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  1. #31
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    Quote Originally Posted by Najataagihe View Post
    I would like to know why a bus bar would make any difference.


    Electrically, there is no difference between a bus bar and properly-sized cables.
    You are correct. There is no electrical difference between a busbar and properly sized cables, particularly at these short distances. If someone thinks there is, please explain the difference between the two systems below. You could even connect the RV in the middle of the bus and it still wouldn't make any difference with properly sized cables. If anything, I would argue the bus is worse because you are adding 2 extra cables and 6 extra connections, all of which add resistance (negligible but present) to the system. The only benefit to a bus is a bit of simplicity in adding or subtracting connections at the cost of taking up space.

    I connected the 12v- cables (3) to the last battery post, eliminating an extra cable and extra connections. The end of the 12v+ cable goes to a fuse holder, fuse holder to shunt, and shunt to a four post bus for all the 12v+ connections. Simple, small, neat, and works great. Also, as long as you have clean, properly sized, copper cable ends, there is no problem with several cable ends on one terminal.
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    Last edited by Tom Traveler; 04-20-2023 at 06:11 PM.
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  2. #32
    Long Hauler huntindog's Avatar
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    Quote Originally Posted by Tom Traveler View Post
    You are correct. There is no electrical difference between a busbar and properly sized cables, particularly at these short distances. If someone thinks there is, please explain the difference between the two systems below. You could even connect the RV in the middle of the bus and it still wouldn't make any difference with properly sized cables. If anything, I would argue the bus is worse because you are adding 2 extra cables and 6 extra connections, all of which add resistance (negligible but present) to the system. The only benefit to a bus is a bit of simplicity in adding or subtracting connections at the cost of taking up space.

    I connected the 12v- cables (3) to the last battery post, eliminating an extra cable and extra connections. The end of the 12v+ cable goes to a fuse holder, fuse holder to shunt, and shunt to a four post bus for all the 12v+ connections. Simple, small, neat, and works great. Also, as long as you have clean, properly sized, copper cable ends, there is no problem with several cable ends on one terminal.
    This is simply incorrect. If you want to know why, read this:
    https://www.mygrandrv.com/forum/show...d+battery+bank
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  3. #33
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    Quote Originally Posted by huntindog View Post
    This is simply incorrect. If you want to know why, read this:
    https://www.mygrandrv.com/forum/show...d+battery+bank
    @huntindog
    The document that is referenced in your link is very informational and does support the use of a bus bar or star (single connection point). While I completely agree that is the best way to balance a battery bank, it doesn’t fully translate to LiFePo4 technology in my opinion. It would be very difficult to get into much detail in a thread like this so I created my own PDF to explain the differences. Again, I make no claims of being an electrical engineer - this is based on my interpretation of a lot of different research.

    Click image for larger version. 

Name:	Battery Charging.pdf 
Views:	13 
Size:	44.8 KB 
ID:	45938
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  4. #34
    Long Hauler huntindog's Avatar
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    Quote Originally Posted by Jomani View Post
    @huntindog
    The document that is referenced in your link is very informational and does support the use of a bus bar or star (single connection point). While I completely agree that is the best way to balance a battery bank, it doesn’t fully translate to LiFePo4 technology in my opinion. It would be very difficult to get into much detail in a thread like this so I created my own PDF to explain the differences. Again, I make no claims of being an electrical engineer - this is based on my interpretation of a lot of different research.

    Click image for larger version. 

Name:	Battery Charging.pdf 
Views:	13 
Size:	44.8 KB 
ID:	45938
    I read that and there is a missing part. What happens when you are unable to charge all batteries to 100%? This is a common scenario when boondocking. In fact I sized my battery bank larger just so I would not need to run the generator when a few days of clouds occur.
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  5. #35
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    Quote Originally Posted by huntindog View Post
    I read that and there is a missing part. What happens when you are unable to charge all batteries to 100%? This is a common scenario when boondocking. In fact I sized my battery bank larger just so I would not need to run the generator when a few days of clouds occur.
    In theory, the battery bank will balance itself out after the charge or load is removed. The internal resistance of LiFePo4 is much less than lead acid and the need to fully charge doesn’t exist which makes them perfect for this application.

