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286Ah 10,5kWh capacitor heltec BMS powerwall
#11
(10-28-2020, 06:40 AM)Lithiumseller Wrote: Heltec capacitor active equalizer is running about temperature  like 25c, active balancer benefit is to have equal cycle life for lithium cells and when discharging there is no cell block what gets empty before others.
Hmm it looks to me that this active balancer will basically hide an underperforming pack.
Now Lithiumseller please do not take this the wrong way as any thing to educate us and make our packs perform better is always a good discussion.
I on the other hand am struggling to see the advantages of this balancing unit.
So taking the scenario of a 4s battery with "100Ah"  and you have 1 pack at 80Ah one at 120Ah one at 100Ah and one at 90Ah. the 120Ah pack will be constantly giving up energy to maintain a "balance". Am I wrong here?
Also is there any reporting  at all with this balancer? I do not see anything in the description. It would be nice to know how much "active balancing" is actually happening to determine if there is a pack in trouble.
If a battery is built with a proper balance of the packs to begin with as in 100AH ±5Ah for each then active balancing really is not necessary as the individual pack voltage when getting close to DOD (3.5V) will be relatively close as in 0.05v ±0.03v . As the Battery charges the packs will start to tighten up all by themselves and if any top balancing is needed it will be very little.
The weather has been dismal in the US north-east over the last couple of days but these charts will show you the point I am trying to make.
This was the solar curve of my 14s pack yesterday as you can see my battery this AM is depleted and idling at 14.5 SOC voltage are between 3.420 and 3.500.

During yesterday's brief encounter with the sun my system started to charge and the cells tighten up. Here is a closeup of the voltages between 14:00 hrs and 15:00 hrs as you can see 0.032 voltage difference with absolutely no balancing required.


As the system approaches 4.1V this self equalization just gets tighter with a full charge showing 0.01±0.01 difference again no balancing interaction required.
This trace was taken in august when I had plenty of sun.


Now if you have  Frankenstein packs (ones with a multitude of cells from different manufactures) and the cells mAh results, IR and SOH are all over the place. Also if the packs where thrown together with minimal attention payed to sorting mAh and trying to equalise  then if you do go below ≈3.4v there will be a seperation of voltage some of it rather dramatic. So yes there I can see the use of an active balancer but then again is it hiding something? I don't know.

Does the ANT BMS have any reporting so you can track the performance of the whole battery and the individual packs? If so do you have any data you can share?
Thanks for all your input and info so far. Nice start on a 14s100p X2  Battery. Big Grin
Wolf
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#12
(10-28-2020, 06:40 AM)Lithiumseller Wrote:
(10-27-2020, 05:05 PM)Bubba Wrote: So question I just thought of.... the pack is well balanced does the BMS run cooler?

Does active higher balance current have a 2nd benefit.  ...   Longer BMS life?
Heltec capacitor active equalizer is running about temperature  like 25c, active balancer benefit is to have equal cycle life for lithium cells and when discharging there is no cell block what gets empty before others.
Healthy packs don't need active balancing in my experience - its amazing.   I have 84 packs that cycle every day and I've not done any balancing since April 25th 2020 when I added the most recent 14 packs, balanced them in and turned balancing off.   They have drifted 10mv since then - within the 'margin of error' one might say as packs seem to take a bit to 'settle in' after an initial balance.    The battery bank has delivered 3,681kwh(s) of power since then - so the battery bank is not sitting idle. 

IMHO and to echo some of what @Daromer said above - I think its a misdirection to go the active balancing route as it 

- Wastes energy on something that's not needed
- I can't see any theory as to why it would extend the life of the battery bank - only adds more stress as balance current is induced
- Could hide a failing pack (to the limit of the active balancing) that needs attention...  I'd rather have the gradual warning (e.g. balance drifting) than hide it till its a serious failure

I get the 'idea'...  its predicated on the idea that packs need balancing...   but that's not true if the packs are healthy and matched within a battery.  
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#13
I use an active balancer as well and I agree with some of the statements regarding drift and the advantage of active balancing. My packs do not drift as well since they were made with similar cells. Some balancers are not programmable, but some are. The current one I use are set to 40mV difference, but my packs never go over that value. So in this case it never get to the point it balances. The JKBMS I will be using next is actually programmable so you can set it to a point where you can have it balance. Therefore it's not balancing all the time. So at the same time it is true that a correctly built pack doesn't require much balancing. Also I don't go past 70% depth of discharge, so the wild swings on voltages usually happen if I go 90% depth of discharge where the small difference in mismatched capacities start to show.

But the real reason for me why I got the board was to build my own BMS, since it does the voltage reporting for me. Through my raspberry pi I also have relays that fire off during events, and emails that go out when threshold are met. It also allows me to graph on graphana. My board only cost me under $100 so it was an inexpensive purchase.
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