Fuse size for prismatic cell bank?

[tammons]

I am building a few 12v 4S battery boxes using prismatic cells to power refrigerators/freezers when the power goes out, and for general use camping etc, and I am confused about the main fuse size for the + battery terminal.
So far I have built a 100 amp with the cells and BMS scavenged out of a Renogy battery and it is working great. Right now I have a 150 amp fuse on it. I have a 120 amp anderson plug (which is also fused) feeding a 1200 watt PSW inverter. All the accessory plugs/outlets are fused to around 120% +- of the outlet rating.

I am in the middle of building a 150 amp box and almost finished. Originally I thought a 200 amp fuse for this one, but now with a 1200 watt inverter, I am thinking a 150 amp main fuse would be best. Would this be correct? This one has a built in 1000w inverter but will run up to 1200 watts.

Next will be a 300 amp 12v 4s box. This one I doubt I will ever use the full 300 amps, so do I size the main fuse for the heaviest load I expect to encounter or main fuse it at 300 amps?

Thanks

 

[FilterGuy]

feeding a 1200 watt PSW inverter.

There is the key to the fuse sizing.

The inverter will be drawing 1200W/12V = 100A. Fuses should be run at 125% of the max continuous current so the proper fuse size is 125A. The wires between the battery and inverter should be sized for 125A as well.

Since it is a PSW, we could argue that the fuse and wiring should be larger due to the phantom load but for this system 125A is probably fine.

Next will be a 300 amp 12v 4s box. This one I doubt I will ever use the full 300 amps, so do I size the main fuse for the heaviest load I expect to encounter or main fuse it at 300 amps?

Fuse to the load.... not the battery capacity.

 

[tammons]

The next question is... I have a battery terminal fuse and also a fuse for the 120 amp anderson connector.
I have been thinking having both is redundant?

 

[FilterGuy]

The next question is... I have a battery terminal fuse and also a fuse for the 120 amp anderson connector.
I have been thinking having both is redundant?

Yes but..... What kind of fuse are they? What is their interrupt rating?

 

[robbob2112]

Just a sample to look at

My cpap backup also does the fridge in a pinch. My fridge is newer and draws around 300w. The cpap draws between 10w and 90w. Both cycle a lot.

In real life the cpap uses 270Wh in 10 hours. The fridge runs 14 hours on 1100Wh or so. Just have to keep the door closed.

I did this 8 months ago and have only used it once for the fridge but I use it every night for the CPAP.

Technically the wire should be 4awg to the inverter and the fuse should be 100amp, but since I never intend to use it close to limits I haven't taken tome to change those. I could also just swap the fuse to 80amps and be good.