Yet Another AGM to Lithium Upgrade

[lwarden]

I'm not on the lunatic fringe when it comes to adding bling to my boat, but since I have a set of 11+ year old AGMs and we are planning on the loop next year I had a difficult decision. Do I just buy a few more AGMs or go all in and upgrade much of the electrical and go LiPo? With some of the Black Friday sales and some encouragement from @Barking Sands I decided to go LiPo... and now I'm waist deep. My goal is to have a longer time before running the generator or hooking up to shore power. The recharge time for my existing AGMs is pretty long, especially once the bulk charge is done. Shedding a few hundred pounds would be nice as a side benefit since we are a plaining boat.
Another issue is with our old Xantex Freedom 25 which the microwave doesn't play well with so we have to run the genny any time we use it which is a pain, so I really wanted to fix that issue as well.

Full disclosure, although I'm an engineer, this LiPo stuff is pretty new to me so I'm interested in any input to help out where I might make mistakes.

Existing setup:
4@8D 250AH AGM's, one for start shared between the two engines and three for house (750ah house capacity).
1X Group 27 AGM for the genny start.
Xantrex 2500W inverter/charger with 130A charger (in theory)
Twin Cummins engines, each with 105A alternators, one connected to the house bank, one to the start battery, also connected via ACR.
6KW Northern Lights Gen

New Setup:
2X 460AH Epoch Essential for the house (820AH total).
2X Group 31 AGM in parallel for the start bank, 1600CCA
1X Group 24 FLA for the genny start, 1000CCA.
Twin Cummins engines, each with 105A alternators, both alternators connected to the start battery bank
6KW Northern Lights Gen
Victron Multiplus 2 3000W inverter/charger
Victron Cerbo GX
Victron Touch 50
Victron Smart Shunt 500A
Victron Orion 50A DC to DC Charger, input from the start bank going to the House Bank.

My questions are:
1. Does all this look OK?
2. I think I'm going backwards with the charging underway. The house used to get one of the 105A alternators on the main, but now I can only get 50A from the Orion. Do I double up those to get more charging? This is the area of the conversion that I'm not happy about and it seems I'm adding a lot of complexity to charge the house from the mains.

Appreciate any thoughts or inputs.

 

[Diep]

I recently designed and implemented a similar upgrade and have it mostly installed.

A few really quick thoughts/comments.
* I believe that after your new house battery Class T's you will need a bank fuse with 920/100 * 5 = 46k Amp AIC rating in order to comply with the newest ABYC standards. You will need to something because right now the wiring downstream of the bank is exposed to 600A and is note likely sized adequately for that. You can move the 400A Multiplus fuse close by and make it a class T with high enough rating. (I posted some pics yesterday of our fuse set up)

* We went with a 1/2 house/start switch without "All" position. We have the ability to parallel the gen start with Main engine start. Thought the tradeoff was worth it vs the possibility of combining banks with different voltages and getting very large balancing currents. This also allowed use to fuse the house load feed at a lower level that might otherwise blow trying to spins the mains. I got feedback that a lot of complexity in the start interconnecting is overall unnecessary and confusing. I have come around to agree. Carry some jumper cables and keep things clean and simple. Maybe upsize the gen start battery

* I would reconsider powering the Cerbo off of an inverter circuit. It is recommended to power it off the house bank directly. This way if you turn off or somehow lose the multiplus you won't lose the cerbo and control of the system.

* We went with (2) orions for house charging. For us it made more sense than upgrading alternators to external regulation at this point.

* Consider keeping the Xantrex Charger. The Orions should be able to harvest charge off it. This will increase your available charge current which will be nice when running the gen.

*You only show one AC run. Are you planning to let the inverter supply everything and just load manage yourself? If you want to take advantage of the inverter and pass through capabilities of the Mplus you'll need another run and maybe some changes in your AC panel or distribution. We did this so the water heater and second battery charger can't be supplied by the inverter.

*Research the Touch device requirements. I think the USB transmits the touch input as well as power? You might need a powered hub but also extend the USB back to the Cerbo.

