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  1. #1
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    Default Compression and Busbars

    Not sure if these topics in context has been discussed before, but these came to mind, with some considerations for my own LifePo4 battery building. I'll also try to explain my own though process, as to what I plan to do. (Given that new 'soundness' does not change that.) I have not yet build a LifePo4 combined mobile setup, but I am with eagerness check all the builds here. Not to waffle, lets start.

    I purchased second hand LiFePo4 cells, and received buss bars with it. So, what I did not like, was the fixed buss bars on the terminals, in a mobile environment shaking. Now, I have no real evidence, other than suspicion, that on a LifePo4 cell, vibration on fixed points on the terminals, might not be the best idea. On further pondering, I also noticed the cells have swollen. Not to concerned, what I then stumbled upon, is that swelling, is actually part of the design parameters. Now, it appears as if some manufacturers actually recommend compressing the cells, to compensate for this swelling, which in turn extends the life span. Lets be clear, this info is 'watching YouTube', a.k.a 'Some-Say' No factual point from me here. What is factual for me at this point, is the swollen cells in hand, and vibration in my FSP (F.... Small Pickup)

    So, for my self, and my build, I've decided on the following two points:
    1. To compress the cells, in order to minimize the already swelling, future planned swelling by manufacturers (still Some-Say) and to reduce vibration among the cells.
    2. Making non-rigid bus bars, just crimped wires, with flex in them, to reduce stress on terminals, due to swelling, and vehicle vibration.

    Anyway, maybe these points has a common approach already, or, might need some consideration.

    Just some thoughts.

    PS: Thanks for all the pics on the builds on the forum! Thubs Up! (..now where is that icon?)

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  3. #2
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    Default Re: Compression and Busbars

    My 2 cents as I just last week had to remove 2 bulging cells.

    Quote Originally Posted by CeeZee View Post
    ... , in a mobile environment shaking.

    So, for my self, and my build, I've decided on the following two points:
    1. To compress the cells, in order to minimize the already swelling, future planned swelling by manufacturers (still Some-Say) and to reduce vibration among the cells.
    2. Making non-rigid bus bars, just crimped wires, with flex in them, to reduce stress on terminals, due to swelling, and vehicle vibration.
    Spot on. If the cells move ever so slightly the busbars are under strain and can cause internal damage, worst case, or the nuts/bolts become lose, also not a good idea.

    I also have 2nd hand 2nd Life LifePo4 cells of which two has swollen. I found them when I saw the casing being pushed apart. The pressure is quite impressive.

    The brackets they come in, there are gaps between the cells for better airflow around the cells for cells to get slightly heated when charging, unless you do it very very slow. So methinks binding the cells together is not conducive for nice clear airflow around the individual cells.

    Binding them together makes sense to keep them unmovable in i.e. a vehicle. Cells must NOT move ever.
    But you idea of the flexible busbars ... genius!

    Re. cells bulging. I've reduced it to two main causes:
    1) The cell has a manufacturing defect.
    2) The cell was abused i.e. charged at too high a voltage or some such.

    Keep a very close eye on bulging cells. Mine actually felt hotter, felt it by hand, so I removed them immediately as that is dangerous. Very bad to have a cell start burning.



    Some views I saw:
    Type D fire extinguisher required: http://robotsforroboticists.com/lith...attery-safety/

    Overcharging - and why group of vehicle battery packs are kept in separate compartments: https://www.youtube.com/watch?v=YuKF8XfCVKQ

    Test: https://www.youtube.com/watch?v=uLzPSN8iagk

    What happens if you overcharge: https://www.facebook.com/watch/?v=526223257939653
    See how the cells bulge.
    Political Correctness
    Political Correctness is a doctrine, fostered by a delusional illogical minority, rabidly promoted by a unscrupulous mainstream media which holds forth the proposition that it is entirely possible to pick up a turd ... by the clean end!

    Saw this in a pub - no idea why the wife does not see it so:
    I'm not opinionated ... I'm just always right!

