Combining lead & lithium batteries

[rslifkin]

Thank you. For a moment I thought that would narrow down the search, , nope, they come in 50, 100, 200 and maybe more Ah. Various colors and brands. Some look like 8D flooded. Then the cost differential.

So if I want to get 400 Ah, is it better with 4-100 or 2-200? if it matters for usage that is.

There's also the choice of drop-in batteries with internal BMS or individual cells with an external BMS. It's definitely an upgrade that takes a little planning before deciding what to buy, but that's far from unique in the boating world.

 

[Jeff F]

I get the attraction to a hybrid bank, but really think that in the end is totally motivated by drop in batteries that don’t provide basic control signals as better BMSes do. With the most basic signals; Allow to Charge, and Allow to Discharge, alternators can be easily and gracefully turned off, and any need for a hybrid bank goes away. The hybrid is just a way to hack around incomplete BMSes.

I agree. But let's agree that despite limitations, some of these hacks are safe, relatively easy to put together and manage, and in most cases significantly less expensive. Sometimes an effective hack is almost as good as the real thing.

Edit to add another point: I've got my oversize alternator charging my house bank based on the belief that rapid charge of the house from the engine was an important capability.

In practice I'm satisfying my house needs with solar 90% of the time, and last summer had my regulator dialed way back to let the panels do most of the charging. I'm planning to add more solar.

I now believe that I could happily do without charging the house bank from the alternator. So maybe I'll repurpose my fancy alternator and regulator to the start bank and reverse the dc-dc charger. For my use case I wouldn't be giving up any functionality.

 

[Jeff F]

So if I want to get 400 Ah, is it better with 4-100 or 2-200? if it matters for usage that is.

Look at BMS capacity for both charge and discharge. It varies. I'd take 2x200 over 4x100 if the BMS rating was higher on the 200, which it usually is.

I have 2x300, each with a 200a dumb BMS. I never charge or discharge at >200a, so in theory I have complete failover capabilities if one battery goes dark.

 

[RedRascal]

So if I want to get 400 Ah, is it better with 4-100 or 2-200? if it matters for usage that is.

I've been noodling on this exact question myself. I've ruled up going the 4-100 route because of 100 amp BMS limits in addition to space required. 1 400AH would be great for saving space BUT I am thinking for redundancy sake 2-200s would be best. My thinking is if you lose the BMS or some other failure on the a single 400 you lose that whole capacity. However if you lose 1 of the 200s you could disconnect it from the system and carrier on with the good or maybe wounded 200. Not sure if this is sound logic as I am new to lithium.

 

[SteveK]

Red, I am with you being new and wonder the same so asked that question. But I will take into consideration what Jeff said as well. it will take time to study.

 

[La Sirena]

The intent of the subject Bank Manager Plus is to "bolt on" LFP batteries to an existing lead battery bank. Whether it is considered a separate bank, or mixing similar chemistries in the same bank is up for debate. I'm attaching a schematic on how the Bank Manager Plus is connected. In case the lead or LFP bank shorts, or has some issue, the BMP will disconnect the two "banks" when the voltage is different. It only connects the banks in series when the voltages are the same (or within a set delta V).

The advantages are it is relatively easy to install without changing alternators, chargers, wire size, etc. It just bolts on. Also, you get advantages of both LFP (quick charging, more useable capacity, longer life) and lead batteries (rugged construction, relatively forgiving to charging abnormalities). What interests me, as being a person that spends 70% of the year at anchor, is the way it will increase the apparent capacity of my solar panels, extend the life of my AGMs, and give me slightly more house bank capacity.

Anyone boasting their AGM (or any other lead construction) batteries last 10+ years don't use them like I do. Last year I cycled my AGMs 40-50% each day for 250 days. Even the best AGM batteries in the best charging/discahrging conditions, won't last 10 years with that type of duty cycle.

 

[DDW]

I get the attraction to a hybrid bank, but really think that in the end is totally motivated by drop in batteries that don’t provide basic control signals as better BMSes do. With the most basic signals; Allow to Charge, and Allow to Discharge, alternators can be easily and gracefully turned off, and any need for a hybrid bank goes away. The hybrid is just a way to hack around incomplete BMSes.