Fun project. Lots of work but you will love the results!

 

[Frosty]

That should serve you very well. Now you have about double the usable amp hours. And no Peukert effect drag. Whee!

I had the same feeling when I first went from AGM to LFP. I was used to understanding basically everything about my setup, and suddenly I had to "go backwards" to figuring stuff out (before there was as much good input available). I resisted for awhile and, like you, thought about how easy it would be to just buy new AGM's.

I'm glad I didn't do that now though - I'm sure you will be too.

I have a comment: I don't have twin engines, so there's probably something I don't understand, but could you split your start bank (which is already two batteries) and thus have a start batt per engine, and then an Orion XS from each start batt? That would be 50 amps output per side (or more if you end up waiting until the new XS 70 amp comes out).

Or do the two start batteries have to work as one bank to be large enough start (either) engine?

Edited to add: Oh, right, I think you can also just put two Orions in parallel, so 100 amps now, or 140 if you could wait for the 70 to become available. I forgot about that.

 

[Frosty]

BTW, I read about the Orion XS 70 on PKYS's blog about new introductions at METS. (This also re-confirms that you can parallel the XS's to double your charging power, in case you don't want to wait for the 70..... I waited for the XS50 to come out and it was delayed a few times, but did finally arrive just in the nick of time.)

Orion XS 12/12-70A battery to battery charger
This is destined to be a best seller and we except them to fly off the shelves as soon as they show up in mid-year. The Orion XS 12/12 70A can be parallel-connected for even more charging power. Orion XS allows you to connect any alternator to any battery. It protects the alternator from Lithium battery high demand. Available with 12V / 24V or mixed 12/24/12 input/output conversion – the 12/12 70A compliments the existing range of high efficiency Orion XS chargers

Sneak preview of new Victron products being announced at Metstrade in November 2025

 

[lwarden]

I recently designed and implemented a similar upgrade and have it mostly installed.

A few really quick thoughts/comments.
* I believe that after your new house battery Class T's you will need a bank fuse with 920/100 * 5 = 46k Amp AIC rating in order to comply with the newest ABYC standards. You will need to something because right now the wiring downstream of the bank is exposed to 600A and is note likely sized adequately for that. You can move the 400A Multiplus fuse close by and make it a class T with high enough rating. (I posted some pics yesterday of our fuse set up)

* We went with a 1/2 house/start switch without "All" position. We have the ability to parallel the gen start with Main engine start. Thought the tradeoff was worth it vs the possibility of combining banks with different voltages and getting very large balancing currents. This also allowed use to fuse the house load feed at a lower level that might otherwise blow trying to spins the mains. I got feedback that a lot of complexity in the start interconnecting is overall unnecessary and confusing. I have come around to agree. Carry some jumper cables and keep things clean and simple. Maybe upsize the gen start battery

* I would reconsider powering the Cerbo off of an inverter circuit. It is recommended to power it off the house bank directly. This way if you turn off or somehow lose the multiplus you won't lose the cerbo and control of the system.

* We went with (2) orions for house charging. For us it made more sense than upgrading alternators to external regulation at this point.

* Consider keeping the Xantrex Charger. The Orions should be able to harvest charge off it. This will increase your available charge current which will be nice when running the gen.

*You only show one AC run. Are you planning to let the inverter supply everything and just load manage yourself? If you want to take advantage of the inverter and pass through capabilities of the Mplus you'll need another run and maybe some changes in your AC panel or distribution. We did this so the water heater and second battery charger can't be supplied by the inverter.

*Research the Touch device requirements. I think the USB transmits the touch input as well as power? You might need a powered hub but also extend the USB back to the Cerbo.

Fun project. Lots of work but you will love the results!

Great feedback @Diep. Some comments.

I missed the need for the additional bank fuse after the new Class T fuses, that seems simple enough to do.

