questions about cell expansion (swelling) while top balancing

ken morgan

Solar Addict
Warning I am dyslexic so you might see some weird spelling (I have to trust auto correct most of the time.) If this question seems foolish, then please bear with me, the cost of these cells causes me to want to be very careful.

so I am building my first LiFePo4 battery bank in a 2p16s configuration. prior to top balancing i measured all of the cells and they were all within reason, 2.232 was the lowest and the highest was 2.236. (calb plastic cells)

I then constructed a quick stand to hold all of the batteries in a 32p configuration while top balancing and started my top balancing with a small charger that self limits to 3.65 volts @ 5 amps. I left the cabin and the batteries to their own devices and came home. then i started thinking, they are all held in place via the stand that while offering no additional compression, will not allow them to swell (2"x12" lumber clamping at the sides with the all-thread torqued to 3 inch pounds.) once they are top balanced I will need to remove the batteries from the clamping system and move the batteries to their new battery box with the permanent clamp, compression and heating pads. If I do remove them from the clamp system will they swell after releasing the clamps? or will they stay the same basic size until I can transfer them to the new battery box... If they are going to swell it might be better to move them to their permanent box first and use jumper wires to wire them in 32p and then buss bars for the final 2p16s when top balancing is finished.

the final battery box will look similar to Zwy's battery pack in this post :https://diysolarforum.com/threads/another-cell-compression-thread-this-time-about-foam.16537/page-3 6mm aluminum plate with all thread rods and heating pads on the bottom.

should I stop top balancing and move them first? or can I release them from the clamps and just move them?
 
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thegoogler

Solar Enthusiast
If you can mount them in the final compression box, I would do so now. That said I did what you're doing/planning (more or less) and mine did not seem to swell when I moved them around. However I was charging at a low C rate (<0.05C, or about 8.5A into a 280Ah battery pack), which I believe helps reduce the likelihood of swelling. I also didn't have them out of the compression frame very long... basically just long enough to rewire from 4P to 4S and to trim down the size of the temporary frame I built to make it permanent.

Side note: If your cells are at 2.2V to my understanding they are REALLY LOW. 2.5V is considered 0%... unless there's something different about the CALB cells?

I will say that I didn't really measure the torque on my compression frame, I just went with "finger tight, and then a couple wrench turns to make the cells fit snug enough they don't slip out of the frame easily if I lift it". (Or as my German mechanic buddy calls it, gutentight). I think if I lifted by the frame and shook the cells would slowly slide out though. Ultimately based on me doing the 4P->4S change I was setting up my compression at ~90% SoC which is pretty high; however the charge rate was so low I don't think I really had any expansion... plus my batteries will operate at 70-95% SoC most of the time so it's probably best I optimize compression for that charge rate.

Before pic:

1623429804182.png

After pic (well, "during pic" really, but after I dropped the frame into the box). Note that I ended up replacing the regular nuts on the threaded road with lock nuts, and I used some 1/4" ID automotive fuel host to cover the threaded rods (which I cut down) to ensure they wouldn't wear through the aluminum cells and short them out. Ultimately it's literally impossible for my box to be any smaller, and in fact I wish I'd given myself another 1/2" to work with on the side sections.
1623429782531.png
 

ken morgan

Solar Addict
sorry typo that i kept carrying over, they were all in the 3.2xx range... not sure why I typed 2.3xx I have trouble sometimes with numbers and transposing when I write or type.
 

ken morgan

Solar Addict
Whew. Ok that's good. So your cells are in the typical ~30% range then.
so as I said I am dyslexic and sometimes screw up words or numbers. all voltages are or were within spec.... Sorry i rely on autocorrect a lot. Its OK, I made it though the high school as an average student, and the USMC with it and found out when I started working as civilian... times change, tests that never existed before came about while I was int he service, and now are tested for... they were not when I was inducted into the Corps so i found out later ;) I screw up sorry.

R/

Ken
 

thegoogler

Solar Enthusiast
No problem, man, I was just worried for you for a minute there ;-)

Post pics when you're all done, and let us know what you end up doing with the compression setup along the way. This was my first LFP build so I'm sure I could do it better next time... always looking for ideas how others build theirs
 

houseofancients

Solar Addict
Warning I am dyslexic so you might see some weird spelling (I have to trust auto correct most of the time.) If this question seems foolish, then please bear with me, the cost of these cells causes me to want to be very careful.

so I am building my first LiFePo4 battery bank in a 2p16s configuration. prior to top balancing i measured all of the cells and they were all within reason, 2.232 was the lowest and the highest was 2.236. (calb plastic cells)

I then constructed a quick stand to hold all of the batteries in a 32p configuration while top balancing and started my top balancing with a small charger that self limits to 3.65 volts @ 5 amps. I left the cabin and the batteries to their own devices and came home. then i started thinking, they are all held in place via the stand that while offering no additional compression, will not allow them to swell (2"x12" lumber clamping at the sides with the all-thread torqued to 3 inch pounds.) once they are top balanced I will need to remove the batteries from the clamping system and move the batteries to their new battery box with the permanent clamp, compression and heating pads. If I do remove them from the clamp system will they swell after releasing the clamps? or will they stay the same basic size until I can transfer them to the new battery box... If they are going to swell it might be better to move them to their permanent box first and use jumper wires to wire them in 32p and then buss bars for the final 2p16s when top balancing is finished.