I don't think "totally motivated". It depends a little on the definition of "hybrid bank". An advantage of LA batteries is they are stone axe simple, and don't suddenly fail. On a modern boat sudden failure of the battery means all nav electronics goes dark, engine stops and all com gear quits. That is a sub-optimal scenario.

In the other thread I was contemplating connecting the LA start and LFP house with a FET isolator. This seems to be recommended against by the ABYC, but the failure contemplated in this thread would not be a hazard - the LFP bank cannot discharge into the LA bank even if is it shorted. In the event of a disconnect of the LFP bank, the instruments might go dark (if wired to the house) but the engine would continue to run and you could flip a switch and get the instruments (and everything else) back on in a few seconds. If the BMS trips for some reason on an all LFP boat, you might be floating there for hours or even days debugging it. Given that the BMS very likely has a higher failure rate that the cells themselves, this is not an imagined concern. Whatever drawbacks "drop-ins" may have, they do have paralleled BMSes, which may (or may not) increase reliability.

If you have an LA engine battery charged by DC-DC, the engine continues to run for a little while until they are depleted. If the alternator instead directly charges the engine battery and the house LFP is charged by DC-DC you need one hell of a DC-DC or a long time to charge.

 

[rslifkin]

If you have an LA engine battery charged by DC-DC, the engine continues to run for a little while until they are depleted. If the alternator instead directly charges the engine battery and the house LFP is charged by DC-DC you need one hell of a DC-DC or a long time to charge.

For that scenario, in my mind, if high charge rates are needed, the engine(s) should have 2 alternators (1 for start, 1 for house). I consider starting power (and power in general for engines that need power to run) safety critical, so I'd always want an alternator on each engine feeding power to its start battery. The idea of feeding the alternator to house and then having start battery charging considered secondary concerns me. Even on a purely mechanical engine, the start battery typically powers the engine instruments so there's still some power desired (and being consumed) when the engine is running.

 

[DDW]

The problem can be that two alternators are hard to fit on some engines. My Cummins QSB for example. Much easier to fit a large single. On that engine, the consumption of the engine alone is around 15 or 20A to keep the ECU, injectors, electronic throttle, etc. alive. This is enough load that within a few minutes, if no source of charge, it will begin alarming for low voltage (as it expects a charge source when running).

 

[rslifkin]

The problem can be that two alternators are hard to fit on some engines. My Cummins QSB for example. Much easier to fit a large single. On that engine, the consumption of the engine alone is around 15 or 20A to keep the ECU, injectors, electronic throttle, etc. alive. This is enough load that within a few minutes, if no source of charge, it will begin alarming for low voltage (as it expects a charge source when running).

In that situation, I'd definitely want the alternator feeding the start battery. Charging the house would have to be either an ACR (if the battery configuration makes that reasonable) or 1 or more large enough DC-DC converters when a second alternator can't be installed.

 

[DDW]

Hard to find a 24V DC-DC that can do 250A, when you do you find it is very expensive. An ACR violates the ABYC's recommendations, and has the problem that the LFP house bank will discharge into a shorted LA start bank. It seems to me that a FET isolator solves all of these problems. Alternator always has a load. Banks can't discharge into each other, ever. Available at least to 200A inexpensively. If BMS disconnects suddenly there are no immediate issues.

One question I have had on DC-DC chargers is what is their step response? If charging at 100A and suddenly disconnected, what happens to voltage regulation? It doesn't have the energy that an alternator has, but it has some energy so I'd assume you'd see a voltage spike on the output. High enough to be damaging? No manufacturer seems to publish that.

 

[rslifkin]

The FET isolator might be viable depending on alternator output voltage, how it's regulated, etc. For DC-DC, it may involve multiple in parallel depending on how big the alternator is.

 

[Jeff F]

If the alternator instead directly charges the engine battery and the house LFP is charged by DC-DC you need one hell of a DC-DC or a long time to charge.

Right. And large dc-dc chargers make little sense. So your alternator is relegated to being a slow charger for the house bank.

For many with solar, a big charger and a generator this may be just fine. Lithium does fine at PSOC. No need to get to full charge every day.

 

[Jeff F]

The more I think about this whole thing, the more I question taking (more) power off the engine to generate electricity.

