Replacing FLA with LiFePo4 charging question

[ForeverDes]

Sorry for yet another LiFePo4 thread!



Background info:
I currently have a single 8D FLA house battery of unknown capacity, and what looks like a group 27 dual use (deep cycle/start) FLA starting battery. I'm limited on space to add batteries, but I could fit 4x 6v 225AH deep cycle Sam's club batteries in a 2S2P configuration. It would be a fairly simple install, and I could keep my current charging scheme, which is: a dual battery onboard charger, 380W (2x190W parallel) solar through a 60 amp mppt controller, and a 65amp alternator.

There's a "1-2-both-off" battery selector switch. Solar is wired to the house bank side, alternator wired directly to the start battery, and the on board charger has dual outputs and is wired to each bank.
In the same space as the 4 FLA batteries I was planning to use, I could fit 400ah of LiFePo4 batteries. (2x200ah 12v). They'd use a little less total space, and they weigh less than 1/2 what the FLA batteries do. The LiFePo4 batteries are longer but less tall, and height is my my limiting dimension. I don't currently have an inverter, but I have plans to add a 2000W pure sine wave inverter at some point in the next year or two. My largest load is the portable, 12v, 45w fridge. At 4 amps and a duty cycle of 50% max, that's 50 AH per day. The other loads probably never exceed 20 AH.

I stay on a mooring ball in the summer and store my boat inside, but not heated, in the winter.

I don't know the state of my current batteries, but I know I don't trust them to last through this summer season.

I'm trying to wrap my head around what changes would be required for upgrading the house bank to LiFePo4.

Is it reasonable to disconnect the onboard charger from the house bank, and then use a dc to dc charger from the start battery to the house bank, while leaving the solar wired (through the appropriately programmed mppt controller) directly to the house bank? Or should all charging sources go through the starting bank?

Solar is more than enough to keep up with my modest house loads for several days of use in the summer.

If the above is reasonable, does the battery selector switch need to be removed? I can't imagine a scenario in which combining mixed chemistry banks would be a good idea.

If disconnecting the battery selector is appropriate in this situation, I'd like to use it to "split" my house bank in two as a measure of redundancy. I'd like to leave all house loads connected through the 1-2-both-off switch and use a battery isolator between the mppt controller (and dc to dc charger) and batteries.

What am I missing, and what am I just plain wrong about?

p.s. my goal with LiFePo4 would be a conservative charging scheme, never trying to reach above 85%-90% soc.

[tkeithlu]

We've got people on the forum who are quite knowledgeable and quite vocal about DC circuits, particularly when you come to lithium. I am not one of them, but I do have a few thoughts.

Why disconnect the charger? Are you never at shore to use it?

I doubt that those knowledgeable people will recommend charging one battery with another. You're losing amp hours in the process. Better to be able to cross them if you must.

Keeping the starter battery isolated and running off the engine alternator is I think a good choice. The engine should recharge from a start very quickly. Keeping it apart from the house bank means that all those other possible DC usues won't leave you without starting voltage. But, again, have a plan B.

If you do separate the starter battery from the house bank, do think redundancy about starting. That is a time to cross banks, at least very briefly, but a simple pair of jumper cables may give you that protection against a dead starting battery.

[ForeverDes]

Originally Posted by tkeithlu

Why disconnect the charger? Are you never at shore to use it?

Correct, I'm never hooked up to shore power in the sailing season.

My charger is also not optimized for LiFePo4 batteries, so I wouldn't want to cause an overcharge and burn them out. Additionally, with a DC to DC charger the house bank SHOULD still get charged. (This may mean I have to keep the ignition switch "on" to energize the charger, and since I've added EFI to my Atomic Four engine that is presumably acceptable) I'm making a very big assumption that a dc to dc charger made for LiFePo4 batteries will have the correct parameters to properly charge the house bank safely.

Originally Posted by tkeithlu

If you do separate the starter battery from the house bank, do think redundancy about starting. That is a time to cross banks, at least very briefly, but a simple pair of jumper cables may give you that protection against a dead starting battery.

