Critique my lithium wiring plan, please

[Peregrine1983]

Hi all,

Looking for critiques of my plan to convert our house bank on our 42 foot ketch to lithium.

This is what I came up with for a general plan. I already have the lithium batteries (1x460ah, 1x100ah), 30 amp Victron Orion DC-DC charger, inverter, wire, terminals, and the solar on the boat in the Bahamas.

I'll be bringing the on/off switch, echo charger, and bus bars from the US.

What worries me about this drawing now is the little 100ah lithium battery on the port side near the solar controller. My concern is this battery will be overcharged and under-utilized with the loads all being closer to the 460ah battery on the starboard side. The batteries are arranged as they are due to the size and location of the boxes.

The boat is rarely, if ever, plugged in. It spends most of its time on a mooring or at anchor when we are not on the move.

I wanted to add an emergency engine start switch to start off lithium if it's absolutely necessary. The 460AH house battery has a 600A (3 sec peak) and 200A continuous BMS.

In this setup, the windlass battery in the bow will remain an AGM fed off an echo charger and the start battery will remain a Group 27 FLA.

I am not an electrical engineer (clearly) so please don't flame me too bad.

Thanks in advance for any help.

[Peregrine1983]

To clarify - the rest of the items in the sketch are already on the boat as well

[hlev00]

Here's a first bit
- You need Class T fuse(s) for your LFP battery main fuses. The interrupt capacity of an MRBF is too low. Since no fuses are shown, it is impossible to comment on where you are missing them.

- What’s the point of the 100Ah LFP battery?
- You have a bunch of connections to the LFP battery. Those obviously need to go to one or more bus bars.
- You should have a separately fused always on DC bus for a few loads - at least the bilge pumps.
- It looks like you are trying to charge your AGM battery with an echo charger off of the LFP bank. This needs to be a DC-DC charger, not an echo charger.
- You are going to be hard pressed to charge 460 Ah LFP, let alone 560 Ah, with only 350 W solar. If you can later add more solar later then that’s fine. Otherwise there is no reason to have so much battery capacity.
- 
You should install a shunt (smart or otherwise) and a battery monitor. The shunt connects between the house battery negatives and all the other system negatives (loads and charging sources).

[hlev00]

Also the site https://marinehowto.com has excellent information for you getting started with LiFePo4. If you find it helpful considering donating a bit. I have no vested interest in the site other than Rod is very knowledgeable and his information is worth paying for even though he doesn't have a pay wall.

[Peregrine1983]

Thanks very much, hlev00. The help is sincerely appreciated!

"- You need Class T fuse(s) for your LFP battery main fuses. The interrupt capacity of an MRBF is too low. Since no fuses are shown, it is impossible to comment on where you are missing them.
" Copy that. I will add Class T fuses sized to the wires.

"- What’s the point of the 100Ah LFP battery?" - Long story. Basically I made a mistake in ordering it and now can't return it, so would like to incorporate it into the house bank.

"- You have a bunch of connections to the LFP battery. Those obviously need to go to one or more bus bars." Copy. Thank you. I will use bus bars.

"- It looks like you are trying to charge your AGM battery with an echo charger off of the LFP bank. This needs to be a DC-DC charger, not an echo charger." Thank you. Could I use an echo charger for the windlass AGM off the Group 27 start batt? Alternatively, I could purchase another Orion.

"- You are going to be hard pressed to charge 460 Ah LFP, let alone 560 Ah, with only 350 W solar. If you can later add more solar later then that’s fine. Otherwise there is no reason to have so much battery capacity." Copy. Adding more solar in the future is the plan... trying to figure out the best way to get a few more panels in the Bahamas.

"- 
You should install a shunt (smart or otherwise) and a battery monitor. The shunt connects between the house battery negatives and all the other system negatives (loads and charging sources)." I actually already have a Victron Smart Shunt, which I will be using in this. Sorry, forgot to mention that

Really appreciate the help

[Peregrine1983]

Originally Posted by hlev00

Also the site https://marinehowto.com has excellent information for you getting started with LiFePo4. If you find it helpful considering donating a bit. I have no vested interest in the site other than Rod is very knowledgeable and his information is worth paying for even though he doesn't have a pay wall.

