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Old 02-09-2016, 10:35   #5341
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by evm1024 View Post
You should pick up a copy of Nigel Calder's book Boatowners Mechanical and Electrical Manual It will help.

In electricity Current is the flow of electrons (e.g. the number of electrons that flow through a wire per second) and is measured in amps.

The "force" that each electron has is the voltage.

It is the current that sets the size of the wire (as was noted above).

Each battery cell has the ability to supply some number of electrons per second (current) and when you put the cells in series they each pass the same number of electrons per second and thus the current is the same for a series string as for each cell. Each cell has a specific voltage (3.2v for LiFePO4 plus or minus) and with them in series the voltages add together thus 4 cells in series have the same current at one cell but 4 times the voltage (4 * 3.2 = 12.8).

When you place the cells in parallel the voltage of the cells do not add and thus is the same as a single cell. But each of the parallel cells supplies some number of electrons per second and those are added together. Thus cells in parallel have a greater current than a single cell.

(this holds true for solar panels too)

Regarding the size of the cells - it has been noted in this thread and in others that larger cells do not handle the movement of a sailboat very well and may fail due to that movement. Internal strength of the cell. It has been noted that the recommended max size of a cell for marine applications was 200 AH. I have no idea how true this is but it does make some sense.

Also, the failure of a single 1000 AH cell in a bank of 4 really screws up your house bank and costs lots to replace. While a failure of 1 200AH cell in a 1000 AH bank (5p4s - 5 200 AH cells to equal 1000 AH, 4 sets of 5 of them in series to equal 12.8 volts) only reduces the total capacity of the bank by 20% (1/5) to 800 AH....


Food for thought.

Regards
Thank you very much for that derailed explanation. It explains parallel and series very well. Your conclusion about the AMP size of each battery is exactly where my mind was going. The good old redundancy and failure planning approach.

I don't buy into the risk of the larger AMP batteries being more susceptible to being damaged because of boat movement. If any sized litho battery isn't properly secured anyway you are playing with fire.

What is the incidence of known good and tested batteries failing in the field? Given the relative low cost now of the very large AMP batteries, isn't economical to have a spare sitting there for redundancy?

But your premise on redundancy is well taken. Thank you.

Happy sailing.

Chaya
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Old 02-09-2016, 10:48   #5342
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Some day, one of these guys will actually publish a more polished "how to" for all this. I suspect some have even started but found that their real jobs get in the way of this..
Bingo...
I know of 4 Marine Equipment Vendors that started and then stopped their entry into the LiFePO4 battery market. They bailed not necessarily out of technical complexity or because the technology isn't quite figured out yet...but because of the realities of the market in dealing with Cruisers and the associated liability from that reality.

This isn't a knock on us, it's just the reality about us.

Boat electrical is just such a weak point for so many cruisers that you would not really be a seller of LiFePO4 batteries, but rather a designer, redesigner, troubleshooter and all around electrical systems engineer for the entire boat. With all the insurance and liability that would entail. Now that is perfectly fine IF that is the line of work you want to go into and your clients would be willing to pay for said services...but....

The more complicated a product you sell, the more you have to build into the price of your product the "Peripheral Customer Education and Assistance Mark-up" to cover the time it will take NOT servicing the equipment you sold, but in educating and troubleshooting the clients equipment that interfaces with what you sold them. No one ever wants to pay for that service separately so if you don't build it into the price of the product you sell, then you are basically working for free (Not a Good Business Model). And if you tell a customer that you sold them a battery, it's not your job/responsibility to know how to set their brand of battery charger, alternator regulator, solar controller, wind generator or flux capacitor then you are in their mind giving them poor after sales support and within a week your name is mud on every internet chat site and marine FakeBook page known to mankind. Since you declined to help them, then they will turn to the underbelly world of internet chat forums for the advice and we all know where that snake-pit can lead...right to a fried $3000 battery bank that they of course would want covered under warranty or they will threaten to give you a 1 start rating on Yelp. (now come on...you know this is true).

It's why some new technology cost so much, not necessarily because the new technology is more expensive, but because there is not the existing knowledge base in the general public and peripheral equipment to use it correctly and that takes money (higher prices) to deal with successfully. Then when you charge those higher prices, you are an evil 1%-er raping and pillaging for obscene profits...ahhhh...
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Old 02-09-2016, 10:53   #5343
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

The internal construction of large cells is what is cited as a cause of vibration failures. Not enough support for large sections of foil... Me, I don't know about the true failure rate.