  4. #3
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    Default Re: Compression and Busbars

    My view is that the bulging is a chemical function and a mechanical compression will just damage the cell to be at a higher risk.
    The flexible buss bars makes sense and should work.
    Current - 2009 Mazda BT50 3.0CRDi 4x4 d/c
    Previous - 2005 Ranger 2.5 tdi 4x2 d/c (277 422km)

  5. #4
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    Default Re: Compression and Busbars

    The bulging is definitely a chemical thing. However, seems some manufacturers recommend it to be presured. A good summary for now is the post below. Also, watch the video in the same post, showing the different influences on life expectancy. One of them, is also pressure applied.

    https://diysolarforum.com/threads/ev...92/post-161742

    So, from what I can see, seems like the 300kgf on the side is the happy number. Now, I have no idea how to calculate pressure, or extrapolate it. The various ways of doing it, I'm not overly ecstatic about. Stuff like electrical tape etc. My main issue with it is that you don't know how much force you actually apply.


    To sum these figures by one poster: "300kgf is 660lbf. Cells are about 53.5 square inches on one side. So pressure is about 12psi. I can apply 12psi to 1 square inch with my thumb, so its not really a major load."
    OR
    "
    If this is accurate, and the broad side of an EVE cell is roughly 17.36cm x 20.48cm (355.53 cm^2 or 55.11 in^2). Would this equate to roughly 12PSI (or 0.844 kg/cm^2)?"

    Now, my question is this, if I place to plates or board to the sides, and I had 4 nuts and threaded rod connection the 4 points, what torque values on the 4 nuts would I need to apply to get the 300kgf on the side of the cells. Assume a side of 17cm x 20cm.

    Can someone help with this calculation?

    Thanks

    EDIT: "seems some manufacturers recommend" = "Some-Say" No factual info from me yet.
    Last edited by CeeZee; 2021/05/07 at 05:43 PM.

  6. #5
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    Default Re: Compression and Busbars

    Quote Originally Posted by the_terrible_triplett View Post

    Re. cells bulging. I've reduced it to two main causes:
    2) The cell was abused i.e. charged at too high a voltage or some such.
    Mine has definitely being abused, and in this instance, is 100W% the culprit. Bought them as such.

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  8. #6
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    Default Re: Compression and Busbars

    Quote Originally Posted by CeeZee View Post


    To sum these figures by one poster: "300kgf is 660lbf. Cells are about 53.5 square inches on one side. So pressure is about 12psi. I can apply 12psi to 1 square inch with my thumb, so its not really a major load."
    OR
    "
    If this is accurate, and the broad side of an EVE cell is roughly 17.36cm x 20.48cm (355.53 cm^2 or 55.11 in^2). Would this equate to roughly 12PSI (or 0.844 kg/cm^2)?"

    Now, my question is this, if I place to plates or board to the sides, and I had 4 nuts and threaded rod connection the 4 points, what torque values on the 4 nuts would I need to apply to get the 300kgf on the side of the cells. Assume a side of 17cm x 20cm.

    Can someone help with this calculation?

    Thanks

    EDIT: "seems some manufacturers recommend" = "Some-Say" No factual info from me yet.
    If I was faced with this problem I would calculate the force needed to say a 10cmx10cm area. Then rework the force needed for this area. Get some very stiff foam and apply the calculated force on this piece between 2 stiff planks and measure the gap between the 2 planks. Now use your 4 bolts and tighten them and measure the torque applied on the specific bolts up to the point that you have the same gap. The same torque can thus be used when you apply it to the sides of your batteries taking into account the area of the cells.

    You can also get someone with a load cell strain gauge that measures force applied to contract or to pull. A number of gate motor manufacturers do use these load cells to measure how hard gate motors push when hitting the end stops.

    Just my 2c

  9. #7
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    Default Re: Compression and Busbars

    Ekkekan, thanks for post. I think you spoke more truth in your signature, in this case! I was convinced I'm over thinking this, but hey, I'm in no hurry to build this pack, so, what the heck. BTW, I like the sponge idea.

    I started off finding some torque values online, but my calculations where, well, kinda tits-up. So I phoned an engineering friend. Now, I'm still not convinced about all the figures, but this is where I'm at. Taking 300kgf or 12psi as the magic number.

    300kgf on the side, divided by 4 points, is 75kgf. Which is 750N. (Give or take)
    T = KfD . K some galavized bolts constant, d the diameter of the thread, and f the force required.
    .2 X 750 X 0.008 (0.008 is for 8mm threaded rod.)
    Gives me 1.2 nm torque or .9 on 6mm rods.

    Now this is, well, a small amount, or as put in below picture 'mild'. So, seems that some forums suggest that maximum torque (excluding Super man and his buddies) can max apply 1.5nm of torque on a wing nut. At this point, without further breaking my head, I'm settling on wing nuts, hand tightened, before breakfast, at 50% or less charge rate. (Less, cause I'm already swollen.)

