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Old 11-02-2018, 13:09   #1
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1400 Ah Lithium from cells

Here is my write-up of our 1418 Ah 4s12p install of 48 100Ah Calb cells for our Lagoon 450 Ad Astra

Many thanks to the various threads here to help me make the decisions behind this build.


1420Ah of Lithium + 2100 Watts of Solar – Sail Ad Astra
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Old 11-02-2018, 13:50   #2
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Re: 1400 Ah Lithium from cells

Great setup! Currently working on a 1000Ah Winston battery 4s for my Lagoon 400
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Old 11-02-2018, 13:58   #3
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Re: 1400 Ah Lithium from cells

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Originally Posted by CatNewBee View Post
Great setup! Currently working on a 1000Ah Winston battery 4s for my Lagoon 400
4 x 1000 amp hour cells?
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Old 11-02-2018, 14:10   #4
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Re: 1400 Ah Lithium from cells

It was a bit disconcerting for me to read this article for various reasons. The physical installation shown on the pictures and most of the description overall indicate that the author knows quite a lot about technology (stating that he he has degrees in aerospace engineering).

I have some formal issues with the article, e. g.
- the calculation in the "how much energy do we need each day" is this disturbing mixture of physical units often seen with technically inexperienced boaters. Here, in a technical article about building a LiFePO4 bank it is very unusual to see a mixup of "amps per hour", "watts per hour", "amps an hour" and the like. This raises red flags on my side for the remainder of the article, but this may be only me.
- I don't really understand why the design is using a 4SnP layout instead of nP4S. It makes things much more complicated (balancing is much more work, and this layout needs BMS probes for each single cell instead of only 4 for the parallel packs of a nP4S design

But that's not my real problem. There's some really bad safety practice shown in this article, and I believe this is outright dangerous for other people who might want to build their own bank.

I give the kids on the images the benefit of the doubt and I assume both are skilled in their work. But they are still kids, and you are responsible for their safety!
In the second image one of the boys can be seen working on the battery bank, terminals exposed. The boy is wearing a necklace which I assume will conduct electricity.
A LiFePO4 cell is capable of generating huge currents in a short situation. If this necklace gets in contact with the terminals, it will spontaneously heat up and possibly cause severe burns.

In one of the later pictures your boy is sitting on the cells. I hope he is not wearing anything made of metal as well. Above the pit a cable with cable shoes is at the edge, a small nudge might send it falling down on the terminals, causing a short. Same for the wires, bolts, tools etc.

Finally it looks to me like the final bank is just sitting in this pit, without any fixture to the boat or compression. That's probably calling for trouble.

Your boat, your responsibility, but I'd suggest readers intending to build their own bank read the excellent thread over here and get a lot of useful information how to improve on some things.
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Old 11-02-2018, 17:25   #5
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Re: 1400 Ah Lithium from cells

Quote:
Originally Posted by mbartosch View Post
- I don't really understand why the design is using a 4SnP layout instead of nP4S. It makes things much more complicated (balancing is much more work, and this layout needs BMS probes for each single cell instead of only 4 for the parallel packs of a nP4S design
The only reasonable argument I've seen for the 4SnP setup is that if you lose one cell, it doesn't known the whole bank down for long.

I did 4P8S for my 32 cell, 24V bank (180Ah CALB cells for 720Ah total). I thought about doing 8S4P the the simple reason that if one cell went bad in an 8 series group, I could easily wire that group out by removing a few bus bars and end up with an 8S3P group with 75% of the capacity to tide me over until I could limp to someplace to get a new cell.

With 4P then 8S, the loss of a single cell means one of my parallel groups is broken, with less capacity than the rest. Wiring out seven other cells is a lot more work, though it could be done I'd have to do a lot of re-arrangement.

But...the odds of an individual cell failure are low, and the benefits of 4P8S are otherwise huge in terms of saved complexity and costs of not buying 32 cell monitors instead of 8 or so I was being charged for them.
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Old 11-02-2018, 20:01   #6
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Re: 1400 Ah Lithium from cells

The children are still alive, and well. Thanks.

The cells are well packed and immobile as a solid unit as discussed at the end of the article.

The mixture of units was to explain how to think about energy consumption mostly for the benefit of land-based readers.

CF, always so much fun.
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Old 11-02-2018, 20:59   #7
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Re: 1400 Ah Lithium from cells

Awesome write up Erik thanks for taking the time to share.
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Old 11-02-2018, 21:15   #8
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Re: 1400 Ah Lithium from cells

Wow that's a lot of usable power for a relatively low price of entry. Thanks for the write up and images.
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Old 11-02-2018, 22:50   #9
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Re: 1400 Ah Lithium from cells

Thank you for sharing your detailed write-up just so we can beat you up over it. It's nice to see another LFP prismatic install >10kWh.