Thanks! I actually used his site while researching batteries and landed on Vatrer because of him.

[hlev00]

Originally Posted by Peregrine1983

Thanks very much, hlev00. The help is sincerely appreciated!

"- It looks like you are trying to charge your AGM battery with an echo charger off of the LFP bank. This needs to be a DC-DC charger, not an echo charger." Thank you. Could I use an echo charger for the windlass AGM off the Group 27 start batt? Alternatively, I could purchase another Orion.

Really appreciate the help

I think you can charge the windlass AGM with the Echo Charger off of the start battery as long as they are both AGM. Check with the vendor or maybe someone else will chime in on that note.

You will want to enable the engine shutdown detection on the DC-DC charger so it only tries to charge the LFP when the engine is running and the alternator is charging.

You're welcome!

[Peregrine1983]

Appreciate it, hlev00.

A wiring size question for the forum:

The house bank is made up of two batteries - a 460ah and a 100ah in parallel. The wire run connecting these batteries is about 15 feet due to the location of the boxes.

Assuming a maximum load on this house bank of 200 amps, am I right to assume that a 200 amp load on a 460ah and a 100ah battery wired in parallel would only be pulling 43 amps from the 100ah?

If so, according to my favorite chart, 2 gauge is more than adequate to connect these batteries and would actually give some significant headroom, but I could be very mistaken.

Any thoughts appreciated.

[HeinSdL]

The smaller LFP battery might already be on board, etc, but given the intricacies of the LFP charging routine I think you would be better off not using it.

When I see discussions about LFP batteries in parallel a lot of attention goes to wiring lengths, voltage drops, ensuring the batteries have similar capacities (?), etc, so in the described set up it might not be clear what is going on during the charge and discharge cycles.

Alternatively... utilize the bus bars as shown but connect to +ve on one battery and the -ve on the other battery. With fairly chunky cabling connecting the two batteries and no other connections to the batteries. Everything to the bus bars. In that way the batteries should always be at the same voltage*, monitored by the shunt as mentioned.

*Although I am not even sure about that, it depends on which battery is at a higher state of charge I suppose. Regardless, the chargers will have a difficult time figuring out when to go into float, which voltage would control that?

[hlev00]

Fuses and wiring always have to take failure modes into consideration. In this case you have to consider that the entire load could come from that single 100Ah battery in the event the BMS shuts down the larger battery.

I'm concerned in general introducing this 100Ah battery. I realize you are "stuck" with it, but it is never a good idea to make up of bank with dissimilar batteries. Do they have internal bluetooth that are capable of communicating with each other? That MIGHT mitigate the inevitable unbalanced usage. I recommend reaching out to the manufacturer for their input on this.

[HeinSdL]

Where is Mr S/V Jedi when you need him?

[Peregrine1983]

Thanks so much, all.

Interesting point about just not using the 100ah. You all may be right that it's more trouble than it's worth.

These batteries have Bluetooth and an app, but I do not know whether they communicate with each other. I will ask the manufacturer now and report back.

This is the 100ah battery and this is the 460ah battery.

[Peregrine1983]

If I can get the two batteries very close to one another, I assume that might mitigate some of the potential issues.

[HeinSdL]

For my benefit, does Bluetooth mean you have access to the individual cell voltages? I imagine with that visibility you have more freedom in terms of balancing and you can intervene once you see a cell or two going out of balance and you don't need to worry too much with your current set up. Except for the bus bar etc comments already made. I am guessing here a bit, only have experience with my single house litime black box battery.

[Peregrine1983]

Originally Posted by HeinSdL

For my benefit, does Bluetooth mean you have access to the individual cell voltages? I imagine with that visibility you have more freedom in terms of balancing and you can intervene once you see a cell or two going out of balance and you don't need to worry too much with your current set up. Except for the bus bar etc comments already made. I am guessing here a bit, only have experience with my single house litime black box battery.

Thanks, HeinSdL. Yes, the app does show the individual cell voltages. They are automatically balanced, so I'm not sure how much intervention the app allows for me to do anything manually. I'm limited in the app right now not having a battery connected, but here is a screenshot from YouTube of what it looks like when the cell voltages are visible.