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Daly BMS Charging Ind Cell

surfride

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Mar 27, 2021
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Ive got a 12v battery (280a primatic) with one outlier cell. Cells came from AliExpress, so I am stuck with them. The Daly BMS was advertised as the new model supporting BT and 485 for the touchscreen, yet I received the old model with only BT support. In my experience on Ali; all sales are final, regardless of quality of goods received or goods as described. If the cells and BMS came from Amazon or ebay, I would have returned. This is the risk of using Ali. I have a documented case for a chargeback, yet that would damage my relationship with Ali. As explained to me, chargebacks are so high my primary bank (bofa) blocks Ali from their cards. Off my soapbox to the issue...

Cells were top level balanced before installation. This battery is for my RV and what I am finding is balancing is not once and done. I am finding the battery requires continual top/bottom balancing and the Daly's 30ma balancing is inadequate. After a few cycles, my cells were out of balancing causing a ind cell over volt fault. Attempting to top level the lagging cell with the battery installed, I was unable to send any current to the cell. I should have recognized this as a clue. To augment the Dalys weak balancing, I added a Heltec active balancer. I should have recognized this was not going to work. What I found, the Heltec running with the Daly, the Heltec was only bleeding off excess voltage from the high cells to match the low cells, no current flowing to the low cells. Pulling the Daly out the equation and running only the Heltec, the Heltic balances as expected; Robinhood -- take from the high give to the low.

This 4s is a primer for building a 16s 48v hybrid system for my residence. I am not in love with the Daly. I am not in love with Ali. For the RV, not a big deal, but for my home, having to mess with 16 mismatched, purported grade A cells out of balance; unsustainable. Is my approach misguided, should I expect to sacrifice up to 20% of cell capacity rendering top/bottom balancing moot? Does continual top/bottom balancing damage the cells, negatively effecting management/longevity? Ive been wrong before...

My next step is to try adjusting section 4 balance settings on the Daly in a likely futile attempt to prevent the BMS from absorbing ind cell charge current.

Am I pumping a dry well with the Daly BMS -or- am I missing underlying cell management?

Thanks!
 
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Daly has their issues, of course, but there's a lot of people successfully using them. Did you top balance the cells yourself? I only ask, because there's plenty instances where folks are told, "Of course we top balanced" and come to find out, they actually didn't. The way I see them, Daly's are meant to keep new, matched and balanced cells in line. Anytime there's a big drift in voltages, they just can't keep up and it becomes a real pain. Yes, active balancers will pull cells down to a balanced level, but at least that's not shutting the battery down and preventing it from being used.
 
This project sat on my work bench for awhile before installation. The cells were deeply discharged/out of balance when I received them. The hits keep coming. The Progressive Dynamics 80amp charger I picked up for the RV was pulling so much current the breaker in my sub panel was buzzing. Threw my clamp on the 110 line and it pulling 16.4 amps, dumping 80amps into the battery. The PD ran until a high volt on C2. I then top leveled the ind cells with my bench charger to 3.6, taking several days.

I need to re-think this, reviewing the lithium charge/discharge curve and considering how Tesla manages their battery, perhaps it best to accept the top/bottom 10% is unusable. Adding to my junk-pile is the Progressive Dynamics charger, it is static at 14.6. live and learn.

My goal is to clear this balancing issue. I am software developer and about to go all-in with Daly communicating with their device. The more I think about it, I created this problem and it go away once I give up the top/bottom 10% capacity of the cell.

Thanks for your feedback; appreciate it.
 
I would recommend to turn OFF the daly balancing, get an active balancer ($30-$40), and..here comes the long part...
take your outlier cell, do a seperate capacity test...THAT is now what you must use to set the capacity of your pack.
for example, if you have tem 300Ah cells in series and your outlier is a 200Ah...then your battery pack Ah capacity is ONLY 200Ah!!
The lowest capacity cell in a series configuration drives the entire battery pack, so you need to configure your BMS to that capacity.
I have not found the daly (or jbd) BMS balance circuits to be of any use at all...I always turn balancing off now and use active balancers that "really" move charge from high cells to low cells.
 
I need to re-think this, reviewing the lithium charge/discharge curve and considering how Tesla manages their battery, perhaps it best to accept the top/bottom 10% is unusable. Adding to my junk-pile is the Progressive Dynamics charger, it is static at 14.6. live and learn.

My goal is to clear this balancing issue. I am software developer and about to go all-in with Daly communicating with their device. The more I think about it, I created this problem and it go away once I give up the top/bottom 10% capacity of the cell.
I am working on (just wrapping it up) the balancing issues with Qty 8, 100 Amp-hr Grade B Ali-express cells myself. I worked out this Parallel Cell Capacity Balancing (PCCB) procedure for a 4S design of paired 100 Amp-hr cells. It extends to larger arrays as well. It appears to have made a significant improvement (3:1 MIN-MAX improvement in voltage dispersion) even without active balancing. With active balancing, it is even better.

 
You don’t want to do both top and bottom balancing.

For Electric Vehicles bottom balancing is your choice, because you want the last drop out of you battery.

For solar (RV, boat, house) applications top balancing is preferred, because you will always hit the top when charging.
 
You don’t want to do both top and bottom balancing.

For Electric Vehicles bottom balancing is your choice, because you want the last drop out of you battery.

For solar (RV, boat, house) applications top balancing is preferred, because you will always hit the top when charging.
Why does a bottom balance get more charge out of a battery than a top balance whether used for solar or EV?

Perhaps it is that if you charge your CV you do this in bulk but do not push all the way to the top meaning there is greater uncertainty in the actual SOC. When you drain the EV battery, you want the closest that you can get at the bottom because you never push to the top.

I don't know if you can confirm this, but it would seem that essentially a balance is most accurate at either the top or bottom ends and not in the flat middle. Accuracy is probably proportional to the rate of change dV/dSOC.
 
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