Critiques:

Others have commented on safety issues, and for new readers those are legitimate concerns. Inadvertently bridging an LFP cell can be a ... life-changing experience. It may be that using teenagers to do pack assembly is an ingenious choice: they have better dexterity, smaller fingers, and superior eyesight. I know all of my sketchiest moments building up my system have come when assembling and disassembling the cells!

One suggestion on nomenclature would be to make clearer the distinction between power and energy. It is usually possible to infer which one someone means when they mix them up, but sloppiness here can lead to mistakes or confusion. In a larger system, it's a good idea to internalize the difference between the two and to discuss engineering choices around both -- each in the right context. And, of course, the units for each are different.

There is a mention of high power consumption on a contactor that was going to be used in conjunction with a LVD, but I didn't see the details. It is possible to design a pretty low consumption design that works for this purpose, so I'm curious what happened here. Did you look at contactors with economizer coils? Do you have any numbers or data you can share here?

I see several times either 3.65v or 3.6v mentioned. I imagine you are not actually charging (or even top-balancing) to those high voltages day to day? Other than to trigger an occasional BMS shunt rebalance, staying lower will get you almost the same capacity and probably a lot more cycle life. Shoot for 3.45 or even lower if you can.

4s12p or 12p4s?

Several people on this thread have espoused a preference for parallel-first pack design. While there are many advantages to going that route, there are also a set of orthogonal advantages to choosing series-first. (Likewise, there are disadvantages to both approaches.) Most of these have been discussed on some of the other threads in this forum, but I'll tack on a few that were skipped over here:

1. It can be the case that there is no easy way to place and wire cells in a parallel-then-serial arrangement in a given enclosure. Layout constraints may make one of the two considerably simpler, cleaner, and more reliable, especially if equalizing interconnect resistance across parallel connections is important (good for wear-leveling and maximizing pack capacity).

2. Parallel-first obfuscates cell-specific issues. It can be quite difficult to identify a specific, underperforming (or failing) cell when it is ganged up in parallel.

3. Parallel-first design introduces the need to fuse between the parallel cells because of how the energy flows if a cell should fail dead short. The fusing itself can become a surprisingly tricky wiring, space, efficiency (electrical), and even cost issue. Most small parallel-first prismatic packs I've seen omit fusing, and that's a risk tradeoff that each person can assess... but it is one that is often overlooked nevertheless.

4. The pack in this thread appears to employ an "active" BMS with top charge-shunting/rebalancing. These BMSes are relatively more expensive and tend to scale the cost unfavorably in a series-first design. It is also possible to design a pack that performs well with only passive monitoring, and then the management component can be much less expensive in absolute terms but also in proportion to the cell costs. This, along with a high ratio of series count to parallel count (say, 16s4p for a 51.2v, 20kWh nominal pack) can certainly tilt the scales in favor of going with s-then-p.

The fun part is, there is no one right answer!
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Old 12-02-2018, 00:07   #10
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Re: 1400 Ah Lithium from cells

Quote:
Originally Posted by nebster View Post
Thank you for sharing your detailed write-up just so we can beat you up over it. It's nice to see another LFP prismatic install >10kWh.

Critiques:

Others have commented on safety issues, and for new readers those are legitimate concerns. Inadvertently bridging an LFP cell can be a ... life-changing experience. It may be that using teenagers to do pack assembly is an ingenious choice: they have better dexterity, smaller fingers, and superior eyesight. I know all of my sketchiest moments building up my system have come when assembling and disassembling the cells!

One suggestion on nomenclature would be to make clearer the distinction between power and energy. It is usually possible to infer which one someone means when they mix them up, but sloppiness here can lead to mistakes or confusion. In a larger system, it's a good idea to internalize the difference between the two and to discuss engineering choices around both -- each in the right context. And, of course, the units for each are different.

There is a mention of high power consumption on a contactor that was going to be used in conjunction with a LVD, but I didn't see the details. It is possible to design a pretty low consumption design that works for this purpose, so I'm curious what happened here. Did you look at contactors with economizer coils? Do you have any numbers or data you can share here?

I see several times either 3.65v or 3.6v mentioned. I imagine you are not actually charging (or even top-balancing) to those high voltages day to day? Other than to trigger an occasional BMS shunt rebalance, staying lower will get you almost the same capacity and probably a lot more cycle life. Shoot for 3.45 or even lower if you can.

4s12p or 12p4s?