I'll start another thread.

 

[DDW]

You need to get a full charge every day if you are going to use it overnight. I've not seen a 24V DC-DC boost-buck charger that can take the 280A the alternator can produce. I doubt that it would be cheap if I find one. And I'm having a hard time understanding what problem it solves compared to a FET isolator. I'd be stuck with a CV charge on the AGM start battery, but this is actually allowed by Lifeline for their AGMs. Not true for a line charger which could be plugged in for weeks, but just fine for an alternator run at most 6-8 hours a day. Most AGM manufacturers recommend 6 hours at Absorb voltage unless you have current sensing to switch to float, and only the Wakespeed regulator has that. The charge voltage for the LFPs I'd use is spec'd at 28.4V, only a tenth or two lower than the ideal for the AGM.

 

[rslifkin]

You need to get a full charge every day if you are going to use it overnight. I've not seen a 24V DC-DC boost-buck charger that can take the 280A the alternator can produce. I doubt that it would be cheap if I find one. And I'm having a hard time understanding what problem it solves compared to a FET isolator. I'd be stuck with a CV charge on the AGM start battery, but this is actually allowed by Lifeline for their AGMs. Not true for a line charger which could be plugged in for weeks, but just fine for an alternator run at most 6-8 hours a day. Most AGM manufacturers recommend 6 hours at Absorb voltage unless you have current sensing to switch to float, and only the Wakespeed regulator has that. The charge voltage for the LFPs I'd use is spec'd at 28.4V, only a tenth or two lower than the ideal for the AGM.

Would the LFPs be happy staying at that voltage for hours and hours if they're already full? Or would you need a somewhat lower set-point? Realistically, for a starting battery, if it's never drawn down more than what's required to crank the engine and it gets an occasional kick from a shore charger, I wouldn't see a problem holding it at a steady float voltage with the alternator (so something like 27 - 27.6 volts for a 24v system).

 

[Jeff F]

You need to get a full charge every day if you are going to use it overnight.

Really? How big is the bank again? You're presenting this as a universal need, but with lithium it goes away almost entirely.

 

[DDW]

Realistically, for a starting battery, if it's never drawn down more than what's required to crank the engine and it gets an occasional kick from a shore charger, I wouldn't see a problem holding it at a steady float voltage with the alternator (so something like 27 - 27.6 volts for a 24v system).

A starting battery could be charged from a DC-DC, though on an electronic diesel it need to be big enough to feed the diesel. But then it doesn't act as a sink for a runaway alternator. AGM will not suffer much from being near absorb voltage for 6 hours a day. Might shorten its life a little. But no where near what most people do to them by undercharging them.

Really? How big is the bank again? You're presenting this as a universal need, but with lithium it goes away almost entirely.

Amps in have to equal amps out. If you don't have enough sun to get the amps back in, and a dock isn't handy, you are going to use diesel. If you oversize the bank it might be tomorrow not today, but it isn't next week. If you live in Florida and have tons of deck space for solar, then it can work. Not everyone is in that situation.

 

[catalinajack]

I'm still using AGMs on my boat. At this point, LFP would be a bit more expensive (but not dramatically from what I've seen) and I'd have to re-design the alternator to house battery charging setup (the rest of my equipment would just need settings adjusted). So up to this point, being that the AGMs work fine for my use case, I haven't felt a reason to switch. I figure I'll assess again when I'm due to replace batteries or have a reason to make other changes and then see how it all looks at that point.




Charging-wise, the best I can do from the engine alternators or solar is about 0.14C on my boat. The inverter/charger is big enough to provide just under 0.2C, however. Interestingly, I've found that while my AGMs will accept more than 0.2C until they're up to somewhere around 80%, if you try to feed them 0.2C or higher continuously they start to get rather warm (but 0.15C causes only a slight temperature increase). One day when they were a bit low, but charging from solar, I fired up the generator for something and found that I was pushing power into the batteries at about 0.25C. At that rate, the battery temps started climbing pretty rapidly and actually got hot enough that the solar dropped to float and the inverter stopped charging until the batteries cooled a bit (around 120* F).

