Going from Lead to Lithium

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Vessel Name
CHiTON
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Tung Hwa Clipper 30
WARNING: Long and rambling post

My present lead-acid battery bank consists of 4 6V batteries in two banks. They are deep cycle 260Ah on a 1-2-Both switch. In theory, I have 560Ah at 12V, although I set my shunt monitor to show only 245 usable amp hours, figuring that is probably 50% of what is remaining on my old batteries. I haven’t done a legitimate load test on them, but my readings with the hygrometer are not inspiring.

So I started looking at replacement. Simple drop in lead-acid, in fact the identical batteries, are $300 each, and I would have to drive to Seattle. I can’t complain about the service I got out of the lead-acid, including using them as the start battery, but they do require maintenance, they have spit out a little acid into the battery box, and they are monstrously heavy. You know, lead-acid.

I looked into alternatives like 6V AGM. No need to water. Not quite as heavy (3# lighter). Available as start/deep cycle. Some said they got 10 years out of them, others much less. Cost was going to be similar or maybe a little more money for only 440Ah (220 usable at 50% SOC). They would be true drop in, including using the same battery cables. So a simple install, never need watering, and maybe a little faster charging was the only benefit.

Lithium was interesting to Google research. Some threads reminded me of the doomsday predictions back in the day about microwave ovens, pushbutton phones, LED lights, induction stoves, etc. Lots of issues to learn about, be confused about, and/or be frightened about. Since my first mate is my wife, my first issue is always safety. Therefore, I had to look at the cases where lithium batteries caused uncontrollable fires. However, as with the “radiophobia” once associated with microwave ovens, I think that the “lithiophobia” surrounding lithium batteries has now receded and need not be addressed when considering LFP batteries.

There are still legitimate concerns about switching to lithium. The first is the possibility that a battery management system (BMS) in a lithium battery can turn itself off. This would be the same as turning off a 1-2-Both-Off battery switch to the Off position (that is probably the historical source of this danger). The alternator doesn’t have anywhere to send its production, causing a voltage spike. The voltage spike can damage the diodes in the alternator (requiring service) and also some of the boat’s electronics. Turning the battery switch to the Off position has happened, but it is sort of like a fighter pilot accidentally yanking on the ejection seat handle. Just don’t do that. Switching to Off has certainly happened and from that we know that a BMS shutdown could cause damage to the alternator (under certain circumstances).

I wondered how to assess the risk. While it is hard to come up with exact numbers on the possibility of an out-of-the-blue BMS shutdown, it might still be possible to do some kind of a risk analysis. Several purported methods of reducing the likelihood of an alternator failure when installing LFP include leaving a lead-acid battery somewhere in the system, often as a start battery. I understand this line of thinking, but I was having difficulty in accessing the risk, or even if there was a risk, other than the “accidental ejection seat.”

It just happens that I live in a house that has a combination wood/electric stove. Woodburning on one side and electric coil elements on the other. When Roosevelt instituted the Rural Electrification Administration in 1935, people were really wary of this new-fangled electricity inside the house. And what if an electric power line broke? How would one cook or heat bath water? So, the Monarch Stove Company came up with the combination wood/electric stove that is in my kitchen. The stove still works fine, but it is now kind of a curiosity. Maybe lead-acid batteries will be the same in a few decades. Maybe sooner.

Leaving lead-acid in the system didn’t seem to be necessary. The work-around sometimes includes the use of a gadget that still allows the alternator to send a charge somewhere to a lead-acid should the BMS shuts down. For instance, one could send the alternator charge to the LFP battery and include a DC/DC transfer to a lead-acid battery. Then, if the BMS shut down, and the DC/DC gadget didn’t fail, it might transfer the current and save the alternator. I say might because I think that all the various proposed protections against BMS shutdown are based on the laws of probability, and nothing is 100%. I didn’t think it made sense to examine the various protections against BMS shutdown without first examining the probability of a BMS shutdown.

I was never intending to have a single LFP battery, either for house or start. My present setup has two banks, two batteries each, and I wanted to re-use as much of the system as possible, including the connection cables. Therefore, four batteries made sense. Also, most single LFP batteries didn’t have as many amp hours as I wanted. Some of the larger ones could work, but they have some problems besides size and weight. The problems tend to be discharge current and redundancy.

