doing what he suggests and possibly swapping / moving cells around (keeping existing layout of 2p4s) to make pairs that are more aligned to the groups (of each parallel 2 cells), and see if you can get a better match where voltages / capacities match more naturally.

 

[MisterSandals]

I would first try just doing what he suggests and possibly swapping / moving cells around (keeping existing layout of 2p4s) to make pairs that are more aligned to the groups (of each parallel 2 cells), and see if you can get a better match where voltages / capacities match more naturally.

If you can see how your 2P4S battery performs before installing, you can save a bit of effort; its already a bit tedious moving cells around.
First label your cells (i like using letters (A, B, C,... because cell position is a number) and take notes. This will be vital to building and maintaining the battery, especially if making changes.

Your cells are fully charged so do a deep discharge to where one of the pairs drops below 3.0V. Disassemble your battery and measure voltage of individual cells. Your weakest (lowest capacity) will have lowest voltage. Take notes!
Rebuild your battery strongest paired with weakest, second strongest with second weakest...

Then charge your 2P4S battery. If you can watch it when any of the cell pairs get near 3.4V, you will see how balanced your battery is. If you get a pair that hits your top charge voltage a lot sooner than any other pair(s), you can disassemble, measure voltages and redo your pairs. Take notes!

This is the best "process" that i know of other than individual cell capacity tests (takes weeks! and a good 4 wire tester is ~$80).

Good luck! If you have questions please ask here or feel free to message me personally.

 

[harbin1234]

@MisterSandals , @mikefitz and @Samsonite801
Here are pictures of my setup. Please overlook the mess, They have been there for over 3 years maybe 4.
When I am at my son or daughter home like I am now, I turn off my inverter and turn on my converter and plug into shore power.

@MisterSandals , I would be more than happy to remove and change locations of the cells, But my back is not has strong as it was 5 years ago and my fingers just do not grip as tight.
But, I take it I do not need another BMS added.
So allow me to ask this, do I need a different Brand/Maker of a bms, since it sounds like the Daly is not the best for managing each cell.
I also need to remove the negative inverter cable and connect it back to the black negative on the bms.
By the way, you are all very nice for taking the time to help me.
What brand bms and amperage should I use? I can go to AliExpress and order a better brand.

​

 

[Samsonite801]

@MisterSandals , @mikefitz and @Samsonite801
Here are pictures of my setup. Please overlook the mess, They have been there for over 3 years maybe 4.
When I am at my son or daughter home like I am now, I turn off my inverter and turn on my converter and plug into shore power.
View attachment 173214View attachment 173215View attachment 173216
@MisterSandals , I would be more than happy to remove and change locations of the cells, But my back is not has strong as it was 5 years ago and my fingers just do not grip as tight.
But, I take it I do not need another BMS added.
So allow me to ask this, do I need a different Brand/Maker of a bms, since it sounds like the Daly is not the best for managing each cell.
I also need to remove the negative inverter cable and connect it back to the black negative on the bms.
By the way, you are all very nice for taking the time to help me.
What brand bms and amperage should I use? I can go to AliExpress and order a better brand.

​

Technically, if the cells are good matching (in your case pairs of cells), and well balanced to begin with, any drift should be minimal, and it doesn't need a lot of balancing to to hold the pack true. But higher balancing amps can help bandaid a system with cells not well matched.

I would say try to swap cells around (per above discussion), get better natural order, then if there is still too much drift, I might add on something like a Neey Active Balancer, or a bit cheaper, a JK Active Balancer or something, if the Daly can't seem to handle keeping them balanced.

And yes, you should have your loads wired through the BMS, as in on the C- cable, not bypassed where the B- cable goes, otherwise the BMS can't shut off the charge/load when things go awry (outside of safety thresholds).

More info on Neey Active Balancer:

I've personally not tried the Neey balancer, I use JK 2a Active Balancers with success, but those Neey balancers look promising...

They just piggy back onto existing battery, not to remove the BMS, as those balancers are only balancers, and do not do the other 4 functions a BMS does (over/under volt, over/under temp), so they just coexist together...

 

[MisterSandals]

So allow me to ask this, do I need a different Brand/Maker of a bms, since it sounds like the Daly is not the best for managing each cell.

I think the Daly is certainly worth giving it a so since you already own it.

The goal is to NEVER have the BMS intervene. The balancing current of most BMSs is dwarfed by the charge/discharge current so don't fret about that now. Its a safety disconnect.

I see you have your battery wired as 2P4S already. Have you been charging and discharging with this setup? Are your measured voltages above from this setup or individually?

 

[harbin1234]

Technically, if the cells are good matching (in your case pairs of cells), and well balanced to begin with, any drift should be minimal, and it doesn't need a lot of balancing to to hold the pack true. But higher balancing amps can help bandaid a system with cells not well matched.

I would say try to swap cells around (per above discussion), get better natural order, then if there is still too much drift, I might add on something like a Neey Active Balancer, or a bit cheaper, a JK Active Balancer or something, if the Daly can't seem to handle keeping them balanced.

And yes, you should have your loads wired through the BMS, as in on the C- cable, not bypassed where the B- cable goes, otherwise the BMS can't shut off the charge/load when things go awry (outside of safety thresholds).

More info on Neey Active Balancer:

I've personally not tried the Neey balancer, I use JK 2a Active Balancers with success, but those Neey balancers look promising...

They just piggy back onto existing battery, not to remove the BMS, as those balancers are only balancers, and do not do the other 4 functions a BMS does (over/under volt, over/under temp), so they just coexist together...

@Samsonite801 Sounds like a good plan. Using another balancer, I physically can not bend over that long any more to take the box apart and move cells.
If I buy a JK or Neey 4S balancer, my question is this, Do I connect the 5 leads (1) Black and the other (4) Red to the same cells the Daly is connected too?
Yes, I know I need to reconnect the Inverter Ground to the BMS on the C- cable. I was going to change that when I get this figured out and leave again.

 

[harbin1234]

I think the Daly is certainly worth giving it a so since you already own it.

The goal is to NEVER have the BMS intervene. The balancing current of most BMSs is dwarfed by the charge/discharge current so don't fret about that now. Its a safety disconnect.

I see you have your battery wired as 2P4S already. Have you been charging and discharging with this setup? Are your measured voltages above from this setup or individually?

I built this about 4 years ago and never changed it. I have had this issue with the same cells being a little more charged than the other five for awhile.
Yes, I do monitor each cell with a voltmeter I use.
I run my electric coffee pot most of the early morning into the afternoon, that is a dead short and draws a lot of amps. I installed a safe-start on my old ac unit, which helps.
My microwave is an old 900 watt unit and it REALLY draws about 1350 watts. (Just used for TV dinners/Popcorn)

What is your thoughts about a JK or Neey 4S BMS like or friend Samsonite suggested.
If you think that would help, how do I wire it.

Again Thank You All.

 

[mikefitz]

your thoughts about a JK or Neely 4S BMS

I will say again, you don't need a new BMS, the cells are not that badly out of balance. The suggestions about rearranging cells is fine in theory, but may not give any significant improvement.

this issue with the same cells being a little more charged than the other five

This I don't understand . You have 4 cells pairs. If the buss bars are making good contact then the cell pairs are at the same voltage. You only have 4 voltages to measure. If on the other hand you are removing the buss bars and measuring each cell , then there could be different voltages. Because under normal operation the BMS 'sees' a cell pair it attempts to balance 4 'big' cells.