Building 100 AH LiFePo4 Battery Box

Eric Hanson wrote:Allen,

Very nice, clean build!  I love it.  And these are 314 amp-hour cells--correct?

Assuming 12v cells, this should give close to 3800 watt-hours of energy available.  And probably that figure is a bit conservative.

Very nice.

And how/what did you do to get those modified battery terminals?  I assume that they did not come like that.  

Eric

314 Ah cells in a 4S configuration = 314 amps x 3.2 volts x 4 cells, which equals 4019.2 watt-hours, or 4 Kwh.

The dual-post terminals did come from the factory like that on some of them, and I was initially disappointed by that, but they also came with compatible bus bars, so I'm trying to use those on the smaller projects and save the single post cells for the 48V systems. It's actually an option when you place an order, as to whether you get single or double posts, so my mixed order was an error in packing, but I'm making it work, vs returning them to the vendor, as the batteries are still grade A quality.

John Weiland wrote:I may have missed it....are you guys top-balancing your cells before assembly?  I've been able to connect the ring-terminals to the BMS balancing wires and will test with a multimeter today to see that all hook-ups to the cell terminals were properly made.  But my cells are still at the factory-shipped 3.2V and it sounds best to try to get them to 3.4-3.6V before getting all set up with the BMS connection, correct?  If you are top-balancing, are you using what appears to be a standard 0-30V benchtop power supply?   If so and can recommend a reliable brand as there seems to be many offerings out there.  Starting to collect photos as well now so will try to document things here soon....Thanks!

I didn't do any balancing prior to assembly, I trusted the active balancer in my BMS to handle that, and just charged the assembled battery as a unit. It took about 5 days to get them balanced, but that was primarily the fault of my low capacity choice for the initial BMS & I did have to restart the charger a few times because it automatically shut off as soon as one cell hit the 3.65v ceiling.  That may be something I can adjust by customizing the advanced features/settings, but I'm still learning how to tweak those.

If you look at the screenshots of my BMS pics, you can see that the cells are pretty closely balanced, and that's all done by the balancer, not manually by me.

My best theory right now, is to lower the charging voltage to 3.45v, and set the absorption time to be longer, which Off-Grid Garage was saying will result in the cells getting just as full, but with less stress to the cells, and likely producing much greater gains in longevity in the process, since these are still 3.2 volt cells, and examining the charge/discharge curves shows the only thing gained from charging to a higher voltage, is the speed of charging it, but at the cost of faster cell degradation.

I don't think I'd be comfortable with trying to balance cells without a BMS installed, because of the very convenient cell monitoring that a BMS brings to the table - I can't go back to the other ways now!

If your BMS has the feature of active balancing, just assemble the battery, and let it do the heavy lifting. I did buy an extra 5 amp active balancer, back when I was considering keeping the anemic 40 amp BMS, but I want to see how well the 2 amp balancer in this 300 amp BMS works first. (One can safely use more than one balancer at a time on the same battery).

Allen Jackson wrote:.........
If your BMS has the feature of active balancing, just assemble the battery, and let it do the heavy lifting. I did buy an extra 5 amp active balancer, back when I was considering keeping the anemic 40 amp BMS, but I want to see how well the 2 amp balancer in this 300 amp BMS works first. (One can safely use more than one balancer at a time on the same battery).

Yes, my JK BMS did come with active balancing and I made sure of that based on comments from various corners about the importance of keeping cells balanced.  So this is good news from your observations, Allen, ..... thanks for including that information.  I have a Victron 12V charger with a Li-Ion setting (Model Blue Smart 12/15) that I hope to use for the charging and will use the JK app that I downloaded for cell monitoring.  It seems to make sense to me, although I may be missing something, that even if the most charged cell triggers BMS shut-off, by letting the system 'rest', the balancer would still function to balance the cells, bringing that highest cell back down through equalization and thereby creating a state where continued charging could (re)-commence, yes?  Or would the BMS need to be 'reset' for this balancer to do its thing?  Note--the BMS did come with an on/off switch--Is this what is used to reset or restart the BMS?  Apologies again for the complete noob questions here but really hoping these discussions can help other noobs including myself.