the final battery box will look similar to Zwy's battery pack in this post :https://diysolarforum.com/threads/another-cell-compression-thread-this-time-about-foam.16537/page-3 6mm aluminum plate with all thread rods and heating pads on the bottom.

should I stop top balancing and move them first? or can I release them from the clamps and just move them?
pleae do share your box and bussbar layout design
 

ken morgan

Solar Addict
pleae do share your box and bussbar layout design
The box is not finished yet as I am still putting it together a little at a time. the cabin is a 3-4 hour drive away and after fridays rainstorms wiped out two of the toll roads to get back and forth it promises to be an even longer drive. all the photos I have are of it in a non finished state as I work through the different issues. so here is the temp controller, the step down transformer and 48volt relay with 12 volt coil. buss bars are simply 5mm x 25mm copper bar drilled to match the spacing of the posts. the buss bars were painted black to prevent corrosion and the the side/area where the bussbar contacts the cell terminal is sanded clean. a generous portion of oxy-guard to prevent corrosion between the bussbar and the terminals was applied. (thats the grey greasy looking stuff you see around the bussbars and nuts.
 

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ken morgan

Solar Addict
sorry can only upload one or two at at time. here you can see the end of the pack with the aluminum plate and rods that apply compression. the end is not sealed no insulated yet. not quite ready for prime time. (you can see one of the old AGM's that the lithium cells are replacing as well.)

The second photo shows the aluminum base plate the two layers of foam insulation, and the lower compression rod. what you cannot see is the heating pads which were taped to bottom of the plate. the reason for the two layers of foam is that the black layer allows a small amount of compression to protect the heating pads and the power leads.

The photo from my earlier post (#8) you saw a temp controller it has a temp sensor embedded in the battery pack about 1/3 of the way up from the bottom. it will cycle the heat pads off and on between the two set points to maintain a temp above the danger zone.

In the last photo you see the space between the foam insulation that forms the sides of the box. I have not decided if I should stuff that area with insulation of some ort, or leave an air gap to help heat rise. I am 6 of one and half a dozen of the other about it. Any Suggestions?

Once I have the layout confirmed I will use expanding foam (just a little) to glue the foam insulation panels together to form an airtight "box" between the sides and the bottom the top will be a piece of the same foam block, but with a friction fit and then tape the seams of the top panels to prevent air leakage. this seals the battery pack as a whole to help trap any heat that the heating pads produce.

I should have pointed out that where my cabin is it gets below freezing, in the past the lead acid agm's self heating during charge and discharge along with the solar charge controller's and the inverter made enough heat to keep the battery "shed" at about 2-5°C without any additional heating required. Due to the higher efficiency of the lithium's during their charge/discharge cycle I feel that I will need to actually heat them in order to keep them warm enough to charge them in the morning.

This years upcoming winter will be a trial by error I am afraid as to what the best temp settings are for the controllers to keep the batteries in the proper range. hoping to keep them around 10°C as measured at the top of the cells the questions are how hot will the bottom get to keep the top at 10° and how much energy will it actually consume to do this? with all of the insulation I should not have much heat loss so we will jsut have to wait and measure to find out.
 

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mikekhi

New Member
I though the compression issue or requirement was only for the aluminum cased cells as they are fairly thin and can bend and it didnt apply to plastic cased cells like calb.
 

RCinFLA

Photon Sorcerer
Just as a reality check for you. If your 3.232v is accurate you are starting out at about 20%-25% state of charge. I did not see what AH's the cells are but with 5 amp charging it could take a lot of time to top balance. Don't get discouraged or impatient. That is where folks screw up and try to do things to speed up the process, usually ending badly. Just make sure your wires are large enough gauge so they don't have too much voltage drop from 5 amp supply. Set 3.65v before loading supply with batteries and don't touch voltage setting while batteries connected. It is good to periodically disconnect supply to make sure it is still capped at 3.65v.

I recommend you calculate the expected time with the 5 amp charging you have. Total sum of all cells AH's x 80% divided by 5 amps is number of hours. Weeks would not be out of line. At least it establishes your expectation on time it will take so you don't think something is going wrong. It can be discouraging when days go by with little increase in cell voltage. This is normal for LFP cells. When cells get to 3.40v voltage starts to rise quickly.
 

SherylinRM

GO GO JUICE BOOMER ZOOMER MAKER
I followed the advice I got from Eve. Which was to drain the cells to about 20 or 25%.
Then make a box I could adjust [like in one of the above pictures].
Put four cells into one box. Adjust it to 71 mm per cell [or 284 mm total].
This is the "depleted" or low or empty size of the cell.
Once adjusted and everything is measured and fine.
Then charge them and they are good to go.
I have never had a problem with them since and they get thrown around a lot because of where I have them. :)

I hope this helps. :)
 
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