Fortunately, both are addressed with the same solution, i.e., more LFP batteries. A 100Ah LFP battery generally has a 1C (100A) maximum continuous discharge rate allowed by the BMS. In theory, one could run a 100A draw (for less than one hour). My engine starter requires about 500A for less than one second, but then still has a substantial draw for another second. Using two 100Ah batteries in parallel would mean less stress per battery for starting. Three would be better. Four would be even better, but the bank would still exceed each individual battery’s continuous discharge rate. Better yet would be batteries that had a larger allowable BMS discharge current available. 280Ah LFP batteries are available that each have a BMS with a 200-300 continuous draw (some also have an 800A maximum draw for 10 seconds). That means that the starting “stress” on a bank of four 280Ah LFP batteries used as a house/starter bank could be <50% of their rated continuous current. And >14% of the bank’s maximum current.

But will discharging LFP batteries (even at less than their designed current rating) damage them? Probably. Just like all batteries, including lead-acid starter batteries. A lead-acid battery is only good for a certain number of starts over a certain amount of time before it wears out. Some get 500 starts, some get 1,000. The 280Ah LFP batteries I bought are rated at 15,000 cycles. That is likely an exaggeration. Maybe with my usage I’ll only get 2,000 cycles. I can live with that, especially since the 4 LFP will give me 6 times the available house amperage in each cycle and twice the number of starts compared to lead.

Then there is the redundancy issue and the law of probability. Instead of a single battery shutting down, I am planning on a bank of four LFP batteries. There is not enough information to support actual numbers, so I had to make something up for the purpose of risk analysis. Let’s say that I have my alternator connected directly to a single LFP battery and the chance of that BMS shutting down is 1:100, meaning that for every 100 times I go cruising there is one possibility of the BMS shutting down. From the reports of those who have cruised for years with the alternator direct to LFP (with a properly adjusted external regulator), we know that the probability of BMS shutdown is much less. Nevertheless, we can use that number. This includes the possible shutdown modes of over-heat, over-charge, under charge, and battery cell imbalance.

The lead acid “fixes” that are proposed generally include a lead battery to accept the charge should the LFP BMS shut down. But lead-acid batteries can also fail and cause damage to an alternator. Common failure modes for lead-acid batteries include overcharging, undercharging, sulfation of the negative plate, acid stratification, water loss, thermal runaway, short circuit, contamination, and premature failure (among others). When a lead-acid battery explodes, that obviously would result in the same voltage spike that a BMS shutdown would cause. But just for fun, let us say that that the possibility of a lead-acid failure is one in a million. LFP alternator damage is one in a hundred and lead-acid is one in a million. Looks like the lead-acid “fix” is the better bet.

But here is where redundancy and the law of probability work their magic. I decided that a single LFP has a 1:100 (.010) chance of a BMS shutdown. The probability of two shutting down at the same time is (.01) X (.01) or a one in ten thousand. For a three-battery bank, simultaneous shutdowns would be (.01) X (.01) X (.01) or a one in a million possibility. Four LFP batteries would be one in a hundred million. That’s just the way the math works. Four LFPs is much safer than the lead-acid battery “fix.” Maybe four LFP are even safer than relying on some kind of a DC/DC gadget. I don’t know how often they fail. Maybe also one in a million chance? Instead of spending $400 on the gadget, simply get another LFP battery to increase the safety factor to one in a billion (if I’m doing the math right). And instead of a lead-acid starter battery, for the same money one could buy still another LFP and increase the safety factor to one in 100 billion (that’s just two banks of 3.) Most LFP can be put in to banks of 4. You can do the math for that one.

The above calculation is based on a BMS shutdown being an independent events, of course. If they are dependent events, meaning that there is some correlation between shutdowns, the math changes. We can pretend that one battery overheating presupposes another battery is soon to overheat (which may also presuppose that the alternator battery heat sensor fails at the same time). Or, if a cell in one battery overcharges, then a cell in each of the other batteries will immediately overcharge. Those scenarios are imaginable, but I think most would likely be premised on a common external fault that isn’t related to whether the battery bank is LFP or lead-acid.

