New Boat: Lithium Now or Later

[Fuss]

I think we should not have lead acid technology onboard boats at all if they have changed the house bank to lifepo4.

[sailingharry]

It might be more accurate to say that most drop in LFP batteries cannot deliver the current. The issue is not the battery, but the inadequate BMS that drop in batteries include.

But even then, I doubt it. On my boat, my windlass draws within a few amps of what my starter draws, 1 KW for the windless and 1.2 KW for the starter. But my inverter is rated at 3 KW, much more than either of them. Granted, motors have an inrush current, and that can be quite large.

The big issue with LFP banks is not inadequate current, but rather the ability to deliver mind blowing current in a short circuit. A small LFP bank can easily deliver 10,000 or more amps. As long as you aren't limited by the BMS, it should start your engine with better cranking turns then a lead acid battery.

[Statistical]

Originally Posted by sailingharry

It might be more accurate to say that most drop in LFP batteries cannot deliver the current. The issue is not the battery, but the inadequate BMS that drop in batteries include.

But even then, I doubt it. On my boat, my windlass draws within a few amps of what my starter draws, 1 KW for the windless and 1.2 KW for the starter. But my inverter is rated at 3 KW, much more than either of them. Granted, motors have an inrush current, and that can be quite large.

The big issue with LFP banks is not inadequate current, but rather the ability to deliver mind blowing current in a short circuit. A small LFP bank can easily deliver 10,000 or more amps. As long as you aren't limited by the BMS, it should start your engine with better cranking turns then a lead acid battery.

Even building your own battery BMS with 200A+ are uncommon. LFP cells don't like current beyond 2C and some manufacturers recommend no more than 1C. A 1200W starter has inrush current around 6,000W so at 12V that is 500A. Even at 24V that is 250A.

Still even if you did have a house bank which could delivery 500A and so 'could' start the motor wouldn't you also want a starter battery. Hard to justify the cost of second LFP just as a starter battery.

Personally I think AGM is dead weight on a boat and lead acid (FLA) is dead man walking for house banks but for a starter battery it is about perfect for the job. Super cheap & hard to get wrong. In theory super caps could replace lead acid as starter batteries but lead acid is just really cheap so the economics just aren't there. It just works and it is cheaper than the alternatives so I think lead acid starter batteries will be with us for a while.

[Dr.No]

SV-Viento, I went through this decision process two years ago, after already having purchased some Mastervolt equipment. Your post #56 sounds fine. I do recommend that you go with a primary 24 volt system, and have 24 to 12 volt converters for necessary electronics and other systems. PM me if you ever want details of multi year refit of a French boat. Cheers!

[sailingharry]

Originally Posted by Statistical

Even building your own battery BMS with 200A+ are uncommon. LFP cells don't like current beyond 2C and some manufacturers recommend no more than 1C. A 1200W starter has inrush current around 6,000W so at 12V that is 500A.

Most of the BMS designs that I have been looking at do not have a current limitation. They output control level signals that operate relays. I will be looking at 500A contactors that can carry much much higher momentary currents.

The 1C and 2C limitations for LFP are continuous operation, not fractional second surges. But even then, at 2C a 250Ah battery can easily supply the 500A inrush. Note that car enthusiasts have been putting on brick-sized LFP to start muscle cars. My 800Ah AGM (don't blame me, it came with the boat!) Be replaced with 600 ah lfb, at 2C it can deliver 1200 a.

You're right, of course, that an engine start battery is necessary. The upthread comment was that the LFP battery cannot start the engine.

[hjohnson]

Originally Posted by sailingharry

Most of the BMS designs that I have been looking at do not have a current limitation. They output control level signals that operate relays. I will be looking at 500A contactors that can carry much much higher momentary currents.

The 1C and 2C limitations for LFP are continuous operation, not fractional second surges. But even then, at 2C a 250Ah battery can easily supply the 500A inrush. Note that car enthusiasts have been putting on brick-sized LFP to start muscle cars. My 800Ah AGM (don't blame me, it came with the boat!) Be replaced with 600 ah lfb, at 2C it can deliver 1200 a.

You're right, of course, that an engine start battery is necessary. The upthread comment was that the LFP battery cannot start the engine.

Most of the BMSs that people initially think about are the FET based units coming in the vanlife/rv world. Things like the jkbms, chins and what not. These have very real current limitations due to the nature of the transistors used to switch the current. Contactor based BMSs, such as what you’re describing, are a different beast. I myself am using a REC BMS, which is dual contactor based.

In my case, I went with a separate starter battery because I was somewhat worried about wear and welding of the solenoid contacts due to the stupidly low internal resistance of my 2p5s battery. Plus, I like the idea of a simple system to get me home if needed. Also, a basic group 24 Marine starter battery is like $90, and will likely last forever as the DCC keeps it pretty much permanently on float. I just lives in a battery box in the bottom of our lazeret.

[CaptainRivet]

Originally Posted by Fuss

Really, I can’t start my engine with Lifepo4….really, I have to have separate lead acid batteries!!
Why??

Well i do, also the windlass no problem with 1088AH hybid starter house LFP and an electrodacus BMS that is neither FET nor contractor based and does not carry any current at all.
One of the reason i chose this BMS as its perfect for hybrid starter/house avoiding the problems with high current inrush for motors and FET or contactors...
I have an FLA as starter for the other hull, that will be soon replaced by an 30AH LTO, the ultimate starter and house backup battery, install and forget about it the next 30 years minimum.

Any >400AH LFP bank can start the engine if it can do 1C constant and 2C peak if you have the 2kw starter that most leisure boat 3 or 4 cylinder engine under 100hp has.

[CaptainRivet]

Originally Posted by SV-Viento

New 40' mono build for weekend to multi month cruises. Demand side of system will have fridge, full electronics with radar and autopilot, etc but at this time no AC or water maker. These items will be serviced by house bank either FLA or Lithium LiFePo.

Other demands loads include windlass, electric headsail furling, and electric primary winches and starter to be serviced by Separate AGMs via DCtoDC relays.

Shore power, 2 alternators (one to starter and one to house and AGM loads). Future solar is also planned.

THE QUESTION: should we have the House System Set up with lithium now or later and the real question is cost. The entire system is a Mastervolt system. To add Lithium, the builder charge is close to 30K. But my simple math indicates we can add later for roughly half of that. What are we missing? and should we simply move forward with it now or later?

I would spec is with smallest FLA bank in 24V and then do install yourself. Take the 3kw/24V mastervolt charger/inverter and make sure MPPT has a lithium profile, if not ask for an upgrade even thats overkill for your FLA.
Do install yourself, DIY your lithium battery bank from cells with a Electrodacus, X2,Tao or REC BMS. Like this can easily switch to LFP, the only thing yiu need to take care are the alternators, everything else switch profile from FLA to LFP and done.
Because of motors like whinches, headsail furling with high inrush but on the other side no huge capacity needs your boat is perfect for a 300 or 400AH LFP Winston cells that can do 3C constant and 6C peak.with the right BMS see above the motor loads are no problem and you can run all feom the lithium and don't need any AGM battery.
Both alternators charge starter&house. Instead a seperate starter just get 100aH more LFP capacity and put the low cut off at 3V, like this you have more then enough to start your engine eveytime you need it. I would just go with 2x Mitsubishi 115A alternators (one is most likely on your volvo or yanmar engine anyhow) and a Norkyn VSR200 regulator, cheap and more then enough for your 40ft. You can add one LFA as starter and backup if you want but being weekender and coastal thats not really needed.