Calendar aging... me, not my LiFePO4's
Build a LiFePO4 battery or buy one already made?
- Thread starter BeerBrewer
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hardtop
Solar Enthusiast
I choose the DIY route, but I haven't finished the build and my batteries have been collecting dust for 2 months lol. I bought 4 EVE LF304 Grade A Cells from 18650 battery store and they told me I don't need to top balance. But once they arrived and I posted about it here everyone says I need to top balance them. Tbh, that was pretty disappointing and I don't want to be buying a DC power supply just for this.
I also need to harness the batteries so they stay together and don't swell. I drafted a design and sent it to a plastic shop. They said they would build it but its been 2 months and they haven't given me a quote yet. I want stainless threaded rod to compress them and nobody carries that around here so I'll need to go online for that. The other tools I'll need to buy to terminate the wire connectors, but I don't have an issue with that because I'll be re-using them. I also want battery heaters and I haven't found quality heaters that are the size of my cells.
The biggest advantage that I'm holding on to is the ability to grow the battery pack by adding more cells and more BMSes.
I think the cells I bought are quality and I'm wondering what is the impact if they aren't top balanced? I don't understand the concequences of skipping that step and why the 18650 tech support would say I don't need to but people here say I do. My cells are very close in voltage together, I just measured them 3.307v, 3.308v, 3.308v, 3.307. That is a one one-hundred thousandths of a volt difference. Pretty good if you ask me, but I should be the guy buying an already setup pack lol.
I also need to harness the batteries so they stay together and don't swell. I drafted a design and sent it to a plastic shop. They said they would build it but its been 2 months and they haven't given me a quote yet. I want stainless threaded rod to compress them and nobody carries that around here so I'll need to go online for that. The other tools I'll need to buy to terminate the wire connectors, but I don't have an issue with that because I'll be re-using them. I also want battery heaters and I haven't found quality heaters that are the size of my cells.
The biggest advantage that I'm holding on to is the ability to grow the battery pack by adding more cells and more BMSes.
I think the cells I bought are quality and I'm wondering what is the impact if they aren't top balanced? I don't understand the concequences of skipping that step and why the 18650 tech support would say I don't need to but people here say I do. My cells are very close in voltage together, I just measured them 3.307v, 3.308v, 3.308v, 3.307. That is a one one-hundred thousandths of a volt difference. Pretty good if you ask me, but I should be the guy buying an already setup pack lol.
Also DIY here. 60kWh total (and definitely not all 'grade A' cells), powering my house for the past 5 years. I'll likely expand this to 100kWh soon-ish, and will go the DIY route for sure.
NCislander
Solar Enthusiast
If UpNorthandPersonal’s experience and recommendation on reliability, along with many others doesn’t speak huge on how reliable these LiFePO4 cells can be nothing will.
My DIY builds much the same in reliability.
Much learning along the way. For those capable its the way to go.
My DIY builds much the same in reliability.
Much learning along the way. For those capable its the way to go.
Tomthumb62
Solar Wizard
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EDIT: @hardtop i missed a key word, not needed to be exact:
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You may be overthinking this one. It’s NOT needed to be exact. You can put the heaters on the cells, between them, or on the battery casing.
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OTRwSolar
Solar Enthusiast
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We purchased the same cells from 18650. The voltage was *exactly* the same on all 4 cells (3.302v). Even so, we still needed to top-balance due to excessive deltas (imbalances) when charging above 3.500v.
You could always pass on the top-balance and charge your cells normally with the BMS installed to see how they do. You may get lucky and experience minimal deltas as charge voltages rise from 3.500 - 3.650v. If you don't get lucky (likely), you'll soon discover a high delta negatively impacts (reduces) the overall ah output of the pack. Probably hard to visualize all this at this point, but suffice to say---large deltas (or a "runner" or two) suck. If this continues to occur after a top-balance, odds are you'll be discussing cell "quality" with 18650.
If you decide to top-balance and you don't want to purchase a DC power supply, you do have the option of using a $25-$30 Heltec 4s 5a active balancer (may want to install an on/off switch for a permanent install). The Heltec will top-balance your cells in an hour or two. If you need to perform another top-balance down the road, simply turn on (or use) the Heltec again.
Always lots of debate about compression. We passed on compression due to important space constraints. If our maximum cycle count drops from 4000 to 2000 because we didn't compress we're fine with that.
As for heating the cells/battery, we found a set of 4, 80x100mm 24w silicone heating pads will heat 200-315ah 4s packs well. Wired them series/parallel for 24w of *total* heat (wired all parallel = too much heat). Applied them to the sides of the cells between layers of heavy-duty aluminum HVAC tape. They keep the cells in a 200-315ah 4s pack above 45-50f even with ambient temps as low as 0-5f (inside a Group 24 or 31 battery box with top and no insulation).