For instance, let’s assume that the alternator suddenly starts putting out 28V. All of the LFP batteries shut down, which causes a voltage spike that blows the diodes in the alternator, but not before burning up most of your sensitive electronics. Now let’s run that scenario with lead-acid. The lead-acid accepts the overvoltage until it melts or explodes, which causes a voltage spike that blows the diodes in the alternator, but not before burning up most of your sensitive electronics. The damage is the same except that all the LFP batteries saved themselves, while the lead acid battery was destroyed and spread acid all over the locker.

I bought LFP batteries with Bluetooth, but I’m not sure how much Bluetooth can save one from a catastrophic failure. It has proven interesting when charging them up for the first time. They were quite low (29-30%) based on what I had seen others say when receiving LFP batteries. I have a motley crew of old lead acid chargers (a 6, 8, and 10A charger) that I put on them and then watched them closely (the next day, as each took overnight). It was interesting watching the individual cells because they were sometimes off by a tenth of a volt, but later the lagging ones might be ahead of the ones that earlier had the higher voltage.

At one point, I was surprised to see an “overvolt notice” on one battery that was at 98%. One cell was at 3.6V and the other three were at 3.5V. While I was trying to understand what this meant, I figured out that although the notice was still on my phone, the event seemed to have passed. The battery was charging normally and soon at 100%. I was unable to tell if the battery had ever actually shut down, and if so, for how long. It was like driving a car that notifies of a flat tire, but before one can pull over, the system fixes the tire and you are on your way. I’m not sure what to think of that.

Besides installing the four LFB batteries, the only other change I plan on making is replacing each bank’s 250A ANL fuse with a 250A T class fuse (my entire electrical system, including the starter cable, is fused as per MarineHowTo). I may also buy a Balmar Alternator Protection Module (APM). I’m still uncertain as to just how much protection it provides and what are the actual chances of four BMSs shutting down at the same time.

Speaking of probability, as part of my research, I looked up the chances of being struck by lightening. A person has a 1:15,300 of being struck by lightening in their lifetime. It is more likely that one will be struck by lightening than four LFP BMSs failing at once and hurting an alternator. What have you done to protect yourself? Fortunately, I’ve already had my lightning strike (unfortunately, it doesn’t work like that.)

Mark
 
From the old school days of start battery for engine, house battery for house loads, made sense then, it still makes sense now. So when I switched to LFP house bank I kept the start battery.
In your own words even a momentary starter load exceeds the combined 400A batteries whether single 100's or less larger ones. But why even consider the designed house batteries to start an engine. Never mind predicted/unproven cycles lost. Whatif starting an engine causes a battery overload/overheat failure by a dual purpose use. Why risk not enough power to start the engine.
But just because I like redundancy does not mean your way is wrong.
Following.
 
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You'll be glad you sprung for the bluetooth units. You are thinking deeply about it all now...but after your done with your install and begin using them...it will all be part of the background again. As it should be.
BTW..I temp installed a single Epoch dual purpose 120ah battery on my old Perkins 6.354.4 along with a DC clamp meter on peak/hold. On the initial start maxed out the clamp meter at just over 600 amps. On subsequent starts, I got a bit over 560 amps. I started the motor 4 or 5 times in a row and the little 120ah battery didnt miss a beat.
 
Congrats on going LFP. You won't go back.

A few thoughts.

#1 I think you're overthinking the concern of BMS shutdown blowing alternator diodes. It's often cited as a possibility but I know of no one who has actually experienced it.

#2 The reason no one really knows how well the Balmar APM works is because #1 - BMS failure is exceedingly rare.

#3 LFP starter batteries are in the market and work well (antigravity being one brand). However they remain expensive.

Peter
 
I'm just dabbling in thinking about maybe going LFP. Maybe. My biggest roadblock is we intend to use the boat for just 2 maybe 3 more cruising seasons. I would have to completely change the charging system, upgrade the cables etc. In terms of $$$ a non trivial exercise. As of this morning my thinking is that I will likely replace the aging FLA batts with like kind.

Now on with my mental ramblings.

