@Camp20144
I read the whole thread again just to have all the details fresh.
I try to take each and all of the specifics and run them all simultaneously against each other, such as design goal, budget, components, how things work, cost, performance, and so on and on till finding the system design golden middle between any and all of the given specifics.
With that said, not certain but this time reading, I've noticed you aren't looking for the cheapest SCC but rather are more interested in the best option for your needs. Is that the case? This might come into play later.
The following is merely my take on your solar build, a mere suggestion or food for thought if you will. Hopefully, you find some of it useful.
Yet, since you are the one who will build, operate and maintain this system, it's mandatory to take the time and learn all the ins and outs of a solar panel system, as your safety is entirely in your hands from the get-go. Ask questions, ask a lot of questions here and in other places such as FB groups etc.
Always triple-check anything and everything anyone, myself included, suggests to you. Run the ideas by other folks in multiple places.
The system voltage part;
Since you already have two 12V 100Ah LiFePO4 batteries and your primary use of this system is to power a CPAP device whose native voltage is 12V, having two batteries in parallel(12V system voltage) is preferable in my opinion. In fact, a system redundancy where possible is a must.
Why?
If you use 2x12V 100Ah in series to get to a 24V system voltage 100Ah capacity, if, for whatever reason one of the batteries stops working your entire system is down. With a CPAP device, I believe this is a big no-no.
Also, on top of that, you would be dealing with either an additional device to keep the two batteries balanced or additional maintenance every 6 months.
With the two 12V 100Ah batteries in parallel to get a 12V system voltage 200Ah capacity, you gain battery storage redundancy where if one of the batteries fails, your system will keep running the device. That's a
in my book.
At this point, things are getting better and better because you could use MRBF fuses now, including for the SCC, Inverter, and even as a main battery terminal fuse.
MRBF is reliable, practical, and compact, but also cheaper than say a class T fuse as a terminal fuse. It has an acceptable Arc breaking capacity @12V/ 10 000A. Heck, If it's safe to be used on boats 100 miles out at the sea, I guess it must be pretty darn safe and reliable altogether.
The nice thing about having 2x 12V batteries in parallel is if you use cables of the same length to connect to a common busbar for both batteries separately, the positive and negative battery terminals, you can fuse each battery separately by a factor of 1.25x max current the battery can deliver. (take BMS rating for reference) See the diagram below.
In doing so, you can use the same gauge wire for these connections, at the same time make sure the charging and load current are equally distributed, and above all, you gain a battery storage redundancy where if one fails, the other keeps running. Also, if one of the batteries stops working, you can take the bad one out till you get the replacement and obviously, keep your system running at half the storage and a reduced inverter capacity in the meantime.
Again, this would not be possible in a 24V system using only two 12V batteries.
Now, the nice thing about the 24V system is that you are dealing with half the amps across the board than you would be at the 12V system. Yet, up to 1500W AC
(post-Inverter efficiency losses and cutout voltage calculation), amps should be very manageable at a 12V system with 200Ah capacity.
More specifically, you've said previously that your biggest planned load is a 900W microwave for a few minutes run so this should not present any problem for such a battery bank in my humble opinion.
To be continued...
I'll wait till you read this post to see what are your thoughts on this before proceeding to the SCC/solar panel part.
Best,
D.