I had considered just doing the start/gen/all/off for the mains and gen and not have the house selector. I can easily be convinced it's not really necessary. I was just being lazy and not wanting to pull out a bunch of wires that are already there, but I will reconsider this.
Edit: I would like to keep the ability to run the house load from the cranking AGM's if the LiPo's die. What I want to avoid is combining both the AGM and LiPo banks, that seems like a bad thing. Perhaps I can make some lockout on the switch to prevent that. All battery switches are new so would like to keep them if possible.

The Cerbo is going to be connected to the inverter power at the breaker, so if the inverter is on, so is the Cerbo. Maybe I need to reconsider, easy enough to do.

I think I'll add a second Orion in parallel which would give 100A off the mains, that's the way I'm leaning.

Can't keep the Xantrex, no room, and I really don't want to rely on a 23 year old unit.

I didn't detail the AC mapping, it's in three banks on the distribution panel, the inverter only feeds the lighter loads on one bank, not AC or water heater, those only get power from the generator or shore power. I will keep that configuration. I don't see trying to run any of the high-load items with the inverter. The Multiplus will just load share charging and the light load bank on the panel.

I read the USB to the Touch is only power and data goes over HDMI, but will check on that.

@Frosty I saw they were coming out with a 70A Orion, I just don't think I can wait. The group 31's don't have enough CCA for my engines so need to parallel them.

 

[Diep]

On the AC side, consider whether you want to take advantage of the throttling/boosting capabilities of the multiplus or not. If you do, you will either need to route all the AC through the multiplus, or use an AC meter to measure the current that doesn't. Its a pretty neat feature and allows you to set a maximum current from shore/gen. The multiplus will then throttle back charging to keep from exceeding the limit or even switch to inverting to supplement briefly.

I understand ditching the Xantrex. However it looks like all you have is a 4A trickle charge for the start bank and nothing for the generator (Unless you combine to all). I would want to have something tending the gen battery. You still might think about adding a new charger for the start/gen.

Circling back to the Orions. You never mentioned whether your alternators are externally regulated or not. If they are, or you could convert for something less than 1.5x the cost of an Orion I would prefer to go that direction with one of the alternators. But if not, head for 2x Orions IMO.

 

[lwarden]

To be honest, I really haven't traced out how the AC routes through the current system and to the two banks of power. I'll have to give it a look-see this weekend. I suspect since the Xantrex could also do load sharing it's setup that way. It's difficult to trace everything out since none of the cables are labeled. I'll see if I can make sense of it. I can say that the AC in and out of the Xantex are only 10 AWG, which seems small if it's carrying the full AC load, so it's possible the main AC is not routed through the Xantex. The AC line from the generator is also 10 AWG, which seems light for a 6kw generator under full load, seems it should be 6 AWG. I poked my head inside the generator and the wires running to the AC connection out are also 10AWG, but it appears they are doubled up.

Second Orion is on order.

The current generator battery is isolated from any charging, but I could easily add an AC trickle charger to maintain it if needed, I had considered that. I haven't had any issues with the generator battery losing charge, but now I have a FLA battery there so it might be more of an issue going forward. I can easily parallel in the main starting battery if needed to get it started. I do have that spare ACR which I was removing from the system, so I suppose I could add that between the main starting bank and the generator.

Thanks again for the great input.

 

[Diep]

This is a schematic of our system showing only the AC supply wiring. There are additional breakers on the Multiplus outputs which are not shown.

The basic path is AC sources feed the main breaker, then to the MPlus and then separate outputs to the inverter and pass thru circuits. The pass thru is only energized when there is an external AC source on line.

This is a 120v boat but you can do the same with 240v split phase and the 2x120v MPlus model, you will just have an additional hot leg wired.

All the wiring we did was 6AWG. The shore power feeds are also 6 but the existing 8KW gen wiring might be 8.

 

[Ertyqway]

I just got done installing a somewhat similar system and love it. One point to consider: rather than focusing on amp-hours, size the system by watt-hours instead. I was looking at doing two 300Ah 12v LFP batteries, but one 300Ah 24v battery has the same capacity in watt=hours. By switching the core house system and inverter/charger to 24v, I was able to have the same capacity with less weight and cheaper wiring. All it needed was a 24v/12v transformer for the DC house system.

