Parallel balancing

[etn06448]

I need advice from the experts. Is parallel balancing a bad idea? I have 8 LG 9.8kw ESS batteries (14s). The plan is parallel them and connect to a 5K charger/inverter (Outback Skybox). Rather than using 8 separate 80A Daly BMS, I'm thinking of using one 400A BMS with a 2A active balancer using the rig i put together. That way, the active balancer can do the bulk of the balancing and not just top balance and the BMS can protect the batteries.
Please give me suggestions. Thanks

 

[MisterSandals]

The plan is parallel them and connect to a 5K charger/inverter (Outback Skybox).

@Ampster is the only Skybox user that i've seen. Maybe he will respond to this incantation. A better title with "Skybox" or "ESS batteries" might have caught the eye of folks who have experience in those niches.

In the meantime, do a search on this site for "Skybox" or a few variations of your particular batteries.

 

[Ampster]

@Ampster is the only Skybox user that i've seen. Maybe he will respond to this incantation..........

Thanks for the magic spell @MisterSandals/
@etn06448 , tell me more about those battery packs? I understand you have eight batteries that are 14s? I saw the pictures of the circuit boards you posted but they don't tell me much about the batteries.
To answer your question about paralleling the only answer I can give without more information is that there are many ways to parallel batteries and each have their pros and cons. I currently have Nissan Leafe modules that I put together in 9 parallel groups which created a pack of 18P 12S. I chose that configuration because it was convenient and the modules were easy to configure that way. I have one BMS.
When you say you have eight 9.8 kW packs do you mean kWhs? How are the cells arranged to get to 14S? Are there lots of little cells or just 14 big cells in series?


Later we can get into the interface with the Skybox.

 

[etn06448]

The batteries I got from Battery Hookup. I have included the information below as it has been referenced in another thread.
https://diysolarforum.com/threads/lg-chem-51-8v-189ah-ess-battery.5490/
I have assembled the BMS lead breakout board (see https://secondlifestorage.com/showthread.php?tid=8454). So now I have 8 batteries, each is 9.8kWhs . I have not taken these batteries apart thus don't know how many cells in parallel but I know for sure each is 14s.

The main positive and negative of each battery of 9.8kWh will be connected to a positive and negative busbar and from there to the Skybox. Since I have the balance leads of each pack, I'm thinking of combining the balance leads of all 8 together using the board I put together, and then to the BMS. In other word, there are 15 BMS leads from each battery. I'm connecting all 8 lead of group 1's together with lead 1 of BMS, all 8 lead of group 2's together with lead 2 of BMS, etc.

Thanks for all the help.

 

[Ampster]

The batteries I got from Battery Hookup. I have included the information below as it has been referenced in another thread.,,,,,,

That was helpful. I don't need the other details now that I understand that battery more.

The main positive and negative of each battery of 9.8kWh will be connected to a positive and negative busbar and from there to the Skybox.

The DC breaker on the Skybox is 125 Amps so even if you have two of those eight out of the pack for maintenance the most any one battery would see would be 30 Amps so the answer to your earlier question is that eight 100 Amp BMSs would work fine. I will address the question of combining them and using one BMS further below.

Since I have the balance leads of each pack, I'm thinking of combining the balance leads of all 8 together using the board I put together, and then to the BMS. In other word, there are 15 BMS leads from each battery. I'm connecting all 8 lead of group 1's together with lead 1 of BMS, all 8 lead of group 2's together with lead 2 of BMS, etc.

The issue you are going to run into is eddy currents between the all of the group 1 cell groups and so on through all the other 7 groups.. Those may be substantial and to allow for that you should fuse those wires and increase the wire size substantially. The big unknown is how balanced those packs are and as far as I understand it there is no way to dissasemble them to put each group in parallel to top balance them. The best strategy is to use 8 BMSs even though that is more costly it is the only way you are going be able to get the data on how each of those packs is performing. A similar issue exists with Tesla modules and my BMS manufacturer actually wrote a technical article that explains it in more detail if you are interested.

 

[etn06448]

That was helpful. I don't need the other details now that I understand that battery more.
The DC breaker on the Skybox is 125 Amps so even if you have two of those eight out of the pack for maintenance the most any one battery would see would be 30 Amps so the answer to your earlier question is that eight 100 Amp BMSs would work fine. I will address the question of combining them and using one BMS further below.

The issue you are going to run into is eddy currents between the all of the group 1 cell groups and so on through all the other 7 groups.. Those may be substantial and to allow for that you should fuse those wires and increase the wire size substantially. The big unknown is how balanced those packs are and as far as I understand it there is no way to dissasemble them to put each group in parallel to top balance them. The best strategy is to use 8 BMSs even though that is more costly it is the only way you are going be able to get the data on how each of those packs is performing. A similar issue exists with Tesla modules and my BMS manufacturer actually wrote a technical article that explains it in more detail if you are interested.