    Below is an interesting extract. (I'm not entirely convinced about some of the figures, but, compression at 50%, as well as side way movement with fixed buss bars, does provide for some additional reading.)

    This would also provide me over time to make some adjustments, if needed.

    Again, any bored readers (depressingly bored..) that would like to verify the numbers, would be appreciated!

    Image extract below from link....
    https://www.homesteadingtoday.com/at...-0a-pdf.93188/
    Attached Images Attached Images  

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  11. #8
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    Default Re: Compression and Busbars

    Quote Originally Posted by CeeZee View Post
    Ekkekan, thanks for post. I think you spoke more truth in your signature, in this case! I was convinced I'm over thinking this, but hey, I'm in no hurry to build this pack, so, what the heck. BTW, I like the sponge idea.

    I started off finding some torque values online, but my calculations where, well, kinda tits-up. So I phoned an engineering friend. Now, I'm still not convinced about all the figures, but this is where I'm at. Taking 300kgf or 12psi as the magic number.

    300kgf on the side, divided by 4 points, is 75kgf. Which is 750N. (Give or take)
    T = KfD . K some galavized bolts constant, d the diameter of the thread, and f the force required.
    .2 X 750 X 0.008 (0.008 is for 8mm threaded rod.)
    Gives me 1.2 nm torque or .9 on 6mm rods.

    Now this is, well, a small amount, or as put in below picture 'mild'. So, seems that some forums suggest that maximum torque (excluding Super man and his buddies) can max apply 1.5nm of torque on a wing nut. At this point, without further breaking my head, I'm settling on wing nuts, hand tightened, before breakfast, at 50% or less charge rate. (Less, cause I'm already swollen.)

    Below is an interesting extract. (I'm not entirely convinced about some of the figures, but, compression at 50%, as well as side way movement with fixed buss bars, does provide for some additional reading.)

    This would also provide me over time to make some adjustments, if needed.

    Again, any bored readers (depressingly bored..) that would like to verify the numbers, would be appreciated!

    Image extract below from link....
    https://www.homesteadingtoday.com/at...-0a-pdf.93188/
    0.2 for K is a it high for gal bolts. More like 0.15 or ~0.12 if you add a bit of lubricant.

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  13. #9
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    Default Re: Compression and Busbars

    I stumbled upon a video last night which talks to this:

    Stuart

    2006 Toyota Land Cruiser 100 4.7L V8

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  15. #10
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    Default Re: Compression and Busbars

    Quote Originally Posted by CeeZee View Post

    I purchased second hand LiFePo4 cells, and received buss bars with it. So, what I did not like, was the fixed buss bars on the terminals, in a mobile environment shaking. Now, I have no real evidence, other than suspicion, that on a LifePo4 cell, vibration on fixed points on the terminals, might not be the best idea.
    What size cable did you use for the Busbars ?

    Busy with my own LiFePO4 build at the moment.

    Great idea by the way !
    Safe Diving - Andy

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  16. #11
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    Default Re: Compression and Busbars

    Wow, I may be sitting on a time bomb! Or are we overthinking things?
    I build a 12 v battery with 4 "new" cells, from lithiumbatteriessa.
    Very little if any, bulging. So i just taped them together using 4x4 directs brown duct tape and put them in the battery box.
    Not once did they became hot, not even warm, during charging at 15 amps. From "empty" to full. Have a Victron battery protector, apart from the bms.
    Did a 2 week trip and detected no problems.
    The bolts fastening the supploed alu busbars still the same as the day tjey were attached.
    Time will have to tell?
    Last edited by hatjohan; 2021/06/02 at 08:52 PM.



  17. #12
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    Default Re: Compression and Busbars

    Quote Originally Posted by slodj View Post
    I stumbled upon a video last night which talks to this:

    Awesome. Here's another video from the same guy with a better configuration.

    https://m.youtube.com/watch?v=nua-mCKiQg4

  18. #13
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    Default Re: Compression and Busbars

    AndyT, I used 10mm2. Not much for 12v but fine for my needs. I could also double up on that, since I have a 2p setup. Camped this weekend with it. Whole weekend, not even used 50%. 240ah.

    Hatjohan, yes. I've convinced myself I'm over thinking it. Time bomb? No. I think it might just help you have a better installion over time.

    Anyway, information is out there.

    Happy camping.

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