Breaker/fuse size question

[TimC]

I'm building two 48v 75 aHr LiFePo4 batteries that I will wire in parallel to a Growatt 3000ES hybrid inverter. I'm using 18" (one way) of 4awg. I'm trying to size a breaker/fuse just downstream of the battery bank. I'm confused by the calculations for determining fuse size. I will pull no more than 12a @ 120v from the inverter.

One suggestion is to use a Class T which seem to start at 200a.
Another suggestion was this calculation... 3000w / 48v * 1.25 = 78amp

And can I use a breaker like this - 63a double pole? Smseace 63a DP breaker

 

[Darren67-72]

"Downstream "... meaning between the batteries and the inverter?
I have purchased 100 and 150amp t-fuses on the Am..z.n.
The breaker you linked is appropriate use. For the system.

 

[TimC]

"Downstream "... meaning between the batteries and the inverter?
I have purchased 100 and 150amp t-fuses on the Am..z.n.
The breaker you linked is appropriate use. For the system.

Yes, the plan is to have the breaker as close to the + side of the battery as practical before the inverter.

 

[Darren67-72]

T-fuses are the recommended short circuit/ fault safety. With your power level, one might think the breaker will be fine. Just remember not to use the breaker as a switch, while under load. It can cause excessive degradation.
That's my thoughts

 

[Darren67-72]

Keep in mind, your 150ah battery could provide over 100amp @48vdc or more if you ever use it to start a large inrush appliance. 3000w x2 likely surge.

 

[TimC]

Thanks again Darren. This system is to charge an EV at Level 1, 12a, 1.4kW. It will also serve as a backup for grid outages to power a fridge and in the winter a furnace, but, never at the same time as I will only have one 120v outlet wired to it. I think I will stick with the 63a breaker. I have a similar one, a 25a dp, in a waterproof case that I'm mounting on the back of my solar array as a emergency shut off. I'll order the 63a with the same type of enclosure as I don't really like how some people just mount the breaker on a DIN rail and leave it exposed.