Need help choosing breakers, dc cutoff switch and busbars.

[Danny1987]

Hi all,

I need some help with choosing the breakers and dc cut off switch and bus bars.

So far I’ve purchased the Growatt 12k inverter, 4 EG4 48volt 100ah batteries. 400 amp t class fuse. 15 amp inline mc4 fuse. 1/0 awg wire. 2 awg wire and PV wire.

2awg wire will run from the batteries to bus bars(parallel). Wires will be same length.

1/0 positive from bus bar to t class fuse to inverter. Negative from bus bar to inverter. Is DC breaker needed between batteries and inverter?



For this setup will 300amp bus bar be enough or higher?

AC and DC breakers amp size? Double pole breaker? Growatt 12k max PV input 2x 3500 watts = 7000w

and a DC cut off switch amperage/wattage size?

Will be connecting to the grid (240v) to recharge the batteries. Solar will be only be 4 or 6 panels for now, due to lack of space.

Please share any advice, tips or concerns. Thanks for all the help.

 

[rmaddy]

Each EG4 48V 100Ah battery has a max continuous discharge current of 100A. Each provides its own 125A breaker. Normally you would want to fuse each parallel battery between the battery and bus bar. Since the EG4 has its own breaker, in theory adding a fuse is redundant and unnecessary.

2AWG wire between each battery and the bus bars is fine for the 100A of each battery and it is safe for use with a 125A breaker.

Make sure the 4 sets of battery/bus bar wires are all the same length, unlike your diagram. You want the same amount of resistance to each battery.

Assuming a Growatt 12k is a 12kW inverter then at 48V it can pull 12kW / 48V / 85% efficiency = 300A battery draw. A 400A Class T fuse would be good between the battery bank and the rest of the system. You don't need a DC breaker between the bus bars and inverter. The Class T fuse is enough.

4/0AWG wire, not 1/0AWG wire, is needed between the bus bars and inverter. This includes the wire on both ends of the Class T fuse. 1/0AWG is only good for about 175A. You can have up to 300A.

Your bus bars must be rated higher than the 400A fuse. You do not want the bus bars to be the weak point. I would recommend 500A bus bars given the 400A fuse.

It's unclear what your solar panel arrangement will be. The diagram seems to show a 4S arrangement but you mention maybe having 6 panels. You do not need an inline fuse with the 4S arrangement. Even if you go to 3S2P you do not need any fuses for the PV. It is helpful to have a DC breaker to act as a disconnect between the panels and SCC. Most people choose a 2-pole breaker. Make sure it is rated for enough DC voltage for your panel arrangement and sufficient amperage that it won't trip under normal use, again determined by the final panel arrangement. At 4S you need something that can handle at least 200V and say 20A or more. Higher amps is fine since it is not there to protect anything, just act as a disconnect.

I don't think you need an AC breaker between the inverter and main panel. The main panel should have a sufficient main breaker. I don't have experience with 240V so someone else will need to address those details.

 

[Danny1987]

Thanks!

 

[Rosstafarian]

I think you will need some king of an interconnect switch/generator switch between the main and the inverter. Assuming you still have grid power coming into your panel?

 

[WYtreasure]

Do you intend to send power to the grid or not? It looks like no & I think that is a smart move.

 

[Danny1987]

No power is sent to the grid at any time. Also, grid power is cut off at the main 100amp breaker before the inverter power to the main panel is switched on.

 

[Rosstafarian]

I wanted to do it the way you have planned. I am in process of building a sub panel with “critical” loads. I don’t think my inverter (the same one you have) can run ALL my loads. Also, without an interconnect switch it could get pretty exciting if both sources of power are feeding the same panel. For 50 or 70 bucks it’s a cheap insurance policy.

 

[Danny1987]

The Growatt had no problems running the 2.5 ton A/C, 6 gallon craftsman shopvac, air compressor, plus fridge, chest freezer, led lights, and whatever else was ON in the background. I was quite impressed with it’s performance. I had no appliances left to plug in for the overload test. It powered everything I threw at it.

 

[Rosstafarian]

That’s encouraging to hear!
I have 2 a/c units/heat pumps, 3.5 ton and a 4 ton.
What size breaker did you install in your panel?
Re thinking how I’m setting my system up, maybe put the larger non solar loads on the sub and the critical loads on the main.
Thanks

 

[Rosstafarian]

Also, how did you end up fusing your batteries?

 

[WYtreasure]

No power is sent to the grid at any time. Also, grid power is cut off at the main 100amp breaker before the inverter power to the main panel is switched on.

My inverter power goes directly to a new panel which feeds 100% new wiring, outlets, switches and fixtures. That new panel could be considered my "critical load panel".
My AIO (All In One) unit is a Hybrid. I believe the term "Hybrid" means it can charge from the grid or a generator. I don't care what it's called, I just know I can send up to 30Amps of grid power to charge to my batteries via my AIO with the flip of a safety switch. ?

 

[Danny1987]

Also, how did you end up fusing your batteries?

T class fuse 400 amp

 

[Danny1987]

My inverter power goes directly to a new panel which feeds 100% new wiring, outlets, switches and fixtures. That new panel could be considered my "critical load panel".
My AIO (All In One) unit is a Hybrid. I believe the term "Hybrid" means it can charge from the grid or a generator. I don't care what it's called, I just know I can send up to 30Amps of grid power to charge to my batteries via my AIO with the flip of a safety switch. ?

Growatt is offgrid but it will charge the batteries from grid if connected. Yours might he able to do net metering(just a guess).

Maybe folks with exerience with those inverters can comment

 

[WYtreasure]

Growatt is offgrid but it will charge the batteries from grid if connected. Yours might he able to do net metering(just a guess).

Maybe folks with exerience with those inverters can comment

I choose not to connect to the grid. Use it if needed yes, feed it no.