Sanwizard
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Excellent points @Steve_S! Having the right tools and skills are very important when creating a solution that can kill you or burn down your home if not done properly.
Certifications for insurance purposes may also very important. You would also need to pass any local inspections on code compliant Wiring, labeling, and fusing, especially if you are building a 280ah battery that may be staying with a property if selling down the road( those 14K batteries are freaking HEAVY!
You CAN rack mount them though for serviceability with the right tools and rack.
Another point is BMS comms with your inverter. You may want to check your inverter manufacturer for supported batteries for closed loop communications.
When Will first started this forum, LiFePo4 had just arrived on the scene, and everything was the wild west.
The industry has come a long way since then, mainly in my opinion due to feedback from all the smart folks on this forum, and also from a few good Youtube channels dedicated to Solar systems and Batteries.
There are a few good vendors out there now who have created solutions that are great, and provide great support, making the cost benefits of DIY less important.
For 12V mobile applications, the new batteries available now are almost on par with the cost of DIY(I like SOK for 12V).
I started building batteries to learn. I watched all of Will's uploads, and all the other Youtube channels on the subject( Andy at offgridgarage is my favorite, and I use the tools he lists on his website). Its a hobby for me, and while its fun, I learn a LOT from the folks here, and my own testing. If your not the hands on type, then absolutely commercially available batteries are the way to go.
If you like to learn everything about it, have the time and money for tools and build skills, then DIY will be your best bet. The good news is after the tools are bought, its just a matter of sourcing the parts from a trusted vendor from then on, which can save you a LOT of money and frustration down the road.
At a minimum, your asking the right questions on the right forum!
Nobodybusiness
Solar Sponge.
Only thing I can telll you on that front is that my cells have been good for little more than 2 years.
Time will tell I guess.
I know some have older DIY batteries on here who might chime in.
BeerBrewer
New Member
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Great info! I've heard about
Unfortunately I haven't read a much about Heltec active balancers so I'm unclear how they'd be used to intially balance the cells. Are you suggesting that I connect the cells together, then wire up the BMS and also wire the Heltec cell balancer to each cell. Then also install a on/off switch to the Heltec so I can turn it off and on periodically? I'd love to see a wiring diagram. Is there a good post or posts to read on this topic? I did a search and got SO MANY hits, that I information over load!
You folks have convinced me to go the DIY route, I was worried about getting quality cells. If I put it together and set it up my self, I'll be better able to properly maintain it in the future.
Greay info, exactly what I was looking for!
Unfortunately I haven't read a much about Heltec active balancers so I'm unclear how they'd be used to intially balance the cells. Are you suggesting that I connect the cells together, then wire up the BMS and also wire the Heltec cell balancer to each cell. Then also install a on/off switch to the Heltec so I can turn it off and on periodically? I'd love to see a wiring diagram. Is there a good post or posts to read on this topic? I did a search and got SO MANY hits, that I information over load!
You folks have convinced me to go the DIY route, I was worried about getting quality cells. If I put it together and set it up my self, I'll be better able to properly maintain it in the future.
OTRwSolar
Solar Enthusiast
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Correct. The Heltec 5a 4s balancer's 5 wires (4 positive cell wires plus neg) will simply parallel with the 4s BMS's 5 sensor wires (also 4 positive cell wires plus neg). Each positive cell wire (from BMS and Heltec) is cell specific (3.2v/6.4v/9.6v/12.8v)---they must be connected in the proper order. Not sure about the Heltec, but you can potentially damage a BMS if you connect these wires in the incorrect order. We crimp the BMS and Heltec wires into one wire terminal to cut down on clutter.
After the BMS and Heltec are connected, simply charge normally to 100% SOC (pack 14.4 - 14.6v; cells 3.60 - 3.65v). As soon as you see the delta for the cells drop to approx. 1-3mv, the top-balance is complete. May take 1-2 hours.
The on/off switch is not mandatory; however, a Heltec balancer can undo a top-balance if it's left active with the pack at a lower SOC. Not the end of the world. Just means you'll need to charge to 100% SOC to allow the Heltec to top-balance again.
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Andy does a video on the Heltec. It's for a 16 cell battery, but I have the same one for a 12 volt battery. I installed mine with an on/off switch.
dareggaemon
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I've been doing DIY solar for the last two years. I just expanded my 24kw system to 52kw and the additional 28kw cost me $3,307 including tax.
The Lifepo4 cells I bought are now cheaper on AliExpress. It took 2 and half months for the batteries and parts to ship from China. I did not buy the cheapest ones. I watched a lot of youtube reviews from people who bought lifepo4 cells and read a lot of reviews and forum posts. In the end I went with a the cheapest supplier I found with creditability. No way could I buy a premade 28kw battery bank for $3,307. This cost includes, the batteries, wiring, JK BMS, fuses, accessories like the 4.3 display for the battery, and tools that made my life easier when building the battery.
