Building 100 AH LiFePo4 Battery Box

An example of an EVE 100 Ah cell specs from this website: https://www.evlithium.com/LiFePO4-Battery/eve-lf100la-100ah-battery.html

Specification
Battery Brand: EVE
Battery Model: LF100LA
Min. Capacity: 100Ah
Min. Energy: 320Wh
Initial internal resistance: ≤0.5mΩ
Nominal Voltage: 3.2V
Charging Cut-off Voltage: 3.65V
Discharging Cut-off Voltage:2.5V (T>0℃), 2.0V (T≤0℃)
Standard Charging Current: 50A(0.5C)
Max. Continuous charging/discharging Current: 100A 1.0C
Max. Pulse charging/discharging Current: 200A 2C(30S)
Cycle Life: 4000 Cycles @80% DOD
Charging Temperature: 0℃~55℃
Discharging Temperature: -20℃~55℃
Dimension: 118.5±0.50mm(H)*160±0.50mm(w)*50.1±0.5mm(T)
Weight: 1.98±0.05 kg
Encapsulation mode: U-shaped capsule

This may not be the same model of cell you're looking, as there are 3 different 100 Ah cells listed, but this gives a good example of what the peak current specs are, and how they derate the lifecycle claims for higher current use.

Amazon actually sells parallel compatible versions of the JK BMS, if you are wanting to do combo series/parallel battery packs

https://www.amazon.com/gp/aw/d/B0FPCZS56M

Eric Hanson wrote:Ok, I will try to explain what is going on in this (mess) picture!

..................................

I still have a few things to tidy up.  I need to shorten some cables and tie other cables together to make things look better, but I think it is coming along.

Thoughts?

Eric

Eric,    I may have missed it in your build description, but do you have plastic/ABS separation sheets between each adjacent cell?  I just received 4 EVE 100 Ah cells that will fit nicely in an ammo-box build but need to confirm the need or not for dividers as has been mentioned elsewhere on internet descriptions.  Thanks!

Allen Jackson wrote:Amazon actually sells parallel compatible versions of the JK BMS, if you are wanting to do combo series/parallel battery packs

https://www.amazon.com/gp/aw/d/B0FPCZS56M

Pasted below is the BMS I purchased for this first 12V/100Ah build.....

John Weiland wrote:Eric,    I may have missed it in your build description, but do you have plastic/ABS separation sheets between each adjacent cell?  I just received 4 EVE 100 Ah cells that will fit nicely in an ammo-box build but need to confirm the need or not for dividers as has been mentioned elsewhere on internet descriptions.  Thanks!

Non-conductive separators are a very good idea if your system is going to be moved around, because that would prevent wear on the outer cases, but I don't think this type of battery is using the outer shell as an electrode. I'll check mine to test if either electrode has continuity with the shell.

Did your batteries come with fiberglass separators? All of the cells I have ever bought, did come with those, but that might be a vendor-supplied bonus.  Admittedly, all my (limited) experience working with LiFePO4 batteries, has been with the larger batteries in bulk, for stationary powerwalls, or ESS (energy storage systems), so I don't know how the smaller ones are sold. On the smaller end of the scale, everything needed to be portable and carry it's own weight (robotics), so while the original ones were lead-acid based, that quickly got swapped to NiMH because NiCad was toxic AND had a vicious memory problem, then lithium polymer as the holy grail.

BTW John, if you are wanting to add battery banks to that one, this is the better model for that - https://www.amazon.com/JKBMS-12V-24V-Bluetooth-Protection-JK-B1A8S10P-HC/dp/B0FPCZS56M?th=1

On a different note, many of the Daly BMS models have parallel functionality too - read the details.

Thanks to the OP and others for continuing this helpful thread.  

I finally have the components to get started with an initial build of a 12V LiFePO4 battery.  This will primarily be for stand-alone applications....running small household lamps, powering remote trail and surveillance cameras, operating emergency back-up for a propane furnace (through inverter), etc.   We will see how this goes and then decide if continued builds are in order or if the price for fully-assembled commercial batteries becomes too low to justify continued DIY on this front.

Although many battery cell sets come with the hardware for cell connection, mine did not so this needed to be ordered separately.  In addition, even though the documentation claimed that the terminal threads were M6, they clearly are M4 which I could not find locally.  So these had to be ordered online also.  A quick check of the cells has them all showing 3.20V.  The JK BMS purchased is shown in a previous post above and is enabled for battery heating as well as Bluetooth monitoring of battery/cell status and BMS configuration.  I've downloaded the phone app for this but need to get all connections set up before it will recognize the BMS.  I don't know how much 'programming' is needed for battery set-up.....hoping this is not terribly difficult.  Also, as I'm only using a subset of the BMS monitoring/balancing wires for a 4-cell build, do I really need to remove the additional wires or can these be isolated with insulators and wrapped out of the way of the other components?  I'm glad to see this comes with an on/off switch although I have to ask, with so many LiFePO4 batteries available that do NOT have on/off switches, what is the main point of having one?...battery drain in storage?...safety?

