Battery set up and configuration

[mrolrac]

Hi Everyone, I am relatively new to solar....I currently have a 48v 10kw hybrid inverter with 3 x 48v 5kw Lifepo4 rack batteries connected in parallel to each other and connected to the inverter.

I want to add further storage capacity to the system and have bought 32 x 304ah Eve cells for this purpose.

What is the most efficient way to connect these, both in terms of electrical wiring and also laying out the cells to make the connections as easy as possible.

To make the packs physically manageable in case I need to move them at some point, I was thinking of making 8 groups of 4 cells 2P2S( not sure if 2P2S is the correct term ?) , then connecting the 8 groups together in series and finally connecting in parallel to the inverter alongside the 3 x rack batteries. The wiring / best layout for this is overwhelming me somewhat.

Any guidance on how best to do this would be very much appreciated.

Thanks

 

[MaikaiLifeDIY]

I’m not sure about the specs on those batteries, but typically mixing chemistries in the same battery array is not a great idea. Since the chemistries will have different characteristics, the inverter will have a harder time, recognizing whether or not there reaching the various stages of the charge cycle.

If I’m understanding you correctly you’re attempting to make 48 V batteries with the additional batteries that you purchased by wiring them together in series?

 

[MaikaiLifeDIY]

It’s also best to provide some links to the equipment that you purchase so that people in the forums can easily locate the information

 

[DIYrich]

I want to add further storage capacity to the system and have bought 32 x 304ah Eve cells for this purpose.

Two 48v battery banks made up of 16 cells each.

Each bank gets its own BMS, wire to BusBar, and Class T fuse. Treat the 3 5kW LIFEPO4 rack as one more "Bank".

The 3 banks will be roughly equal in capacity to/from the busbar.

10kW is roughly 200 amps, so a 200amp BMS should work. I believe 2/0 wire between each "Bank" and the Busbar, and a 200 amp Class T Fuse.

BTW: If you are going to move the batteries, you will probably want to completely disassemble down to individual cells. Each cell weighs 12 pounds. While you can lift 4, I wouldn't want to lift 4 and not put any stress on connectors. Hence move each battery separately.

 

[mrolrac]

I’m not sure about the specs on those batteries, but typically mixing chemistries in the same battery array is not a great idea. Since the chemistries will have different characteristics, the inverter will have a harder time, recognizing whether or not there reaching the various stages of the charge cycle.

If I’m understanding you correctly you’re attempting to make 48 V batteries with the additional batteries that you purchased by wiring them together in series?

Thx....all batteries are LifePO4....yes, I have a 48v 10.2kw inverter and the 3 x 5kw rack batteries are each 48v and connected in parallel to each other and then to a main breaker and the inverter.

 

[mrolrac]

Two 48v battery banks made up of 16 cells each.

Each bank gets its own BMS, wire to BusBar, and Class T fuse. Treat the 3 5kW LIFEPO4 rack as one more "Bank".

The 3 banks will be roughly equal in capacity to/from the busbar.

10kW is roughly 200 amps, so a 200amp BMS should work. I believe 2/0 wire between each "Bank" and the Busbar, and a 200 amp Class T Fuse.

BTW: If you are going to move the batteries, you will probably want to completely disassemble down to individual cells. Each cell weighs 12 pounds. While you can lift 4, I wouldn't want to lift 4 and not put any stress on connectors. Hence move each battery separately.

Thx....Your suggestion was what I was originally thinking, 16 cells in series in each string with its own BMS and balancer and then adding both strings in parallel along with the existing 3 rack batteries. However, I have now been told (by Daly) that doing that requires each BMS to have a parallel module installed to maintain a balance between the BMS on each separate string. Having reviewed a configuration variation table provided by one of the forum members , I think the 2P16S (parallel first) configuration on P9 (variation B)) suits my space best, it requires only 1 BMS and doesn't require any parallel modules, so I will probably go with that set up....just need to work out the BMS wiring sequence now....

 

[mrolrac]

Two 48v battery banks made up of 16 cells each.

Each bank gets its own BMS, wire to BusBar, and Class T fuse. Treat the 3 5kW LIFEPO4 rack as one more "Bank".

The 3 banks will be roughly equal in capacity to/from the busbar.

