cells out of balance

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Peter Kuczynski

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May 3, 2021, 1:38:55 PMMay 3
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I set the charger to 28.8 to bring up the batteries to a full change. I admit I probably should not have gone to 28.8 or 3.6 per cell.
The sbms0 cut the voltage to the cells at some point to prevent over changing on some of the cells that came up faster then the rest.
Im going to wait till the sbms0 balances the cells out now.
Question is why are some cells too high vs the rest. Seems the sbms0 didnt balance the 8s cells allowing some to come up much faster then the others?
I understand the max recommended change is around 27.2 volts or 3.4 per cell. Im not sure if I should re-top balance all cells now or do a bottom balance..

Thanks!
Peter
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Peter Kuczynski

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May 3, 2021, 1:45:39 PMMay 3
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On Monday, May 3, 2021 at 12:43:53 PM UTC-5 Peter Kuczynski wrote:
Trying to post a picture, but google is kicking out error: message is too long, try posting a shorter message. All Im doing is attaching 1 screen shot.

Dacian Todea

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May 3, 2021, 1:49:53 PMMay 3
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Peter,

Not quite sure I understand what you were doing. The charger should have been always setup above 28.4V so 28.8V will have been fine. The battery will never get to 28.8V as the SBMS will stop the charger when any cell gets to 3.55V (assuming you did not mess up with the default settings).
There will always be a cell to get first to 3.55V no matter how perfect the cells are as there will always be small difference between cells both in terms of capacity and internal resistance.
A photo of the SBMS monitoring page 1 while was at 100% SOC will have helped me know if battery is properly balanced or not. I just seen your second post while I was writing this. What is the size of the photo maybe it is to large not sure if there are limits. Try to reduce the resolution if it will not work send it to me by email and I will post it here.
If you had that charger set at much lower voltage then maybe your battery was not fully charged before and then cell balancing can not be properly done.

Below a graph I posted many times on this forum showing typical voltage vs SOC and is clear that you can not know SOC based on voltage so you need to fully charge get in to that steep part of the graph to make sure you know SOC is at 100% and that is how the SBMS will calibrate to 100% SOC from the SBMS0 just calculates SOC based on energy in and out of the battery. 

LFP.gif

Dacian Todea

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May 3, 2021, 1:52:57 PMMay 3
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Peter,

Now I see your photo and your charger is not controlled by the SBMS0 so you are overcharging the battery. You are not allowed to have a charger that the SBMS0 can not control as then the SBMS0 can not protect your battery.

Peter Kuczynski

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May 3, 2021, 2:00:43 PMMay 3
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Well that explains it then.
The charger is/was certainly not controlled by the sbms0. I use a Drok external charger hooked up to the pv breaker pos, and main Neg.
That is my "shore power" solution.
So now that I know this is not the way to do this. What would be the recommendation for setting up a charger to charge the batteries that is controlled by the sbms0, for shore power.
Do I need to purchase another charger? If so can you recommend which, that the sbms0 can control.

Also, when the sbms0 detected a over charge condition, it also cut power to the the Inverter. So now im just waiting till the cells balance out and power returns.
Thank you for that graph btw.

Peter

Dacian Todea

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May 3, 2021, 2:09:53 PMMay 3
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Peter,

When any cell gets to 3.55V the SBMS0 will stop the charge sources (EXT IO4 set as type 1 need's to be controlling the charger for this to work) and no the inverter will not be turned OFF as that is controlled by EXT IO3 set as type 2 but your inverter likely turned OFF because one cell exceeded 3.75V secondary high limit and that is considered a fault as charger was not responding (in your case not properly connected) and then the SBMS0 will shut off everything it can including the inverter just in case that is an inverter/charger not properly connected.
Sorry not sure what model of charger you have but if that has no option for remote ON/OFF (a link to your model will help) then some other solution like a BP65 or similar needs to be found so that SBMS0 can stop the charging.
 

Will OBrien

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May 3, 2021, 2:15:42 PMMay 3
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On a similar note, I noticed something odd on my new pack and meant to ask.
When I charged up my new pack, the first two cells spiked up around 200mv above the rest.
Once I added load back in, they dropped back down to 70mv.
Is that relatively normal drift or should I be concerned about the behavior?

Peter Kuczynski

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May 3, 2021, 2:23:53 PMMay 3
to electrodacus
Thanks for that explanation, I understand. Im sure a cell exceeded 3.75.
Ok, so I do have a Victron BP 12/24 | 100, but im not sure how to set it up for AC to DC charging to prevent this from happening again.
The Drok is this unit here: https://www.ebay.com/itm/392044274271 It has no option for remote On/Off.

Peter Kuczynski

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May 3, 2021, 3:10:01 PMMay 3
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Reading up on the BP 12/24 100 https://amsolar.com/victron/relay-vtsmb100
If I was going to use it for AC to DC charg protection.
On the Victron....
I would connect the Out terminal to my main POS busbar.
I would connect  the IN terminal to the pos from the Charger.
Sbms0 then connect to EXT IO4 set as type 1 need's to be controlling the charger.