Anyway, hoping to learn here from Eric's build and other comments...fun project and hope all goes well with it!  Open to questions and further commentary....

Edited to add:  If anyone knows of a good step-by-step YouTube video (Will Prowse?...others?) that they can recommend for simple LiFePO4 builds, I would be grateful. Thanks!....

John Weiland wrote:Thanks to the OP and others for continuing this helpful thread.  

I finally have the components to get started with an initial build of a 12V LiFePO4 battery.  This will primarily be for stand-alone applications....running small household lamps, powering remote trail and surveillance cameras, operating emergency back-up for a propane furnace (through inverter), etc.   We will see how this goes and then decide if continued builds are in order or if the price for fully-assembled commercial batteries becomes too low to justify continued DIY on this front.

Although many battery cell sets come with the hardware for cell connection, mine did not so this needed to be ordered separately.  In addition, even though the documentation claimed that the terminal threads were M6, they clearly are M4 which I could not find locally.  So these had to be ordered online also.  A quick check of the cells has them all showing 3.20V.  The JK BMS purchased is shown in a previous post above and is enabled for battery heating as well as Bluetooth monitoring of battery/cell status and BMS configuration.  I've downloaded the phone app for this but need to get all connections set up before it will recognize the BMS.  I don't know how much 'programming' is needed for battery set-up.....hoping this is not terribly difficult.  Also, as I'm only using a subset of the BMS monitoring/balancing wires for a 4-cell build, do I really need to remove the additional wires or can these be isolated with insulators and wrapped out of the way of the other components?  I'm glad to see this comes with an on/off switch although I have to ask, with so many LiFePO4 batteries available that do NOT have on/off switches, what is the main point of having one?...battery drain in storage?...safety?

Anyway, hoping to learn here from Eric's build and other comments...fun project and hope all goes well with it!  Open to questions and further commentary....

Edited to add:  If anyone knows of a good step-by-step YouTube video (Will Prowse?...others?) that they can recommend for simple LiFePO4 builds, I would be grateful. Thanks!....

The process is simple enough that you don't really need a "How to" video, to do it well.

Install bus bars between cells

Connect battery cable between the negative most battery terminal and the B- terminal of the BMS

Get the balancing wiring harness, and start with the black wire, adding it to the negative battery terminal.

The cells of the battery will be seen by the BMS counting from the negative terminal - B1, B2, B3, and B4.

Working from the black wire of the balancing harness, connect the next (red) wire to the positive post of the first battery (B1) of the group.

Connect each subsequent (red) wire to the next cell positive post until B4 is done.

All unused balancing wires can be looped up and taped out of the way, or cut off, but looping them lets you reuse the BMS for a larger battery later, if your plans change...

The last red wire, farthest from the black wire, is the power positive wire, and should be connected to the far positive end of the whole battery.

Technically, it will work to run the BMS with any power supply that is something like +7.2 Vdc to +30 Vdc, but most folks just run it from the battery it's managing.

The main battery positive post is B+, and what you connect to the main bus bar, fuse box positive, or DC load

The P- terminal of the BMS is now the main negative terminal for the battery system.  Connect it to your negative bus bar.

Install the JK BMS app, plug in your temp probes and tape one to the middle of the top of the battery, and the other one to the side of the pack.

Turn on the BMS with the power switch.  It should beep and flash a red LED

On your phone, turn on Bluetooth and pair to the BMS (default code = 1234)

Once paired, go the battery settings and enter the system password to change (default system password is 123456)

Double-check the battery type, ampere-hour capacity and other settings

If you have an AC charger or solar power, connect it & turn on.  You should be able to observe the charging process.

You will need to fully charge & fully discharge the battery in order to calibrate the state of charge, and until then, you're just guessing how charged the battery is.

Off-grid Garage has some pretty good videos on fine tuning the settings of the BMS, and if I find them, I'll post here, but the default settings will be enough to get started.
Edit:
https://www.youtube.com/watch?v=rVXyM-uU_0M
https://www.youtube.com/watch?v=xBu7ScAdKrg  is another one with really useful information about charging for longevity
https://www.youtube.com/watch?v=pijPu7t-akM

If you turn off the BMS, it shuts down the entire system, and you'd need to manually turn it back on, or possibly connect an active charger to it.  I haven't tried the latter yet, but I skipped installing a main-battery shutoff switch because the BMS power button seemed to serve that function well enough.