I'd have a pair of dedicated jumpers as well as a jump pack for emergencies. The idea is to have nothing that can accidentally be left on or switched incorrectly that will cause issues with the house bank.

[newhaul]

Originally Posted by ForeverDes

Sorry for yet another LiFePo4 thread!



Background info:
I currently have a single 8D FLA house battery of unknown capacity, and what looks like a group 27 dual use (deep cycle/start) FLA starting battery. I'm limited on space to add batteries, but I could fit 4x 6v 225AH deep cycle Sam's club batteries in a 2S2P configuration. It would be a fairly simple install, and I could keep my current charging scheme, which is: a dual battery onboard charger, 380W (2x190W parallel) solar through a 60 amp mppt controller, and a 65amp alternator.

There's a "1-2-both-off" battery selector switch. Solar is wired to the house bank side, alternator wired directly to the start battery, and the on board charger has dual outputs and is wired to each bank.
In the same space as the 4 FLA batteries I was planning to use, I could fit 400ah of LiFePo4 batteries. (2x200ah 12v). They'd use a little less total space, and they weigh less than 1/2 what the FLA batteries do. The LiFePo4 batteries are longer but less tall, and height is my my limiting dimension. I don't currently have an inverter, but I have plans to add a 2000W pure sine wave inverter at some point in the next year or two. My largest load is the portable, 12v, 45w fridge. At 4 amps and a duty cycle of 50% max, that's 50 AH per day. The other loads probably never exceed 20 AH.

I stay on a mooring ball in the summer and store my boat inside, but not heated, in the winter.

I don't know the state of my current batteries, but I know I don't trust them to last through this summer season.

I'm trying to wrap my head around what changes would be required for upgrading the house bank to LiFePo4.

Is it reasonable to disconnect the onboard charger from the house bank, and then use a dc to dc charger from the start battery to the house bank, while leaving the solar wired (through the appropriately programmed mppt controller) directly to the house bank? Or should all charging sources go through the starting bank?

Solar is more than enough to keep up with my modest house loads for several days of use in the summer.

If the above is reasonable, does the battery selector switch need to be removed? I can't imagine a scenario in which combining mixed chemistry banks would be a good idea.

If disconnecting the battery selector is appropriate in this situation, I'd like to use it to "split" my house bank in two as a measure of redundancy. I'd like to leave all house loads connected through the 1-2-both-off switch and use a battery isolator between the mppt controller (and dc to dc charger) and batteries.

What am I missing, and what am I just plain wrong about?

p.s. my goal with LiFePo4 would be a conservative charging scheme, never trying to reach above 85%-90% soc.

So far so good . The solar would be plenty to feed the planned lfp. Personally I would disconnect the house leg of the shore power charger . Installing a 40 amp b2b . ( derating will protect your alternator ) .
Leave the battery selector switch in place in the event you ever need to parallel the house bank with the start bank to start the engine.

Now I would run all of the lfp as a single bank .
With the fla start battery split for starting duty only.

[CarlF]

I don't understand why you don't want to stay with flooded. Those 6V Sams Club batteries are a good match for your charging. And the weight of a few batteries is not a problem on a monohull.

But if you wanted to be able to discharge the batteries more than 50%, I'd look at Firefly. Same 80% safe discharge as Lithium. 8-10 year life. Half the price. No changes to your charging. No water to add.

Lithium really only makes sense if you have 200 amps+ charging capability (and have a power hungry enough boat to need it)

[newhaul]

Originally Posted by CarlF

Lithium really only makes sense if you have 200 amps+ charging capability (and have a power hungry enough boat to need it)

And where did you learn this ?

I personally run 250ah lfp 400 watts solar and a 55 amp alternator if I ever need it.
My current power needs are approx 35ah a day.

Retired shipwright here and your statement really makes no sense

[Pete7]

I agree with Carl, can't see what can be gain by changing to LFP in this instance. Other than enriching someone else's pension fund.

Its a 25ft yacht with simple low requirements electrical system. Stay with the KISS approach.