10kW is roughly 200 amps, so a 200amp BMS should work. I believe 2/0 wire between each "Bank" and the Busbar, and a 200 amp Class T Fuse.

BTW: If you are going to move the batteries, you will probably want to completely disassemble down to individual cells. Each cell weighs 12 pounds. While you can lift 4, I wouldn't want to lift 4 and not put any stress on connectors. Hence move each battery separately.

PS....I only envisage slight movement (if necessary), I will have the battery groups well taped together both for compression and to make any movement easier, I am also using 2AWG cable and flexible busbars to avoid any terminal stress either during expansion / contraction of the cells or if a group has to be slightly moved, but thank you for highlighting the potential for a problem

 

[DIYrich]

However, I have now been told (by Daly) that doing that requires each BMS to have a parallel module installed to maintain a balance between the BMS on each separate string.

Parallel batteries, by the physics, maintain balance between the battery banks. They are all at the same voltage. If one deviates, the others add or take power to rebalance.

 

[mrolrac]

Parallel batteries, by the physics, maintain balance between the battery banks. They are all at the same voltage. If one deviates, the others add or take power to rebalance.

Thanks....that's where I got to with my thinking....It seems Daly is just trying to sell a new product to solve a problem that doesn't materially exist, particularly if one applies care with voltages and SOC when adding batteries / cells together....what do you think of the 2P16S vs 2 x 16S?..the cost of an extra BMS and balancer is the obvious downside of the latter, but are there any other considerations that would make one approach more attractive/beneficial than the other? Thanks

 

[DIYrich]

Thanks....that's where I got to with my thinking....It seems Daly is just trying to sell a new product to solve a problem that doesn't materially exist, particularly if one applies care with voltages and SOC when adding batteries / cells together....what do you think of the 2P16S vs 2 x 16S?..the cost of an extra BMS and balancer is the obvious downside of the latter, but are there any other considerations that would make one approach more attractive/beneficial than the other? Thanks

BMS is 200 amps. With one BMS (2p16s), you are limited to 9,600 watts (just shy of your inverter 10kW).
With two 16s batteries, each with its own BMS, either battery can supply the 9,600 watts, and max out the inverter with both.

Also, it will look like you have 3 15kw banks (treating the 3 rack batteries you have as one bank). They should be worked more evenly that way.

Two is One, and One is None. Three is better.

BTW: 2 amp active balance is spread over 4,864 amps of a 16s 304ah battery. The balancing time will double in a 2p configuration (double the amps to balance). Not a real issue once they get into balance. The initial balance may take a while. Note: You are not balancing the full 4,864 amps. More likely the last 1-3% when balancing kicks in.

 

[mrolrac]

BMS is 200 amps. With one BMS (2p16s), you are limited to 9,600 watts (just shy of your inverter 10kW).
With two 16s batteries, each with its own BMS, either battery can supply the 9,600 watts from either bank, and max out the inverter with both.

Two is One, and One is None.

Many thanks...I have purchased a Daly 300a 16S Smart BMS and Smart Active Balancer which I believe is capable of maxing out the inverter ?....I take your point about redundancy, although I am not so worried about that aspect as I have the other 3 x 5kw rack batteries connected in the system. I have no experience with these BMS, so I don't know how reliable they are? or if they are prone to regular failure? that would be a deciding factor for me....the cost of 250 Euros for another BMS isn't an insignificant aspect of the equation either.

 

[DIYrich]

I have no experience with these BMS, so I don't know how reliable they are? or if they are prone to regular failure?

They seem to be pretty reliable (once you get past the 30 day break-in period), just like most electronics. The either fail early, or last. Since it is 300a, you are not pushing it to the limit with a 10kw inverter.

Note: 300a wire is big. Hard enough working with 200a wire.

 

[mrolrac]

They seem to be pretty reliable (once you get past the 30 day break-in period), just like most electronics. The either fail early, or last. Since it is 300a, you are not pushing it to the limit with a 10kw inverter.

Note: 300a wire is big. Hard enough working with 200a wire.

Thank you, that's very useful to know....would doubling up 35mm (2AWG) cable be more workable than using 300a wire and most importantly, sufficient for purpose...From your earlier comment, I assume my 10.2kw inverter is only capable of around 220 amps max, in which case is 35mm cable sufficient ?