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.

Post charging update....

It took most of the day, but the Victron charger reached 14.2V at which time it turns off.  Prior to that, it had tapered off the amps finally reaching 0 and indicating a charge completed status.  Having turned the charger off and removed the alligator clamps, the BMS readout indicated continued balancing of the cells, so I will leave it on overnight for balancing.  The voltage differential between the cells now is at 0.058, much lower than the >0.15 of around the time charging started.  It seems like the balancer is moving all cells towards a final voltage of 3.4 which would give a battery pack voltage of 13.6V.  So if the cell diferential voltage is mostly negligible tomorrow, it would seem that this approach to balancing cells in a new build...without 'top balancing'....may work okay as long as an active balancer is part of the BMS or possibly added as a supplement.  A few photos added along the way.   The very crude charging set=up is shown with alligator clamps coming from the charger to the appropriate terminals. Screenshots of the BMS App on an iPhone 12 were taken with an iPhone 6s an emailed through Wifi to my laptop.  Still so much to learn considering app parameters and good battery maintenance.  More again as advances made on nestling the cell block and BMS into their new home!

The final cell voltage differential reached 0.005V at which time the active balancer shuts down.  Two interesting things:   The pack voltage drifted down to around 13.3 overnight as the balancing was underway and the final cell voltages were hovering around and above 3.3.  This seems a bit low, but is this a part of the "break-in" phase for a new LiFePO4 battery?....In other words, will this slightly improve with repeated charge/discharge cycles?  Second, probing the + and - terminals of the battery pack yields 13.3V and probing the + pack terminal along with the P- terminal on the BMS also gives 13.3.....when the BMS is turned on.  However, when the BMS is turned off, the latter test gives 9-10V, not 0 as I would have expected if the BMS is shutting off discharge out from the battery (as opposed to internal self-discharge that all batteries do to some degree).  Why would the BMS allow for this 'leakage' in the 'OFF' position?  At any rate, more of the hardware for the final installation is to arrive today so I hope to get my plans square on the placement of the cell pack and BMS within the container.  Then the decision on the external post and on/off switch locations.  Getting closer......   Thanks again for continued input, insight and advice!.....

Don't sweat the "13.3 volts" part. That's normal, and something Andy at the Off-Grid Garage YouTube channel was trying to explain.




These cells are 3.2 volt cells. That makes the nominal voltage of the pack, 12.8 volts. If every cell were perfectly matched, you could theoretically charge the whole pack up to 14.6 volts, but it won't stay there, even if you just let the pack rest for a day without any use. The voltage will always drop off to the resting voltage, and it will STILL be fully charged. Trying to get more into it will only risk cell degradation and/or acceleration of aging.

This can be seen from the charge/discharge curves more clearly, but once the cells have absorbed all the energy they can hold, further charging will drive up the voltage, but it won't put significantly more available power into the cell. That's why he suggests only charging to 3.45 volts/cell, but stretching the absorb time out for an hour or so, contending that the result is a cell that's just as "full", but lives much longer.

The major case for charging to a higher voltage/cell, is the speed of charging, so if one is in a hurry or impatient, charge to 3.65 volts/cell, and they'll get to that same "fully charged" level faster, but they'll also degrade faster, and they'll still drop down to their resting voltage afterwards...

Oh, and congrats on your balancer knocking it out of the park!

On the topic of the measured voltage when the balancer is off - is the balancer actually off, or did it just shut off charging?

I'm led to believe that these BMS units will always have some sensing that's active, so they can tell if a charger or a load is connected, so they can't just cut the connection entirely or it will require a mechanical switch to turn back on.

To that point, one could install a main battery switch on the negative terminal before anything else, and it would fully shut down the entire system, including the BMS, which might be suitable for longer-term storage... Otherwise the BMS will slowly drain the battery, but it's probably cheaper to just disconnect the battery terminal.

On a related note, if anyone installs any additional balances to their systems, MAKE SURE to also install a switch on them to disable the balancer during any long-term storage, or they'll probably kill the entire battery - use them when you need to, and then turn them off!

Allen Jackson wrote:On the topic of the measured voltage when the balancer is off - is the balancer actually off, or did it just shut off charging?