    I am not disagreeing that a bus bar offers the best scenario. All I am saying is that LiFePo4 has a built-in mechanism for limiting battery degradation where lead acid does not.
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  6. #36
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    Quote Originally Posted by Jomani View Post
    In theory, the battery bank will balance itself out after the charge or load is removed. The internal resistance of LiFePo4 is much less than lead acid and the need to fully charge doesn’t exist which makes them perfect for this application.

    I am not disagreeing that a bus bar offers the best scenario. All I am saying is that LiFePo4 has a built-in mechanism for limiting battery degradation where lead acid does not.
    So when it balances itself, the batteries that are full experience a discharge as they feed charge to the ones that are less full.
    That is an unbalanced operation and will work some batteries harder than others.
    One other point: If you have a large charger and/or inverter, having batteries turning off individually can cause problems
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  7. #37
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    Quote Originally Posted by huntindog View Post
    So when it balances itself, the batteries that are full experience a discharge as they feed charge to the ones that are less full.
    That is an unbalanced operation and will work some batteries harder than others.
    One other point: If you have a large charger and/or inverter, having batteries turning off individually can cause problems
    I would love to have about ten grand laying around to be able to test this in a real time side by side test. As much as I enjoy this type of dialog, I think at this point we are splitting hairs - probably talking about voltage differences measured in tenths or hundredths of a volt. Given your boon-docking situation, I understand your desire to get all the potential you can from your batteries. For most of us, our LiFePo4 batteries will age out long before they die from cycling.
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  8. #38
    Long Hauler huntindog's Avatar
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    Quote Originally Posted by Jomani View Post
    I would love to have about ten grand laying around to be able to test this in a real time side by side test. As much as I enjoy this type of dialog, I think at this point we are splitting hairs - probably talking about voltage differences measured in tenths or hundredths of a volt. Given your boon-docking situation, I understand your desire to get all the potential you can from your batteries. For most of us, our LiFePo4 batteries will age out long before they die from cycling.
    If you go back and reread that paper I linked to, he did test it.

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  9. #39
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    Quote Originally Posted by huntindog View Post
    If you go back and reread that paper I linked to, he did test it.

    Agreed, but unless I am missing something, all of his calculations and tests were based on lead acid battery banks. Since internal resistance plays a significant role in his calculations, I was having trouble wrapping my head around how significant this is with lithium.

    I did find a video by Will Prowse that actually proves some of my assumption wrong. His video is focused more on connecting mismatched batteries in parallel strings, but the first few minutes covers exactly what we have been talking about. Evidently, LiFePo4 batteries will not self balance. He also shows the different SOC levels in a parallel battery bank.

    I still want ten grand to prove it to myself, but I think I am finally onboard…

    https://youtu.be/oXBT8lSC25M
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  10. #40
    Long Hauler huntindog's Avatar
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    Quote Originally Posted by Jomani View Post
    Agreed, but unless I am missing something, all of his calculations and tests were based on lead acid battery banks. Since internal resistance plays a significant role in his calculations, I was having trouble wrapping my head around how significant this is with lithium.

    I did find a video by Will Prowse that actually proves some of my assumption wrong. His video is focused more on connecting mismatched batteries in parallel strings, but the first few minutes covers exactly what we have been talking about. Evidently, LiFePo4 batteries will not self balance. He also shows the different SOC levels in a parallel battery bank.

    I still want ten grand to prove it to myself, but I think I am finally onboard…

    https://youtu.be/oXBT8lSC25M
    Here is a quote from that paper that also addresses the issue:
    "Well, the better the quality of the batteries, the more important it becomes. The lower the internal resistance
    of the batteries, the more important it is to get them properly balanced."
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