Argentina huh - I climbed Aconcagua back in the 80's. Spent a fair time in Mandoza. Lovely place, good beer, great steaks and fine people.
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Old 02-09-2016, 11:17   #5344
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by evm1024 View Post
The internal construction of large cells is what is cited as a cause of vibration failures. Not enough support for large sections of foil... Me, I don't know about the true failure rate.

Argentina huh - I climbed Aconcagua back in the 80's. Spent a fair time in Mandoza. Lovely place, good beer, great steaks and fine people.
I understand. Thank you. Given the lack of test data and trial experience of the very large batteries I do believe it's sensible to go for smaller. Not necessarily 200AMP but at least 400AMP. And yes, I would look at carrying a spare. Just in case.

Mendoza is wonderful. Last year I toured the winery's. I really enjoy their Marbec. Also last year I went on an all day trail ride on horse back in the Andes. Absolutely amazing experience. I usually go to Mendoza once a year. I also go south to Patagonia. Also an absolutely amazing part of the world.

You are right about the meat. Grass fed free range cattle. Steaks are huge, thick and juicy. Without the chemicals and hormones you get from beef in other parts of the world.

I'm lucky my income comes from the USA while I have the cost of living of Argentina. A full breakfast for the cost of a Starbucks in the States is hard to argue against.

I like Argentina. It has its issues but after the political change it has a great future ahead. In a selfish way I just hope the good things don't change.

Regards,

Chaya
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Old 02-09-2016, 17:51   #5345
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by GoingWalkabout View Post
I understand. Thank you. Given the lack of test data and trial experience of the very large batteries I do believe it's sensible to go for smaller. Not necessarily 200AMP but at least 400AMP. And yes, I would look at carrying a spare. Just in case.
Actually, the point that folks are trying to make is that using smaller cells gives you built-in spares (if you will).

Let's ignore voltage for a moment (to make it simpler). You are trying to achieve around 1000AH of capacity. You can get that from a single 1000AH cell, or 5x 200AH cells (in parallel), or 10x 100AH cells (in parallel). (or several other combinations, but you get the idea).

Now, if your bank is made from 1000AH cells, and a cell fails - you have no power.

However, if your bank is made from 5 of the 200AH cells, and a single cell fails, then you can re-wire to bypass that failed cell, and still have the remaining 4 cells at 800AH available to you. You might have to skip using the Air Conditioning or ration power in other ways, but at least you can limp back to port.

That is another benefit (besides internal strength) to combining the smaller cells to make larger banks.

Make sense?

(Oh, and I got this from reading the whole 5000 post thread, which took me several weeks, but was VERY educational).

-Greg Kulosa
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Old 02-09-2016, 18:22   #5346
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by greg_kulosa View Post
Actually, the point that folks are trying to make is that using smaller cells gives you built-in spares (if you will).

Let's ignore voltage for a moment (to make it simpler). You are trying to achieve around 1000AH of capacity. You can get that from a single 1000AH cell, or 5x 200AH cells (in parallel), or 10x 100AH cells (in parallel). (or several other combinations, but you get the idea).

Now, if your bank is made from 1000AH cells, and a cell fails - you have no power.

However, if your bank is made from 5 of the 200AH cells, and a single cell fails, then you can re-wire to bypass that failed cell, and still have the remaining 4 cells at 800AH available to you. You might have to skip using the Air Conditioning or ration power in other ways, but at least you can limp back to port.

That is another benefit (besides internal strength) to combining the smaller cells to make larger banks.

Make sense?

(Oh, and I got this from reading the whole 5000 post thread, which took me several weeks, but was VERY educational).

-Greg Kulosa
Thanks Greg. I understand the point on redundancy. It could be just as easy for me to have a spare 1,000AH. It has been said that there could be an issue of internal stability inside the much larger LifePO4 batteries. This for me is the biggest argument for going smaller. I need to research this point further. If it is true then I could see the sense in going with more 400AH. Also I think tacking into account if I want to have a 24V system may change my thinking.

So many questions still remain. For instance, what effect is there in having power balancing built into the batteries from the factory in the MPPT?

I also think given the real life experience of sailors deploying large LifePO4 banks along with large solar banks we should have a new thread perhaps called 2016 LifePO4 and solar power systems for sailboats.

