4S battery, Fuse or breaker?

[Azycray]

System background: Just finished assembly yesterday, Growatt 5k inverter w/transformer to split phase, 4 Renegy 320w panels and 4 LiTime 12v 230ah in series. The issue that prompted this was a microwave and a toaster oven running at the same time, before dinner so no direct sun anymore. This morning I tested the microwave at 1600 watts and the toaster at 1500, these both running have never been an issue on grid with a 20 amp breaker. But when I do the math, they should be pulling 25 amps, so I can't explain that. Running on solar from batteries it didn't pop the breaker in the Reliance transfer switch, it popped the 50 amp DC breaker (cheap and undersized). Doing research this morning I find out I should be using a 62.5amp breaker using a .25 surge factor. Also I should be using a class T fuse instead? I get on the horn with Sig Solar and speak with "technical support", he asks what I'm using and I tell him the Growatt 5k and he puts me on hold to research and comes back to tell me I need a 200amp breaker. I said you don't even know what batteries I'm using, he made an assumption. I told him I have 4 12v in series (which they are rated for) and rated at 200 amps continuous discharge. He puts me on hold again and come back with the same recommendation. I told him that in 4S the continuous discharge would drop to 50 amps, correct me if I'm wrong. He stuck to his recommendation so I thanked him for his "help". That brought me here, in the recent past coming here I know there is a wealth of knowledge and this one should be fairly easy to solve. The choice is a class T fuse, suggested rating of 62.5 amps so I'm guessing a 60 will work but is a 70amp too large? Or, I'm also looking at a Blue Sea Systems 60 breaker. I realize I have a lot more potential to add more panels and batteries but this is what I have right now. I'm looking for oppinions, what should I use? Thanks in advance, RJ

 

[Azycray]

On another note I found out I shouldn't put anything on the battery bank negative except the cable when using a shunt. In addition to some small connections for volt meters and battery balancer I have an AC to DC charger attached there also. Should I move all of them to the inverter side of the shunt? And what about the positive side, is it OK to leave the charger hooked up on the battery or should I move it also to the inverter side of the fuse /circuit breaker discussed above?

 

[TacomaJoe]

In 4S the current doesn't divide. If the inverter needs 200A, that current will be the same in each battery. I have a 12V system with my batteries in parallel and in my installation, the current does divide between the batteries.

On the battery negative post, only the shunt should be connected. Any other wire on the negative post will not be read by the shunt and will give you bad data.

 

[Azycray]

In 4S the current doesn't divide. If the inverter needs 200A, that current will be the same in each battery. I have a 12V system with my batteries in parallel and in my installation, the current does divide between the batteries.

This is how I understand it, in parallel the volts stay the same, the watts increase. So one 12v battery is 12.8v x 200amps (continuous rating) would be 2560 watts. In parallel they would stay 12.8v but the watts would increase to 10,240w, simply multiply 4, the number of batteries in parallel by the single battery watts. Volts x amps = watts, right? In series the voltage goes up but the watts stay the same. So four of the same batteries in series would be 2560 watts, that stay the same, divided by the volts 51.2v = 50 amps. I'm not considering what my inverter can do with more input, I need to figure what my battery can deliver and protect it with the properly sized breaker or fuse. I might have to limit how much I demand from the inverter until I get more power coming in or more storage, but I need to use the proper size fuse for my current (no pun intended) storage capacity. In a 48v configuration, the amps go down to 50.

 

[TacomaJoe]

So one 12v battery is 12.8v x 200amps (continuous rating) would be 2560 watts. That is correct. Now put two in parallel and you have 12.8V X 400A for 5120W. Take the same two in series and your bank is 25.6V x 200A for the same 5120W. Same watts whether in series or parallel.

With that said, take a 5kW inverter powered with a 51.2V (4 in series) bank it would pull about 100A and need wire/fuse for that current. A different 5kW inverter (I don't know if they exist, nor would I use one) powered with a 12.8V bank would pull 400A needing bigger wire and fuse.

My trailer has a 2kW inverter on a 12.8V bank of three 280Ah batteries. At 2kW (full power) I would pull 150A which splits 3 ways so each battery is providing about 50A. My batteries aren't be taxed very heavily with BMS capable of 150A each.

Now back to the original post. The microwave and toaster add up to 3100W and would pull about 60A in the perfect world but the system isn't 100% efficient and I would guess closer to 75A. That is minimum for 3100W, you should plan wire size and fusing to cover the full 5000W.

 

[mikefitz]

Your 4 off 12v 230Ah batteries store around 12000 watt hours of energy. Maximum current output delivery 200 amps. The current maximum for similar batteries in series is the same as a single battery.
A 5000 watt inverter in a 48 volts lithium system will pull 100 amps at full power, add 10% for losses and fuse at 125%, nearest fuse value 150 amps. Use a class T fuse and cables 1AWG to the inverter and battery interconnections.

With a full battery, your microwave and toaster together will run for almost 4 hours before a recharge is needed.

 

[mikefitz]

Duplicate post made in error

 

[Azycray]

So one 12v battery is 12.8v x 200amps (continuous rating) would be 2560 watts. That is correct. Now put two in parallel and you have 12.8V X 400A for 5120W. Take the same two in series and your bank is 25.6V x 200A for the same 5120W. Same watts whether in series or parallel.

With that said, take a 5kW inverter powered with a 51.2V (4 in series) bank it would pull about 100A and need wire/fuse for that current. A different 5kW inverter (I don't know if they exist, nor would I use one) powered with a 12.8V bank would pull 400A needing bigger wire and fuse.

My trailer has a 2kW inverter on a 12.8V bank of three 280Ah batteries. At 2kW (full power) I would pull 150A which splits 3 ways so each battery is providing about 50A. My batteries aren't be taxed very heavily with BMS capable of 150A each.

Now back to the original post. The microwave and toaster add up to 3100W and would pull about 60A in the perfect world but the system isn't 100% efficient and I would guess closer to 75A. That is minimum for 3100W, you should plan wire size and fusing to cover the full 5000W.

Thanks TJ and mikefitz, the light bulb is close to going on over my head. I have over sized all my cables. I have run 1/0 into the inverter, and every cable in the series connections, that should carry 150 amps. I just ordered a couple of 150 amp bus bars to add another 48v bank of storage in the future. Should I stick with the 230ah I already have, or since they will connect to a bus bar, could I jump up to 280ah? But for now, my 50 amp breaker needs to be replaced with a 150 amp class T fuse between the bus bar and the inverter. And when I want to run the AC charger my connections on the negative side should be between the shunt and the inverter. On the positive side, should I connect the charger between the fuse and the inverter? If not, what would be best? Thanks again for your help, RJ