Getting from 50% to truly 100% topped off in 5.5 hours with any lead chemistry is pretty unlikely. 99% is quite possible, but truly topped off takes a lot longer. With a 920ah bank, you'd have 460ah to make up. Assuming you're charging at 100 amps and you make it to 90% before getting to absorption voltage and the resulting current tapering, you'd be in bulk for about 3:45 to get to 90% SoC. I'd expect 1.5 - 3 hours in absorption depending on the batteries and your end absorb target. But even then, they'll still be taking some power once the charger drops to float, so they're not quite full (although close enough on flooded batteries that get equalized periodically, especially if they do see a longer float sometimes).

As an example, for my Fullriver AGMs, the recommended charging profile is to bulk to 14.7 volts, absorb at 14.7 volts until current is down to 0.02 - 0.012C, then float at 13.65 volts for 8 hours before they're considered truly full. Realistically, that'll only ever happen when we're on shore power, so I have my solar keep them in absorb down to 0.01C, figuring the slightly longer absorption phase will get them closer to topped off when they only get a couple/few hours of float before the sun goes down.

99% vs 100%, yes, a distinction with a miniscule difference.

 

[catalinajack]

The Lifeline AGMs in my sailboat would accept over 0.5C when discharged to 50% SOC. This would drop to about 0.2C by 80% SOC. They would not temperature limit. That is faster than flooded cells are likely to charge. However the weak point of AGMs is the need to fully recharge periodically (like weekly at least), and that takes just as long with flooded as AGM. It is best for flooded to also recharge fully, but they can be equalized to minimize the sulfation that results from partial state of charge.

LFP are really much better suited to the task of live aboard boating. Their downside is the complexity of installation and management. Lifecycle costs now favor them.

Life cycle costs do indeed favor LFP if you live long enough or keep the boat long enough.

 

[catalinajack]

The intent of the subject Bank Manager Plus is to "bolt on" LFP batteries to an existing lead battery bank. Whether it is considered a separate bank, or mixing similar chemistries in the same bank is up for debate. I'm attaching a schematic on how the Bank Manager Plus is connected. In case the lead or LFP bank shorts, or has some issue, the BMP will disconnect the two "banks" when the voltage is different. It only connects the banks in series when the voltages are the same (or within a set delta V).



The advantages are it is relatively easy to install without changing alternators, chargers, wire size, etc. It just bolts on. Also, you get advantages of both LFP (quick charging, more useable capacity, longer life) and lead batteries (rugged construction, relatively forgiving to charging abnormalities). What interests me, as being a person that spends 70% of the year at anchor, is the way it will increase the apparent capacity of my solar panels, extend the life of my AGMs, and give me slightly more house bank capacity.



Anyone boasting their AGM (or any other lead construction) batteries last 10+ years don't use them like I do. Last year I cycled my AGMs 40-50% each day for 250 days. Even the best AGM batteries in the best charging/discahrging conditions, won't last 10 years with that type of duty cycle.

"Anyone boasting their AGM (or any other lead construction) batteries last 10+ years don't use them like I do. Last year I cycled my AGMs 40-50% each day for 250 days. Even the best AGM batteries in the best charging/discahrging conditions, won't last 10 years with that type of duty cycle."

I am certain you are quite correct, but the folks doing the "boasting" are not boasting at all. They are merely stating that, for their use case, their batteries last "X" number of years. Your use case (and needs) are simply different.

So, let me boast about my batteries, simple FLA golf car batteries. They are now almost six years old, have been 50% cycled about 150 times, and test to 97% of original capacity. I suspect they will last at least 10 years and will cost about $1,500 to replace. LFP would add nothing to my style of use. For others, it clearly does.

 

[catalinajack]

For that scenario, in my mind, if high charge rates are needed, the engine(s) should have 2 alternators (1 for start, 1 for house). I consider starting power (and power in general for engines that need power to run) safety critical, so I'd always want an alternator on each engine feeding power to its start battery. The idea of feeding the alternator to house and then having start battery charging considered secondary concerns me. Even on a purely mechanical engine, the start battery typically powers the engine instruments so there's still some power desired (and being consumed) when the engine is running.

Why bother with having a dedicated starting battery. Just use your giant house bank to start your engines.