Just a thought.
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Old 03-09-2016, 10:49   #5347
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Bingo...
I know of 4 Marine Equipment Vendors that started and then stopped their entry into the LiFePO4 battery market. They bailed not necessarily out of technical complexity or because the technology isn't quite figured out yet...but because of the realities of the market in dealing with Cruisers and the associated liability from that reality.

This isn't a knock on us, it's just the reality about us.

Boat electrical is just such a weak point for so many cruisers that you would not really be a seller of LiFePO4 batteries, but rather a designer, redesigner, troubleshooter and all around electrical systems engineer for the entire boat. With all the insurance and liability that would entail. Now that is perfectly fine IF that is the line of work you want to go into and your clients would be willing to pay for said services...but....

The more complicated a product you sell, the more you have to build into the price of your product the "Peripheral Customer Education and Assistance Mark-up" to cover the time it will take NOT servicing the equipment you sold, but in educating and troubleshooting the clients equipment that interfaces with what you sold them. No one ever wants to pay for that service separately so if you don't build it into the price of the product you sell, then you are basically working for free (Not a Good Business Model). And if you tell a customer that you sold them a battery, it's not your job/responsibility to know how to set their brand of battery charger, alternator regulator, solar controller, wind generator or flux capacitor then you are in their mind giving them poor after sales support and within a week your name is mud on every internet chat site and marine FakeBook page known to mankind. Since you declined to help them, then they will turn to the underbelly world of internet chat forums for the advice and we all know where that snake-pit can lead...right to a fried $3000 battery bank that they of course would want covered under warranty or they will threaten to give you a 1 start rating on Yelp. (now come on...you know this is true).

It's why some new technology cost so much, not necessarily because the new technology is more expensive, but because there is not the existing knowledge base in the general public and peripheral equipment to use it correctly and that takes money (higher prices) to deal with successfully. Then when you charge those higher prices, you are an evil 1%-er raping and pillaging for obscene profits...ahhhh...
You are entirely right in all of the above Rich. You still have huge numbers of customers who buy Trojan 105's who proceed to destroy them in a year with poor charging and usage practices. Some how the market has accepted that the batteries aren't always at fault (usually not as we all know). Still many of these customers will blame the tech installer or battery seller and want "free" support. We had to established the true problems and then give some "free" support which mostly entailed telling the customer what they needed to do that they didn't do and then let them fight it out with the battery manufacturer after that. Or we insisted of upgrading their overall battery system to prevent preventable problems.

The issue, as you note, is that lithium tech requirements are much more stringent and extensive with a complete support system around the lithium batteries. And the customers require an extensive education and reset of how to manage the system. In reality that isn't wildly different from a complete propulsion system. It harder for many to grasp invisible electrons than it is to see prop shaft alignment, proper cooling systems, and clean fuel supplies for engines, with proper attention to gauges and procedures. This is old hat stuff now yet there are still customers who screw it up daily. Techs still charge by the drink to fix problems that everyone knows are customer caused. Lithium batteries are in the early knowledge, understanding, acceptance, and support stages. It is starting to change though. If I were providing tech support now for a brand new lithium installation it would probably be too expensive for most customers, again as you note, as it would have to include extensive education, training, and the setting of who is responsible for what costs.

The issue of the bad apple customer is unfortunately a reality of the modern world with easy promulgation of slurs and slander whether deserved or not. I'm not sure how you solve that issue or just have to counteract it somehow. I'm sure you have had some of those types of issues yet you still get customers who recognize you know a few things about the products you sell and provide the right level of support. And it is entirely different selling product versus just selling services. Based on what I have seen you provide more hand-holding than most.

I write too long and I just deleted a much longer set of thoughts. Suffice it to say I believe that the overall market is slowly developing. In the US, at least, a better distribution system for cells is required so you can actually buy what the vendors advertise. And more techs need to be around to support the installations and provide ongoing support. At first it won't be techs selling the batteries (like you do your watermakers and refrigeration systems). They will provide consultation and installations only, like it seems Maine Sail does. And the overall acceptance of lithium as a viable option needs to be established in the trade press and in local markets.

And some of the noise level on how much cell management overhead is required has to settle down. The controversy only serves to intimidate customers who might otherwise get lithium systems. With the overall costs of robust charging regulation and battery monitoring being as high as they are, the systems will not be for every boater. But we are seeing more and more boaters who want the systems and are installing them, many of them under the radar like the several around my area that I didn't even know where there. It isn't just the cruisers on this forum even though this forum seems to be the most active and useful of any I have seen.