I wanted it hidden and out of the way so I built it in a corner in my garage. I wanted to also be able to store things on top of it. but I ended up installing the screen on top so I can check the status without having to check the bms or inverter app. The enclosure is bigger than it needs to be because I wanted a lot of space for maintenance if needed.
I really want to put everything in a power shed but not ready to spend that money yet.
The Lifepo4 cells I bought are now cheaper on AliExpress. It took 2 and half months for the batteries and parts to ship from China. I did not buy the cheapest ones. I watched a lot of youtube reviews from people who bought lifepo4 cells and read a lot of reviews and forum posts. In the end I went with a the cheapest supplier I found with creditability. No way could I buy a premade 28kw battery bank for $3,307. This cost includes, the batteries, wiring, JK BMS, fuses, accessories like the 4.3 display for the battery, and tools that made my life easier when building the battery.
I wanted it hidden and out of the way so I built it in a corner in my garage. I wanted to also be able to store things on top of it. but I ended up installing the screen on top so I can check the status without having to check the bms or inverter app. The enclosure is bigger than it needs to be because I wanted a lot of space for maintenance if needed.
I really want to put everything in a power shed but not ready to spend that money yet.
Attachments
Hello @dareggaemon . Could you please share what parts and where did you buy? I'm interested in buying parts for the new system and would be great to get some parts list and a reliable supplier.
dareggaemon
New Member
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Batteries - https://www.aliexpress.us/item/3256....0.0.455a38dahr9LNq&mp=1&gatewayAdapt=glo2usa
JK BMS - https://www.aliexpress.us/item/3256....0.0.455a38dahr9LNq&mp=1&gatewayAdapt=glo2usa
JK BMS Screen - https://www.aliexpress.us/item/3256....0.0.455a38dahr9LNq&mp=1&gatewayAdapt=glo2usa
200 AMP Terminals - https://www.aliexpress.us/item/3256....0.0.455a38dahr9LNq&mp=1&gatewayAdapt=glo2usa
Red 1/0 Wire - https://www.ebay.com/itm/381800686134
Black 1/0 Wire - https://www.ebay.com/itm/381800685887
Be careful with buying cells from Aliexpress. Many of the listings there are plain scams, and a lot of other sellers are less than honest to say it mildly. Aliexpress is good for many things, but battery cells aren't one of them.
For cells in Europe, go with e.g. NKON in The Netherlands.
dareggaemon
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I agree, which is why I bought from and recommended a seller from Will Prowse battery recommendation page. Better to buy from a trusted store then to give your money away to scammers.
Will Prowse's recommendation was good. The cells arrived in great condition and were all the same voltage. None of the cells showed any signs of swelling. They arrived on time and were well packaged. I've watched a lot of Will's videos and the math makes since for my use case. You do have to buy for your use case though. In my case buying more expensive cells would not yield any additional benefits, because I do not cycle them hard. I also used Wills recommended parameters for LifePo4 batteries. So it's unlikely that I will ever need replace them. Plus, will already tested them against more expensive cells and found no difference.
The link reflects the battery specs.
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HighDesertDrifter
Teaching is a rare skill, Thanks to those who do!
I'm just learning and would very much appreciate anyone who can help me understand the above statement better! Thanks, here is a direct question concerning this issue.
1.) As long as my batteries are reaching "Absorb Voltage Parameters" several hours a day while under load, does it make any difference if my CC stays in BULK mode all day and never cycles into the ABSORB setting?
If so please explain why. Thanks in advance for your valuable time...
1.5 kw SA
Out Back FM 80 CC
3 x 100 ah 24v Li Time
4000 w Inverter
Tulex
Solar Wizard
I built my own. First 2 were over a year ago, before prices started to drop. Added a third toward the end of last year. Finishing 3 more right now for a total of around 95kWh. Overall I've saved money even with buying all the tools and stuff. But, have to admit that I'm not enjoying this last build as much as the first. They take time, and time is the most important thing I don't have an endless supply of.
But now I have 6 batteries that I know are well built, that are built to fit in the area they needed to fit into, and can be repaired if needed, as they all share the same common components.
One piece of advise I would offer. Build as much as you can up front. Honestly, I wish I knew that I would end up with 6 batteries, as I would have built them all at once. Yes, these last 3 cost me quite a bit less than the first 3, but I would have saved on shipping, some quantity discounts, but more than anything, would have done them quicker as one large build.
But now I have 6 batteries that I know are well built, that are built to fit in the area they needed to fit into, and can be repaired if needed, as they all share the same common components.
One piece of advise I would offer. Build as much as you can up front. Honestly, I wish I knew that I would end up with 6 batteries, as I would have built them all at once. Yes, these last 3 cost me quite a bit less than the first 3, but I would have saved on shipping, some quantity discounts, but more than anything, would have done them quicker as one large build.