One of the big concerns is as OP says the fear of fire. A lithium fire is a frightening event. How often does it happen with LifePo4? Not very often, in fact it seems to be rare. I have searched for good technical information on the safety of LifePo4 and been unable to find any. I can find lots of info by manufacturers. But no independent studies. I can find lots of "We KNOW they are safe." But who is we and how do we know. For instance just because I read here on TF everyone knows LifePo4 safe how do we know? I can relate one trustworthy source who will no longer install LifePo4 or any lithium batteries. He's a knowledgeable skilled outfitter of RVs and has 1st hand experience with a LifePo4 thermal runaway. Yes, the BMS shut down, but the thermal runaway did not stop.

OP and others discuss the risk to the alternators from a BMS shutdown. Like fires, rare. I saw a video by Nigel Calder about the "best" way to connect batteries in parallel. It is similar to the attached image. Maybe this would work? Alternator(s) connected to the busses that gather all the leads. Any one LFP BMS shutting down might not bring the entire system down and kill the alternator(s).

Batteries in parallel.png
 
Google "lifepo4 battery fires" and read
You bet I searched that topic. Also searched LifePo4 battery safety. What turns up from the top down are links to:
DIY Solar Forum. A public forum that "knows" LifePo4 is safe.
Relion battery. A battery manufacturer.
Definitive Technology Group. Seems to be a manufacturer of systems using LifePo4.
Reddit.
Evlithium. A marketer of lithium batteries as well as other batteries
Electrical Engineering Stack Exchange. Seems to be a forum.
National Fire Protection Association. I had hopes for meaningful info here. Nothing on LifePo4. Very little good info at all.

None of the above are independent authoritative sources. None get to the point that we here on TF and on other forums "Know" LifePo4 is safe. And why we know that beyond seeing it on the internet and repeating to ourselves.

Today, in response to your post, I searched again and found a new one to me. It was at the bottom of the page of search results. Probably the best source I have yet found.
ScienceDirect. Thermal runaway and fire behaviors of lithium iron phosphate battery induced by over heating To see more than an overview of the abstract I'll need to purchase the PDF. At $24.95 I'm sure it's worth the cost. The paper seems to be studying thermal run away caused by external heating.

I'm not fear mongering. I'm trying to answer a question. I'll use a technology or system others won't touch as long as I understand the risks and how to mitigate them. All of my boats have had propane cooking. One had propane heating, propane fridge and propane cooking. I removed the heating because of the moisture generated. That boat also had gasoline engines. Eventually disconnected the refer because the insurance company pitched a fit. Nearly any system can be managed safely once the risks are understood. Simply saying we "know" something is safe is not enough. My question of how do we know LifePo4 is safe is valid.
 
I will submit that the title is a misprint "iron" is only mentioned in the title "ion" is seen nine times in the article.
But go ahead and search that title for other links
"Thermal runaway and fire behaviors of lithium iron phosphate battery induced by over heating"

Just do not heat your lifepo4 batteries to 270*C on purpose
HERE is a PDF of a study
 
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I will submit that the title is a misprint "iron" is only mentioned in the title "ion" is seen nine times in the article.
But go ahead and search that title for other links
"Thermal runaway and fire behaviors of lithium iron phosphate battery induced by over heating"

Just do not heat your lifepo4 batteries to 270*C on purpose
HERE is a PDF of a study
Yes, the weakness of the link I posted was intentional overheating of the batteries. Not particularly valuable. Use of "Iron" vs "Ion" in the title, looking at the name of the authors the paper is likely a translation. The link you have posted is better info.
 
My question of how do we know LifePo4 is safe is valid.
I've been down this rabbit hole and recognize the above literature, internet posts, etc. It has now been 5 years since Will Prowse posted his challenge to reward anybody who could produce credible proof that a LFP battery could suffer from thermal runaway. Nope, nada, nothing. So maybe it's like proving the permanence of gravity. Sure it's here today, but what about tomorrow? We need proof and nobody can provide it! And gravity is probably the ultimate safety issue.

From the published data, thermal runaway requires a cell's core temperature to exceed 500F. That's why the only study that allegedly produced thermal runaway in an LFP battery had to use a hot plate. A hot plate that would be glowing red. A hot plate that was heated above the ignition temperature of gasoline and diesel. What this means to boaters is, if your vessel is on fire long enough, the thermoplastic casing on an LFP battery could melt and the internal cells would get hot enough to support a thermal runaway! Anybody see a problem with this "danger?"