Let me know how that sounds,
Thanks
Peter

Dacian Todea

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May 3, 2021, 7:57:53 PMMay 3
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Will,

200mV seems a bit much as if the highest cell was 3.55V (max it can possibly be and just for a few seconds before charges ends) then lowest cell should have been below 3.35V and I will expect all other cells to be very close to 3.4V if they are fully charged thus your pack may be fairly out of balance for some reason.
You may also be looking when cell balancing is active and those voltage are wrong due to voltage drop on sense wires (from cell balancing current). A photo of the SBMS screen showing the cell voltages will be more helpful.

Peter,

There is no mention anywhere that that is a constant current power supply so it may be just a constant voltage and I'm surprised it even worked and did not tripped when connected to battery.
Yes BP100 when used to disconnect a charger will have the IN connected to charger positive and OUT to battery+
Negative from charger will connect directly to battery and yes EXT IO4 set as type 1 will control ON/OFF the BP100
But if that is not a constant current regulated power supply then it will not work as a charger.

Peter Kuczynski

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May 3, 2021, 11:44:16 PMMay 3
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Hi Dacian,
so i cant seem to find a constant current power supply, can you recommend one?
I also do not have any spare extio4 ports, but have extio5+ and -  Can I use one of those?. I'm assuming 5+ is connected to POS via a 1000 ohm resistor, then [ - ] goes to the Vic Batteryprotect On/Off.
OR, can i just use a jumper from my Victron 1200 inverter?

Also after reconnecting the ribbon cable, I've regained control over the sbms0, the inverter is working once again, and the voltage is even across all cells.

If I connect to the Drac constant current dc power supply to the Victron Smart, what can happen ?

Thanks!
Peter

Dacian Todea

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May 4, 2021, 3:06:27 PMMay 4
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Peter,

Yes you can use the EXT IO5 just set that in menu as type 1 and then go to Device settings and push the Save device settings button so the setting remains permanent even if you power cycle the SBMS0
You can connect the EXT IO5+ to Victron BatteryProtect L pin and the EXT IO5- to H pin or you can connect the EXT IO5+ to battery+ through a 1000Ohm(1KOhm) resistor and connect the EXT IO5- to H pin.
The Drok power supply in the ebay link is a constant voltage power supply only and no constant current limiting. Not sure what Victron smart model you have.

Peter Kuczynski

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May 4, 2021, 6:57:46 PMMay 4
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Ok, thanks Dacian
I am familiar with that set up by now. I am also using this victron: https://amsolar.com/victron/relay-vtsmb100 . So next I'm going to searh for a constant current poser supply.
Thanks!
Peter

Peter Kuczynski

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May 4, 2021, 8:49:53 PMMay 4
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I made the settings like you recommended, connect the EXT IO5+ to Victron BatteryProtect L pin and the EXT IO5- to H
I reconnected the Droc constant voltage power supply.
But I am not sure how the Sbms0 cuts off the Victron Battery Protect to prevent over charging of the batteries?
Should I change the SOC for esxio5 ?

Peter Kuczynski

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May 4, 2021, 9:30:00 PMMay 4
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After a little more reading, I found I can set the type to 3 and then the SOC to 88%, and the Sbms0 cuts the power shortly after it reaches the SOC. Nice.
I'm still going to find a constant current PSU, but for now this is working great.
If you have any recommendations on a 24v Ac/Dc PSU please let me know. Im looking at An Ames unit, I just dont want to spend too much money on this.

Thanks Dacian

Peter Kuczynski

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May 5, 2021, 9:42:00 AM (13 days ago) May 5
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Here are a couple AC/DC power supplies I located, if you wouldnt mind reviewing.
None mention that they are "constant current".
and
Im not sure which is applicable to a 24v Lifpo battery, seems the second link talk more so about its for RV applications.

Since connecting the Victron BatteryProtect 100, the cells have all charged very evenly. I still have it set at Type 3 on Ext5
The SOC is at 98%, which did cut of charging last evening, since then its been steadily discharging under slight load from a ait-purifier plugged in. But has not started to charge again. Not sure why.
electrodacus.png

Dacian Todea

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May 5, 2021, 1:03:15 PM (13 days ago) May 5
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Peter,

I will not use type 3 on EXT IOx for charging control since battery is never fully charged that way and if there is no other source to fully charge the battery the SOC errors can add up over time and a 88% SOC may be in reality just 5% or less.
To test just set the EXT IO5 as type 0 and the Victron BP should be OFF if installed correctly.
As long as something is called a battery charger then it is clearly a constant current  limited supply as all chargers are. Same thing for Iota so both will work but neither of them has remote ON/OFF so you still need to use the BP100 for remote ON/OFF.
As mentioned that power supply you have is a constant voltage only so likely it entered in overcurrent protection so it stopped outputting anything 

Chris Card

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May 6, 2021, 2:13:40 AM (13 days ago) May 6
to electrodacus

Peter, your EXTIO5 should be set to type 1, which is charger control.  Then the battery protect will be on until the highest cell voltage reaches the level set as “over voltage” in advanced parameters, when it will switch off.  The EXTIO5 SOC % setting is not used for type 1, so don’t worry about that. 

As Dacian said, first change EXTIO5 to type 0 to demonstrate that the SBMS0 is controlling the battery protect (battery protect should switch off), then change EXTIO5 to type 1 and verify your “over voltage” parameter is set to a sensible level.
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