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How unbalanced
#21
The problem is how you mixed and assume they will work Wink No hard feelings but the best way is to MIX aka MIX...

1. The opus is not accurate. You dont have 260Ah +-1AH. Perhaps more 260Ah +-15Ah
2. Problem with Row 2 is how you did build it. You should have mixed all your strings to 100%. Aka every one of the 14 packs need to have same total amount of cells, same amount of each type of cell, Same amount of low capacity as high capacity, same total capacity. If you do it this way you will get even packs and more even even end result.

Top balancing is fine and they will run within your desired voltage range IF and only IF you mix them properly and have same balance. If you have packs sagging = less high current cells or high IR. And if you have packs getting lower faster = less capacity in that pack compare to the other.

Building packs with exactly same type of cells are good if you have cell for the whole string that is true. But if you dont have that you need to mix it to gain the same result as the other packs.

This is actually just common sense in the battery world Smile I have done such tests some years back to and still have packs running for over 3 years that are mixed like that. The ones standing out are the packs not mixed.

Your plan sounds like a plan.
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#22
You seem to know what's wrong. I currently have three rows as well, but what I did was I interlinked each cell pack with each other. So instead of my standard 1S60P cell pack, it essentially became a 1S180P cell pack. I interlink them with just a 12ga or 10ga wire, just enough for it to balance each other out. Now it won't be as sexy if you have Batrium to see the 14*3 bars on the screen like on hbpowerall's batrium, but instead only see 14 bars, but then you are now merging all the batteries together for a better mix.

Is it bad that your sony packs is the first to charge up and the first to discharge? Not really. So your Sony packs could have a lower amp hours, therefore it makes sense it takes less to charge and faster to discharge. Mix the sonys evenly throughout the 14 packs and you'll probably be fine.

But the one thing you don't want is a self-discharging pack. That causes imbalance in the system. If you don't trust your Sonys, then charge it up and leave it alone for weeks and see if it self discharges.

I literally just put my chinese BMS back on again last weekend, and I removed it well over two months ago. During that period my cell packs did not deviate more than 50-60mV. All that without testing for IR or using repackr. It's now back in the 20-30mV range. So a BMS shouldn't have to work hard keeping your packs in line. Instead just work harder making sure your packs are equally balanced.
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#23
An update.
I replaced the 5 packs with 'wildest' voltage swings with packs of same cell make up as the others and balanced at 4.05v using Batrium over 24hours.   Balanced within 0.02v, waiting several hours and kicked off the inverter.   Here's a pictorial.



On my first discharge to 47.5v (3.39v per pack in theory)  things gradually drifted to a 0.06v min/max until the very end (last 30mins) when the gap opened up to 0.14v.


I have definitely solved my 5 pack 'wild swing' problem.  Now I'll work on adjusting the remaining 5 went a little deeper than the rest  - but overall this is looking great.

The bad packs:
The 5 bad packs with wildest voltage swings were Sony Green G5/G7(s).   The main thing I found was the average internal resistance  (reported by OPUS BT-C3100) was about 200 millohms (170 - 230).   I didn't measure these Sony's when I built the pack because I was not as aware back then.   These days, my packs are all <160 (e.g. 90-160) with average of 130'ish.   

 In conclusion  
- Original 5 Bad Packs -  1) concentrated G5/G7 packs rather than distributing mixed cells evenly  and 2) high IR most likely explain my problems.
- DIY's comment about adding mah of individual cells to get pack mah can cause significant pack difference is absolutely true.   Most of my packs are reasonable, but out of the 42 packs - 8 of them were mis-matched enough to cause 0.05v (or higher) difference.   In these cases I have extra cells to add to pack to bolster them.


Thanks again for this discussion - I believe I'm now operating in a 'reasonable' zone of expectations Smile

(02-18-2019, 06:55 PM)not2bme Wrote: You seem to know what's wrong. I currently have three rows as well, but what I did was I interlinked each cell pack with each other. So instead of my standard 1S60P cell pack, it essentially became a 1S180P cell pack. I interlink them with just a 12ga or 10ga wire, just enough for it to balance each other out. Now it won't be as sexy if you have Batrium to see the 14*3 bars on the screen like on hbpowerall's batrium, but instead only see 14 bars, but then you are now merging all the batteries together for a better mix.

Is it bad that your sony packs is the first to charge up and the first to discharge? Not really. So your Sony packs could have a lower amp hours, therefore it makes sense it takes less to charge and faster to discharge. Mix the sonys evenly throughout the 14 packs and you'll probably be fine.

But the one thing you don't want is a self-discharging pack. That causes imbalance in the system. If you don't trust your Sonys, then charge it up and leave it alone for weeks and see if it self discharges.

I literally just put my chinese BMS back on again last weekend, and I removed it well over two months ago. During that period my cell packs did not deviate more than 50-60mV. All that without testing for IR or using repackr. It's now back in the 20-30mV range. So a BMS shouldn't have to work hard keeping your packs in line. Instead just work harder making sure your packs are equally balanced.

I thought about interlinking my packs but because I have them horizontal on shelves I could not run wire at back of shelf.  Also, I wanted Batrium to have the ability to balance each pack in reasonable amount of time.   My packs are 260ah and it takes about 10hrs to balance 0.03v-0.04v difference.  A 780ah pack would likely take 30hrs to do the same balance.

Not clear I made the right decision - just sharing my thoughts.
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#24
(02-18-2019, 06:55 PM)not2bme Wrote: I literally just put my chinese BMS back on again last weekend, and I removed it well over two months ago. During that period my cell packs did not deviate more than 50-60mV. 

How many cycles, or Ah throughput has your battery seen over that two month period ?
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