Swap out AGM house battery for LiPO batteries, an inverter charger and solar. This will let me have an induction plate (to replace alchohol stove), a microwave (for heating bachelor chow) and maybe refrigeration. Keep it under $4,000, so I have something left over for canvas.

Lithium iron phosphate batteries are the cat's pajamas (today), light, really deep discharge and quick to recharge. An inverter-charger can power AC-only appliances, like the highly desirable microwave. Solar replenishes a day's cruising, reducing need for engine idling increases my on-the-hook duration.

Lots has been written about how to plan an electrical power upgrade,

Consumption and Generation

Power budget (a constant work in progress)

https://docs.google.com/spreadsheets/d/e/2PACX-1vT5PfsyfHNBDaOzkocSclP_LtR123HO87QvCdScR92lClzX4c9KL34ryBtbX-9ZwBrMlMUjkIoqFLFC/pubhtml?gid=1042857315&single=true

Current power deficit is 200 Ah / day, when passagemaking and assuming 3 hours of engine run. Break-even or better for a day sail. Assumes refrig 24x7, full electronics when moving and over-generous allowances for electric cooking, but completely unvalidated assumptions.

Sizing

I'm looking at:

• 200Ah of LiFePO4 battery (2 or 3 grp 31 size 100's)
• A 2000 or 3000w inverter charger, with built in transfer switch
• 150w solar panel
• Shore power only circuit for hot water and air conditioning. On hook, hot water can come from engine heat, A/C will be replaced by (many) fans and hope for the best.

Design considerations

Galvanic corrosion protection

Don't currently have any, shore power AC ground wired directly to boat ground. My understanding is this might allow ground fault current to find a circuit between boats that can accelerate zinc erosion. So I need some way to isolate DC ground from shore power ground.

Could be a new failsafe galvanic isolator. Cost about 380.

Could it come for free from the inverter charger? Mastervolt specs for Combimaster hint they might provide this function built in, but user manual doesn't confirm, so I'm inquiring directly. Victron and Xantrex son't claim it. So this seems unlikely.

An isolation transformer is another possibility, but they are big and also expensive.

Ground fault protection - AC

Separate from galvanic considerations on shore power ground is cutting off AC (high voltage) power when there's a fault and leakage current to ground. When on shore power, the ground return includes a path through the (conductive, salt) water, and this path is used heavily when the shore ground path is not working. When on inverter AC, my underestanding is none of the fault current gets into the water because the current doesn't have any reference to shore power. Best recommendation today is to install an ELCI or RCD (30ma GFI) < 10 ft from shore power plug, and another one on the output side of the inverter. These are typically 2 pole and break hot and neutral when tripped. 5ma GFI single pole GFIs are required on branch circuits in head and galley and (god forbid) weather decks.

Do I want an inverter charger, or separate?

Looking at Victron and MasterVolt (and maybe Xantrex), all well regarded. There are horror stories about both Victron and Xantrex (because they cater to DYI?), not so many about MV. The inverter/chargers from all 3 offer lots of high end features, some of which I don't see me using.

Automatic transfer from shore power to inverter without visible blink. Would be important if I wanted to run the TV or lights when I cut over. But I'm mostly using AC for cooking and am unlikely to have anything on the stove when I cut over, wouldn't care if it cut out.

When on shore power, prioritize non-charging loads. e.g if there's not enough shore AC capacity, taper off battery charging to avoid tripping shore power. But my (LiPo) batteries have max charge acceptance of 100A, which would be 10 of (usually) 30 amps. Inverter Charger may have even lower charging limit. And most of the time, actual charging demand will be much less than that.

When on shore power, start drawing inverter power from batteries to augment weak shore power. My max draw from galley would be 1440 + 1000 w, about 20A. Seems unlikely.

Single box, fewer wiring connections. Might be more reliable. But single failue in that box could mean I have no charging and no AC to cook with either. The benefit of single box is more compact and tidy installation, and that is unarguably good in my small boat. Also modestly cheaper than separate boxes, also good.

Modern monitoring, many with NMEA 2000 networking. Nice! But also true of modern 2 box solutions.