Pete

[ForeverDes]

Originally Posted by newhaul

So far so good . The solar would be plenty to feed the planned lfp. Personally I would disconnect the house leg of the shore power charger . Installing a 40 amp b2b . ( derating will protect your alternator ) .
Leave the battery selector switch in place in the event you ever need to parallel the house bank with the start bank to start the engine.

Now I would run all of the lfp as a single bank .
With the fla start battery split for starting duty only.

I am planning to disconnect the house leg of the charger.

My only concern leaving the selector switch in place is accidentally selecting "Both" and causing a problem with the house bank. Maybe that's not a valid concern though.
Also, what would be the procedure for starting the battery this way? Turn the switch from house to start, start the battery, then switch back?



I had thought isolating the two house bank batteries would prevent trouble on one battery or the other from causing a catastrophic failure of the entire bank. Leaving it as a single bank would certainly be simpler, and from some additional research I don't think an isolator is optimal in this situation anyway.

[tkeithlu]

ForeverDes, I really like your goal, and your thinking in reaching it. Too many boaters (I won't call them cruisers) don't think a thing about redundancy. They essentially have no Plan B.

My only remaining question (like unto CarlF) is going to Lithium. I did a purchase price versus amp/hour calculation awhile back for another thread, and found that installing a lithium house bank of the same amp/hrs as a flooded bank cost ten times as much. Are you going to eat up ten replacements of your flooded bank in the time you destroy one bank of lithium, or do you have another reason (weight?) to make the change?

[ForeverDes]

Originally Posted by Pete7

I agree with Carl, can't see what can be gain by changing to LFP in this instance. Other than enriching someone else's pension fund.

Its a 25ft yacht with simple low requirements electrical system. Stay with the KISS approach.

Pete

That's certainly an option, as is chancing the current batteries another year. With a jump pack for back up starting, of course!

Originally Posted by newhaul

And where did you learn this ?

I personally run 250ah lfp 400 watts solar and a 55 amp alternator if I ever need it.
My current power needs are approx 35ah a day.

Retired shipwright here and your statement really makes no sense

However, I tend to align more closely with this approach.
I've never seen anyone build a pole barn and afterwards wish they had built it smaller, and I've yet to see anyone on this forum or elsewhere downsizing a working house bank's capacity after the fact.

Originally Posted by CarlF

Those 6V Sams Club batteries are a good match for your charging. And the weight of a few batteries is not a problem on a monohull.

Yes, and possibly yes, however I'm already stern heavy imo, so weight distribution would improve considerably, or at least not deteriorate further with the added weight of a bigger LFA bank. I'm not certain it will make a lot of difference, but it is a consideration.

Originally Posted by CarlF

But if you wanted to be able to discharge the batteries more than 50%, I'd look at Firefly. Same 80% safe discharge as Lithium. 8-10 year life. Half the price. No changes to your charging. No water to add.

Fireflies are not any cheaper at all than what I have in mind for LiFePo4. I'm not talking Battleborns here. Which is another reason I'm so concerned with my charging sources.

[ScottMeilicke]

I think KISS is good, until you have some reason to make it more complicated. Sounds like your situation doesn’t require extreme redundancy - you aren’t crossing oceans to isolated atolls. You have start and house, plus a battery pack. That is probably plenty.

My advice then is to put all charge sources to the same bank, probably house, and DC-DC to the other. Keep your house in one bank. Keep the shore charger.

Lots of pro/con discussions around lead vs li vs firefly. Assess your needs, with an eye toward the future, and what will make you happy. The 6v FLA will probably be just fine for you. Solar trickles in, which is good for FLA. Plenty of folks have used a FLA bank like you are considering while living aboard with much larger power loads than you.

Lithium is a system, and requires a careful evaluation of all charge sources, cabling, etc. sounds like you know that, but it would involve significant work and it sounds like upgrading charge sources.

Firefly to me is a good compromise, with most of the Li benefits while still able to use existing charge sources designed for AGM. just be careful with your alternator. Firefly s can ingest a ton of power, and may burn out your alt if your alt charge controller doesn’t have a limiter. Firefly also tolerate partial state of charge better than FLA, so may be better for you on the mooring when you don’t get sufficient sun to top off.