The actual voltage level of each cell has nothing to do with the state of charge of the cells, so don't be fooled by that.

Battery heating is not built-in to the BMS, you'd need a separate external heating pad to use that feature, but your BMS can use such a device if you connect it.  I bought battery heating mats for some of my larger battery boxes, for future deployment when I retire off-grid, but I don't have them installed in this house - not needed here.

On a related note, I've found that cell compression doesn't make as much sense as is commonly thought, for reasons that most folks aren't even considering.  EVE has published test data, showing a marked increase in cell lifespan from compressing the cells, but it turns out, those benefits aren't for the reasons that most think!

During cell manufacturing, the electrolyte paste, the electrode separator and the positive and negative electrodes are sandwiched into a large "jelly roll", under a vacuum, to remove gas bubbles, but the vacuum isn't perfect, and compressing the cells for the first several cycles of it's life will help to extract any remaining gas bubbles from the sandwich.  After that, compression no longer matters.  If the cells are cycled for testing in the beginning, without compression, any damaging delamination from expanding gases is already done, so if your vendor or seller tested the cells before they sold them to you, but they didn't compress them, you won't gain any benefit from compressing them...

Allen, John,

How did I miss this whole conversation?!  I know that I have been a touch overwhelmed at school, but I have popped in and out but somehow missed all of this!!

So, wow!  Great work on your projects.


As for mine—at the moment I do not have any nonconducting sheets in between the cells.  And here is where I start getting conflicting information.  Some sources say I need plastic sheets between cells.  Some say I need that and and compression on both sides to prevent the cells from swelling.  And other sites just say secure them together.

AAAAARRRGGHH!!


Ok, so for the moment, I am just going to put the battery pack (4 cells) in the housing, wrapped with painters tape.  The painters tape will provide basic structural integrity. Now if I decide later, maybe I will add plastic and compression via two boards (plywood) bolted together, with the bolts set such that I can fine tune the compression.

As it is, it is very close to being done which is usually when I get dragged away to do something else.  

And to answer a question, the case is plastic—an ammo can designated as being as a 5.56 mag case.

Thanks for the feedback guys!!


Eric

Hi Eric.

Yes, you don't technically "need" plastic sheets between the cells, but all the commercial kits I've bought, with or without batteries, and all the batteries I've ever bought, came with them, so they're all at least covering their own butts. Using them is optional, but recommended. If you aren't going to be moving your battery system after building it, you can completely skip that part with no fear of problems.  If you are planning to be mobile with it, 100 Ah is a lot of energy to have a short circuit with, especially since there are no fuses between the cells...

As far as compression, that's something that you can skip, and probably never miss. You'll only get benefit from compression if your cells are new, & have been under compression each and every time they have been cycled or tested, prior to you getting them, but if your vendor tested them prior to selling them to you, and they didn't compress them, that ship has probably sailed.

There will always be a certain amount of expansion of the cells during use, because the lithium ions will migrate into the carbon electrode, so at the molecular level there's a force too strong to resist, no matter what you do, but it's the natural process of the cell working, don't sweat it. If you didn't buy your cells directly from the factory or a factory authorized vendor, it's probably not worth bothering compressing them.

As far as this conversation, we've been hoping to hear from you this whole time - hopefully your project is going well, and I hope this discussion is helpful to you.

My "small DC" solar project build isn't using 100 Ah cells, but it's done enough to be useful for charging my phone/tablet and/or any 12 Vdc loads I want to plug in, but I'm a bit conflicted about some aspects of it.

For just running small DC loads or USB charging, the 40 amp BMS is more than sufficient for the job, but it's still inside the warranty return period (from Amazon), and I won't be able to fully cycle this size battery, for possibly a few months because the BMS is too small to either charge or discharge very fast... (One must fully charge & discharge such a system a few times, to calibrate the state of charge). The DC loads I have, aren't much, and the BMS can't support a continuous load much higher than 500 watts anyway. It took 1.5 days to fully charge the battery and 2 more days to balance the cells... My current "normal" use has only dropped it down something like 2 Ah in the past few days, it will take over 3 months to discharge it...

I either need a smaller battery, or a larger BMS, and I can't really justify buying more & smaller capacity cells.

Because I don't know exactly how I'll want to use this system down the road, I don't know what to contain it in... Everything is connected inside of one of these 50 gallon Husky tool boxes, but that's way to big for going anywhere but my back yard, as it doesn't easily fit into my car. Everything is wired up, and it works, but it's not ready for presentation.

I'm also weighing the choice of combining the AC charger connection and the solar controller connection, since it's highly unlikely that I'd ever need to use both of them at the same time, they could share the same Anderson SB50 connection (my AC charger doesn't produce enough juice to blow the 40 amp breaker), but the schematic above, is how it is currently connected..

