Wow! What a huge topic! But one near and dear to my heart, as i am currently approacking a long-considered overhaul of my 12v system.
Here's answers to a couple of your questions:
What MPPT charge controllers is everyone using?I am using a Midnite Solar "KID" MPPT controller, with two 100W panels in parallel, soon to be upgraded to two 200W panels. The KID can handle up to about 600 watts on a 12V system.
I was originally given BAD advice by Midnite Solar regarding the need for their optional "WhizBang Jr" current sensor. Their experience seems to be more focused on off-grid type installations with separate charge and load busses, and they don't really understand the unique needs of a marine installation. At any rate, the lack of a proper battery current sensor virtually guaranteed that I would consistently overcharge my batteries because the charger couldn't distinguish between the current charging the battery and the current being consumed by the boat's house loads such as refrigeration. The end result was that I destroyed an expensive pair of Gel Cells in two years when the previous pair had lasted me ten years! I am in the process of adding a WhizBang Jr sensor which will allow me to program the charger to terminate the acceptance phase when the battery's charge current drops below a specified limit instead of using an arbitrary timer.
Battery monitor? Which one's are you currently using and do you like it? Accuracy?I installed the Xantrex LinkPRO battery monitor years ago, and I use it constantly while we are out cruising. The interface is somewhat cumbersome, but it works. I tested the voltage calibration against two different high quality DVMs and all were in agreement. Have not tested the current reading accuracy but have no reason to question it. If I were doing it over today, I might pick the Victron.
Alternators? Stock or larger Balmar etc?I replaced the Mando 55 Amp alternator that came with the boat with a 110 Amp Amp-Tech alternator. Because of the low speed that my Atomic 4 engine spins its alternator, I will never see 110 amps of output. When starting cold into a partially discharged battery bank, It briefly gets up to 60 amps, then quickly comes down to a bulk charge rate of about 40 amps. This is to be expected. The benefit of the larger alternator is that it is not running anywhere close to its maximum output and runs cooler and will last longer. I use a Balmar MC612 external regulator to control it. The Balmar is almost infinitely programmable, but has the same flaw that plagued my Midnite Solar installation: No battery current sensor! Thus, there is NO possible combination of settings that will always fully charge without frequently overcharging! Flooded batteries can tolerate this, if they are kept well watered, but Gel Cells cannot! They incur some permanent damage each time they are overcharged. (And Lithium's are even worse, suffering catastrophic failure if they are allowed to overcharge.) Again, if doing it over, I would consider the Wakespeed WS500 alternator regulator, as its the only one I have been able to identify that uses a battery current sensor.
Batteries- How many and where did you tuck them away?Saved the biggest item for last.
The house bank currently consists of two 100 amp-hour Group 31 deep cycle
Gel Cells (NOT AGM!) wired in parallel. A separate 32 amp-hour U1 gel cell is used for a starter battery. All three batteries are located in the port-side cockpit locker. This provided a house bank of about 200 amp-hours. But since you should not discharge lead-acid batteries below 50%, this means that there is only about 100 amp-hours of usable capacity. Further, since the last 20% of charging is the acceptance phase, which can take hours, it means that unless I plug into shore power, I rarely have the batteries up to more than 80% after the first night. In effect this means that I really only have about 30% (60 amp-hours) of usable capacity!! Since the refrigeration consumes most of this, I have to charge whatever I can with solar during the day, and make up any shortfall by running a small 1000w Honda generator which powers my 40 amp shore charger.
Although this worked, I would really like to to be able to go several days on available capacity, as well as harvest more solar power (hence the panel upgrade) so as to not regularly need the generator.
And so, I am in the early stages of coming up with a complete redesign incorporating Lithium-Iron-Phosphate (LiFePO4) batteries. The batteries will be built up out of four separate 280 amp-hour prismatic cells. There will be two separate batteries, each protected by its own battery-management-system (BMS) board, for a total raw capacity of 560 amp-hours. Because LiFePO4 batteries can be safely discharged to around 20%, and remain in bulk charging almost all the way up to 100%, this gives a usable capacity of about 80% or close to 450 amp-hours!
Because LiFePO4 batteries have a 150 deg F operating limit, and the locker adjacent to the engine gets too hot when the engine runs, I am considering moving the batteries to the space occupied by the storage bin under the nav station. Each battery will occupy a footprint of aprox. 7" x 11 1/2" and stand 8" or 9" tall, so they should fit there, with room for the required bus bars and BMS boards.
But I need to warn you (and anybody reading this) that I really have gone down the rabbit hole on this one! The engineering required to do this right is significant, and there are no commercial products out there that get it all right, requiring a high degree of custom design. Don't believe a word of it when anybody tries to convince you that there is a "drop-in" lithium battery that can replace your lead-acid ones. It just isn't true. These installations will work great, in the short haul, but will not last and will destroy your expensive investment long before its promised life. A proper LiFePO4 battery has to be part of a
system, including the BMS, the solar charger, the alternator & regulator, and the shore charger. ALL must conform to the unique charging requirements of Lithium batteries, and cooperate in the task. There's a lot of information and cautionary tales on this topic at Compass Marine (
https://marinehowto.com/lifepo4-batteries-on-boats/) and Nordkin Design (
http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/). If you're at all considering going down this route, I
strongly suggest you read it all.