 

[SteveK]

I just got done installing a somewhat similar system and love it. One point to consider: rather than focusing on amp-hours, size the system by watt-hours instead. I was looking at doing two 300Ah 12v LFP batteries, but one 300Ah 24v battery has the same capacity in watt=hours. By switching the core house system and inverter/charger to 24v, I was able to have the same capacity with less weight and cheaper wiring. All it needed was a 24v/12v transformer for the DC house system.

In addition to 24>12V transformer, what other components did you change to charge 24V. I am thinking an 24V ALT and a 24V inverter/charger. To late with my boat already working on 12V LFP, sure sounds like a consideration for a fresh conversion to LifePO4.

 

[CharlieO.]

I just got done installing a somewhat similar system and love it. One point to consider: rather than focusing on amp-hours, size the system by watt-hours instead. I was looking at doing two 300Ah 12v LFP batteries, but one 300Ah 24v battery has the same capacity in watt=hours. By switching the core house system and inverter/charger to 24v, I was able to have the same capacity with less weight and cheaper wiring. All it needed was a 24v/12v transformer for the DC house system.

Interesting, didn't know that. Gives me a new rabbit hole to go down.

 

[Frosty]

Sounds like a plan to re-purpose your ACR for charging the generator start batt (at least from here, not looking at your boat).

 

[Ertyqway]

In addition to 24>12V transformer, what other components did you change to charge 24V. I am thinking an 24V ALT and a 24V inverter/charger. To late with my boat already working on 12V LFP, sure sounds like a consideration for a fresh conversion to LifePO4.

I actually kept the old 12v alternators, so I have step-up transformers to boost their output from 12v to 24v going to the inverter/charger and LFP battery, and step-down from 24v to 12v to feed the house DC circuit.

 

[Ertyqway]

For reference, here is the schematic for the system I just finished installing....

 

[tpbrady]

Why the reluctance to combining the AGM start bank with the LFP house bank? Last spring when I contemplated switching the house bank to LFP, using a DC-DC charger with a 200A alternator on a single engine trawler didn’t seem like the right approach. While I had a flooded start bank and a sealed 8D battery for the bow thruster, the difference in charging requirements was minimal since those two lead acid banks were not used heavily. My approach was to externally regulate the alternator and separate the start bank from the LFP bank using a Victron MOSFET isolator when the main engine was running. This approach was dictated mainly by space in the engine room. In this approach, the alternator was protected by the isolator being connected to both banks so if the LFP ruthlessly disconnected, the start bank and bow thruster batteries were still there. I ran in this manner all last summer with no problems. Even with the bow thruster battery still connected in parallel with the LFP, the current flow between the two was less than 2 amps if I didn’t manually disconnect them.

Tom

 

[lwarden]

I get the approach of going 24V, but since the boat is almost all wired with 2/0 it doesn't make sense, there is plenty of ampacity to cover the current usage. Makes lots of sense if redoing much of the system.

There was a question on the alternators regarding regulation, they are internally regulated.

My reluctance to combining the LiPo bank with AGM is just the difference in charging profiles if it were left in that position by mistake. Perhaps I'm worrying about it more than necessary. @tpbrady, I'm not sure I understand your approach fully.

 

[tpbrady]

Lwarden,

The major difference between lead acid and LFP charging profiles is absorption voltage and time in absorption to reach full charge. Since in normal operations the start bank and thruster/windlass bank are close to full charge after being used they will reach full charge quickly when underway from the alternator. They are very tolerant of different voltages over a wide range unlike LFP batteries, where the BMS will do unwanted things if the battery is fed the wrong voltage at the wrong time.

Tom

 

[Ertyqway]

Another huge difference is that LFP batteries do not need float charging (which will actually destroy them) and AGM/LA batteries do.