On a brighter note, I do have a 12/24 volt refrigerator/freezer coming in tomorrow, so that will help, but if I replace the BMS with the 300 amp one, I can connect a 1000 watt load & discharge the battery in 4 hrs...  I have to decide the future of this box or the future of the 40 amp BMS. It's a good match for the BB small solar project, but almost of the things I might want to do, require an inverter to be useful, so I don't really have a good use for a "small solar system" as defined by the BB, and I don't think I will ever qualify for the electrical "Sand" level badge without doing a small solar system, the way the scoring is set up, as I just don't have enough points in the basic tasks they're looking for (without duplication), and I'm not going back to lead acid batteries, just to show a BB of doing maintenance on lead acid batteries...

When I try to envision how I might realistically use such a system going forward, one possibility is to provide portable jobsite lighting (I've been to "demolition sales", where there's a house that's being taken down the next day, but one can purchase windows/doors/appliances, whatever is still there, for really cheap, but there's no power on site, and no lights in the house.)

I've also been involved with cleanup after a house fire (not my house), and again, there's no power and no lights inside, which hinders progress, so this could be useful for that too (hopefully not too often). If I were camping, I'm likely to want to have 120 volt power if I'm camping heavy enough to want power.

BTW, the small blank box on the AC side, is a 300 amp DC breaker.

I just grabbed a new pristine cell, and scratched a tiny hole in the outer blue plastic covering, then measured to see if there was any voltage or connection between the outer skin and either of the terminals. The results were surprising...

I measured 0.78 volts to the negative terminal and 2.5 volts to the positive terminal, with there being 3.29 volts between the two terminals.

The outer shell is not directly connected to either terminal, but it's still connected to the cell guts, so yeah, put some non-conductive protection between the cells!

Allen Jackson wrote:............... so yeah, put some non-conductive protection between the cells!

I neither would have thought, nor had the guts, to try that test!  Glad your expertise weighed in here and provided extra information on this issue.  Will be making sure to insert thin ABS sheeting between the cells when assembling the battery.  Thanks for this, Allen, as well as for the added links and diagrams!

I noticed that Harbor Freight had some toolbox choices I hadn't checked out yet, but they have a plastic toolbox sold as a group of 4 nested ones, where the outer one has the right inside measurements to fit my battery into. Now if only I could get some decent replacements for the really cheap low quality battery terminal lugs?

So close!

https://www.amazon.com/haisstronica-10pcs-AWG-Connectors-Connector/dp/B0CWGXS5X5?  Looks like a great option, and my wife has Prime, so if I'm nice to her, she might get these for me by tomorrow...

The ammo box I'm using and showed above is from Runnings and I searched quite a bit to find something that would fit the intended build.  These cells fit nicely....and hope the insulating sheets that I end up using between the cells don't cause issues with fit when they are installed.

Also, I'm hoping to use the kind of recessed battery connectors shown in the additional photo....M6-threaded female, recessed into the plastic housing. I want these to be the main connectors on the top of the battery box when done.  Having a very hard time finding these...does anyone know of a source?  I'm hoping it would have male threads on the other side of the housing that one could thread a nut onto for securing the inner + and - cables coming from the cell and BMS, respectively.  Thanks!....

I suspect that's going to be a tough item to find, and if you do, it will end up being something from allibabba.com, with a minimum order quantity of 1000...

May I suggest an Anderson SB50 connector instead? Much greater availability and compatibility...
https://www.amazon.com/gp/product/B0DCG25GC4?

You can get them in a variety of mounting choices from powerwerx.com too.
https://powerwerx.com/panel-mount-components-panels

Technically, the red ones are supposed to be for 24 Vdc and the yellow ones are supposed to be 12 Vdc, but Amazon seems to mostly sell the red ones and the gray ones (which are supposed to be for 36 Vdc). You can also buy the blank plastic shells in whatever colors you want from Powerwerx, even though they don't seem to carry the panel mounts with weather covers, and the connectors are interchangeable, so if you got a grey panel mount from Amazon, you can swap out the grey plastic connector for a yellow one with 2 screws, if you want.

Keep in mind, red plugs into red, grey plugs into grey, yellow plugs into yellow, etc., so whatever color you choose, the other end has to match. There are also different size/capacities, and the SB75 and the SB50 are physically the same size, so they can swap panel mount brackets, but a red SB50 won't plug into a red SB75.

Allen,

Nice job with those Anderson connectors!  I am using much smaller ones, but if I go to higher current, you be that those or similar will be on my parts list.

And I like that rolling case--my first build was similar.  I used a smaller rolling case (a Craftsman case I bought at Lowes).  But my desire was to go smaller and not bigger.