One could claim that there hasn't been an authoritative and dispositive answer to the issue. I was hoping for an ex cathedra ruling on LFP safety by the Pope, but I got tired of waiting. I'll just have to rely on the ABYC.
 
How about "Has anyone here that has been using these batteries had a thermal problem"

I don't think so. More like "Does anyone here regret the LiFePO4 changeover"

Silence.

Yeah, if you heat your batteries to 270C which is 518F you will have a problem. But that means the boat was already on fire and the battery problem doesn't matter anymore.
 
From the old school days of start battery for engine, house battery for house loads, made sense then, it still makes sense now. So when I switched to LFP house bank I kept the start battery.
In your own words even a momentary starter load exceeds the combined 400A batteries whether single 100's or less larger ones. But why even consider the designed house batteries to start an engine. Never mind predicted/unproven cycles lost. Whatif starting an engine causes a battery overload/overheat failure by a dual purpose use. Why risk not enough power to start the engine.
But just because I like redundancy does not mean your way is wrong.
Following.
@SteveK Steve, old school for me (GB36) is 2 8Ds, one for each engine, handing both starting and house. Many older GBs are still wired this way ;-)
 
@SteveK Steve, old school for me (GB36) is 2 8Ds, one for each engine, handing both starting and house. Many older GBs are still wired this way ;-)
My GB36 came to me with 2-8D, one for start both engines and one for house with a 1-2-all switch.
The 8D for both was way more battery than they needed due to fast starts the battery hardly got used, the dedicated port alternator hardly worked.
 
I can relate one trustworthy source who will no longer install LifePo4 or any lithium batteries. He's a knowledgeable skilled outfitter of RVs and has 1st hand experience with a LifePo4 thermal runaway. Yes, the BMS shut down, but the thermal runaway did not stop.
Even a skilled outfitter can be wrong. There are different ways to deem something as acceptably safe. There is product and engineering data. And there is also field data. I think the feedback of the field data confirms a high level of safety on par with lead acid. There are some trade offs possibly in favor of one vs the other. But there are some safety factors that are rarely considered that heavily favor a quality Lifepo4.

Ill bring up one. In full disclosure, I do tech support for Epoch Batteries. As such I get many many calls, texts and emails with problems from the field. Over the past year I have received approximately 5 or 6 calls regarding the large Epoch 460 marine battery banks being installed in either boats or campers where the battery had no output and had triggered a warning on the app. In the most recent, the customer was trying all manner of things and flipping switches to get the system online to no avail. Of course the customer assumed the battery or batteries were to blame since there was no output. During the call I asked them to open the app and look and see what the warning actually said. In these cases the app had a warning of "SC PROT". That is the abbreviation of Short Circuit Protection. I told him to shut everything down and disconnect the cables and that we would do some testing. To set the conditions for SC PROT on the 460ah Marine battery the BMS has to sense 1650 amps for 400uS (.0004 seconds) and it will then instantly shut down output via the mosfets. He had two of the 460 Marine batteries, both in SC Prot. This event is so anticlimactic that users tend to have no idea they just short circuited a very large battery system. The customer was then directed to ohm out the positive and negative battery cables and sure enough, direct short. Had this been a large lead acid bank and he threw the battery master on...the actual location of that short would have been know fairly quickly. So that is a handful of actual examples where a quality BMS saved the day from something that could have been minor damage to completely catastrophic. Please dont ask why there was no fusing because I cant answer that. In most cases the boat electrical was being worked on so who knows what was happening at the time. The customer did finally state that during the course of working electrical issues the previous day (prior to the Epoch install) the tech had some arcing in the area of the alternator and ended up making some changes. In another case the boat was just purchased and they were trying to get system power to test the DC system. It had just had a survey too. In the other scenarios it was usually just an accidental short when moving wires with power on that resulted in barely an arc. So these are real world scenarios IMO being in favor of a good Lifepo4.