On a related note, if anyone installs any additional balances to their systems, MAKE SURE to also install a switch on them to disable the balancer during any long-term storage, or they'll probably kill the entire battery - use them when you need to, and then turn them off!

The app still showed that charging and discharging still were enabled, so only the balancer was shut off.  With regard to shutting it off manually, are you indicating that an active balancer that is always "on" might constantly drain other cells to serve one bad one and eventually drain all past a point of repair/rechargability?  Yeah, that would suck.  At this point I'm waiting for other items to arrive in the mail and occasionally turn on the BMS to see what parameters may have changed.....but if the BMS is turned completely off when I'm not using the battery, the balancer also should be deactivated, yes?

The built-in balancer is controlled by your BMS, and it will be shut off as appropriate, when appropriate, but balancers can be installed in parallel, and any additional ones need to have a power switch to turn them off when not actively charging the battery, or they will unnecessarily drain the battery.

I have a 5-amp balancer I bought when I was still trying to get the 40 amp BMS to work. I don't expect to want any other 12 Vdc system I could use this with, so I might as well use it on this one.

There's a blob of solder on the lower left corner area, with the word "RUN" stenciled above it. There are 2 pads below that the blob is bridging, and the blob should be replaced by a switch, so it can be turned on only when needed.

Update:  Apparently this model balancer has a shutoff voltage of 2.7 volts/cell, so it's claimed to be safe to leave on & connected to the battery all the time, although one is still free to replace the solder bridge with a switch.

If left on, it will keep the battery balanced all through the entire range of operation.

I've recently been getting BB submissions approved, and the way the rules are set up, I can't qualify for the entry "Sand" level badge in electricity, without submitting a "small DC solar system", because I can't do several things on the "Sand" list.

I have:

No lead acid batteries to maintain
No electric water heater or electric dryer
No place to set up a solar water pump
No use for a "Micro heat bubble" - I wear shorts/short sleeves, even in Chicago winters because I'm too warm...
No fans in bathrooms (in rented house, so adding them is questionable...)
& no extension cords needing repair

So, I'd come up short of 5 points without duplication, unless I submit a small DC solar system, even though I now have 27 out of 35 points to apply toward the "Straw" level...

Because of this & and the fact that everything I'd need to submit for this is sitting in the room with me, I'm going to stop adding features & post what I have (no rain in tomorrow's forecast, but expected to be cloudy all day), and hope I can get enough power from solar to make it worth dragging all this out into the back yard to take beautiful pictures of the assembly.  Wed and Thurs are options if the weather/solar aren't available & cooperative.

I don't know if I'll get the 2nd balancer installed prior to, but I figure I need to get past the sand and straw levels before I post my higher capacity "Charge and Carry" lithium power station, or I won't get full points for it.

Stay tuned!

This morning was a bust for solar - it was raining and it's been cloudy and overcast all day, until late afternoon, where I suspect the sunshine is coming in from the side, with clouds still overhead...

I've still had some progress though. Early this morning, my battery (finally) was depleted. I was awake at the time, and got to observe the process, so I understand some of the BMS settings better now. BTW, the cliff is real, and the end comes very quickly by the time the cell voltage has dropped below 2.7 Vdc. There's just not much left in the battery then, so it's not worth chasing that tail for MAYBE a few Ah of energy.

Since it was still dark outside, I plugged in the AC charger to start the recovery process, and I found that the "Cell UVPR" is the recovery voltage it must achieve on ALL cells before it will re-enable discharging. So, it turns off discharging at 2.5 Vdc (can be customized), and it doesn't turn it back on until 2.9 Vdc. The built-in balancer also shuts off below 3.0 Vdc and turns back on at the same level (this is also customizable in the advanced settings).

I still don't know what my actual capacity is for this battery, because it hasn't been through a full charge/discharge (with this BMS installed) but the estimated capacity suggests that it might be fully charged in another 6-8 hours (while all the while still running the DC refrigerator/freezer).  I received another DC refrigerator (larger capacity model) via UPS this afternoon, so by tomorrow afternoon, I can safely turn it on (suppose to let them sit upright for a full day after receiving so the oil can drain into the right parts of the system, and I know this one hasn't been upright, 'cause UPS left it up on its end when it was delivered).

