02-11-2019, 01:58 PM | #11 |
Gone Wild
Join Date: Aug 2008
Location: Leander TX
Posts: 166
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Re: Want 7 more Leaf Modules...knew this would happen
I don’t think the zeva will see them as individual cells, it still sees the pack the way you had it.
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02-11-2019, 02:54 PM | #12 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Want 7 more Leaf Modules...knew this would happen
DaveTM, You need to connect the center taps of the modules that are in parallel.
Each Zeva channel will be balancing 4 cells (2 modules in parallel) instead of 2 cells (1 module) like before. Once you put all of the buss-bars together, You will connect a single BMS wire to each buss-bar, it will make more sense when you draw it out. |
02-11-2019, 04:32 PM | #13 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,204
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Re: Want 7 more Leaf Modules...knew this would happen
Thanks Gents!! I wasn't even thinking of the center tap. I "upgraded" my little diagram to reflect how the center taps would have buss-bars and then be wired to the ZEVA. All totaled up, there will be 15 connections to the ZEVA. (If my diagram is correct....which I believe it is.)
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02-11-2019, 05:50 PM | #14 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,119
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Re: Want 7 more Leaf Modules...knew this would happen
Not how I would do it. You should parallel the old and new so it would go in your diagram
OLD NEW OLD NEW OLD NEW etc Otherwise the pack will not stay in balance if the old and new cells are different capacities (which they probably will be) Your connection diagram is correct for a 14 module pack. |
02-12-2019, 08:34 AM | #15 | |
Gone Insane
Join Date: Oct 2015
Location: TN/NC/GA Tri-state area
Posts: 3,952
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Re: Want 7 more Leaf Modules...knew this would happen
Quote:
would be Pack+ +new/old parallel- +new/old parallel- +new/old parallel- +new/old parallel- +new/old parallel- +new/old parallel- +new/old parallel- Pack- Seven new/old pairs in series! Each parallel pair would have all 3 terminals paired together. Bob |
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02-12-2019, 08:55 AM | #16 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Want 7 more Leaf Modules...knew this would happen
At least we all agree that you should not wire strings of batteries in parallel.
The reason I suggested keeping the cells in parallel matched by their age/capacity is that there are studies that show that placing batteries of different capacities in parallel causes a reduction of their useful life. It also causes the parallel cell with the lowest internal resistance to carry the brunt of the load, which is why I suggested keeping the temperature probe near the mismatch pair. https://www.sciencedirect.com/scienc...78775316300015 |
02-12-2019, 10:06 AM | #17 |
Gone Insane
Join Date: Oct 2015
Location: TN/NC/GA Tri-state area
Posts: 3,952
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Re: Want 7 more Leaf Modules...knew this would happen
But you also cannot connect cells of much differing capacities in series. That causes much more issues with overcharge attempt of lesser capacity cells and chronic undercharge of higher capacity cells.
The BMS will be working overtime trying to deal with that much imbalance. |
02-12-2019, 10:19 AM | #18 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Want 7 more Leaf Modules...knew this would happen
He is using a good BMS with Cell monitoring so neither one of those issues exist.
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02-12-2019, 10:59 AM | #19 | |
Gone Insane
Join Date: Oct 2015
Location: TN/NC/GA Tri-state area
Posts: 3,952
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Re: Want 7 more Leaf Modules...knew this would happen
Quote:
A good BMS is one that does not waste energy by dissipating it in resistors. It has isolated DC-DC converters with a common source/sink bus that allows excess energy to be redistributed amongst the packs cells until balance is achieved. For golf carts, it is not cost effective to design such a BMS, so we tend to use more commonly available resistor balance BMS systems. But a resistor balance BMS would waste much more energy when faced with the task of constantly having to dissipate power from the lesser capacity cells, just to keep them in voltage balance with higher capacity cells in the pack. It is far better to parallel the old and new cells, as the alternative would.greatly diminish usability capacity during each and every charge cycle to that of the rebalanced weakest cell. That would result in a much lower effective cycle life of the pack. |
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02-12-2019, 11:41 AM | #20 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Want 7 more Leaf Modules...knew this would happen
Well, You are kind of changing this debate and creating other discussion topics.
We are not talking about "Aerospace Applications", but a golf cart. We are not talking about the "BMS efficiency", but is ability to disconnect the pack when any cell goes below or above the preset limits. The only energy "wasted" is the delta between the "Max Cell Voltage" and the "Balancing Voltage" settings since the charging will stop as soon as the first cell(s) reach the "Max Cell Voltage" setting. I do agree that pairing the old and new cells will likely yield a slight higher SOC for the pack, and it may not make much difference either way if the cells are close in capacity, but it adds another point to consider when deciding how to proceed. |
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