Advice Requested re Conversion to LFP House Bank

[Singularity]

A separate charger and inverter is never cost-effective (a stated priority) unless one uses an off-brand inverter (i.e. a name-brand charger/inverter is less expensive than a name-brand charger and a name-brand inverter). It otherwise unnecessarily over-complicates a boat that will be use domestically.

True a separate charger offers distinct utility in a boat that will travel far and wide, but that's not the case here.

[AndyEss]

Originally Posted by Q Xopa

Alternators. Hmmm, these can really lighten your wallet. Going to the popular marine elec suppliers and getting off the shelf High output marine alternators is not for the financially timid.

I went the 'school bus' style alternator option. I got large case Delco 28si's 24V 110A at under $400 ea. I have also splurged for a 2nd hand Serpentine pulley kit, off CF. Ive also had to play around fabricating some pullies and brakets so if your not up for some DIY then probably not the best option.

Others have different views but going to the expense and trouble of doing an LFP install I dont see skimping on increased charging rate when the motor is on doesnt really make much sense to me.

I have a lot of the components ready for LFP but havent quite got to that point myself.

Still considering my options here.

This all comes down to a lot of personal preferences and which aspects are important to you. There are obviously so many iterations possible.

You can bet the more people you ask the more varied replies you'll get.

I agree that going the school bus alternator is the way to upgrade, but the OP already has a 75A alternator. I for one, would use the saved bucks from not upgrading the alternator for buying more solar panels.

As for paying someone $50 to hump LA batteries, I sorta like to be able to do most anything on my boat (within reason). I bet even those who get extra help with moving batteries still have their hands in the process somewhere, and one bad move - ouch or worse.

LFP is a pretty proven technology, and is getting cheaper (or are new tariffs in play?) so it is not as if we are talking really early adopters here.

I'm still not clear as to the storage you want/need JMardiat. I think what you seem to be saying is you are going to replace what I take is one 8D AGM (about 225-250Ahrs) with one 300 AHr LFP 8D.

The single AGM only had 112-125 AHrs of usable capacity, so you will in effect have triple what you had. Maybe first go for one ~150 AHr LFP first, and add a second 150 if this isn't enough? It's the same consideration for keeping weights and package size down.

My primary pack is built out of 73AHr 3.3V cells in a 4s2p array for 146 AHrs, and my handling weights are really low. I got a great deal on the cells from a defunct Department of Energy research program, and am bummed that I didn't buy more.

My engine compartment requires the skills of a contortionist so that is one reason I am anal on battery weights - no space to handle heavy LA batteries properly. I felt 340 lbs lighter after getting rid of the main LA bank.

Overnight, I'm usually in the 40-60 AHr usage rate with fridge, lights, some TV and music, and my CPAP.

Right now I am having some problems with one of my MPPT controllers, and can't get to putting in my replacement controller, but I am recharged using my solar panels and have a bit extra for my water maker by 4pm or so. I have 480W of solar in 8 panels (esthetics and safety are important to me, hence the large numbers of small panels) and other than at noon, 1/2 are usually shaded at least partially by my boom and rigging. I do have a wind generator, and it proved useful in the winter months.

[dakno]

These fla, agm, gel, and lfp discussions are always black holes. You don't say what year or what the oe equipment was with your boat. My boat was designed by engineers hopefully and it came with three 4d agm's. The charging, inverter, monitors were set for agm's. It could all be changed but why. Gcb... can you safely crawl around the dark spaces of your boat with a headlamp and baster and chemistry tester every 30 days? Are these tight dark spaces ventilated well enough for a constantly gassing fla battery? ..so you can save $150 a year in amortized battery cost...?

[newhaul]

Originally Posted by dakno

These fla, agm, gel, and lfp discussions are always black holes. You don't say what year or what the oe equipment was with your boat. My boat was designed by engineers hopefully and it came with three 4d agm's. The charging, inverter, monitors were set for agm's. It could all be changed but why. Gcb... can you safely crawl around the dark spaces of your boat with a headlamp and baster and chemistry tester every 30 days? Are these tight dark spaces ventilated well enough for a constantly gassing fla battery? ..so you can save $150 a year in amortized battery cost...?

did you not read the op that started this thread?

He stated it is a Catalina 36 mk1
So built between 1984 and 1994
And an 8D agm battery
He is converting to Lfp so the battery maintenance bit is not an issue.
Do you have anything constructive to add to the discussion.

[Yellowjacket]

Originally Posted by AndyEss

You will probably see more belt stretching, dusting and belt breakage due to the LFP much higher acceptance rates, so get plenty of spare belts and become proficient at checking, adjusting and replacing them. I think the wider use of LFP will drive marine engine makers to switch all but the smallest engines to serpentine toothed belt drive instead of v-belt.