[newhaul]

Originally Posted by tkeithlu

ForeverDes, I really like your goal, and your thinking in reaching it. Too many boaters (I won't call them cruisers) don't think a thing about redundancy. They essentially have no Plan B.

My only remaining question (like unto CarlF) is going to Lithium. I did a purchase price versus amp/hour calculation awhile back for another thread, and found that installing a lithium house bank of the same amp/hrs as a flooded bank cost ten times as much. Are you going to eat up ten replacements of your flooded bank in the time you destroy one bank of lithium, or do you have another reason (weight?) to make the change?

Much better cost ratio if you go the diy route
For example a gc2 battery from auto zone is $140 x 4 = $560 for approx 250ah usable for longevity of approx 5 years . Say 400 cycles
My bank 250ah lfp cells for 200ah usable with a 30 year lifespan ( longevity linked more with charge rate than discharge ) say conservative 3500 cycles. Just over $600 all in including a battery monitor similar to the balmar sg200.

Lastly lfp don't actually like being fully charged.

Even if you go the cheap walmart/sams club route itscheaper at the 6 year mark.

[ForeverDes]

Originally Posted by tkeithlu

ForeverDes, I really like your goal, and your thinking in reaching it. Too many boaters (I won't call them cruisers) don't think a thing about redundancy. They essentially have no Plan B.

My only remaining question (like unto CarlF) is going to Lithium. I did a purchase price versus amp/hour calculation awhile back for another thread, and found that installing a lithium house bank of the same amp/hrs as a flooded bank cost ten times as much. Are you going to eat up ten replacements of your flooded bank in the time you destroy one bank of lithium, or do you have another reason (weight?) to make the change?

Thank you! I really appreciate the encouraging words!


I'll rephrase my reply from another response. I am not expecting to spend 10x what I would on FLA. My total cost would be 4x what Sam's Club 6v GC batteries would be, all in, and perhaps a bit less due to fewer interconnecting battery cables, trays, tie downs, etc needed. It would be a very large risk, because I'm sure I wouldn't have the warranty or customer support with these batteries as I would with a more expensive name brand option. If they stop working after 1 season, I'd be out the entire purchase price with no recourse.
Now, bring on the comments about "not being the guinea pig" etc.

For the record, I'm not opposed to taking a few risks, as long as they are calculated and I mitigate as much of that risk as I reasonably can.

Btw, Battleborn batteries would be problematic at best to fit 400AH worth of in the space I "want" to use for this. It might be possible, but I wouldn't chance it without a complete mock-up of the configuration first.

[Adelie]

There are several issues to consider.

Let's start with winter storage. Does it get below freezing during winter storage? Is there shore power available during storage. LFP doesn't like to be stored below freezing, I understand that it damages the battery. Is removal from the boat realistic? For sure trying to charge it below freezing damages the battery. When a LFP battery goes into storage make sure it is down between 50-60% SoC, storing at 100% is bad for them. If it goes down to 0-32F then leaving a small 40-60W light bulb in the battery compartment that is sealed from the rest of the boat is probably enough to maintain battery temp above 32F. Below 0F I would probably install a small 350W forced air heater with a thermostat.

I believe BattleBorn batteries use their internal BMS to provide fine control of battery charging so your regular charger should continue working. The big thing to worry about is frying your alternator because the batteries will accept so much power, so you need a special regulator. If you are going with a different brand you should look into how that brand's BMS works.

For cold storage, if an FLA is fully charged it should be able tolerate temperatures below -50F without freezing. As charge state drops, ability to withstand cold temps drops too. If the start at full charge it is reasonable to believe they will make it thru the winter. If the boat has access to power a trickle charger could maintain the batteries at full charge. Alternatively if some light is still falling on the panels, they will be putting out a trickle charge, maybe enough to maintain the batteries.

Regarding your starting battery. A 10-30W panel with a PWM controller will provide 2-7Ahr/d. Each time you start your engine it uses less than 1Ahr of power. You don't need special electronics to charge the starting battery.