 

[Insequent]

Why bother with having a dedicated starting battery. Just use your giant house bank to start your engines.

After x days at anchor, the purpose of a giant house bank, it may not have enough juice left to start the engines. Seperate start batteries, either for mains or a generator are prudent.

 

[rslifkin]

Why bother with having a dedicated starting battery. Just use your giant house bank to start your engines.

I consider engine starting power to be safety critical, so I wouldn't want to risk any scenario where it's possible to drain the batteries used to start the engines. And if you're going to have a separate battery bank as a backup, you might as well use it as the primary starting bank and keep the big load spike from engine cranking away from the house loads (especially with a lead-acid house bank where you'll see a noticeable voltage dip). I also have engines that need power to run after they're started, so the more independent I can make the systems that keep the engines running, the better.


That same logic is why I have 2 start batteries. Then in an emergency even if 1 of the start batteries were to fail, I'd still get one engine running right away (and could go down and switch the other one to the good start battery and fire it up as soon as I'm able). Basically, other than charging from the engine alternators underway, the house and engine battery systems are kept completely independent. And either engine (and the generator) can be selected to use either starting battery.



Basically, my goal was a system that minimizes the risk of mistakes in operation, avoids needing to manually flip switches around, and minimizes the risk that I'll turn the key and have an engine not start due to insufficient power.

 

[catalinajack]

I consider engine starting power to be safety critical, so I wouldn't want to risk any scenario where it's possible to drain the batteries used to start the engines. And if you're going to have a separate battery bank as a backup, you might as well use it as the primary starting bank and keep the big load spike from engine cranking away from the house loads (especially with a lead-acid house bank where you'll see a noticeable voltage dip). I also have engines that need power to run after they're started, so the more independent I can make the systems that keep the engines running, the better.


That same logic is why I have 2 start batteries. Then in an emergency even if 1 of the start batteries were to fail, I'd still get one engine running right away (and could go down and switch the other one to the good start battery and fire it up as soon as I'm able). Basically, other than charging from the engine alternators underway, the house and engine battery systems are kept completely independent. And either engine (and the generator) can be selected to use either starting battery.



Basically, my goal was a system that minimizes the risk of mistakes in operation, avoids needing to manually flip switches around, and minimizes the risk that I'll turn the key and have an engine not start due to insufficient power.

I do have generator starting batteries. That is all the redundancy I need. Jumper cables word as does a switch to parallel the generator batteries to the mains. Question: In what scenario would you drain your house batteries too low to start your engines. Are we all not absolute fanatics about juice use and monitoring thereof?

 

[rslifkin]

I do have generator starting batteries. That is all the redundancy I need. Jumper cables word as does a switch to parallel the generator batteries to the mains. Question: In what scenario would you drain your house batteries too low to start your engines. Are we all not absolute fanatics about juice use and monitoring thereof?

I wouldn't expect it to happen in any normal situation. But the house batteries are the ones with all of the loads connected to them, while there's nothing connected to the engine batteries that isn't controlled by the key switch. So in the event of some kind of systems failure, having the house batteries drained or house power interrupted is far more likely than having something draw the engine batteries down (other than one of the batteries failing suddenly).

My engines also have the big, old school, direct drive starters, not modern reduction geared starters. So the initial current inrush when you start cranking is quite significant, and I'm not sure a half-charged house bank would be enough to prevent the voltage dip from rebooting electronics. I know from before the battery layout was changed that a pair of G31 batteries (fully charged and with the shore charger running) would suffer a big enough voltage dip from cranking an engine to reboot the stereo, chartplotter, etc. Having the separate start batteries eliminates that concern.

In my case, I deleted the generator start battery instead of engine start batteries and let the gen just share with the engines. I could drop to 1 start bank and have the "2" position on the switches allow a start from the house bank, but I haven't had a reason to do it.

 

[Bitstream]

I came across an interesting product that allows you to combine LiFePo4 batteries with AGMs in a house bank. There are several advantages, including getting more capacity from your battery bank, more capacity from solar panels, and extending your AGM battery life. The cost of it is $530 with a necessary contactor. You can watch a video of it here: https://youtu.be/AJIFW_2GEwc

The product is called the "Battery Bank Manager Plus" and is made and sold by Clark of Emily & Clark's Adventures, a sailing Youtube channel. I have no association with them except as an interested potential paying customer. It seems to have a lot of advantages, but I'm not keen on installing a little black box with questionable long term support that controls an important function on the boat.