It certainly doesn't help that you "have to read all 5,341 posts to understand how to install and use lithium batteries on your boat". A professional manual/book from a respected source would go a long way to help with that issue, much like Nigel Calder's books. It's remarkable how helpful his one big book has been to the overall DIY market. A lithium book, even a rough one, would be a hlepful start.
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Old 03-09-2016, 11:11   #5348
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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It has been said that there could be an issue of internal stability inside the much larger LifePO4 batteries. This for me is the biggest argument for going smaller. I need to research this point further.
I have reached out to both Winston and CALB regarding cells up to 400Ah about vibration testing and stability and both companies stated their 400Ah cells are built to the same standards for vibration as the smaller cells. Neither manufacturer had any qualms about cells between 200Ah & 400Ah for use on boats.

When I asked what the specific testing was (which standard they were tested to) neither company replied other than to say they are tested to our own high standards for vibration.

CALB did say that one competitor has been know to spread rumors that are unfounded and they through perhaps that is where this started.

CALB right now is not currently building 400Ah cells (lower demand for sizes above 200Ah and high demand for sub 200Ah cells) but can still build them if demand warrants it.. Winston is not currently available in the US unless you buy it under the Voltronix label.

I did not ask about cells larger than 400Ah so can't comment on that.
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Old 03-09-2016, 12:18   #5349
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

... I am starting to get interested in solar to have another charging source for my 400Ah LiFePO4 (4S) Winston cells.

I am considering a Fox260Li regulator and came across this warning in the manual:

The solar regulator should never used parallel to other chargers! A secure monitoring of the charging currents will be impossible than.

I am a little bit lost about this statement (or are they only trying to say that the regulator will not monitor the supplied current from another charging source, e.g. an alternator running at the same time?) Thoughts?

Thanks!

Carsten
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Old 03-09-2016, 14:32   #5350
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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I completed the testing of my new Lithium install today and thought I'd share the setup and a few photos with the folks here that provided me so much help and guidance.

So this is for my 2011 Lagoon 450. The boat was built for the charter trade and has extensive dc loads (2 not too well insulated fridges, a freezer, all electric winches, etc) and a large 13KW generator along with full air conditioning. In charter, the mode of operation was sail/motor during the day, run the generator (and air conditioning) all night which also recharged the 800 AH of AGM batteries. My wife and I will be living aboard in the Bahamas and did not want to be a slave to the generator and are willing to give up air conditioning (or at least cut back it's use to every other week or so). I bought the boat in March not in great shape; two years of charter and three years of utter neglect had taken its toll so Iíve been busy with restoration and repair since then but converting to a large Lithium bank and upgrading the solar have been high priorities.

So I started with the size and weight of the pre-existing batteries - they weighed about 520 lbs and fit under the berth in the master cabin along with a really disturbing rats nest of cables and wires that connected them and connected the master switches for the house batteries and starboard engine. I considered a 4P4S arrangement with CALB CA400AH (1600AH) cells but they were hard to get and seemed to be getting harder to get rather than easier. The 180AH cells were plentiful and I was told (and have since confirmed) that they actually have at least 200AH capacity. So I opted for an 8P4S configuration (1440AH). I got the cells from Kelly Larsen at the Electric Car Parts Company in Utah. They actually shipped from CALB USA in California and arrived at my local freight depot. I picked them up (not easy in a Subaru, but thatís another story) and moved them to my basement for few months to ďget to know them.Ē

I followed Maine Sailís advice and got a decent bench supply (0-60A, 015V) and top balanced them in groups and ultimately together (32P - takes time to top balance with 50 or so amps spread over 32 cells). I then configured them in the 8P4S setup and, using my new Victron Multi 3K inverter/charger started cycling them - charging and discharging all the while monitoring the stability, behavior, and performance. The Victron was a little tricky to program but I followed the general advice of Rolf Roetter and Rich Boren and tried to set it up for a consistent 13.8v in absorption with no float. BTW, this is also where I learned a valuable lesson - connections matter! (duh) After fooling with jumper cables and finally replacing them with cheap but decent automobile battery cables the charging and discharging behavior settled down and I started getting predictable and expected behaviors. I also started being careful in assembly of the configurations, polishing the terminals and using dielectric grease for all the bus bar connections.

