Upgrade 12V to 24V LiFePo4?

[ohthetrees]

Hi! This forum has been a huge help, I really have learned a lot. I’m in the middle of planning a LiFePo4 upgrade for my 50’ boat. I’ve thought a lot about it, studied a lot, and I think I have a good idea of how to proceed with a 12V AGM —> 12V LiFePo4 upgrade. I still have a few details to work out, like which particular Victron inverter to get, and a few other things, but those are details.

The real uncertainty I have right now is I can’t get rid of the idea of switching to a 12v —> 24 upgrade. The motivation is because the inverter I can drive from the 12v system is just barely big enough for my projected loads, and a 24v system would solve that issue with more powerful available inverters, and bring a bunch of other nice stuff, like smaller wiring, less wire losses, etc.

The challenge is that I have several low-duration, high current 12v loads that are cost prohibitive to switch to 24v. They are my anchor windless, electric sailing winches, a large hydraulic actuator, and engine starter. The electric winches can theoretically top out at 350a at 12v, and the windless is similar. I’m not aware of a 24v-12v converter that could handle those loads. So that leaves me with a hybrid 24v/12v system, where I’d move the large draw items to the start battery, rename it the Big Load Battery or something, and run all other normal house loads on a 24-12v converter. The inverter would be the only native 24v device connected.

What do people think of this idea, or can anyone think of better ideas?


I’m also interested in any general comments on my original 12v—>12v upgrade, the details of which I’ll post below.

Thanks for your help and thoughts!

 

[ohthetrees]

Below is my current 12v-->12v plan...

Background
I have a Hanse 505 “Sauvage” built in 2015 that I have owned for 2 years now. Our family of 4 have been full time live-aboard for 1.5 years, and have covered about 6000nm in that time, starting in Hawaii, then Seattle, now Mexico. Despite being a “production” boat, it is serving us very well, is extremely comfortable, and we’ve been putting on a lot of miles, and sailing where others can only motor, so we are very happy. While relatively new, the boat has 35,000nm already, and has been in near constant use since being launched. The boat is currently in dry storage in Mexico, but close to the US border while we visit relatives in the US. We intend to cruise and live aboard indefinitely, so I want to upgrade our electrical system while we still have access to US parts availability. I have 2 months to accumulate all the parts necessary for this upgrade.


Reasons for the upgrade:

• Original factory AGM battery bank (4x 160ah) is very tired.
• My spouse (and I!) desire certain comforts of home if she is to be happy as a full-time cruiser for the next 10+ years. Currently we have to run a generator to do laundry, make hot water, or make water. Our current batteries and inverter are not up to the task.
• I want to prepare the ground for a substantial increase in how much solar we have. Currently we have 750w nominal, but the stern arch is poorly made and designed, the panels are inefficient, the wiring undersized, the mounting poor. It all needs to be replaced anyway, and I have room for at least 1000w nominal with more efficient panels.
• We like to cook using solar or electric (induction) as much as possible. In sunny Mexico, we are able to do about half of our cooking with non-propane sources, and we would like to increase that as much as possible.
• Decrease energy losses associated with energy going in and out of a Lead Acid battery
• Avoid opportunity cost of not being able to harvest available energy because Lead Acid batteries are already full.

Goal:
Install a large 13kW LiFePo4 battery bank and a large inverter, safely and sensibly installed, but making no more changes to existing system than necessary.



Current System:

• House bank (12v): 4X 160ah AGM linked to start battery by a VSR
• Engine Start 90ah AGM
• 750w solar, 2X Victron MPPT 30a charge controllers
• Volvo Penta D2-75 with stock alternator
• D400 wind generator (I will likely decommission this in favor of more solar area, and less shading)
• 230v 50hz “Euro style” AC system
• 5kw generator
• 100amp Mastervolt Mastercharge world voltage (can accept nearly any shore power) (PO installed, but seems very nicely done)
• Mastervolt Mass Combi 12/1600-60 inverter/charger (factory)

Proposed Changes (and some questions)

1. Delete AGM, add 1120ah 12v bank in a 4P4S config
   1. I already bought 16X 280ah EVE brand cells. Is 4P4S the best config?
2. Install REC Active 4S BMS with active balancing and victron bus compatiblity.
   1. Is this a good choice of BMS?
   2. If I did other than 4P4S I’d have to get multiple BMS units, correct?
   3. What cables and connectors do I need to purchase to get the REC to talk to the Victron stuff?
3. Delete Mastervolt 1600w inverter/charger in favor of a 3000VA Victron unit that can be controlled by the BMS
   1. My wiring schematic lists 2X 70mm2 wires supply current inverter. Will this be adequate for the new inverter?
   2. I’d hoped for a more powerful inverter than 2400w supplied by Victron 3000VA unit, but that is max I can find for 12v.
4. Delete VSR in favor of a 160a diode battery isolator.
5. Change alternator charge control to Nordkyn VRC-200
6. Install a dedicated positive charge bus
7. Install separate Blue Sea 500a remote relays for load bus and charge bus disconnects
8. KEEP mastervolt 100a charger, but must figure some way of BMS remotely disabling it.
   1. Maybe a small relay wired in series with the mechanical “on-off” rocker switch?