Batrium with Different Battery Capacities

[Henderson]

Hello all. So I've been doing quite alot of research on the Batrium BMS system. It's certainly a rather complex BMS but I've really warmed up to it alot and absolutely love that I could use a remote trip breaker that I can control even if I'm not home. This type of remote functionality is very important for me. My understanding about Batrium is this, and please correct me if I'm wrong....for the Batrium setup if I'm using 2 batteries (LifePo4), each with their own K9 for example, and if any of those individual batteries has an issue, Batrium will shut down the entire bank and not just the battery that has the issue. Further, my understanding is if one of the batteries (one and not both) reaches its low SOC threshold, the entire battery bank will be disconnected and not just the one with the low SOC. If my understanding is correct, then consider this scenario. Let's say I start off with a single battery with Batrium, say 560Ah. I then add another battery a few months down the road with its own K9, but this time the battery is 840Ah. With this configuration, I'm assuming the 560Ah battery will reach low SOC first, whereas the 840Ah battery may still have a decent amount of Ah left. Does this mean that Batrium will disconnect the entire battery bank because the 560Ah battery has low SOC even though the 840Ah battery still has plenty of charge left? Somehow this doesn't make sense. Am I even looking at this right? I know the obvious solution would be to keep all the batteries at the same Ah, but as I add to my system in the future the cells required to build a battery with the same capacity as what I started out with may not even be available or I may only be able to afford something smaller. Before I pull the trigger on the Batrium purchase, I just need to fully understand what limitations I will be taking on.

Thanks in advance for your feedback.

 

[OffGridInTheCity]

I run Batrium. Batrium is "cell based" rather than battery based. For example, I have 8 batteries of 14s = 112 cells. I tell Batrium that it's 14 cells per battery so it knows about the overall battery voltage but it's also cell oriented. If ANY cell of the 112 get's out of bounds various events are fired and this can be associated with relays to cause external action such sending a pulse to a shunt-trip breaker.

Here's a portion of the cell settings page - notice I list 112 cells (1 -> 112) and the "Nom Series" = 14 (e.g. 14s).
I have 3.10v/5C as the low trip point and 4.16v/40C as the hi trip point.

If ANY cell goes above/below these thresholds a "Critical Fault" state turns on - which I hare associated with Relay 1 to trip the shunt.



In you're case you probably will have 16s? per battery. If you have 2 batteries it would be 32cells with "Nom Series" = 16 type of thing.

There are also overall battery bank voltage and current alerts you can set - but primarily I think of Batrium as cell level monitoring.

Here's the full list I can associate with relays - but unfortunately it's only 1 event type per relay. For example, you can't assign the "Critical Fault" to multiple relays.

 

[Henderson]

I run Batrium. Batrium is "cell based" rather than battery based. For example, I have 8 batteries of 14s = 112 cells. I tell Batrium that it's 14 cells per battery so it knows about the overall battery voltage but it's also cell oriented. If ANY cell of the 112 get's out of bounds a "Critical Event" is fired and this can be used to trip the shunt.

Here's a portion of the cell oriented settings page - notice I list 112 cells oriented as "Nom Series" = 14 (e.g. 14s).
I have 3.10v/5C as the low trip point and 4.16v/40C as the hi trip point.
View attachment 104603
If ANY cell goes above/below these thresholds a "Cricital Event" state truns on - which I hare associated with Relay 1 to trip the shunt.
View attachment 104604

There are also 'battery bank level' events you can set such as max hi and low voltage to fire events - but primarily I think of Batrium as cell level monitoring.

In youre case you probably will have 16s? per battery. If you have 2 batteries it would be 32cells with "Nom Series" = 16 type of thing.

Hi, yes, in my scenario each of the 2 batteries will have 16S with each 16S having its own K9. Each cell will be paralleled then combined to make the 16S and that repeated again to make the 2nd 16S. Given my scenario, is it that the Batrium will disconnect the entire battery bank or only the low SOC 16S battery?