As an aside and related to balancing between full battery builds, I'm still on the fence about using 4 X 12V LiFePO4 batteries (series connected) verses 2X 48V (parallel connected) for modifying my farmyard golf cart.  I like the weight and versatility of 12V batteries, but the simplicity push for 48V batteries in this usage is very evident when shopping around.  Where this is relevant to the present discussion is in the need for a battery balancer to exist in the case of series-connected 12V batteries to ensure one or more is not falling behind with repeated charge/discharge cycles.

This conversation continues to be very helpful, inspiring, and cause for reflection.  Our house, built in 1915, was reportedly equipped with large (Edison?) batteries in the basement before rural electrification came along.  There's a part of me, if socio-economic factors push in that direction, that would like to see this old farmstead once again be off the water and electrical grid.  Hoping our well-pump won't need changing again before we need to leave (old age) and would like to get something in place soon as doing it when much older may prove difficult.

John,

I have not top balanced yet--but I need to do that before I start using this as a dedicated device.  I know that it is not ideal, but I will probably assemble all of the components before I do the top balancing.

I need to buy a dedicated charger to charge each individual cell.  I have a couple in mind from Amazon.  They are not terrible expensive--maybe in the $50-$60 zone.

As is typical when I do one of these projects, I make a lot of mistakes--not terrible mistakes, but mistakes in the category of "I could have done this better" or I wish I would have done that first".  Its a learning project.  Maybe I will make another one, but at the moment, this is a fun little project and we will see how it works out.







Eric

Allen,

Thanks for the more precise specifications.  Over 4000 watt-hours capacity.  That's pretty good.  Actually, it is excellent for such a small package.


And I have to say again that I like your nice, clean build.  It is clear that you really know what you are doing.




Eric

First hurdle encountered:  Can't get iPhone to recognize the BMS through the App.  The phone is an iPhone 12 and the BMS app downloaded through the Apple App Store.  A scan of the QR code on the BMS itself gets me to a site half and half for English and Chinese, but I could not tell which icon to press for downloading the iPhone app.  So at this point, I have the app from the Apple Store on my phone.   The BMS appears to be powering fine--I plugged the on/off switch into a recommended port and the BMS blinked and beeped on immediately.  Unfortunately, it also went into red blinking LED mode, apparently indicating failure to find bluetooth signal. My phone readily recognizes all other solar/battery devices on the property via bluetooth apps and is running iOS 26.3.1.  When I try to open the app, I just see a bluetooth insignia with an 'X' indicating no connection.  Would the app store app be out of date somehow? Better to get it from the QR code link?  Thanks....

Hardware connections shown below.  Based on the nice builds previously documented in this thread, I've clearly LOWERED the bar on the aesthetics.... lol.    But was glad to see all functioning.  I did not know if the larger black (-) cable needed to be attached to the B(-) terminal of the BMS in order for it to turn on properly, so made sure that was connected (4 gauge wire).  Balancing wire plug and on/off switch seemed easy enough to figure out as was the temperature sensors.  The device powered on as noted, but I'm stalled at where it's looking for the phone app.  Any insights here appreciated.d... Thanks!

Don't feel bad about the asthetics - this is a picture of my FULLY wired and working system before taking it apart to move to a prettier build... Electrically, it was fully operational and functional even if digging through the extra parts was needed to find some of the components...  Initially I connected everything to mock it up and make sure it was going to be what I wanted. And find out if I had any bad components while I could still return them.

It was fully working then, but it probably would be very hard to judge it as a BB submission, and it wasn't nearly as portable as I want it to become.