I should probably stop charging it now, to save room for the solar charger function check

The DC socket assembly I was using also gave me an education, as the fuse housing softened up and warped so it wouldn't stay together (all without blowing the fuse!), so I know these cheap 12/24 Vdc outlets are flashy with their blue LEDs, but they are NOT heavy-duty and may actually be a safety hazard. I will find better before I'm willing to ignore it.

A minor annoyance about the JK BMS - it doesn't display charging current at all... I knew it was charging because I saw the cell voltage rising, but until there was an active load, the displayed current was "0" ☹️

Tomorrow is another day, the forecast is a bit better, for what that's worth, but I may have to compete with the lawncare service for the use of the back yard... Hopefully they come early and leave early too?  (I can't remember if they show up on Wed or Thur).

Allen Jackson wrote:
A minor annoyance about the JK BMS - it doesn't display charging current at all... I knew it was charging because I saw the cell voltage rising, but until there was an active load, the displayed current was "0" ☹️

Do you mean just the particular model of JK BMS?   Because if you look back up a few entries at my screenshot while charging, mine was displaying 7.4A.   Since the charger itself was set for a 7.5A delivery, I assumed the BMS was reading the input properly....... or no?

Not sure if it was just my model or not, but specifically during the early part of the recharge cycle, I noticed that the current stayed at 0 amps on the display, even though I was sure the voltage couldn't possibly be going up without current flowing into the battery. Once it had risen enough to clear the under-voltage recovery threshold, the discharge was re-enabled and the normal expected load current showed up (the refrigerator was still plugged in).

Today was a better day for solar, but it also turned out to be the day the lawncare team chose to visit. I'm not compatible with sharing space with them, so I found other stuff to do.

Yesterday afternoon, when I was pondering turning off the charger, I got interrupted by my wife, because I'd chosen Tuesday evening to go to the theater to see Project Hail Mary - and I'd forgotten about it... I dropped everything and went to the theater ((&forgot to turn off the charger)!

Needless to say, the battery was fully charged by the time I got back to paying attention to it, but on the plus side, the heavy duty 12 Vdc sockets arrived from Amazon. I was also expecting some black Anderson SB50 shells to arrive, but apparently they won't be here until Thursday. I wanted the black shells for the solar connection, because the panel configuration I'm trying to use, creates a string voltage of over 72 volts, and I don't want that plug to ever be compatible with my 12 or 24 Vdc sockets. That would be poor engineering at its worst. With those installed, I will never have to worry about getting a phone call saying "So an so plugged in my battery pack and blew it up!" or something like that.

The heavy-duty 12 volt sockets are impressively sturdy, and they come with 105 degree C rated insulation, which could carry a whopping 51 amps, even though it's only 12 AWG, because of the high-temp insulation. I think they'll do just fine for my use.

https://www.amazon.com/gp/product/B0FX4G52YZ?

To be fair, the other ones didn't have a socket failure, and replacing the wiring on them would produce acceptable results up to the limit of the fuse.

On a related note, I am seeing my highest power draw on this battery yet, now that I have both DC refrigerators connected and every USB device I can reach, plugged in and charging.

Today was mostly a good day for solar, sans the afternoon pop-up shower, but Amazon didn't opt to deliver my black SB50 shells until after 5:30 pm... I've got everything now, the new 12 Vdc sockets are working perfectly, and there's not "supposed" to be any more rain for the next few days.

I'm not available most of Saturday thru Monday late, and by then, the weather is questionable, but tomorrow morning looks good right now.  In the meantime, the 2 refrigerators are working to draw down the battery 😉

Good to see that build coming along, Allen, and to hear of your experiences adding practical loads to it that we can all relate to.   I'm finding myself wishing that I would have known more about the RV world of using 12-24V appliances sooner....it may have altered my choices of purchasing such appliances for hope use in earlier days.

I'm at the stage now of fitting everything into the case.  It won't be pretty, but I feel still quite functional.  The battery terminal posts will go on top after all at opposite sides of the lid.  At this point I plan to just leave the BMS on top of the battery cells and fill in gaps with pieces of packing styrofoam, cut to fit.  In order the keep the BMS somewhat immobile, I'm planning to lay a sheet of styrofoam across it and then the lid will press gently down when closing to keep the BMS in place.  HOWEVER!...if this BMS placement is judged to be thermally dangerous or not recommended then I will reconsider and may just use tape to keep it in place.   The temperature sensing wires will be placed between the case wall and the side of the battery and the on/off button fixed into a hole on the side of the case to allow access from outside of the case. The cables that will attached to the battery posts from inside of the case are stranded 4 AWG which I'm thinking should suffice for my anticipated loads.  More updates soon....