FYI..the 460ah Marine does have an internal 500amp gR fuse that is similar to a Class T fuse with a 50k AIC rating. But in all short circuit cases but one, the BMS beat the big fuse to the punch due to the time scales involved for the BMS. Obviously appropriate fusing of a lead acid system is needed. But who knows what happens out there. Mistakes are occasionally made.

I think your boat would essentially already have to be on fire for lifepo4 to be an issue.
 
I have completed 3 years on my Li house bank. I am very happy I went down that road, other than the price dropped about 40%.

I kept the AGM starting bank and used a DC to DC charger for the LI back. I can get into it if needed.

Suggestions in picking a Li battery. Do you want Bluetooth? Personally I like it! I live just out side Boston . Since life04 cant be charged below 32, I bought a battery with an internal heater. So its goof proof for me.

Good luck with the install!
 
@SteveK Steve, old school for me (GB36) is 2 8Ds, one for each engine, handing both starting and house. Many older GBs are still wired this way ;-)
That is how my single engine MT came to me. I added a DC2DC charger and a 100ah battery to power an inverter to run my refrigerator at anchor. We have no gen set.
 
Barking Sands,

Thank you for the very informative post. Your position as tech support for Epoch Batteries puts you in a position to evaluate the safety issue.

SteveK and Marco,

My thinking is that LifePo4 is safe when installed and managed correctly as is any potentially dangerous system on a boat. Trying to find good info on LifePo4 safety is as Marco says falling down a rabbit hole.

As I said in my first post on this thread I probably will replace the ten 6 volt golf car batts with like kind because our projected ownership is too short to make the full expense of the change to LFP sensible.
 
From the old school days of start battery for engine, house battery for house loads, made sense then, it still makes sense now. So when I switched to LFP house bank I kept the start battery.
Like with my wood/electric cookstove, I predict one technology will win and the other become a curiosity. My wood cookstove still works, in fact I use it most cold mornings. But most people have moved on the the new technology despite the grave concerns in the old school days.
But why even consider the designed house batteries to start an engine. Never mind predicted/unproven cycles lost. What if starting an engine causes a battery overload/overheat failure by a dual purpose use.
I'm not sure what a "designed house battery" is. Is it the common use at present? Is it what the marketing department calls it? A starter might pull too much amperage for a small LFP battery's BMS, causing it to shut down. One solution is more batteries. But what if it blows up like lead-acid batteries do? Probably should not Google that. Some of the pictures show what happens from sulfuric acid burns. Not pretty. Especially when it gets in the eyes. If there is a battery technology worthy of unfounded fear, it is probably lead-acid.
Why risk not enough power to start the engine.
My battery bank will have over 1,000 amp hours available, so sort of like having a 1,000 MCC battery. Actually, the MCC rating for a lead-acid battery is only for 30 seconds, because lead poops out so fast. My battery bank will be exceed 30 seconds (by about an hour) as 1,000 amps from the LFP battery bank is its continuous current rating. And the MCC rating includes the ability to keep the discharge voltage above 7 volts. Not a problem with lithium. Unlike the problem of lead quickly pooping out, the issue with lithium is fusing all that power. And if they suddenly go dead like lead, I have a portable NOCO starter. It is also lithium. I wonder why?

I'm not picking on SteveK. I shared these same concerns and they are understandable when doing research. I've found that most don't stand up.
I've looked at various diagrams that claim a buss bar improves a bank's performance and I just can't get there for my two 2 battery banks. The configuration is lightly more complex and costly for a possible minimal gain. Using a buss bar does not increase the safety factor should one battery shut down. When the batteries are paralleled "in a train," each can still function independently of the others should one shut down, although with less available amperage, as is the case with a buss bar system.

If I understand correctly, the purpose of the buss is merely to equalize the charge/discharge of each battery. In theory, the length of the charge and ground cables are equal for each battery, therefore the batteries charge and discharge equally, allegedly improving performance and maybe longevity. But I'm skeptical. I can think of three main things that effect the voltage to and from the batteries. 1) the length of the cables, 2) the size of the cables, and 3) the quality of the connections. Looking at the picture, it is clear that the conductor length for each connection is not exactly the same. Batteries 1 and 3 are further downstream. How far downstream depends on the length of the buss. If all three battery lugs and the main conductor lug were simply bolted together, that could be equal but the issue then would likely be getting a clean connection when mashing four lugs together, i.e., problem 3).