Thank you for your advice. I was thinking of making things simpler and cheaper. I'll probably will go with 8 ANT BMS or the new Daly smart BMS. Since you have the Skybox, do you know if getting the CANBUS version of the Daly smart BMS would be able to interact with it?

https://www.aliexpress.com/item/4000989135422.html?spm=2114.12010612.8148356.4.791c55e2Sju0M9

 

[Ampster]

Since you have the Skybox, do you know if getting the CANBUS version of the Daly smart BMS would be able to interact with it?

No, not unless Daly. wants to work with Outback on developing a protocol. I originally thought my $600 Orion Jr BMS would be able to talk to the Skybox because they both do CANBUS but it is a matter of using the same words in CANBUS and there is no common CANBUS dictionary. Orion mostly works with the EV community of chargers and they had no interest in developing a CANBUS protocol. It turns out it is not that big of an issue. I already had the Orion BMS when I bought the Skybox or I would have gone with one of those that are recommended on this forum. Lots of good feedback.
Tell me about how you are going to use the Skybox? Do you have a grid tie inverter you will be AC coupling with? Are you adding solar panels to the Skybox? Until recently I have just let it work in the background as strickly backup. Recently I have been using TOU schedule and fine tuning the charging parameters. I am going to try to self consume more and ordered 28 kWhrs of batteries from China to replace my ageing Nissan Leaf pack.

 

[etn06448]

I already have gridtie solar (microinverters panels) and will use the Skybox for AC coupling. The primary reason is for backup and use solar during power outage here in California. I will try to use it for TOU as well if possible. That's my reason for sizing my battery bank of about 70kWh (hopefully as these batteries are supposed to have about 90% capacity remaining).
Since the CANBUS does not work, I will go with just bluetooth monitoring on the BMS. I will need your help and advice on the charging parameters of the Skybox as I am so new at this. It's a fun project, learning quite a bit from everyone in these forums.

 

[Ampster]

I am happy to help. I have spent a little time on the Outback Forum. I was missing a fundemental setting before I could get the TOU setting working and a guy on that forum got me started in the right direction and Outback support was great. I am out of breaker space to AC couple my larger GT system to the Skybox but I have 4 Enphase IQ7s AC coupled. I am going to upgrade that critical loads panel to be able to add the GT inverter to the AC coupling. I wanted to have a larger pack for that because then I think the AC coupling will work better.
I live in Sonoma County and we had several of those Public Safety Power Outages last fall. Arr you with PG&E?

 

[etn06448]

Yep, I'm with PG&E in Contra Costa county. Hopefully my project this weekend would be moving some breakers to make a critical load panel. Now off to order BMS, 4/0 wires, crimper, lugs.

 

[Ampster]

After seeing a few Powerwall installs and some other inverter installs I am a big fan of wiring gutters. My main panel is on the exterior wall of my garage and my subpanels are on the inside wall. I intercepted my circuits and fed them through and upper wiring gutter to the sub panels below the wiring gutters. In some cases the wire was not long enough and it is legal to use wire nuts in gutters because the are considered large junction boxes. You can't do that in electrical panels.

What I also like is the later flexibility to swing circuits from one panel to the next as my needs change. For example currently my AC is on my optional loads panel. When I get my new pack and AC couple my bigger GT inverter I will swing it to my critical loads panel. Good luck with your install.

We have good friends in Dublin that we often visit. He has had a GT system for a while but was coming up short on his PG&E bill so I helped him add 6 panels to his garage with mocros. His brother in Walnut Creek has a couple of Powerwalls and I can see sibling rivalry creating envy. He keeps asking about my Skybox so now that the price has dropped maybe that will be his next project.

 

[etn06448]

I did originally planned to get 3 Tesla Powerwall. They overpromised everything at the time of sale and when installation comes, they told me that only about 1/3 of my loads can be backed up. That along with all the limitations of the Powerwall made me cancel my install and going this route with the Skybox. Hopefully I can have total control of my backup load and TOU. It's a lot more work, hopefully this will work out.

 

[Ampster]

I did originally planned to get 3 Tesla Powerwall. They overpromised everything at the time of sale and when installation comes, they told me that only about 1/3 of my loads can be backed up. That along with all the limitations of the Powerwall made me cancel my install and going this route with the Skybox. Hopefully I can have total control of my backup load and TOU. It's a lot more work, hopefully this will work out.

That was very similar to my thinking. It would also have taken 3 Powerwalls to have given me the energy capacity in kWhs that I wanted. I do not need more than the 5kW power capacity that the Skybox provides. I do spend some time on the TMC forum and am envious of the constant firmware upgrades and the large user base with lots of help from others. I am retired so I treat this as a hobby and I enjoy the learning process.