Allen, John,

I am at the end of the year and I am terribly busy getting senior grades ready while still teaching my other classes.

What I am trying to say—clumsily—is that I have had little time to post a response.


This has been an amazing addition to this thread!! I want to get myself back in gear and finish what I started, but you two have some awesome builds yourself!


Keep at it!!



Eric

This morning by dawn, the forecast had changed to "morning showers" & while it did clear up quite a bit by afternoon, I had to work then...

Now it's 6 pm, and the sun is very brightly shining above the western horizon, so I don't know if I have time, or enough direct sunlight to test what I really want to test.

To clarify, I'm trying to settle on the placement of the solar controller, which has some really impressive heatsink fins on the back side of it. Size-wise, it's a very convenient fit horizontally, in the inset that one of the small parts trays was, but I don't know if it generates too much heat to sit there during normal operation, or if I really need to mount it on the side of the toolbox, to allow convection through the now vertical fins.

Since the placement on the end is also where I was hoping to be able to install the solar input connectors and AC charger connectors, I have to know if that spot is available or if it will be best served holding the charge controller... Can't tell if the charge controller gets hot during use without good sunlight to heat it up...

Allen Jackson wrote:......Since the placement on the end is also where I was hoping to be able to install the solar input connectors and AC charger connectors, I have to know if that spot is available or if it will be best served holding the charge controller... Can't tell if the charge controller gets hot during use without good sunlight to heat it up...

Are both ends of the box slated for connectors and/or outlets?  If you were to use the lid, then perhaps on hotter days you could prop the lid open in a way to allow the controller to orient vertically and promote the air upward siphoning effect to aid in cooling.  I can't recall....are the PV panels fixed in their location or something that you desire to be mobile?  Looks like it will be  nice unit when completed!

Make sure you have adequate ventilation everywhere.

John Weiland wrote:Are both ends of the box slated for connectors and/or outlets?  If you were to use the lid, then perhaps on hotter days you could prop the lid open in a way to allow the controller to orient vertically and promote the air upward siphoning effect to aid in cooling.  I can't recall....are the PV panels fixed in their location or something that you desire to be mobile?  Looks like it will be  nice unit when completed!

The opposite end is intended to be where the 12 Vdc & USB outputs are placed, and I'm wanting to severely limit the intrusions in the lid, because of the weight - I don't want to weaken the top, since picking it up by the handle puts all the stress on the lid to hold the entire unit. I am guessing that select limited intrusions in the ends won't be as weakening, because the lid attaches to the back via the hinges, and the front via the latches, but not to the ends. I'm hoping to make it usable with the lid secured, not opening it except for maintenance.

The solar panels are all portable 200 watt panels from Harbor Freight that fold up and have their own carrying bags. I have 6 of them and a pair of "Y" cables, so I can use all 6 at the same time, for 1200 watts of solar input... Should be enough to keep up with the use (overkill for this one, but probably not for the 24 Vdc 8 Kwh build)

The DC refrigerator/freezer actually does freeze if you give it enough time - I forgot I put my water bottle inside it and about 18 hours later, it was well on its way to freezing, albeit not yet completely solid. This is a 128 oz bottle that was nearly full. I drank it down as much as possible, to hasten the thawing around the captured straw.

This has been a rather monumental and educational experience so far today...

Pretty good day for solar, and I made much of it. There were some clouds, and I learned from them too.  I have 1200 watts of solar panels, but I only pulled out 800 watts (4 x 200 watt panels) and connected them in a 2S2P configuration. Looking at the Victron app, I saw my voltage was maxing out around 42 Vdc, which means I could get away with running a 4S string (85 Vdc) without overvolting the charge controller & in theory, I could use my "Y" cables to quadruple that, to 3200 watts of solar input, if I had 11 more panels...  Very good so far!