Problem 2) is cable gauge. Obviously, if Batt 1 is connected with 2/0 and Batt 3 is connected with 4/0, they would not be equal despite equal length cables. Unless (maybe) the ground for Batt 1 was 4/0 and the ground for Batt 3 was 2/0. That would likely equalize the effective resistance to the batteries and they would charge the same. All of this seems a little silly because, in my mind, it is really problem 3) that is at issue.

If any one of the lug connections, buss bar or battery terminal, has more or less resistance than the others, that will effect the charge/discharge rate of that particular battery. The dreaded hot terminal. A buss bar doesn't fix that. A battery in the rear of a "train" configuration might have an extra 3 feet of cable, meaning that the "caboose" battery is three feet from the "locomotive" battery. It might be a .003 voltage drop because of increased cable length. Now figure what a bad lug connection/crimp in the system can do. It seems to me that the quality of the connections is always, always, always going to be more important than any tiny attempt to equalize the length of the cables by using a buss bar. So much so that screwing with a buss bar, especially with my 2 battery bank, simply doesn't matter. My locomotive is next to the caboose.

That's my theory (today).

Mark
 
You do not need a buss bar for two batteries as it was proven to not make a difference worth worrying about.

Designed for means they are house load batteries which we have been talking about. House batteries are designed for continuous draw usage.
They make batteries that are designed for a short large draw for starters.
Yes I have heard there is a new combo coming out.

I am not ready to wake up and be unable to start the engines because something drew down the combo battery system overnight. Still old school.
Maybe the next Generation will have one battery the size of a cell phone to do it all.
 
Marco,

Regarding parallel connections. I'm not going to quote your entire post, I'm only responding to your thoughts on paralleling. Where I got the idea in my post #5 was a YouTube by Nigel Calder The BEST way to Parallel Batteries on a Boat. Fast forward to 1:40 where he begins to talk about the method and where he got the info. Current Affairs - Making the Right Connections. The test was run on both AGM and LifePo4 batteries. Attached is a graphic of the test results.

Current_Affairs_Test_results.png


You are correct, all cables must be identical length. That was not well represented in the cartoon image I attached to post #5. I'm sure you are also correct that all aspects of the cables need to be equal. Size, conditions at the terminals, quality of the crimps.

While valuable data I would only go to the trouble on a new installation or a significant upgrade such as you are considering where I would reconfigure everything.

I should have taken the time to dig out Calder's video and test he was referencing. Might have saved you having to write up an excellent though long response to my post. The bookmarks were on a different PC and I was being lazy.
 
Marco,

Regarding parallel connections. I'm not going to quote your entire post, I'm only responding to your thoughts on paralleling. Where I got the idea in my post #5 was a YouTube by Nigel Calder The BEST way to Parallel Batteries on a Boat. Fast forward to 1:40 where he begins to talk about the method and where he got the info. Current Affairs - Making the Right Connections. The test was run on both AGM and LifePo4 batteries. Attached is a graphic of the test results.

View attachment 160834

You are correct, all cables must be identical length. That was not well represented in the cartoon image I attached to post #5. I'm sure you are also correct that all aspects of the cables need to be equal. Size, conditions at the terminals, quality of the crimps.

While valuable data I would only go to the trouble on a new installation or a significant upgrade such as you are considering where I would reconfigure everything.

I should have taken the time to dig out Calder's video and test he was referencing. Might have saved you having to write up an excellent though long response to my post. The bookmarks were on a different PC and I was being lazy.


I just got done installing LiFeP04 batteries on my boat. Three, 300AH 12 volt batteries in parallel.

I could have used equal length cables, I chose not to. Yes intentionally.

My batteries all go to buss bars mounted on the new battery box that I built. I used the buss bar to make cabling easier, and to make removing a cell easier if I have a problem.

Why not equal length cables??? Simple answer. I could not bring myself to make a ugly installation with excess cable all over the place.

Now to the reality that I personally saw, and see, using the app supplied for each battery.

After running all night all three batteries are within 2 percentage points of SOC from each other. Yep two percent.

