Different options of wiring 16 cells 280Ah into 24V bank 8s2p

martan

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Hello,
I'll be expanding my battery bank to double the capacity. I wonder what is the best way to wire it. Currently I have 8 cells at 280Ah (EVE cells) with one BMS of course. If I add 8 more cells to keep it 24V, can I just make it one bank and use one BMS? I'm thinking about going 2 cells in parallel to make 8 560Ah cells, then connect them is series to get the whole bank at 24V. I would wire 1 200A (or 250A) BMS to the terminals for the whole battery.
It seems it would work, but I'm trying to see if there is a problem with it or if there is a better solution out there. MY old cells are not that old, only have about 40-50 cycles, so I think adding 8 new cells brand new , matching it all and balancing should not be a problem.
Thank you !
 

ereams65

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I think you'll be fine. Make sure to top balance all the cells, but having one BMS makes it a lot simpler and smarter, imho. Not to mention, some BMS manufacturers advise against paralleling BMS'.
 

martan

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Thank you for your input. I just wish there was a decent 200A and above BMS for 8S at 24V with BT monitoring. I purchased recently HEYO 8S smart BMS and I think that thing is dead. Can't activate it and it shows wrong voltage. I'm afraid to buy another Smart BMS and waste another $200 or more. I do have one Overkill , but the 100A limitation is not good in my case, so I won't use that one. I guess back to regular Daly 200A dumb bms.

I've seen another thread here about this, a guy mixing a new and old cells in parallel, sounds like a good idea.
 

ereams65

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What size BMS are you using now and are you anticipating drawing a lot more amps?
 

Horsefly

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I think you'll be fine. Make sure to top balance all the cells, but having one BMS makes it a lot simpler and smarter, imho. Not to mention, some BMS manufacturers advise against paralleling BMS'.
I'm not sure why someone would advise not to have two BMSs on parallel strings. Maybe you are saying they don't recommend having two BMSs on one string? I have heard that before.
Hello,
I'll be expanding my battery bank to double the capacity. I wonder what is the best way to wire it. Currently I have 8 cells at 280Ah (EVE cells) with one BMS of course. If I add 8 more cells to keep it 24V, can I just make it one bank and use one BMS? I'm thinking about going 2 cells in parallel to make 8 560Ah cells, then connect them is series to get the whole bank at 24V. I would wire 1 200A (or 250A) BMS to the terminals for the whole battery.
It seems it would work, but I'm trying to see if there is a problem with it or if there is a better solution out there. MY old cells are not that old, only have about 40-50 cycles, so I think adding 8 new cells brand new , matching it all and balancing should not be a problem.
Thank you !
Having cells in parallel in a pack is not ideal. It's best of the BMS is monitoring one physical cell with each balance lead. If you have a cell going bad, it will drag it's parallel mate down with it. I think it is generally recommended that in your situation you wire up two 8S packs, each with their own BMS. Then you have two operational batteries, and you can run those in parallel. Comparing other pros and cons of this approach: Pro, you would have two separate batteries, so if you to take one down or a cell goes bad, you still have the other one to run off of until you get it fixed. Con, you would have to buy a second BMS.
 

martan

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I've been using Overkill solar 100A BMS, but recently I had to change it to my older Daly 200A (no Bluetooth monitoring) because I was getting really close to 100A and a few times over that limit. I do anticipate more load, that's why I'm doubling my bank. But I do relly like the capability to monitor the cells and the whole battery on my phone or PC.
I really wish Overkill would make one model that is 200A or more.
 

ereams65

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There's a thread around here somewhere where the folks at Daly recommend to not use their BMS's in parallel situations. I was shocked by that as well, as I've done it without issue on 2 48v batteries in my golf cart, but he shared the email response and the followup when he asked for clarity. Sorry I don't have the link right now but it was recent as last week.
 

ereams65

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You might be able to find that Overkill BMS in a larger Amperage by searching "Xiaoxiang BMS" (I hope that spelling is correct) on Aliexpress. I know at one time, the folks over at batteryhookup had it up to 150a I think? I'm getting old so my memory isn't what it used to be.
 

martan

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I'm not sure why someone would advise not to have two BMSs on parallel strings. Maybe you are saying they don't recommend having two BMSs on one string? I have heard that before.

Having cells in parallel in a pack is not ideal. It's best of the BMS is monitoring one physical cell with each balance lead. If you have a cell going bad, it will drag it's parallel mate down with it. I think it is generally recommended that in your situation you wire up two 8S packs, each with their own BMS. Then you have two operational batteries, and you can run those in parallel. Comparing other pros and cons of this approach: Pro, you would have two separate batteries, so if you to take one down or a cell goes bad, you still have the other one to run off of until you get it fixed. Con, you would have to buy a second BMS.
That's the reason I posted this post, to have people with different opinions chime in. I'm trying to find a best solution. Adding another BMS is not that bad, if I go with another Overkill, it would increase my load capability to 200A, solving my issue. It just seems simpler to go with one bank and one BMS. But I see your point about redundancy and overall cell "health".
 
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DLTooley

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Horsefly makes sense to me. FWIW, you can probably use a non Bluetooth bms for the second system if you want to save a few bucks and then just manually check to see that they are calibrated and balanced. That’s a good idea anyway.
 

Boondock Saint

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And this would hold true also using 32 cells to make 4 of the 8s=24v batteries, each with it's own BMS and then putting the 4 banks in parallel?

This would require my buying 4 of BMS ?
 

HRTKD

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And this would hold true also using 32 cells to make 4 of the 8s=24v batteries, each with it's own BMS and then putting the 4 banks in parallel?

This would require my buying 4 of BMS ?

Correct.

There are much more expensive BMS that you can buy where you buy a single main unit and then add modular subunits for the cells of each battery. Batrium is one vendor to look at.
 

Boondock Saint

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Thx, looks god-aweful complicated, expensive and in AU. I'm told that with Victron the Daly is not recommended.

Any other suggestions?
 

HRTKD

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Batrium is definitely a step up on complexity. But you have one device to look at all the cells. With four BMS you have to look at each BMS to get the whole picture.
 

Boondock Saint

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Thanks, if I DO have 4 BMS across these parallel banks, and I pull the load from the + and - of opposing banks, will these BMS be a limiting factor on the amount of current I can pull from, going to the Quatro?
 

Horsefly

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Thanks, if I DO have 4 BMS across these parallel banks, and I pull the load from the + and - of opposing banks, will these BMS be a limiting factor on the amount of current I can pull from, going to the Quatro?
If they are parallel, the + from each pack are connected together, and the - from each BMS is connected together. So there is no "opposing" banks, unless I just don't understand what you are asking. If each pack is the same size (in Ah) the total current pulled should be one-fourth of the total, theoretically. So if each BMS is rated for 100A continuous (for example), you should be able to pull 400A from the parallel combined packs.
 

Boondock Saint

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Yes each ARE, but the "goiing into the Quatro" is the keypoint. Those final output cables will be heavier and NOT going through the output of any one BMS . . . right?

That's the clarification.
 

Horsefly

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Yes each ARE, but the "goiing into the Quatro" is the keypoint. Those final output cables will be heavier and NOT going through the output of any one BMS . . . right?

That's the clarification.
I guess I'll drop out of this discussion, as I have no idea what you are saying. I may be the only one who doesn't know what "the Quatro" is. Anyway, sorry if I confused.
 
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