If you are even close to the maximum horsepower of a v-belt driving an alternator trying to feed your LFPs, change it to a seprentine. My experience with "stretching, dusting and breakage (eventually, all three at once!) is that it happens at the worst possbile moment. There are many work arounds, such as easy ramp regulators, but don't let an overheating engine reduce your options when you need it the most.

[jmardiat]

I truly appreciate everyone's responses to date. The recommendation for more solar paneling is understandable but I only have the dodger to mount a flexible panel on. There's no Bimini or transom arch for additional mounting.

If I stay with my 75 Amp alternator is it at risk of becoming fried charging up the FLP house bank?

[john61ct]

Yes.

The two solutions are fitting a smart external VR, like Balmar MC-614, or front-ending the bank with a Sterling DCDC, BB series.

The latter is better value IMO and certainly offers more flexibility.

[john61ct]

Note leaving things stock, even if the alt protects itself from burning out, it will likely do so by dropping voltage rather than current, thus in effect stopping charging.

[newhaul]

Originally Posted by jmardiat

I truly appreciate everyone's responses to date. The recommendation for more solar paneling is understandable but I only have the dodger to mount a flexible panel on. There's no Bimini or transom arch for additional mounting.

If I stay with my 75 Amp alternator is it at risk of becoming fried charging up the FLP house bank?

an external regulator is a good option however the alternator with the stock internal regulator will thermal limit itself by reducing the output . Whether a 75 amp alternator is big enough would depend on the size of your bank. It would be a good fit for banks up to
A max of ( in my opinion ) about 200ah Lfp bank . That will put you somewhere in the .3C to .5C charge range that is recommended by most manufacturers for optimum battery life .

[newhaul]

Originally Posted by john61ct

Note leaving things stock, even if the alt protects itself from burning out, it will likely do so by dropping voltage rather than current, thus in effect stopping charging.

alternator reduce the output amperage not the voltage.

[john61ct]

Not talking pedantically about the alt internal workings, but as a black box, looking at final measured output of the VR.

Only the more sophisticated VRs handle overheating by putting out de-rated current at the correct setpoint voltage.

Most stock setups, including modern Euro-style cars with ECM / ECU regulation, just in effect halt effective charging, because the output voltage has dropped below the desired setpoint.

Plus VRs like MC-614 allow the owner to **prevent** the overheating by explicit de-rating settings based on ambient temps and other current conditions.

The DCDC option does the same, but for any charge source, not just that one alternator.

[Q Xopa]

Originally Posted by john61ct

Yes.

The two solutions are fitting a smart external VR, like Balmar MC-614, or front-ending the bank with a Sterling DCDC, BB series.

The latter is better value IMO and certainly offers more flexibility.

The B2B would choke a 75A alternator to 60A as that is the max output of the B2Bs. This seems a bit counter productive reducing your charging by 20-25% ( depending on which way you calculate it).

Yes the External Regulator option with a temperature sensor should work well. However the Alternator will most likely also need to be modified to External regulation.

[john61ct]

No the de-rating is exactly the point, actually pulling the max rating from 99% of alts out there for more than a couple minutes in high temp conditions either destroys them, or their protection measures effectively ends charging.

With all current-limiting solutions, it is up to the owner to determine how high a rate to pull given the current conditions, and set that as a maximum.

No need to fully refill in just an hour anyway, ICE's usually running for other reasons anyway.

Anyway, I'm not saying spending tons of money on just that one alt is never worth it, just that B2Bs are often a better value due to their flexibility, used with multiple sources, even other vehicles or in your home, whatever.

And finally, B2Bs can be stacked as needed.

[john61ct]

Whether a given Amps source is "big enough" has little to do with the size of the bank.

More to do with the Ah used per 24 hours and number of hours that source will be active, usually including for other reasons.

The size of the bank is more to do with how many days buffer you want when you have no "power on demand" or it's not convenient.

Sure, if you want to charge up a whole weeks' worth of usage in a couple hours turn of the switch and sit on the hook in silence rest of the time, then a high-current source would be appropriate.

But if regular motoring or making water at high gph is part of the scenario, there may be no need to put in a bigger alt.

Lots of use-case variables, too easy to over-generalize

[newhaul]

Originally Posted by john61ct

Whether a given Amps source is "big enough" has little to do with the size of the bank.

More to do with the Ah used per 24 hours and number of hours that source will be active, usually including for other reasons.

The size of the bank is more to do with how many days buffer you want when you have no "power on demand" or it's not convenient.

Sure, if you want to charge up a whole weeks' worth of usage in a couple hours turn of the switch and sit on the hook in silence rest of the time, then a high-current source would be appropriate.

But if regular motoring or making water at high gph is part of the scenario, there may be no need to put in a bigger alt.

Lots of use-case variables, too easy to over-generalize

john if an alternator is not at least big enough to hit the .3C charge amperage it will be well and truly disappointing ( if it is your primary charge source. )

I don't even have an alternator on my engine . It is started with a low amperage dynostarter ( charges at 10 amps to recharge the start battery only. )