RCinFLA
Solar Wizard
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If you are doing absorb to 28.0-28.4v for several hours every day, then you are keeping up with balancing.
Probably biggest mistake is reducing absorb voltage to 27.0 to 27.2v under the misguided impression that lower absorb voltage will help LFP battery last longer.
BMS's do not balance bleed a cell until it reaches 3.4v. Many 12v self-contained LFP battery BMS's only balance dumps 50-100 mA of bleed current. Roughly when misbalance between cells approaches 0.5% to 1% capacity difference, depending on charge current rate, there will likely be charge shutdown issue due to a cell going overvoltage when a full charge is attempted.
1% of 100AH battery is 1AH / 0.050 A BMS bleed takes 20 hours of balancing to equalize. You want to avoid getting into that condition by keeping up with balancing on a continuous basis.
A self-contained 12v LPF battery with no Bluetooth monitoring of individual cells is flying blind making it more likely to evolve into an unbalanced condition that takes a lot of absorb time to correct.
By the time you notice battery capacity reduction due to lowest SoC cell, you are likely several % of rated capacity misbalanced between cells and may take a week or more of absorb level voltage to rebalance battery.
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HighDesertDrifter
Teaching is a rare skill, Thanks to those who do!
Thanks a Lot! This is my situation I want to correct..
Probably biggest mistake is reducing absorb voltage to 27.0 to 27.2v under the misguided impression that it will provide longer life.
Am I under-paneled if my current set up, charge / use ratio doesn't ever allow the Batteries o reach above 27.1 all day into the recommended Absorb cycle of 28.0 - 28.4?
What is my solution to obtain what's needed? Or can I run like this and shut things down on the load side say once a month and bring them up to Absorb for the day?
Must the batteries reach Absorb every 24 hours for no worries, or just a monthly maintenance cycle would be enough?
I've only been running these for about 2 weeks now, so I want to be sure and correct any mistakes now rather than later! THANKS!
RCinFLA
Solar Wizard
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If charging to lower absorb voltage, eventually the misbalance will get to the point where one of the cells reaches 3.4v and will start to bleed. But this is slow and will not fully balance battery.
Best way to ensure full balancing is to have a battery absorb voltage of 3.5v times number of series cells. 3.5v x 8 = 28.0v.
If you do at least two to four hours once or twice a week you should keep up with balancing. As battery ages, or you run higher discharge currents on battery, more balancing time may be required.
Keep in mind a new self-contained 12v LFP battery, as received by you, may be somewhat out of balance due to sitting in a hot container on a ship or on warehouse shelf for several months with variable individual cell self-discharge rate. You should do a full charge / absorb time to balance battery when you first receive it.
Best way to ensure full balancing is to have a battery absorb voltage of 3.5v times number of series cells. 3.5v x 8 = 28.0v.
If you do at least two to four hours once or twice a week you should keep up with balancing. As battery ages, or you run higher discharge currents on battery, more balancing time may be required.
Keep in mind a new self-contained 12v LFP battery, as received by you, may be somewhat out of balance due to sitting in a hot container on a ship or on warehouse shelf for several months with variable individual cell self-discharge rate. You should do a full charge / absorb time to balance battery when you first receive it.
HighDesertDrifter
Teaching is a rare skill, Thanks to those who do!
Thanks NOW we are getting to the crux of my misunderstanding as to how often must batteries be brought up to Absorb to maintain proper balance.
Yes, I did the Full bulk charge, absorb thing with a Victron smart charger before connecting in parallel and putting into service 2 weeks ago.
3 x 100 ah 24 volt batteries
HighDesertDrifter
Teaching is a rare skill, Thanks to those who do!
Question on Non Bluetooth LFP batteries? Can I just add a Shunt to help me keep an eye on individual cells? If the BMS is working properly, shouldn't it keep me with in safe parameters for longevity? Thanks for your valuable input
My set up doesn't bring me up to the .05% C which for 100 ah is 50 amps correct? My charging is all Solar array and for 3 - 4 hours peak each day I'm pushing about 40 amps at the batteries.
One last question here, should I look at 3 x 100 ah LFP batteries in parallel as 1 - 300 ah battery when it comes to the .05 C rating for best charge parameters? Or 3 separate 100 ah batteries? This gets a little confusing to me also, but I'm leaning to looking at the bank as 1 - 300 ah battery when considering my .05 C ,
How does this affect my preferred target of what is best amperage to charge with. My SA currently charges 3-4 hours a day @ 40 amps.
I very much appreciate others attempts to help with the learning curve here! Thanks!
Mulcra
Houston, Texas USA
My 320ah 3.2v 16s LiFePo4 batteries from Aliexpress came very well packaged and had no issues; $1,200 total; bought the case with BMS separately. Batteries do take a long time to get here; month and a half.
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