HOWEVER it wasn't all sunshine and roses then, because on closer inspection, I realized that I was only charging around 400-415 watts, even though I have 800 watts of connected panels! I was limited by the 30 amp output of the charge controller and no matter how many more panels I added, it would still be limited to that same 400 watts (13.56 Vdc x 30.x amps), and the only way to get around that, was to increase the system voltage, or augment or upgrade the charge controller!

Now to be fair, I did notice that when I unplugged half of the panels in full sunlight, I was still getting about 345 watts from 400 watts of panels, so I can't really ask much more from these panels, plus when I had all of them connected, I tended to still get the max output more frequently with a little cloud cover, as twice the panels producing half-power still gives 400-ish watts.

Another bright spot for the morning, is that the charge controller heatsink fins were cooler to the touch while producing that 400 watts than what the solar loading was doing to the black plastic toolbox, and even it wasn't too warm to touch, so it should be OK to mount the charge controller horizontally in the tray lid slot and save the ends for charging connections and load connections on the other end.

I checked the price of a 100 amp Victron, and it was running $489 - not sure I need it that badly at this time... I do have a 35 amp version for the 24 Vdc system and I now realize that I should have planned the higher current one for the lower voltage battery. I could even use both of them on the same system at the same time, if I were desperate - and the Victron components are networkable, so they can talk to each other.

Now by the numbers, IF I were trying to actually use the full 4 Kwh capacity of the battery each day, and I can get the equivalent of 5 hours of full sunlight, I'd have to be able to charge at at least 800 watts per hour. Since I haven't been able to draw much more than 100 watts, and then, not continuously, being able to charge at 400 watts is adequate for the current usage & the avaliable solar (nominally 2 Kwh/day = 400 watts x 5 hrs). Swapping to the 35 amp controller would give me a buffer, 'cause I could then charge at 475 watts instead, but by the numbers, I should probably get a 60 amp charger for the 8 Kwh build, because that one will have an inverter and much higher loads.

I can even check the BMS and charge controller from inside the house because the range is good on the Bluetooth for both of them, (so I can go inside and read the screen on the tablet better).

Wow, what a morning!

Also while charging with solar, the charge current DID show in the BMS...

This thread continues to educate and inspire!....

So to clarify something:   Our Polaris Ranger EV (48V), currently running on 8 lead acid batteries in a 4S2P configuration of 12V batteries is characterized, in sum, as 48V/300 Ah.  Since my wife only uses this machine to move animal feed around to different feeding stations and the distance would total no more than 1 mile, depletion of the bank is minimal.  (Re)charging of the cart starts around 10 am when I plug it into the controller.  The single PV panel (380W) is rated for a maximum ~10A output....well below a recommended (?) 0.5C charging rate.  Yet charging the cart back to full only takes 1-2 hrs max in full sunlight.  Is this likely just due to the low amount of depletion on the battery bank at the end of each day?  The batts are pretty new so this may impact that apparently quick charging time.  

Sooooooo...Is the reason that you are looking for high amperage in your charging due to the fact of the high Ah capacity (and low voltage) of your build?  Just thinking now about my 100Ah box, for which I have a 100W/17V PV panel (~6A) laying around that could pair with this?....  Also, although I need to check the surge and running specs on the blower motor for our furnace (propane), was hoping to use this with an inverter for emergency back-up prior to installing a beefier back-up system.

I hope to finally install battery posts today...and give it a trial run with a load!  Will continue to photograph and post here....  Much fun so far!

John Weiland wrote:This thread continues to educate and inspire!....

So to clarify something:   Our Polaris Ranger EV (48V), currently running on 8 lead acid batteries in a 4S2P configuration of 12V batteries is characterized, in sum, as 48V/300 Ah.  Since my wife only uses this machine to move animal feed around to different feeding stations and the distance would total no more than 1 mile, depletion of the bank is minimal.  (Re)charging of the cart starts around 10 am when I plug it into the controller.  The single PV panel (380W) is rated for a maximum ~10A output....well below a recommended (?) 0.5C charging rate.  Yet charging the cart back to full only takes 1-2 hrs max in full sunlight.  Is this likely just due to the low amount of depletion on the battery bank at the end of each day?  The batts are pretty new so this may impact that apparently quick charging time.  