Several people on this thread have espoused a preference for parallel-first pack design. While there are many advantages to going that route, there are also a set of orthogonal advantages to choosing series-first. (Likewise, there are disadvantages to both approaches.) Most of these have been discussed on some of the other threads in this forum, but I'll tack on a few that were skipped over here:

1. It can be the case that there is no easy way to place and wire cells in a parallel-then-serial arrangement in a given enclosure. Layout constraints may make one of the two considerably simpler, cleaner, and more reliable, especially if equalizing interconnect resistance across parallel connections is important (good for wear-leveling and maximizing pack capacity).

2. Parallel-first obfuscates cell-specific issues. It can be quite difficult to identify a specific, underperforming (or failing) cell when it is ganged up in parallel.

3. Parallel-first design introduces the need to fuse between the parallel cells because of how the energy flows if a cell should fail dead short. The fusing itself can become a surprisingly tricky wiring, space, efficiency (electrical), and even cost issue. Most small parallel-first prismatic packs I've seen omit fusing, and that's a risk tradeoff that each person can assess... but it is one that is often overlooked nevertheless.

4. The pack in this thread appears to employ an "active" BMS with top charge-shunting/rebalancing. These BMSes are relatively more expensive and tend to scale the cost unfavorably in a series-first design. It is also possible to design a pack that performs well with only passive monitoring, and then the management component can be much less expensive in absolute terms but also in proportion to the cell costs. This, along with a high ratio of series count to parallel count (say, 16s4p for a 51.2v, 20kWh nominal pack) can certainly tilt the scales in favor of going with s-then-p.

The fun part is, there is no one right answer!
If you're curious for more > 10kWh LiFePO4 stories, check out my blog.

I've not 100% finished the updates on it, but there's a decent overview even if I bored myself with the excruciating details...
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Old 12-02-2018, 02:58   #11
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Re: 1400 Ah Lithium from cells

Hey mr Exitstrategy. You have finally done it! I think i now understand. Thanks for such a well written and informative article. I have read lots about LiFePO and been thoroughly flummoxed. Thanks
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Old 12-02-2018, 04:07   #12
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Re: 1400 Ah Lithium from cells

We have had 1000AH winston cells for 3 years living onboard and sailing more than 9000NM last year. Tested the capasity last week and its still more than 1100AH.
So, no doubt LIFEPO4 is great, and it delivers as promised.

I would never have made 12 separate strings like that, just seems way to over-complicated. I guess you do get more control over each cell, but i still would never install it like that. We have 4 cells, each 1000AH.. very simple.
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Old 12-02-2018, 05:21   #13
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Re: 1400 Ah Lithium from cells

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Originally Posted by 44'cruisingcat View Post
4 x 1000 amp hour cells?
Yes, the yellow bricks from Winston
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Old 12-02-2018, 05:42   #14
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Re: 1400 Ah Lithium from cells

I use a 20Ah, 12V LiFePO4 battery to power the VHF radio, depth finder, cell phones, tablet, and lights. I used to charge it with a 60W solar panel but found that it was way more than necessary so I replaced the 60W panel with a smaller 30W panel. Without charging, the battery can last over a week. The 30W panel can charge it easily.
I find it hard to believe a 1400Ah bank is necessary on a boat.
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Old 12-02-2018, 05:50   #15
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Re: 1400 Ah Lithium from cells

I am impressed by the work done, however I would not chose such a setup. either. I would keep it as simple as possible. To many bridges over the cells and too many possible weak points. Also this bridges can fail when not propperly squeezed, soldered or fastened.

I am testing my setup and you can see on high loads how some torque on the screws can change the heat creation or the resistance of the set up. When in series internal resistance is also key for balancing. A meshed network of cells makes things even more complicated.

Even on initial charging and putting all cells in parallel you can measure voltage differences on the connectors on each cell, while the outer cells charge faster, the inner need longer. A setup with so many cell is really tricky.

Of course you can build 12 independent LFP Batteries with balancer on each cell, but still it is a lot of work to keep an eye on the cell drift and monitor the system. A parallel first set up (usually done with no more than 2 cells for good reason) is even more tricky. It depends on what point the balancer measures the voltage in the matrix, so one balancer for 12 cells is like no balancer at all. Also the issue with cell fuses comes up.

I dont know how the Calb cells behave, but I know, the winston need a tight clamp around, so if one cells goes rogue, there will be enough pressure to blow the safety vent instead of blow the cell. Also this meshed setups are more dangerous, because the energy of the other battery packs can discharge on a comparable very small cell. This is not comparable to an incident on a single cell string at all.

Btw., you need far more material / cable / cable shoes / heat-shrink / balancer and lots of elbow grease. In the end I guess you will not save a lot on this setup.

But I guess you managed it somehow. So congratulations to the great work!

Fair winds!
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