About the battery cells, I will have to do a little bit of testing once I get everything finished.  At the moment, those 100 AH cells are circuit broken to 30 amps--and I doubt it will draw even close to that much.  This build is all about longevity, not intense power output.


Eric

The Anderson PowerPole connectors are available in 15 amp capacity, on the smallest end of the scale (I think there are 15, 30, & 45 amp sizes)

I am using those 30/45 amp connectors.  When I get them in right, they are great.  But I am still learning and I put them in upside down more often than I would like to admit.

Just to reiterate, this was originally going to be an 80 AH build, but the 80 AH cells became unavailable.  The 100 AH cells fit, though it gets a little tight.

A note on ordering cells:  From now on, I will just buy the Amazon ones.  I thought I was going to save some money by purchasing direct overseas.  Bad choice.  Shipping was outrageous, and this was not clearly indicated until the item was in transit which tool weeks.  I thought they lost the cells so I bought another set of cells and they did not show up so I broke down and bought some from Amazon.  And all three sets showed up on the same day!

I guess I have a 100A, 24v, 2400Ah system in my future!


Eric

I was wondering why those Anderson connectors looked familiar.....then realized it's the plug and receptacle combination for my EZGO golf cart!  The amps delivered when charging is ~15 - 20 so this would make sense for a low amp battery build as well, even as they may be able to tolerate higher amps at low voltage.

Which also brings me to my rationale for the desired battery box receptacle (+ and - terminals).....   I'm somewhat enamored with the cable-end connectors shown below, actually having replaced the standard lead cable terminals on cars, tractors, lawn equipment, generators, etc. with these.  My intent is to use a standard battery post that screws into the M6 female threads on the receptable of the new build, then use the quick-connect cable ends shown to connect the desired device to the battery.  If I have a situation where the device to be powered has ring terminals, I can either use the same post as a bolt to screw down the ring terminal or just used a short M6 bolt (hex head) for that purpose.  It's quite likely that the contact made by these quick connectors is not as robust or firm as the Anderson connectors or ring-terminal connectors, but at least the starting of many vehicles many times over using them gives me confidence they can withstand the amp delivery at 12V (rated at 500A continuous and 800A surge), even if not in a sustained manner.  Their strong point is the quick release when needing to switch batteries or powered devices.  One such device would be starting a single-cylinder key-start  9000W generator.  I can still pull the cord on it to start, but both wife and I would prefer the key start.  Yet we don't leave a battery attached for this purpose since it gets used too infrequently.  Since small engine starters don't draw more than 200A and the current battery build is with cells that can do 2C for short bursts, I'm hoping this *may* work as a starter battery for this special case.  Otherwise the battery will be shuttled between various low-power devices and appliances.  I do have a 1500W *modified* sine wave inverter (wondering if I should ditch it for pure sine wave) that might work for emergency powering of propane furnace electrical, but need to do some wiring in the furnace in advance of deploying that option.  Also on tap soon is assembly of an irrigation pump system (head height ~25 ft) to pull water from pond for nearby garden.  Looking at 24V/48V system that would recharge batteries with solar and be contained on a skiddable platform, but seems to be limited centrifugal pump offerings available in DC for this purpose.  So much to do, so little time.... ;-)   Great comments here and thanks for continued input!...

Eric Hanson wrote:I am using those 30/45 amp connectors.  When I get them in right, they are great.  But I am still learning and I put them in upside down more often than I would like to admit.

My golf cart connectors are Anderson and still work....but they are cracked and the plug needs replacing.  I've avoided doing this because it looks a little complicated, but the new plug is gathering dust on my workbench shelf and needs some attention soon.  On the other hand, if I convert the cart from 36V to 48V, I won't be using that old 36V charger anyway and may need to put that plug onto a 48V LiFePO4 charger for the newer batteries.  Decisions, decisions.....

Those terminals are nice, and I have thought about putting them in various designs for battery boxes, including this one.  The short story is that These have always been about longevity, not high power.  But that might not always be the case.

Eric

Eric Hanson wrote:Just to reiterate, this was originally going to be an 80 AH build, but the 80 AH cells became unavailable.  The 100 AH cells fit, though it gets a little tight.

A note on ordering cells:  From now on, I will just buy the Amazon ones.  I thought I was going to save some money by purchasing direct overseas.  Bad choice.  Shipping was outrageous, and this was not clearly indicated until the item was in transit which tool weeks.  I thought they lost the cells so I bought another set of cells and they did not show up so I broke down and bought some from Amazon.  And all three sets showed up on the same day!

I guess I have a 100A, 24v, 2400Ah system in my future!


