Battery wiring limits for large systems?

[MattSapp]

I may be using the wrong search terms, but I've been unable to find a definitive answer...

I'm designing an off-grid system that needs significant storage (along with significant number of panels) as it it up at high elevation and short days with snow are not uncommon in the winter.

I've in the past connected multiple 48v 100ah (EG4 LifePower4) batteries by paralleling them and connecting the inverter positive to the "top" battery and the inverter negative to the "bottom" battery. I've done this with up to four batteries.

Is there a practical limit to how many can be strung together like this, assuming cable sizes are sufficient to carry the load? Could I connect 12 batteries in this manner without worrying about significant imbalances? 24?

 

[marionw]

Ideally with the EG4 LifePower4 batteries you would install 6 each in two 6 Battery EG4 Battery racks. The positive and negative cables from each battery racks bus bars would then through appropriate breakers/class t fuses connect to external bus bars to which the inverter battery connections would also connect to. That is to say each battery rack would be connected in parallel (through appropriate breakers/class t fuses) to a short bus bar external to the battery racks.

With less than 15 batteries you can connect an ethernet cable from a battery in the first rack to a battery in the second rack to "daisy chain" the batteries as long as the batteries in the second rack have addresses not used by the batteries in the first rack. This would allow the "Master" battery to collect data from all batteries and would also allow you to monitor/view all batteries with the "BMS_Tool" software.

Once you add more batteries you might consider adding an EG4 Communications Hub as it can handle up to 30 batteries allowing single point communications to all (You could also use the Hub to connect both racks of 6 batteries as it has two "Bat/BMS" ports)

There is always a chance for imbalance. If you use the "same cable length" between each battery rack's bus bars to the short bus bar (again; appropriate breakers/class t fuses) you will minimize imbalance.

As always, when introducing a new battery into the system ensure the battery is fully charged to the point where the BMS starts cell balancing. You can monitor this with the BMS_Tool.

 

[OffGridForGood]

To build a large ESS I found it easier to use large cell capacity - ie although I do have a couple 100Ah SR packs from my initial build, since making the decision to build a 100kWh ESS, I moved to 280 and 304Ah cells - this reduces the number of packs by about a factor of 3. - per my signature below, I have 99.6kWh ESS with only 8 packs, instead of 19.

 

[millsan1]

Ideally with the EG4 LifePower4 batteries you would install 6 each in two 6 Battery EG4 Battery racks. The positive and negative cables from each battery racks bus bars would then through appropriate breakers/class t fuses connect to external bus bars to which the inverter battery connections would also connect to. That is to say each battery rack would be connected in parallel (through appropriate breakers/class t fuses) to a short bus bar external to the battery racks.

With less than 15 batteries you can connect an ethernet cable from a battery in the first rack to a battery in the second rack to "daisy chain" the batteries as long as the batteries in the second rack have addresses not used by the batteries in the first rack. This would allow the "Master" battery to collect data from all batteries and would also allow you to monitor/view all batteries with the "BMS_Tool" software.

Once you add more batteries you might consider adding an EG4 Communications Hub as it can handle up to 30 batteries allowing single point communications to all (You could also use the Hub to connect both racks of 6 batteries as it has two "Bat/BMS" ports)

This is how I have my 12 batteries connected.

Two, 6 battery racks, positive and neagative on opposite ends.

Connected to this:

Victron Energy Lynx Distributor | 1000A

Signature Solar provides solar panels, off-grid solar systems, grid-tie, and hybrid systems. Quality solar inverters, bifacial solar panels, complete solar kits, solar batteries. Featuring brands such as EG4 Electronics with their solar battery, LifePower4 and EG4 LLifePower4 and EG4 LL

signaturesolar.com

Each connection has a fuse.

The above is conencted to inverter, and wired for generator.

I also have the comms hub, which also works nicely.