I have 6 Lifeline 4D AGM batteries, each with 210A-Hr capacity at 12V. I have a 24V DC system, so my combined house bank capacity is 6 x 210 / 2 = 630A-Hr at 24V. Or half of that, 315A-Hr, if you discharge to only 50% of the bank's capacity. I'd like to exchange 2 existing AGMs for 2 new Battleborn 8D 12V LiFePo4, each with 270A-hr capacity. I would be losing 105A-Hr of AGM capacity but gaining 190A-Hr of lithium capacity (assuming I can use 70% of the lithium capacity) for a total gain in capacity of 85A-Hr (27% more capacity than I have now). That doesn't sound like a lot, but I will also be extending the life of AGM batteries and getting more capacity from my solar.

The total cost of this would be between $5K assuming I can sell my 1 year old AGMs for something. Have any of you seen this product, installed it, or considered something similar?

Sterling offers a separate device the call a "Battery Chemistry Module" that allows a single charger to handle multiple battery types. Its about $300 US.
https://www.sterling-power-usa.com/batterychemistrymodule-2.aspx
I just installed a Sterling Power ProCharge Ultra : 12 Volt, 50 Amp Marine Battery Charger to handle the 2 new 8D AGM batteries in my house bank. So far I am very happy with it. I like the remote panel in the pilothouse!

 

[Slowmo]

Most people don't really understand the chemistry of LiPo batteries. The claims that Li-iron are 'safe' is a relative statement. They are safer that Li-cobalt but not safer than lead acid. What layman don't understand is that Li itself is highly flammable as is the electrolyte used which contains Li ions. Li is extremely reactive to oxygen and water. Any puncture of a Li battery is extremely dangerous and can lead to fires. Also internal shorts can cause fires. So the claims of how safe these batteries are must be put in the proper context. If you have one in a boat you should really consider a fire proof container to contain any fire should one occur. This is how aircraft (e.g. Boeing 787) help contain the risk.

 

[twistedtree]

Most people don't really understand the chemistry of LiPo batteries. The claims that Li-iron are 'safe' is a relative statement. They are safer that Li-cobalt but not safer than lead acid. What layman don't understand is that Li itself is highly flammable as is the electrolyte used which contains Li ions. Li is extremely reactive to oxygen and water. Any puncture of a Li battery is extremely dangerous and can lead to fires. Also internal shorts can cause fires. So the claims of how safe these batteries are must be put in the proper context. If you have one in a boat you should really consider a fire proof container to contain any fire should one occur. This is how aircraft (e.g. Boeing 787) help contain the risk.

Speaking of not being understood... Yes, Li (lithium metal) is reactive with water, but there is virtually zero Li metal in a Lithium Ion battery. The cathode is Lithium Iron Phosphate which contains Li atoms, but they are part of a more complex molecule. It's no different from H2O. Hydrogen is extremely explosive, but water isn't even though it contains hydrogen atoms.


I think in pretty much every way, LFP are safer than lead acid batteries, not more dangerous. Remember, lead acid batteries 1) contain lead, one of the most poisonous substances on earth, 2) contain sulfuric acid, one of the most corrosive substances on earth, and 3) emit hydrogen gas, one of the most explosive substances on earth. I'll take LFP any day over lead acid.

 

[dannc]

...
I think in pretty much every way, LFP are safer than lead acid batteries, not more dangerous. Remember, lead acid batteries 1) contain lead, one of the most poisonous substances on earth, 2) contain sulfuric acid, one of the most corrosive substances on earth, and 3) emit hydrogen gas, one of the most explosive substances on earth. I'll take LFP any day over lead acid.

Exactly.

I know of two boats that had lead acid battery explosions. One boat ended up with a mess and decreased battery capacity during a Pacific crossing. The other boat sank.

I don't know of any boat using LiFePo batteries that has exploded and sunk or exploded without sinking. Even with poor quality, suspect LiFePo batteries. I would surely like to know of any incident involving LiFePo batteries.

Later,
Dan