Eric

If you are buying in bulk, it's cheaper to buy directly from a reputable authorized vendor, and they will tell you up front that it's 50-60 days transit to your address. The variation that's not directly under their control, is how soon the container ship is loaded, so your order can be sitting for up to 10 days in dock, waiting for the ship to be fully loaded before departing port.

Also, buying directly from a top tier vendor, their communication about the whole process is much better than your typical alibabba experience. When I bought my large batch of cells, they wouldn't start the process until my payment was verified (understandably), but as soon as my money was verified, they let me know every step of the way, what the status of my order was. I knew when they'd finished testing/matching the cells, when they were packed up for shipping, when they arrived at the sea port, and I even got a link to track the specific container ship after it left port. Things were a bit fuzzy during customs clearance & the transition to a US courier, but as soon as the US courier had possession, I got their tracking info too.

One shipment was delivered by FedEx and one was delivered by UPS, but I never was left in the dark about where my order was.

If you're not buying in bulk, you might have to get from Amazon, just to get the minimum order quantity, as the factory outlets are usually not willing to start an order without a larger minimum quantity. I really would avoid aliexpress, that's like a "Wild West" of poorly regulated marketplace, and the consumer protections we take for granted in the US don't apply there. Alibabba is much better if you have to go shopping at strangers, but I now have a vendor account representative I deal with, because of my previous business, so at least for battery purchases, I go directly through them.

John Weiland wrote:I was wondering why those Anderson connectors looked familiar.....then realized it's the plug and receptacle combination for my EZGO golf cart!  The amps delivered when charging is ~15 - 20 so this would make sense for a low amp battery build as well, even as they may be able to tolerate higher amps at low voltage.

Which also brings me to my rationale for the desired battery box receptacle (+ and - terminals).....   I'm somewhat enamored with the cable-end connectors shown below, actually having replaced the standard lead cable terminals on cars, tractors, lawn equipment, generators, etc. with these.  My intent is to use a standard battery post that screws into the M6 female threads on the receptable of the new build, then use the quick-connect cable ends shown to connect the desired device to the battery...

How's your metal working skills? It wouldn't take much to make terminals like that, if you have a drill press or a steady hand and an M6 x 1.0 mm tap?  Double-check your post thread for the pitch, but the most common metric bolt in American automotive fasteners is the M6 x 1.0 mm.

Allen Jackson wrote:
.........
How's your metal working skills?

..... the most common metric bolt in American automotive fasteners is the M6 x 1.0 mm.

My metal working skills are pretty non-existent, unless sharpening an axe head and lawnmower blade counts..?? :-)  

I'm going to try the item shown below and see if (a) I can find some sort of washer that would allow pass-through of the threaded insert just up to the 11.6 mm  flange, (b) I can find some sort of coarse-threaded nut to spin onto the outer threads of that bolt, (c) the inner M6 threads will match the pitch (1.0) of the bolts and battery posts that I have on hand, and (d) the hex key portion of the insert is not so deep that it prohibits adequate access of the inner M6 threads from the top of the insert.  The end result would be a fixture on top of the battery case that is a washer with an M6 threaded female insert on the outside of the case and inner-case surface threads on which to attach the cabling.  (hoping that's all clear and understandable...)  Even if I can't find a perfect matching nut for those coarse surface threads of that insert, I may be able to use extra washers or bushings to spin on a nut just enough to provide good contact between the battery cable and that post.

Weather has been decent lately so outdoor chores have taken priority.  With rain moving in, hoping to get on with cell-wrapping and BMS wire attachments in a few days.  Those balancing wires did not come with eyes attached, so need to crimp those on before starting.  This brings up a quick question:  So much discussion about making sure the cells are balanced between them before assembly---but if the BMS provides "active balancing", why wouldn't this function serve to balance at least slightly imbalanced cells after the first few charge/discharge cycles?  Thanks....looking forward to finally diving in!

Edit:  Now thinking,....probably makes more sense to put case-exterior posts on the *side* of the box instead of top, yes?  That way am not opening a lid (when needed) that itself is attached to cables...??

Well, I've finally got the last parts I wanted to finish my "small DC solar build" and a few other bonus items too. (I also got most of the other parts I need to do the larger capacity 24 Vdc "Charge and carry" BB build too)

The missing link is some decent copper cable lugs to replace the thin cheap ones I bought first. These are heavy duty and won't snap off when the wires are moved.  They have multiple sizes too.

https://www.amazon.com/dp/B0CWGXS5X5?

Now I just need to find the time to build it? I have a prior commitment tomorrow afternoon, and it's supposed to start raining at some point too, so any solar testing will have to work around that too.

The DC refrigerator/freezer came in too, and after letting it sit for the recommended 24 hrs upright, it's making a fine load for testing this 12  Vdc system. I can't seem to take screenshots of the JK BMS app while running, so I may have to break down and try it on my phone, not my tablet.

