11-19-2019, 07:16 AM | #21 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,215
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Re: Adding 2nd set of 7 module
I think I'm attempting to say the same thing. All I'm saying is before an install, you want the "old pak" and the "new pak" to have as close to the same voltage (preferably each cell) as possible so the BMS does not get over heated or over worked when balancing.
But...maybe that's my non-engineer brain that's telling me this. |
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11-19-2019, 09:21 AM | #22 | |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Adding 2nd set of 7 module
Setting up all cells to the same random intermediate voltage is not balancing.
A 100AH battery and a 60AH battery will have the exact same voltage at their 50% capacity. The issue is that when you wire and charge then back in series, you are adding the exact same amount of AH to each battery. So after 30AH are returned the batteries, the 60AH would be full, but the 100AH is only at 80AH capacity, so your BMS will work overtime trying to correct the imbalance by continuously bleeding the lower capacity cell. That is why I said: Quote:
Attempting to equalize the voltage at a middle point will have the BMS bleed the voltage from the higher capacity cells during discharge and then bleed the voltage from the lower capacity cells again during a charge cycle, so basically the BMS can not get out of its own way. Amazingly some folks recommend that method for their BMS setups. |
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11-19-2019, 09:40 AM | #23 |
Gone Wild
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 6,215
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Re: Adding 2nd set of 7 module
Thanks Sergio. Now it makes sense....more sense (better sense?) to me anyway.
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11-19-2019, 01:08 PM | #24 | |
Getting Wild
Join Date: Nov 2018
Posts: 92
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Re: Adding 2nd set of 7 module
Quote:
Can't quite recall - did I have "an argument" with you about internal cell resistance, or was it somebody else ? Either way, I yield to your wisdom :) |
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11-19-2019, 02:54 PM | #25 |
Gone Wild
Join Date: Jan 2013
Location: Saint Petersburg, FL
Posts: 2,089
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Re: Adding 2nd set of 7 module
How so? A 60AH and a 100AH in parallel won't charge well in parallel?
If I start at 54.6v (3.90vpc). Both packs are wired in parallel. I put the charger on for an hour and now it is at 56.0v (4.00vpc). Both packs are still wired in parallel so both packs will be at 56.0v... The 60AH pack will not be at 58v and the 100ah at 55v specifically because they are wired together in parallel. I'm not talking about individual cell imbalance, that can happen on a single pack as well as a parallel pack. But I am seriously confused that you state a 60ah pack can be overcharged when wired parallel with a 100ah pack (even though at the exact same pack V)... We commonly use V as a way to gauge SOC. If you are using a much more intelligent charger that measures internal cell resistance or other factors than V, ok then I understand. But if your charger and your BMS are all based on V then how can two parallel packs being at the same V be also at different SOC? |
11-19-2019, 03:07 PM | #26 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Adding 2nd set of 7 module
Who said parallel?
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11-19-2019, 03:20 PM | #27 |
Gone Wild
Join Date: Jan 2013
Location: Saint Petersburg, FL
Posts: 2,089
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Re: Adding 2nd set of 7 module
AH, OK. I re-read your post and you specifically said series. I missed that.
I thought the OP was talking about adding another 7 cells in parallel making two 7S packs and running those parallel to each other. I didn't realize the conversation had changed. |
11-19-2019, 04:26 PM | #28 |
Gone Wild
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 9,329
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Re: Adding 2nd set of 7 module
The context of that reply was preparing both old and new 7S1P packs to be reconfigured as 7S2P.
Wiring two 7S1P packs in parallel would require two separate BMS and ideally a master controller. It would also introduce a lot of possible dangers in case a cell in one pack has an issue or the due to the imbalanced current between the two packs during discharge and should have a means of isolating the two packs when not being used. Here is some good information on this subject from a different source: https://www.orionbms.com/manuals/pdf...ngs.pdf#page=6 |
11-19-2019, 07:10 PM | #29 | |
Gone Wild
Join Date: Mar 2019
Posts: 323
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Re: Adding 2nd set of 7 module
Quote:
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12-13-2019, 08:54 PM | #30 |
Not Yet Wild
Join Date: Sep 2016
Location: Roseville CA
Posts: 17
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Re: Adding 2nd set of 7 module
I purchased and will be adding another 7 modules as well. I initially thought it would be good to have two sets in parallel however I can not figure out a way to add the second set to my Zeva BMS. Seems in my case the only option will be to re configure the packs so its one and wire like others have kindly shared on this site.
It anyone has any suggestions I would welcome them. |
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