I then added the components of a homegrown BMS. I used the Lightobject programmable voltmeter (discussed extensively in this thread) driving a pair of BlueSea 7713 remote battery switches. Programming the Lightobject was easy and I ultimately wired the on board relays in series with the manual remote switches that came with the 7713s and (on the boat) used those switches to replace the Battery Master switch. The Lightobject voltmeter has 4 programmable settings that translate to Charger cutoff (14.1v), Charger restart (13.6v), Load cutoff (12.6), Load restart (12.8). These are initial settings and may change as I gain more experience. I also purchased a Junsi 8s logger for cell level monitoring but have not yet decided whether I will install that on the boat - the 8P cells are just incredibly stable and with the careful top balancing Iíve done, they never seem to drift more than a couple of millivolts apart.

While still set up in my basement I also wired up (and got to know) a Victron BMV 700 battery monitor - a marvel of a device that has really helped me understand and anticipate the behavior of the bank. It also drives alarms for high and low voltage (inside the range of the HVC/LVC) as well as for low capacity. It has much more capability that Iím just beginning to explore but I canít say enough good about this product. Peter Kennedy (Peter Kennedy Yacht Services - Marine Electrical Systems) helped with all the products I wound up buying - all the Victron and Blusea stuff Iíve mentioned plus busbars, fuses, remotes, etc.

Once I started moving the setup from my basement to the boat, things got serious and I sought some advice and help. I had all the pieces and parts (charge bus, load bus, ground bus, remote switches, shunts, etc) but was unsure about where to put everything. Andy and Rouric from Yacht Electronic Systems suggested a layout for all the components and offered to help with the recabling. I installed everything the way Andy suggested and then gladly accepted their help in removing the old batteries and untangling the ratís nest of cables in the existing setup. They did beautiful work and when that was completed I did the actual installation of the batteries. They are installed carefully inside a frame I designed and built and that also accommodated full length ratcheting hold down straps.

I also reprogrammed the existing Cristec chargers to 13.8 volts and use them primarily as back up to the Victron Multi Charger. When it has external power (shoreside or generator), the Victron will throw 120 Amps non-stop at the new batteries until they reach 13.8v at which point it will switch to absorption and rapidly tail off current and eventually float (which Iíve programmed to be effectively off).

I also replaced the crappy controller that came with the pre-existing solar panels mounted over the davits as practice for my upcoming solar upgrade (also another story).

I completely sidestepped the (seemingly endless) debates about the best approach to deal with the alternators. I view the alternators as a backup to the solar (primary) and the Victron (primary when the generator is on or when docked with shore power and backed up by the Cristecs). We also donít motor very much - itís a sail boat ya know. Anyway, I didnít have the money to upgrade the rudimentary hitachi 80 amp alternators so I just left them attached to the starter batteries and ran the house bank connections to a switch that allows me to turn them on as chargers when I need to and have the time to monitor them and turn them off when I donít.

Finally, I also had to cut back the drawer that fits under the berth to accomodate the Victron. That space is pretty tight now and I'll probably have to add better ventilation but for now am just monitoring the temperature in there.

Anyway, weíre just getting used to the new setup and I still have to tackle the solar upgrade. But Iím pretty proud of the way it turned out and attached some photos of the install for anyone whose interested. Happy to answer any questions or provide more photos if anyone is curious about the details.

And a big thanks to all of you for your help and advice!
Nice setup! One thing that I may add.. If you could, cover the tops of the batteries with some kind of plexiglass or similar to prevent anything from falling on the terminals. In the highly unlikely event that the Victron falls off the board it won't ground out on a couple posts. Like I said, highly unlikely, but anything could happen and I hate saying that.

Other than that's very nice. Another thing, who made that electrical panel? Very snazzy.!

See more @ redemptiverepair.com
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Old 03-09-2016, 16:56   #5351
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I am certainly not an expert on this thread, but I'll try to help if I can.

Quote:
Originally Posted by GoingWalkabout View Post
Thanks Greg. I understand the point on redundancy. It could be just as easy for me to have a spare 1,000AH. It has been said that there could be an issue of internal stability inside the much larger LifePO4 batteries. This for me is the biggest argument for going smaller. I need to research this point further. If it is true then I could see the sense in going with more 400AH. Also I think tacking into account if I want to have a 24V system may change my thinking.
I think you need to continue to read and study - especially about balancing these LiFEPO4 battery banks. It will not work well to just "have a spare 1,000AH" cell. It is very unlikely to be at the same state of charge as the other cells, and that will cause you problems if you need to swap it in. It also won't have aged the same, because it has not been in use.