John Weiland wrote:My metal working skills are pretty non-existent, unless sharpening an axe head and lawnmower blade counts..??  

I'm going to try the item shown below and see if (a) I can find some sort of washer that would allow pass-through of the threaded insert just up to the 11.6 mm  flange, (b) I can find some sort of coarse-threaded nut to spin onto the outer threads of that bolt, (c) the inner M6 threads will match the pitch (1.0) of the bolts and battery posts that I have on hand, and (d) the hex key portion of the insert is not so deep that it prohibits adequate access of the inner M6 threads from the top of the insert.  The end result would be a fixture on top of the battery case that is a washer with an M6 threaded female insert on the outside of the case and inner-case surface threads on which to attach the cabling.  (hoping that's all clear and understandable...)  Even if I can't find a perfect matching nut for those coarse surface threads of that insert, I may be able to use extra washers or bushings to spin on a nut just enough to provide good contact between the battery cable and that post.

Weather has been decent lately so outdoor chores have taken priority.  With rain moving in, hoping to get on with cell-wrapping and BMS wire attachments in a few days.  Those balancing wires did not come with eyes attached, so need to crimp those on before starting.  This brings up a quick question:  So much discussion about making sure the cells are balanced between them before assembly---but if the BMS provides "active balancing", why wouldn't this function serve to balance at least slightly imbalanced cells after the first few charge/discharge cycles?  Thanks....looking forward to finally diving in!

Edit:  Now thinking,....probably makes more sense to put case-exterior posts on the *side* of the box instead of top, yes?  That way am not opening a lid (when needed) that itself is attached to cables...??

I was suggesting Anderson connectors also for safety, because it's much harder to accidentally drop a tool across the battery terminals, but the terminals you describe seem like you could bump into them with lots of bad accident potential, to the limit of your BMS short circuit protection. Be careful with whatever you choose.

I can't get the JK BMS app to run on my phone, so the best I can do to show that screen, is to take a picture of it with my phone...

This is the power draw while charging the tablet, the phone, AND running the DC freezer/refrigerator (it will do either, one at a time, not both at once).

Since it's showing the resistance of the monitoring wires, it would appear that it can tell how long they are and compensate for that, so I'd bet it's safe to cut and/or splice them to fit with whatever setups you want to have.

Fridge/freezer is still running well, but I think it will still be over a week to deplete the battery...

Allen Jackson wrote:............I think it will still be over a week to deplete the battery...

Allen, It looks like the EnergyStar ratings found for many US-marketed appliances shows that a standard fridge/freezer combo that meets EnergyStar standards consumes ~350 kWh per year.  How does this compare to your new fridge/freezer?  Also, is there a favored 12V appliance vendor (or more?) that you prefer for browsing and purchasing such items?  Thanks!...

This is more like an electric drink cooler (no ice needed), as it's on the small side. I got this model because it was surprisingly cheap ($236 +tax), and if it worked I'd expect to need at least one more, so one could be a fridge and the other could be a freezer.  I've thought about making a freezer from scratch, but I can't build one for that price - I think this one is cheaper than what a 12 V compressor would cost me...

https://www.amazon.com/dp/B08NCZF438?

Allen--OOOOOHHH, you are so right about the local vendor--even if that local vendor is on Amazon!

At least there is a shipping process that is easily tracked and Amazon has a return and complaint process.  

I will at the very least be buying these from Amazon in the future.




Eric

Just an addendum to what I just posted, if a local vendor opened up in my hometown or nearby (driving distance) and had their prices set at 50% over the cheapest competitor, I would consider it a bargain--no shipping, and a local vendor to rely on if things don't go right.



Eric

In the last year and a half, I've bought 144 MB31 314 Ah batteries and when I started, Amazon wasn't really a good option.

64 have been for clients, and the other 80 were for me to (hopefully) set up a large capacity powerwall/whole house UPS, spread over 2 different shipments, that took a few months to arrive. Since then, I've come to the realization that I don't really want a "whole house" UPS, because my dear wife is already too disconnected from the electric bill, and takes for granted that the lights are always available (leaving lights on casually/often).

I do want to set up large UPS systems for my home office computers and the servers in the basement.  I would like to get enough small-scale solar set up to offset the use of AC before summer, and maybe expand the solar enough to cover or make a dent in the electric demand of the servers that are on 24/7, at the same time replacing their UPS functionality with LiFePO4 battery banks for much cheaper and larger capacity than they currently have.

I really wish there was a nearby local vendor I could drive to (ideally just across state line in Indiana, 'cause their sales tax is much lower).