With separate inverter, I must have some anti-islanding protection, to prevent the inverter from energizing the shore power circuit (or trying to parallel it without phase sync. Would also need an external transfer or just a switch.

Alternator vs LiPO battery

Current alternator is original stock 35 A. Probably can't provide 30A continuous into a depleted LiPO bank without overheating. Probably plan on upgrade to ≤ 60 A alternator, little Yanmar diesel probably can't handle much more. What kind of continuous output can I get from that?

Alternator protection

Bogeyman of LiPO batteries is that the internal BMS may decide to do a load dump to protect batteries from over charging, suddenly presenting alternator with an open circuit and frying its diodes. I think I mitigate that risk by retaining one AGM battery as the starting battery and installing a DCDC charger between it and the LiPO bank. So the alternator always sees the starting battery, worst case. Not sure I need a battery switch, though, might just leave the starter and LiPO bank always paralleled (and rely on DCDC charger to isolate one bank from the other if it drains or shorts out).

Number of cells in LiPO bank

I could get 300Ah in a single box. This gives best power and cost density and would still weigh < 80 lbs. But then I have only a single BMS and maybe the risk that failure of a single internal cell would kill the whole battery. So prudence seems to argue for a minimum of 2 batteries. Slightly more wiring, so more risk there, but certainly less than the single BMS or cell failure.

Can always parallel more batteries later.

Solar

I want to add some solar capability, so I'm getting some background charging when on the move and not motoring. And my motor charging capacity may be limited, so will appreciate solar boost. I'm not aiming to be completely self-sufficient from just solar.

But, it's a small boat. I don't want to try to make a permanent roof of solar panels (orientiation would usually be bad or shaded). I probably won't have davits or a convenient rear arch. Best bet right now seems to be a single top-of-pole mounted panel of about 150w. This would tend to not be shadowed and would be orientable for maximum efficiency. Would not invest in an automatic tracking system.

This will be more exposed to weather. May need to be able to disassemble and stow it if it's too windy.

Big picture

Parts

Components

• Inverter Charger -- 3000w Shore power goes direct to this.

• DCDC battery charger w/ MPPT Dual input DCDC charger, combines alternator and MPPT solar charge controller into one box. Protects the alternator from lithium BMS load dumps because the (old, AGM) starting battery stays connected at all times. The Renogy draws a max of 15 A from alternator if solar is doing anything, but could (try to) draw 30A from alternator. This will probably burn out the alternator someday.

• stock 35A alternator Trying to retain existing alternator.

• LiFePO4 batteries
  Settled on 2 x SOK 206Ah marine batteries, gives me 400 Ah house bank.
  Retained existing 2 x 100 Ah AGM starter batteries.
  Considered cheapo Amazon batteries, couldn't find any with low temp charge cutoff.
  Considered Renogy 200Ah, but chose SOK:

  • smaller dimensions (especially front to back, to preserve room in lazarette)
  • prismatic cells vs cylindrical. Fewer cells needed and prismatic has bolts and busbars vs spot welds, will be more rugged and reliable.
  • user servicable parts inside! The big win for me. (Plastic) case can be opened (has a seal), can use commodity cells and BMS.

• Solar panels -- ((vendor?))

• Solar panel pole mount Custom marine Products has a nice kit of panels and pole mount to allow a small panel to track the sun and be more efficient. On my boat, mounting on the stern keeps the panels well out of any rigging shade.

• 2nd AC subpanel for inverter AC Couldn't find space near the galley to install this. Settled on Blue Sea 8100 ELCI main panel installed above existing main panel on starboard side. This is 30A, double pole ELCI breaker with pilot light and reverse polarity but no branch circuit positions, and it just fits.
  How to take best advantage of this?
  Shore power goes direct to AC input of Inverter/Charger (not split off for hot water or AC). < 10 feet, should be OK for ABYC.
  All on-boat appliances wired to AC output of Inverter/Charger, so ELCI goes here and protects the whole boat.
  MV Inverter/Charger has its own 30A breaker protecting transfer switch and all inputs. Only downside of this is I do not have ground fault protection from shore power into Inverter Charger, though I do have it on the rest of the boat when connected to shore power.