LiFePO4 gives $21k Return

[Submariner]

I am curious for folks who did the drop in replacement path for a house LFP and use a DC to DC charger from the engine AGM - what your real world experience is of being able to charge the house battery quickly enough off the engine alternator and shorepower (that are wired to the AGM)

I get 30 amps of engine charging, but with the boat underway, it consumes power also, leaving me about 15 amps an hour surplus that goes to house battery charging. The 420 watts of solar I have runs from sunrise to sunset and provides us with about 80% of all the power we consume, daily.

On shorepower, I have a 60 amp battery charger dedicated to my LFP house bank.

The best I could ever do for LFP charging, on the dock with shorepower: 60 Amps battery charger and 30 amps from solar. My Li3 supports up to 150 amps of charging.

 

[Pandion]

I am curious for folks who did the drop in replacement path for a house LFP and use a DC to DC charger from the engine AGM - what your real world experience is of being able to charge the house battery quickly enough off the engine alternator and shorepower (that are wired to the AGM)

Our '21 R27OB has a Victron LiFePo4 330AH house battery, so not exactly "drop-in" but close enough for the discussion.

Our Victron Orion XS DC-DC charger will pass up to 50 amps from whatever source is connected to the AGM start battery once the start battery reaches the voltage threshold for the Orion XS to start charging the house battery. The start battery is usually at (or close to) 100%, so the pass-through current usually happens relatively quickly.

When the AGM charge source is only the Yamaha F300, the Orion XS will generally pass between 40-50 amps to the house battery.

On shore power, the house battery is charged directly by 120V Victron charger that outputs 50A. The AGM start battery is still charged by the factory 20A Kisae charger. Once the start battery is full, the Orion XS will pass that 20A on to the house battery. Between the two 120V chargers, we can put ~70 amps into the house on shore power.

 

[Mike and Sarah]

Ok to through more fun in the mix.
We have a Solara S310 SB.
900 amp hours LiFePo. We are a full electric boat. That said from cooking to heat to extra portable freezer and hot water the boat is all electric. The inverter is used a lot. But we have done some modifications. Added a Webasto diesel heater. So no need to run heat pump. Changed out cooktop from regular glass cooktop to induction, and added solar.
We have 420 watts of solar now. We do have a Bimini so at times it gets partially shaded. But that can be mitigated by partial folding of Bimini on anchor or a dock. But during late spring to late fall we get well over 2000 W/h a day from it.
Since all the improvements we can have hot water anytime and SOC only got down to 70 percent on our spring PLI Desolation 3 week trip. No need to plug into shore power.
Twin 300 Yamahas put out 43 amps out of the DC-DC chargers. So with electric consumption we net over 75 amps from the engines. Throw in solar and we are in mid 90s.
Slow down and run one engine plus solar and still get 40 plus amps. With double the run time of slow boating it equals out to the same net charge.

One note. Due to the amount of time we are away from marinas to plug in. We usually never get back to 100 percent until we are back to a marina.
Solar will also top off to 100 percent in a day or 2 after a big trip even without shore power if we are not using the boat.

 

[Cutwater28GG]

interesting. after I posted the question, for some reason it finally dawned on me that a 50a Dc to DC charger is pretty equivalent to the amps from a shore power connection and even the amount of continous amps id get out of the alternator on the volvo D4. so there isnt a penalty for doing the dc to dc charge route.

i do wonder how the life of the engine battery behaves when running it this way

 

[NorthernFocus]

interesting. after I posted the question, for some reason it finally dawned on me that a 50a Dc to DC charger is pretty equivalent to the amps from a shore power connection and even the amount of continous amps id get out of the alternator on the volvo D4. so there isnt a penalty for doing the dc to dc charge route.

i do wonder how the life of the engine battery behaves when running it this way

I don't see how/why the starter battery is impacted any more than when wired with additional lead acid batteries "downstream" in the charge circuit. The cabling that carries charge current to the house bank is landed on the same buss as the alternator/charger input. So the charge current doesn't pass through the starter battery. It floats on the voltage coming off of the alternator just as in a conventional setup. The only reason that a lead acid battery is needed is to protect the alternator if/when the LFP shuts off the charge current. With a smart alternator the lead/acid battery in the circuit isn't necessary(as I understand).

 

[Submariner]

interesting. after I posted the question, for some reason it finally dawned on me that a 50a Dc to DC charger is pretty equivalent to the amps from a shore power connection and even the amount of continous amps id get out of the alternator on the volvo D4. so there isnt a penalty for doing the dc to dc charge route.

i do wonder how the life of the engine battery behaves when running it this way

The Victron Orion-TR DC to DC charger I installed on Channel Surfing has a configuration setting to delay charging the house bank until the engine battery has been recharged after starting the engine. Engine start uses a lot of amps for about a second. The OrionTR waits a configurable amount of time to let the engine battery fully recharge, then it’ll start charging the house bank.

We took deliveryJune ‘20. I’ve had LFP on my boat since Feb ‘22. I am still on the factory/OEM engine AGM start battery and the factory OEM AGM thruster battery, today.

The end of this season, I’ll replace both with an engine starting battery, AGM, just due to age and lifecycle. I’ll make my thruster battery the same as the engine starting battery which will give me a spare engine battery onboard.

 

[NorthernFocus]

View attachment 27782

Interpretation of how the Victron DC/DC "engine shutdown detection" works:

If the charger sees 14.0V or above in the input side it immediately starts charging(i.e. passing current to the output side)
If the charger sees 13.8-13.99V on the input side it waits the time specified in "delayed stat voltage delay" before charging begins
If the charger sees 13.5V or less on the input side it stops charging(i.e. breaks the circuit between input/output)

 

[Cutwater28GG]

Ah Dan, thats a critical piece of data I was missing. I was assuming that for the capacitative capabilities of having the engine battery between the alternator and the DC charger meant that it had to isolate the power through the battery but from what you describe its just sitting on the same bus bar. therefore if I have it correct, if and when the BMS shuts down battery from taking power, the power from the alternator just flows to the engine batter as its on the same bus bar, thereby not smoking the alternator

do I have that right?
I need to go look at the wiring diagram!

 

[NorthernFocus]

Ah Dan, thats a critical piece of data I was missing. I was assuming that for the capacitative capabilities of having the engine battery between the alternator and the DC charger meant that it had to isolate the power through the battery but from what you describe its just sitting on the same bus bar. therefore if I have it correct, if and when the BMS shuts down battery from taking power, the power from the alternator just flows to the engine batter as its on the same bus bar, thereby not smoking the alternator

do I have that right?
I need to go look at the wiring diagram!

Yes you've got it correct. The conventional battery just has to be connected to the buss so there is an alternate path for current from the alternator if/when the charge circuit is blocked.

 

[Cutwater28GG]

im curious why folks opted for LFP batteries that can start the engine if there is an engine starting battery available? another backup option? seems that a cheaper LFP unit could have been used?

 

[NorthernFocus]

im curious why folks opted for LFP batteries that can start the engine if there is an engine starting battery available? another backup option? seems that a cheaper LFP unit could have been used?

In my case the 300 Ah battery with IP67 rating and capable of driving the thruster also has the necessary amps to start the engine. So it was an easy decision. Plus we boat all the time in remote areas so having a backup is a good idea.