Having a connection switch so that the house bank can start the engine is not a bad idea. The harder to get to the better so it isn't accidentally turned to combine the banks and not noticed for a long time.

Economics.
LFP batteries are going to max out somewhere near 10yr. They need BMSs and the electronics in there will have a calendar life expectancy. If for no other reason than some of the capacitors will start leaking electrolyte. Depends on exactly what is in the electronic package. If the BMSs are external to the battery then replacement is easier and will depend on whether the vendor is still in business and supplying replacements for 10yr old equipment. The cells themselves could last nearly 30yr cycling every day. Hard to say. Best to count on 3,000 or so cycles. LFP batteries are considered dead when they reach 70% capacity. LFPs should be cycled between 80-20% capacity. I believe Battleborn cuts of charging when they get to 80% so you can't damage the battery. So for a 100Ahr battery you really get to use 80Ahr and you don't know about that top 20%.

Deep cylcle FLA will go 1,000 or so cycles if not cycled too deep too often and are recharged as soon as possible. Death is usually defined as 80% original capacity remains.

So how do you compare costs when batteries have different capacities and life expediencies? By calculating all the energy you will get out of them over all the battery cycles then dividing by purchase cost.

I don't know what your Sams club batteries are but I can get info for Trojan 6v golfcart batteries.:
Trojan T-105, 6v, 225Ahr@R20 rate, 1200 cycles per trojan but we will use 1,000 anyway, $150-185 online, lets say $170. 80% capacity at death, so average will be 90%. Batteries are cycled from 100-50% so 50% of capacity is used.
https://www.trojanbattery.com/produc...ine-flooded-2/

BattleBorn 12v-100Ahr, 3600cycles (10yr), $899 from BB, 70% capacity at death of cells, but we are looking at about 1/3 that time so 90% when electronic dies and we'll say 95% average. As indicated about you will cycle thru 80% of battery capacity.

Formula is Voltage x Ahr (gives Whr) x Ave % lifetime capacity x Average % used per cycle x cycles / $
Trojan T-105: 6v x 225Ahr x 90% x 50% x 1,000 / $170 = 3,573Whr/$
BattleBorn: 12v x 100Ahr x 95% x 80% x 3,000 / $899 = 3,043Whr/$

Here in San Diego I can get T-105s for $125+9% tax no shipping. Using that price I get 4,433Whr/$ purchase price. That's about 50% more power for the money. If I was using the batteries daily year round I would have to replace the battery bank about every 3yr or so so there is an inconvenience price to be paid too.

In reality given your usage patterns, the FLAs will probably last as long as BattleBorns would.

It doesn't sound like you are getting BBs so the particulars of what you are looking at will be slightly different but not much so.

If you want to convert to an electric galley, the lithium would be the better way to go, they can support the high current draws for cooking. With FLAs you probably would want to have an 700-1,000Ahr house bank and you've said you don't have room.

[ForeverDes]

Originally Posted by newhaul

Much better cost ratio if you go the diy route
For example a gc2 battery from auto zone is $140 x 4 = $560 for approx 250ah usable for longevity of approx 5 years . Say 400 cycles
My bank 250ah lfp cells for 200ah usable with a 30 year lifespan ( longevity linked more with charge rate than discharge ) say conservative 3500 cycles. Just over $600 all in including a battery monitor similar to the balmar sg200.

Lastly lfp don't actually like being fully charged.

Even if you go the cheap walmart/sams club route itscheaper at the 6 year mark.

You've certainly hit the nail on the head there! I will do all the work myself, and if I had to pay someone else to do the work I'd have never even considered it.


Another reason I would eventually like to forego FLA is with no shore charging for an entire summer I know I rarely top my house bank off completely. I'm afraid FLA will degrade considerably from that, even in a short few seasons, whereas LiFePo4 probably wouldn't even notice it.

My solar is enough to keep up with my power draw, but the sun simply doesn't shine long enough and bright enough to overcome the charging curve of FLA.