Again, that goes back to the recommendation to make a bank from multiple smaller cells. If you need to remove some cells, the remaining ones are presumably all the same age, and should be at the same SOC, so you still have a nicely balanced bank.

The smaller cells are also lighter, and easier for a single person to move around, especially under bunks, etc.

24 or 12 volt systems don't really change this, except that for 24volt you have twice the number of cells in series.


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So many questions still remain. For instance, what effect is there in having power balancing built into the batteries from the factory in the MPPT?
This is a non-sensical question. MPPT is a type of Solar charge regulator. It does not affect battery balance at all (except that you want to program your charge source to stop charging when the batteries are full, which is different for LifePO4 than for lead-acid).

You might be referring to the commercial Lithium packs that have internal BMS (Battery Management Systems). But those have no relation to MPPT.
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Old 03-09-2016, 18:20   #5352
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Interesting discussion from MIT "Why We Still Don't Have Better Batteries"
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Old 04-09-2016, 15:35   #5353
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by Maine Sail View Post
I have reached out to both Winston and CALB regarding cells up to 400Ah about vibration testing and stability and both companies stated their 400Ah cells are built to the same standards for vibration as the smaller cells. Neither manufacturer had any qualms about cells between 200Ah & 400Ah for use on boats.

When I asked what the specific testing was (which standard they were tested to) neither company replied other than to say they are tested to our own high standards for vibration.

CALB did say that one competitor has been know to spread rumors that are unfounded and they through perhaps that is where this started.

CALB right now is not currently building 400Ah cells (lower demand for sizes above 200Ah and high demand for sub 200Ah cells) but can still build them if demand warrants it.. Winston is not currently available in the US unless you buy it under the Voltronix label.

I did not ask about cells larger than 400Ah so can't comment on that.
Very interesting. Thanks for sharing. Both manufacturers don't see a problem with internal vibration.
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Old 05-09-2016, 10:37   #5354
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

As that this is the Prime LiFePO4 thread I thought I would post this here.

In the various lithium threads we always measure the voltage of the cells. In the thousands of post we have only talked about what we measure the voltage with a (very) few times. As I recall, Mainesail did point out that he used a calibrated Fluke multimeter. And that is the point of this posting.

Perhaps you are like me and have 5 or 6 handheld multimeters ranging from a really poorly performing model that I picked up in Ukraine (Chinese copy of a fluke) to 2 Tektronix bench models to a rather nice Fluke handheld.

When I started on my LiFePO4 install I decided that rather than send the Tek modules off to Tertronix to be calibrated I would buy a new Fluke 87-v that had been calibrated and use that to calibrate the Tek and other DVM that I had.

https://www.amazon.com/Fluke-FLUKE-8...multimeter+87v

I can say that all of the multimeters that I have were 10's of mV off and in the case of the fluke copy 100's of mV off. My Mytex meters were not too bad.

Accuracy (reading the correct "true") in voltage is important and that is where calibration comes in. But, in the case of measuring the difference in cell voltages precision is very important too... My less expensive meters often would read 3 or 4 mV different second to second. (measure, wait a second measure the same cell and see a difference).

So the bottom line is that you should take a look at your meter and decide if it is up to the task. See if you can get a guestemate of it accuracy by comparing to a meter of known accuracy. Also, check its precision by repeatedly measuring a cell and see if it reads the same each time.

If you have any doubts consider upgrading your meter. You do not have to spend $400 to get a good meter. But having known accuracy and having 4 or 5 digits is oh so nice.
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Old 05-09-2016, 11:02   #5355
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

FWIW, regarding single large or multiple smaller banks...over the past year we have seen at least one CALB 180Ah cell in a 180Ah x 24V pack/bank die for no reason. The QC seems to have been going downhill for some time, as in the Genasun shop they have seen wildly varying columbic efficiencies between cells when cycling testing packs. In any case, the client had two independent 24V banks running in parallel, so he only had to switch the bad one off and still had a working system (albeit at 1/2 capacity). The pack/bank with the bad cell had to be warrantied, which involved sending a new one to the boat in Tahiti...not much fun but it finally got there and client is off & running.
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