2P2S impact on charge/discharge rates

I plan to put 4 of these Lion Energy UT 1200s (photo below) together for a 2P2S 24V bank. How would you configure charge rates and size battery cables and fuses for peak discharge rates?

My assumption would be to double everything so

- discharge rate: 300A max continuous (2P)
- charge rate: 90A ideal with max 200A charge rate (2P) obviously at double the voltage range (2S).

Is this correct?

- Can someone recommend a good fuse for this configuration? Leaning towards 4/0 cable. Starting with 2.4kwh inverter, but plan to double to 5kwh. Will's recommendation of Windy Nation only goes up to 300A. If continuous can go to 300A, then I'd think this should be at least 400A. (EDIT: found 400A ANLs. Can start with 300A and change if needed. But, finding an ANL fuse holder for 4/0 isn't so easy.)

- How about good short cables for connecting in series? I haven't been able to find any really short cables. I was thinking maybe 6 inches.

I plan to buy all cables with lugs on them because I do not have the tools to crimp welding cables.



My current collection of cables and connectors research

I generally use this type of fuse holder connected to the battery with a fuse sized based on the inverter spec. For example, on one old 12V system I have a Xantrex 2000W inverter (3000W surge) that specifically calls for a 250A fuse in the manual. I'd check your inverter manual for guidance.

In your case, even though the batteries can supply huge continuous current, your 2.4kW inverter @ 24V is drawing ~100A from the battery bank if at full load. So a 400A fuse seems too large to me. If the surge rating on the inverter is double the continuous, you're at ~200A. I suspect you're more in the 250A fuse range.

I like to use these cables but the shortest are 12-13 inches depending on gauge.

I have looked at this vendor for short cables but haven't pulled the trigger on any.

Keep your battery interconnects as short as possible but not tight. The size of the batteries & terminal locations dictate lengths, so I can't say how many inches they should be for you. Bars could be an option but not flexible then. Whether you use a Fuse or DC Breaker the inverter documentation is your guide as Bob142 said. Fuses are much cheaper than breakers, so if your thinking an upgrade in a reasonable time frame, go fuse.

Another point on wire, you can use a larger gauge than you need, it won't hurt anything. So if your planning on 5kw with a surge potential of 15 then buy your "expensive" wire for that now, rather than buy more or replacing it later. lesson learned, I started with 2/0 and had to replace and see what it cost me below, penny wise, dollar foolish, eh.

I used 10", 4/0 interconnects for my FLA Bank. 10' for Battery bank to is attached to a 250A Breaker in the E-Panel (recommended sizing by Samlex Docs) with a Blue Sea Switch (cutoff) in between. From the E-Panel to inverter 4' 4/0 cable.

Inverter cables 4/0 AWG, 10 ft (pair), flexible wire, red/black with 3/8" lugs, red cut to 7' & 3' with lugs $192.18
Inverter cables 4/0 AWG, 4 ft (pair), flexible wire, red/black with 3/8" lugs $94.84
Battery interconnect 4/0 AWG, 10", flexible wire with 3/8" lugs $130
* Royal Excelene 4/0 AWG welding cable, black, finely stranded copper, 600V, rated 260 Amp
** Canadian Dollars, May 2019 prices.
Just to give you an example, how fast the cost of quality wire can add up.

Bob142 said:

I generally use this type of fuse holder connected to the battery with a fuse sized based on the inverter spec. For example, on one old 12V system I have a Xantrex 2000W inverter (3000W surge) that specifically calls for a 250A fuse in the manual. I'd check your inverter manual for guidance.

In your case, even though the batteries can supply huge continuous current, your 2.4kW inverter @ 24V is drawing ~100A from the battery bank if at full load. So a 400A fuse seems too large to me. If the surge rating on the inverter is double the continuous, you're at ~200A. I suspect you're more in the 250A fuse range.

I like to use these cables but the shortest are 12-13 inches depending on gauge.

I have looked at this vendor for short cables but haven't pulled the trigger on any.

Click to expand...

Thanks for the links! I like that fuse option. The 6" 4/0 option is nice, too. Added to list.

Steve_S said:

Another point on wire, you can use a larger gauge than you need, it won't hurt anything.

Click to expand...

I'm spec'ing the cables for the 5kW I plan to have later. I believe I am good with 4/0, but am open to hearing if that is enough. Under 7" to fuse from bank, then 12' or less to inverters (with appropriate switches/fuses/breakers).

The load side of the inverters will all go through a breaker panel.

I agree 100%, Steve. There is no reason to spec the cables for 2.4kW only to have to replace them when you add another inverter to the bank. I'm spec'ing this fuse to protect the cables, not the inverters. It's sole purpose is to keep the cables from melting. I'll worry about protecting the inverters independently, which would require independent fuses for each inverter.

I'll likely start with 300A, with the ability to go to 400A when I add the 2nd inverter. While the purpose is to protect the cables, it does not hurt to go lower if it won't trip from normal use.

Thank you both of you for your valuable input and links to new options! This is one part I really want to do right since this is going in my home and will be used 24/7 for years.

Steve_S said:

Another point on wire, you can use a larger gauge than you need, it won't hurt anything. So if your planning on 5kw with a surge potential of 15 then buy your "expensive" wire for that now, rather than buy more or replacing it later.

Click to expand...

Thanks for re-enforcing my decision, Steve!

I was feeling a bit guilty about once again taking things to the extreme... sizing my bat/inv/chg connections with 4/0, and my panels to chgr run with 4 AWG when using 10 for my panel run would have seen a 1.5v drop. 200' of tinned Ancor Marine 4 AWG cable was delivered today. Buy once/cry once