Upon supplying the full output of my parallel Victron inverter/chargers, 240 amps total, I watched the new batteries charge. The closest one reached 100% first, and the BMS would not allow more current to go into the battery. Then battery #2 did the same thing. Within less than 5 minutes of each other all three batteries had stopped accepting current. They were not disconnected from the loads, they are smart enough to not accept current when they are full.

At this point the voltage was at 14.2 volts and the Victrons after a period of time went into float mode and the voltage gradually decayed to 13.5 volts, where it sits today.

Here in lies the problem. Nobody, with all of their measurements and lab equipment have shown that I am going to significantly lower the life expectancy of my batteries by connecting them with whatever length cables work best for my boat. Yes, they make great measurements, and nifty looking graphs, but not one of them has shown any significant real world difference in my batteries that have what, a 5,000 cycle lifespan?

Now before someone comes out and says "well joe is an expert and you are not" I'll just say that I am a recently retired degreed electrical engineering professional that spent my life working on electrical systems. Everything from battery plants to power grid operations, and grid automation. No I am not a LiFeP04 expert, but... I'm not inexperienced either.
 
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Kevin thanks for that report. That app shows what is seldom seen otherwise.
These new fangled LFP with a BMS in each do self balance.
 
Kevin thanks for that report. That app shows what is seldom seen otherwise.
These new fangled LFP with a BMS in each do self balance.
Yes, until I saw it with my own eyes I did not completely envision the concept of how it works.

I was thinking of a very old fashioned BMS that just opened up a relay if the batteries exceeded certain parameters. That was i think how BMS's used to work.

What I observed was a BMS that would stop current flowing into the battery when it was full, but not disconnect the battery, so it continued to power the loads.

With each of the three batteries operating independently it's easy to envision that the batteries each reach 100% charge.

I wish I had more or better screen shots, but I'm traveling for the holidays.

Here is a screen shot that shows two of the three batteries recharging.
 

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SteveK,

Agree completely, dedicated start bank. Redundancy is important. I go so far that the gen start batt could start the mains. And the dingy batt could start the gen. Both are a bit undersized but would do the job if needed.
I am not ready to wake up and be unable to start the engines because something drew down the combo battery system overnight. Still old school.
Maybe the next Generation will have one battery the size of a cell phone to do it all.
 
Yes, until I saw it with my own eyes I did not completely envision the concept of how it works.



Here is a screen shot that shows two of the three batteries recharging.
Looks like you have the 300ah Essentials. If havent done so already, you click the little pencil in the box icon at the end of the serial number you can rename each battery. In addition there should be an improved app in the next few months.
 
Looks like you have the 300ah Essentials. If havent done so already, you click the little pencil in the box icon at the end of the serial number you can rename each battery.
yes, that's what I have and great idea. I'll rename them.
 
Excellent write up. With a pair of jumper cables and gen set LA battery lithium is suddenly very interesting. The jumper cables can start the main engine once the genset is running if lithium fails.
 
I went the route of of 2 buss bars and equal size cables. I did use 4/0 cables, over kill but the price difference was small. This was for four 200A batteries. After 3 years of use, and being able to Bluetooth into each on. The batteries SOC are no more than 0 to 2% off from each other.

As far as being neat. I placed the buss bars on the opposite sides of the 4 batteries. Looks neater, but I do understand! Its only 30" form one side of the bank to the other. Not too bad.

If I had to use different cable lengths. Going with larger gauge cables would off set this. Do less of a volage drop along the cable.
 
Ksanders,
thanks for your real world experience report. Very informative! It's easy to fall down the rabbit hole of over researching and over thinking. Analysis paralysis.
I just got done installing LiFeP04 batteries on my boat. Three, 300AH 12 volt batteries in parallel.

I could have used equal length cables, I chose not to. Yes intentionally.
...
After running all night all three batteries are within 2 percentage points of SOC from each other. Yep two percent.
 
I just got done installing LiFeP04 batteries on my boat. Three, 300AH 12 volt batteries in parallel.

Related question. How did you get the batteries in La Paz? Heck, finding AGMs can be difficult in Mexico - what's the backstory on 300ah LFPs?

Peter
 
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