Review of 12v solar system with DIY lithium

[Fryguy1111]

Hello. I apologize for the long post, but I am a total beginner at this but have been reading and researching building a lithium system for a boat. I'll be retiring in a few years and my wife and I bought a boat in Mexico and I'm going to be upgrading her for us to move aboard in a couple of months. Sometimes in a marina with shore power and sometimes on the hook, being self-sufficient.

First of all, there is an existing solar system (2 x 250w panels) and 2 banks batteries made up of 2 x 6v/225AH Trojan lead-acid batteries. So there's a total of 450AH in two 12v/225AH banks. The existing solar charge controller is a Blue Sky Energy Solar Boost 3000i 12v 30/22 amp MPPT controller. My calculations show that this setup wasn't the best, but folks can correct me if I'm wrong (I'm still learning). I figured that 500w/12v= 42A. So my solar charge controller should have be rated for a minimum of 42A...preferrably 60A. Again, let me know if I'm barking up the wrong tree...

Currently, all 4 of the 6v batteries are 100% dead as the boat was sitting unused for almost 3 years when I bought it just a couple of months ago. Hence, this is my opportunity to upgrade the entire system .

To get the most for my money, I plan on going the DIY lithium battery route. I've researched my options and found some 3.2v/280AH cells that will fit my needs. Here's what I want to build her out to:

3 x 250 watt solar panels for 750 total watts
1120AH of lithium batteries - 4 x 12v/280AH packs
Solar Charge Controller - 750w/12v=63A - use an 80A controller?

Question #1, am I sizing the solar charge controller properly? Any recommendations on makes or models?
Question #2, how do I size a BMS? Is there such a spec? I couldn't find anything on that other than noting they're all 4 or 8 wire/cell systems. I won't need a low-temp cutoff as I'll never have the boat in an area below 32 degrees. But will need one with a low-voltage cutoff, of course. I assume I'll need to monitor every cell, so am I right in assuming I'd need four 4-cell BMS' for a 12v system? Recommendations and corrections would be greatly appreciated.

Lastly, I need to know how to calculate the fuse sizes. In my design, I've placed one between the positive battery bank and the positive on my 12v fuse block and 1500 watt inverter. I thought I was to size that fuse on the positive battery bank based on my 1500kw inverter as I have both coming off that fuse. 1500w/12v=125A?? Is that correct? Should it be larger? Recommended fuse size?

I also have a fuse on the positive between my solar charge controller and my positive of my battery bank. I thought the fuse from my solar charge controller to my battery bank was to be based on the solar charge controller size. 750w/12v=63A (or 80A for safety/growth)?? Is that correct? Recommended fuse size?

I've attached a draft of what I'm trying to do, so I'm hoping folks can review and offer any suggestions.

Thank you.

 

[DThames]

What are your largest power loads? Do you know what their power requirements are for a normal day? What loads are daytime loads and which ones are night loads?

Do you have room for more panels?

 

[Fryguy1111]

I've calculated that I'd be using about 1200 watt hours a day under anchor....maybe more depending on how much my wife uses her kitchen appliances?. I've not calculated use by day or night, but under sail, I expect only 1000 watt hours per day.

I currently have the 2 x 250w panels and room for 1 more of the same given their current placement. If I toss those and go with ones with a smaller size (and wattage), I may be able to jigsaw puzzle more of them to get more than 750 watts. Then again, I've not researched 300 (or larger) watt panel sizes as my bimini (location where my panels are placed) has a size of 90" (7' 6") x 165" (13' 9"). I maybe able to get 3 of those and get 900 watts.

But I'm trying to keep costs down and use what I currently have if at all possible.

 

[DThames]

Using about 1.2KWH per day, with that battery you could go over a week without sun. I was asking about more panels, thinking you had a larger load and how long would it take with 750 watts to charge that size battery. But if you are that lightly loaded, your battery will be full for the most part, not demanding a lot of charge.

 

[Fryguy1111]

Thanks for that confirmation. I did figure that with over 10,000 watt hours, I'd be able to go for a week on the hook without worry.

Have you had a chance to review my info on the solar charge controllers, BMS, and the fuses? That's the part I'd like to make sure I'm sizing things properly as I hope to start building this in a few weeks while I'm back home in the states, and then in a couple of months, head down to the boat to get it all installed.

Thank again for the replies.

 

[usnoozeulose]

Check your panels for amperage and voc voltage. If u r running your panels in series, your voltage will go up and your amperage will stay the same. If u r running them in parallel, then your voltage will stay the same and your amperage will go up. If u r doing 750w with 3 panels in parallel, a 60a mppt should work. My 60a MPPT is rated at 720w for 12v. But even with 750w of solar panel, u would never do 675 in the real world. just make sure you stay within the parameters of the voltage and amperage of your MPPT.