Sooooooo...Is the reason that you are looking for high amperage in your charging due to the fact of the high Ah capacity (and low voltage) of your build?  Just thinking now about my 100Ah box, for which I have a 100W/17V PV panel (~6A) laying around that could pair with this?....  Also, although I need to check the surge and running specs on the blower motor for our furnace (propane), was hoping to use this with an inverter for emergency back-up prior to installing a beefier back-up system.

I hope to finally install battery posts today...and give it a trial run with a load!  Will continue to photograph and post here....  Much fun so far!

As with any/every project, it's always best to start with the end goal in mind and work backwards from it. Your Polaris doesn't appear to be using much more than about 400 Wh of energy per day, maybe less. Otherwise a 380 watt panel couldn't possibly recharge it in an hour. Your Polaris battery is technically a 14.4 Kwh battery (48 Vdc x 300 Ah = 14,400 VAh = 14.4 KVAh = 14.4 KWh), and you don't seem to be using more than 0.4 KWh per day of the total battery capacity, although with lead acid batteries, that's for the best, because if you did deplete it, the lifetime of the battery would quickly deteriorate.

Lead acid batteries can discharge quickly (high "C" rate discharge, but comparatively low charge rates), whereas lithium batteries tend to have much higher charge "C" rates, compared to lead acid, so I'd like to take advantage of that.

I'm looking for higher amperage charging on my battery for a few reasons - 1:  Make hay solar while the sun shines weather cooperates (technically, the sun is VERY reliable, but the weather?)!  I observed first-hand today that a passing cloud could drop production from 800 watts of solar down to under 200 watts. If one needed to depend upon the system, it needs to be dependable, with little to no excuses, like "Well, we only got a little sunshine today/this week/etc.  Build in reserve and then make it available!  2:  This battery can charge at a 0.5 C rate of 157 amps (or a near 1C rate of 300 amps before the BMS clamps down) ... My charging system is way under-matched to that now, and I can't always be sure I'd have even 4 hours to charge it at 0.25 C (78 amps), but most places I'm going to use it will have a reasonably reliable 4 hours of effective sunlight per day, so I have to fit any and all charging into a 4-hour window, just to be safe (in case I actually need to use that 4 Kwh on consecutive days).

7 years ago, when Jehu Garcia posted the YouTube video of the charge and carry lithium battery box/DIY version of the Inergy Kodiak "Solar Generator", I was very critical of the charge controller in both his and the commercial product, because they were so wimpy it effectively made the boxes a one-hit wonder party trick. The Inergy Kodiak was being marketed as a viable solution to doing things like being able to provide ongoing/indefinite emergency power for grid power outages, natural disasters, etc., but with only a 600 watt charger capacity, one wouldn't be able to keep up with the 1500 watt inverter, and the box could be depleted in less than 2 hrs, but might not even be usable to following day because of the time to recharge... Jehu's DIY version was better in most ways, but much worse for the charge controller - it was only a 300 watt solar charger! Use it once, then not be able to use it again, maybe for a few days!?!?!  I knew he could do better and I told him so...

Now I'm trying not to repeat what I viewed as a major flaw in his build. Real-world repeatable performance requires the system be practical to recharge fast enough that it could be used daily, just in case you actually need to do so (or just want to do so... Like a week-long camping trip, etc. Especially since now I have solar panels to play with/test out, and I can see firsthand that I'm not getting my money's worth from my solar panels, all because of the bottleneck of my charge controller - I really need to better match ALL the system components. This, I write off to the cost of education - first the BMS was too small too, now the charge controller is, but I'm getting better and learning the "why" various design choices are better than others.

The next ("24 Vdc") system has the advantage of a higher voltage, so it automatically can charge at twice the power, with no other changes (the Victron is compatible with 12/24/36/48 Vdc systems and automatically produces more power on higher voltage systems), but as it's planned to have an 8 Kwh battery, with a possible daily draw of 6 Kwh+, I want to be able to feed the beast so it's available for use every day I want to use it (well, "we", as I have to include the things my wife will want to do that require off-grid power too). Might seem like being a "Prepper" but the only thing I'm prepping for, is a week-long visit to Wheaton Labs in Oct and not overly stressing my marriage in the process. 😉