 

[SteveK]

Another huge difference is that LFP batteries do not need float charging (which will actually destroy them) and AGM/LA batteries do.

I wonder where this came from, have heard it said, but why?

 

[Ertyqway]

I wonder where this came from, have heard it said, but why?

LiFePo batteries are much less susceptible to thermal runaway due to overcharging (which is the reason you should absolutely never float charge other kinds of lithium batteries...they blow up), but float charging LFP dramatically degrades them due to charger power dissipation, thermal aging, and lithium leaching. You won't blow up an LFP battery by float charging it, but you will reduce its operational lifespan and capacity by a lot. So don't do it.

 

[SteveK]

LiFePo batteries are much less susceptible to thermal runaway due to overcharging (which is the reason you should absolutely never float charge other kinds of lithium batteries...they blow up), but float charging LFP dramatically degrades them due to charger power dissipation, thermal aging, and lithium leaching. You won't blow up an LFP battery by float charging it, but you will reduce its operational lifespan and capacity by a lot. So don't do it.

Thank you.

 

[Ertyqway]

Sure thing. Another issue is that LFP batteries have MUCH lower impedance than AGM/LA, so constant-voltage charging does not really work to charge them effectively. That's why they all need Battery Management Systems (BMS) to control the voltage served to the battery at levels it needs (and why they charge so much faster).

LFP batteries also have a more optimal operational life cycle if they are kept at around 70% to 80% charge in "storage" mode (under no load). Unlike AGM/LA batteries, LFP has a nearly constant discharge voltage down to about 15% charge, so keeping them charged at 100% all the time isn't necessary or optimal.

 

[tpbrady]

I use a float voltage setting of 13.2v on the Victron Multiplus to keep my LFP bank at 50-60% SOC over the winter. In this respect float “charging” an LFP battery is part of maintaining the battery in the recommended state.

Tom

 

[Frosty]

Another huge difference is that LFP batteries do not need float charging (which will actually destroy them) and AGM/LA batteries do.

I run a 13.5v float on my LFP house bank. That's when I'm out cruising and cycling the house bank every day. So not like setting a dock charger float to 13.5 and leaving for two weeks.

Hence I wouldn't across the board say float charging "will actually destroy them."

 

[Delta Riverat]

As long as they are not held at 13.5 for long periods of time you are good.

 

[Delta Riverat]

Like Tom above, during the winter months when I don't visit the boat as often, I set charger float at 13 and absorb at 13.2 which let's the batts swing a bit as well as making sure the fridges and the bilge pumps stay active.

 

[SteveK]

OK, I have done some reading and this is what it boils down to

• Float Amps: The current (amps) during the float stage will be low, typically a fraction of an amp or close to 0A, as it only needs to offset the battery's minor self-discharge and support small parasitic loads.

I can see why float is not needed since LFP voltage stays above 13 even below 50% SOC, but I do not understand how float degrades the battery by maintaining a full charge (and balances all cells) when you want it to be ready to power the inverter when shore power is lost.

 

[Delta Riverat]

Yes, the amps will be really low but the voltage will be high.

Do some research, that's what I did and I have read that LiFePO4 does not like to be held at max charge, it likes to swing. It's not like lead that likes to live at 13.5 to avoid sulfation. It likes to charge/discharge.

Maybe you have read different.

 

[Diep]

It is kind of a question of priority.

If the priority is maximum bank capacity available in the event of shore power failure, you will sacrifice some battery life. If you want to maximize battery life, you can float lower at the expense of less available bank if power is cut.

I expect that we will float (and maybe absorb) lower than normal when we are away from the boat (Storage mode). If we lose shore power the bank will have enough capacity for days even if 50-60% charged. Then we will kick it up to normal either when we are on the way to the boat or when we arrive. Then we will be topped up to go cruising.

 

[SteveK]

A fully charged LiFePO4 (LFP) battery cell typically has a resting voltage of around 3.35V to 3.40V, or 13.4-13.6V
My batteries sit 13.5-13.6 with near 0 current