Especially for large solar panels, it would be really nice to have a local source for pick up!  That's my last obstacle to unplugging from the grid power. The system I set up for the client proved it's value with only 32 KWh of batteries connected, when the local utility had a major outage (over 4 hrs). Thankfully we don't have major outages that often, but occasionally, we do and those who are prepared, thrive. I'm still willing to put 80 KWh toward home computer/server backup, but I'm also now seeing excuses to get even more cells for smaller projects too, like the portable power for camping and a possible replacement of the lead acid battery in my car, etc.

Quick question on how other have dealt with the balancing wire length.  My BMS was shipped with balancing wires over 2 ft in length, much longer than I would need for the build.  Allen J. mentioned just coiling up *unused* wires in a safe and compact manner in case the BMS would be used for a larger build in the future.  I'm inclined to also coil up, for space reasons and to preserve the wire length, the wires used actively in the balancing of the cells, rather than trim the wires for a 'cleaner' build.  Is there any reason why it's recommended to keep the active wires shorter?....or could I keep the wires long and just  wrap them up the box as cleanly as possible after making the connections to the cell terminals?  Thanks!.....

John Weiland wrote:Quick question on how other have dealt with the balancing wire length.  My BMS was shipped with balancing wires over 2 ft in length, much longer than I would need for the build.  Allen J. mentioned just coiling up *unused* wires in a safe and compact manner in case the BMS would be used for a larger build in the future.  I'm inclined to also coil up, for space reasons and to preserve the wire length, the wires used actively in the balancing of the cells, rather than trim the wires for a 'cleaner' build.  Is there any reason why it's recommended to keep the active wires shorter?....or could I keep the wires long and just  wrap them up the box as cleanly as possible after making the connections to the cell terminals?  Thanks!.....

Look closely at the lower section of the JK BMS display screen (on my tablet view, it's on the lower left side), where it shows the resistance of each monitoring wire. If it can measure the resistance of each wire, it doesn't matter how long or short they are because it is taking all that into consideration when managing each cell. That's the only reason why it would check those values.

I didn't clip mine because I was still on the fence about returning the BMS (as it's really too small for this battery) and I wanted to keep it in original condition - it works perfectly, just too small for the battery bank, so I won't be able to calibrate the state of charge before the end of the return window.

Well, I started doing my "upgrade" and re-packaging into its final container, so I thought I'd take pictures of the process that parallels the list of instructions I'd posted earlier. It hasn't gone all that smoothly, as I realized that I wasn't really prepared for the upgrade - I was still thinking in terms of the old BMS I was replacing... I don't have all the correct size terminal lugs to connect the new cabling...

Anyway, here's the first parts...

I wrapped the stack of cells with fiberglass reinforced packing tape, with insulating epoxy sheets between them, then I used some of the foam the cells came with from China, to wedge the stack into place so it wouldn't slide around.

I'll check if the hardware store has terminal lugs for 2/0 awg wire tomorrow, but until then, I can't connect the battery to anything...

Going from a 40-amp BMS to a 300-amp BMS should involve some changes in the cabling & circuit protection, or one may be preparing to start a fire (or one may simply be unable to utilize the system capacity). The previous battery cable was 6 awg, which is normally considered safe up to 55 amps. Since the old BMS could only pass 40 amps continuously, that was a good match. The new BMS is much closer to the battery capacity of 314 amps continuous, as it's rated for 300 amps & 6 awg wire is now way too small to safely use in this system.  While I don't have to have full access to the capacity of the battery, I do want to be able to discharge it in a reasonable amount of time, so I'm not spending 2 weeks, just to calibrate the state of charge.

I can limit maximum output with a smaller fuse than 300 amps, say 150 amps, and still be able to pull about 1.9 kilowatts from the system before blowing the fuse. 150 amps on this system, is just shy of the 0.5 C rate for these cells but if I can now pull at least a kilowatt from the system, I should be able to drain the battery in 3-4 hrs or so, which is a big improvement in my book.

I'll be using 2/0 awg copper cable as soon as I can get some lugs suitable for connecting with these M6 battery terminals.

This also starts to illustrate why higher power systems need to be higher voltages - the correct size wiring to handle 300 amps continuously, is something like 350 MCM, which is 3 sizes larger than 4/0 cable... The 2/0 copper I'm switching to, will safely carry 175 amps, so a 150 amp fuse should be the weak link.

Update - This 2/0 copper cable is probably safe for 200+ amps continuous, as the insulation is rated for 105 degrees C, although I still won't get anywhere near that kind of a power draw with this system...

This JK BMS is rated for 300 amps continuous, so it stands to reason that it would have the option connect cables in parallel. I'd need to make custom battery lugs to connect 3 parallel cables to, but these 2-hole cells would allow me to use dual battery cables if I needed to.

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

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!