John Weiland wrote:Yes, my JK BMS did come with active balancing and I made sure of that based on comments from various corners about the importance of keeping cells balanced.  So this is good news from your observations, Allen, ..... thanks for including that information.  I have a Victron 12V charger with a Li-Ion setting (Model Blue Smart 12/15) that I hope to use for the charging and will use the JK app that I downloaded for cell monitoring.  It seems to make sense to me, although I may be missing something, that even if the most charged cell triggers BMS shut-off, by letting the system 'rest', the balancer would still function to balance the cells, bringing that highest cell back down through equalization and thereby creating a state where continued charging could (re)-commence, yes?  Or would the BMS need to be 'reset' for this balancer to do its thing?  Note--the BMS did come with an on/off switch--Is this what is used to reset or restart the BMS?  Apologies again for the complete noob questions here but really hoping these discussions can help other noobs including myself.

As an aside and related to balancing between full battery builds, I'm still on the fence about using 4 X 12V LiFePO4 batteries (series connected) verses 2X 48V (parallel connected) for modifying my farmyard golf cart.  I like the weight and versatility of 12V batteries, but the simplicity push for 48V batteries in this usage is very evident when shopping around.  Where this is relevant to the present discussion is in the need for a battery balancer to exist in the case of series-connected 12V batteries to ensure one or more is not falling behind with repeated charge/discharge cycles.

This conversation continues to be very helpful, inspiring, and cause for reflection.  Our house, built in 1915, was reportedly equipped with large (Edison?) batteries in the basement before rural electrification came along.  There's a part of me, if socio-economic factors push in that direction, that would like to see this old farmstead once again be off the water and electrical grid.  Hoping our well-pump won't need changing again before we need to leave (old age) and would like to get something in place soon as doing it when much older may prove difficult.

My lithium battery charger is the component that shut off, and I had to unplug it and plug it back in. The battery did do some balancing, but it tended to stop unless it was actively being charged, and some of that could have been my inexperience in configuring the settings of the balancer, and much of it was due to my impatience, combined with the realization of how long the process could take with such low-capacity balancing tools vs such a large battery system.

John Weiland wrote:First hurdle encountered:  Can't get iPhone to recognize the BMS through the App.  The phone is an iPhone 12 and the BMS app downloaded through the Apple App Store.  A scan of the QR code on the BMS itself gets me to a site half and half for English and Chinese, but I could not tell which icon to press for downloading the iPhone app.  So at this point, I have the app from the Apple Store on my phone.   The BMS appears to be powering fine--I plugged the on/off switch into a recommended port and the BMS blinked and beeped on immediately.  Unfortunately, it also went into red blinking LED mode, apparently indicating failure to find bluetooth signal. My phone readily recognizes all other solar/battery devices on the property via bluetooth apps and is running iOS 26.3.1.  When I try to open the app, I just see a bluetooth insignia with an 'X' indicating no connection.  Would the app store app be out of date somehow? Better to get it from the QR code link?  Thanks....

Hardware connections shown below.  Based on the nice builds previously documented in this thread, I've clearly LOWERED the bar on the aesthetics.... lol.    But was glad to see all functioning.  I did not know if the larger black (-) cable needed to be attached to the B(-) terminal of the BMS in order for it to turn on properly, so made sure that was connected (4 gauge wire).  Balancing wire plug and on/off switch seemed easy enough to figure out as was the temperature sensors.  The device powered on as noted, but I'm stalled at where it's looking for the phone app.  Any insights here appreciated.d... Thanks!

I can't speak to the situation with the Apple platform, as I'm on Android with everything don't have any Apple devices to use for testing that.

It's possible that the "P-" of the BMS may need to be connected to a charger, along with the battery positive, too. Unfortunately the first time you use it, it probably won't enable power, until you can change the configuration and save the settings, because the default is to have the maximum number of cells active as the unit can support - it's looking for cells 5-8 until you can tell it that they're not connected.