 

[OffGridInTheCity]

Hi, yes, in my scenario each of the 2 batteries will have 16S with each 16S having its own K9. Each cell will be paralleled then combined to make the 16S and that repeated again to make the 2nd 16S. Given my scenario, is it that the Batrium will disconnect the entire battery bank or only the low SOC 16S battery?

Neither. Batrium will let you toggle an external relay or send a pulse to a shunt-trip... so it's entirely up to you what happens.

Since you can only use "Critical Fault" on 1 relay, the common use is to have an overall battery bank shunt-trip relay that disconnects the entire entire battery bank till you clear the fault. It's NOT oriented to manage current flow of individual 'batteries' in a battery bank.

Here's my setup - notice the overall battery bank ABB SACE shunt-trip in top left? - that's what Batrium turns OFF if any cell exceeds the parameters I've set - disconnecting the entire battery bank.

 

[rhino]

Since you can only use "Critical Fault" on 1 relay, the common use is to have an overall battery bank shunt-trip relay that disconnects the entire entire battery bank till you clear the fault. Its is NOT oriented to manage current flow of individual 'batteries' in a battery bank.

So if you didn't want to disconnect both 16S battery banks that is not possible because as you said there is only 1 critical fault on 1 relay.. so if you set that up to only turn off relay for one bank there would be no way to trigger a critical fault on the 2nd battery bank if something happens to it?

 

[Henderson]

Neither. Batrium will let you toggle an external relay or send a pulse to a shunt-trip... so it's entirely up to you what happens.

Since you can only use "Critical Fault" on 1 relay, the common use is to have an overall battery bank shunt-trip relay that disconnects the entire entire battery bank till you clear the fault. Its is NOT oriented to manage current flow of individual 'batteries' in a battery bank.

Here's my setup - notice the overall battery bank ABB SACE shunt-trip in top left? - that's what Batrium turns OFF if any cell exceeds the parameters I've set - disconnecting the entire battery bank.
View attachment 104607

Ahhhh, I see. Ok, I think this makes sense now. So if I'm understanding you correctly. I shouldn't be mixing multiple capacity batteries to the same Batrium system then?

 

[OffGridInTheCity]

So if you didn't want to disconnect both 16S battery banks that is not possible because as you said there is only 1 critical fault on 1 relay.. so if you set that up to only turn off relay for one bank there would be no way to trigger a critical fault on the 2nd battery bank if something happens to it?

Correct.

 

[OffGridInTheCity]

Ahhhh, I see. Ok, I think this makes sense now. So if I'm understanding you correctly. I shouldn't be mixing multiple capacity batteries to the same Batrium system then?

No, you can parallel multiple capacity batteries. The weaker ones (and the cells in it) will be bolstered by the stronger ones. Of course it's best not to have a huge difference as it will stress the weaker ones. This is why most of use try to have each parallel battery at similar capacity.

Let's say you had a 16s with 200ah cells and a 16s with 100ah cells - that's a huge difference. But 16s w/200ah cells and 16s w/180ah cells - not so bad.

You can also reconfigure the 2 existing 16s battery as a single 16s - and then plan for the next one to be much closer. That's essentially what happened in my case. After creating battery 1 - I just made battery 2, 3, ... to be the same ah by being deliberate in my ordering.

 

[jtvt]

The thing here is that you are not going to be wanting to disconnect just one string because you can't just randomly add that string back. You can't because voltages will change with continued use and be mismatched. If you parallel strings with widely different voltages, you may see a huge amperage flow with the higher voltage string trying to charge the lower voltage string. This is one of the reasons people use a single shunt trip to disconnect all strings. Also, if you disconnect just one or more strings, you may find that the strings still online can't power your inverter or loads because current draw will be outside of the battery specs. Toggling single strings on and off introduces a bunch of issues and IMO not worth it.

The batrium should work fine with similar sized strings. I'm not sure with widely different sizes especially when cells of one of the strings gets toward the knees. IIRC, dissimilar size strings work OK until you get to about 20% SoC. Generally, I think it's something to avoid.

 

[Henderson]

Thanks for the feedback all. This is all very good information.