This mandates getting the Bluetooth connection to work, or connecting the optional touch panel display to configure it directly. At least that's what I think the manual is saying? I have a display unit still in the box, that I was planning to use for my 28 volt build, but they're supposed to be compatible. I'll keep trying with my phone too, since our phone connection failures may be related.

I'm in!!...It was an iPhone burp at this point.  Had to get to the place in general settings waaayyyyy down on the list where Apps can be interrogated for particulars.  For some reason "access by Bluetooth" was disabled....and easily activated.  JK BMS app connected with no problems after that.  A new issue has emerged, however, that may solve itself after a hard re-boot. (aka...dinner time!)  As Allen noted, the BMS has its knickers in a twist over the fact that it is built for 8 cells and only seeing 4 of them.  In order to make modifications, it wants a password...and the default password provided was not granting access.  So I changed the password, but still no joy.  The error message is something along the lines of password being incorrect for access of that alteration panel.  I can still see the main home screen where it is showing the cell voltage and other data, but I'm locked out of modifications until I can resolve the password issue. Oh well....it's the journey, not the destination, right? ;-)   Will update again soon....

I found that some recent versions of the JK BMS app were horribly broken, and the latest version may be the problem. I was able to find an older version and install it on my phone, but I'm at a restaurant with my wife (too far away from the BMS) to test it right now.

John Weiland wrote:I'm in!!...It was an iPhone burp at this point.  Had to get to the place in general settings waaayyyyy down on the list where Apps can be interrogated for particulars.  For some reason "access by Bluetooth" was disabled....and easily activated.  JK BMS app connected with no problems after that.  A new issue has emerged, however, that may solve itself after a hard re-boot. (aka...dinner time!)  As Allen noted, the BMS has its knickers in a twist over the fact that it is built for 8 cells and only seeing 4 of them.  In order to make modifications, it wants a password...and the default password provided was not granting access.  So I changed the password, but still no joy.  The error message is something along the lines of password being incorrect for access of that alteration panel.  I can still see the main home screen where it is showing the cell voltage and other data, but I'm locked out of modifications until I can resolve the password issue. Oh well....it's the journey, not the destination, right?   Will update again soon....

The Bluetooth pairing password is 1234, but the default system password is 123456.  I changed it to the same as the the pairing password, and it seemed happy afterwards.

I've made it home & I can connect using my phone now but the feature I was most hoping for, still doesn't work - the ability to take screenshots of the status and settings.

On a different note, my first electrical badge bit was approved, so you can see more of my handywork by clicking on the BB icon below my posts. That's a full-blown 64 Kwh 48 volt system, with a pair of ganged 6 Kw inverters.  🙂

Allen Jackson wrote:
The Bluetooth pairing password is 1234, but the default system password is 123456.  

123456!!??


Doh!!  I'd been following the installation manual available from the purchase website at Amazon.com and confirmed that no mention of that password was made, even as the '1234' is in there for accessing the app home screen.  But sure enough, that was the magic number!  I've now modified the settings so that the alarms indicating cell quantity discrepancy and battery amp-hour values are consistent with the hardware installed.  All systems go now for charging and discharging as indicated on the real-time readout window.  Will try a pilot charging tomorrow and see how everything goes.  I'm more convinced now than before that the BMS **really** is just a micro-roboticized crew of nuclear engineers and the cells are probably mini nuclear fission reactors sans cooling tower... .[.. ;-)   kidding].  Looking forward now to getting past the validation stage and getting all players into the compact little box for some test runs.  Much thanks again, Allen and others, and hope to have updates over the next few days.

Doing a test charge now....  Victron charger set for Li-ION currently delivering 14V and 7.5A on bulk charge stage (Victon Connect app).  The JK-BMS app showing 13.88V on battery, 7.3A current, and active balancing 'on'.  Avg cell voltage currently is 3.47 and balancing current hovering around -1.0A.  Highest cell voltage is 3.636 and lowest is 3.346.  Will edit this entry later with final numbers when fully charged .... and assuming that full balancing may take several charge/discharge cycles.