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New SOK 100ah Cells Out of Balance

brdcrtr

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Joined
Feb 10, 2022
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I have 2 new SOK 100ah batteries with Bluetooth, wired in parallel. I'm using a Victron Multiplus 12/3000 set to 50a for charging, 14.4 absorption, 13.6 float.

Both batteries have one cell that hits 3.7v and the BMS will disconnect.

When charging, one cell of a battery is hitting 3.7v while the other cells will hover around 3.45v. Once the BMS disconnects the Victron voltage will jump past 15v and the other battery's BMS will disconnect. Rinse and repeat.

I tried setting the Multiplus to 14.0v for absorption and reduced the current to 5a which gave me about 1a input to each battery (RV DC system is using the rest). I still hit the 3.7v ceiling on one of the cells.

Should I be having cells this far out of balance on new batteries? From what I understand I can use a bench supply and charge each low cell to 3.65v to get things balanced out. Or, put a load on the higher voltage cell while charging to bring it down?

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I recommend contacting SOK on how to proceed within their warranty.

Your efforts are correct if this was a DIY battery or out of warranty.
 
Does it happen every single charge cycle or just out of the blue? Reason is I glanced at my EGLL once, and it had a few cells at 3.8! But I am unable to reproduce it. Just once. Ever since then 3.55ish

Wondering if this is a fundamental issue and not specific to vendor but maybe same BMS or BMS internals?
 
It happens every time. To try to ease the voltage up I just set the absorption to 13.95 but it will still hit the 3.7v on that cell. I read in the the SOK Facebook group that they say to let it sit idle and as long as a cell is over 3.5v it will start to balance.

The one thing I didn't mention, if I put a load on the batteries the cells will be balanced. I'm new to LifePo4 but I think I remember reading that can be normal since the voltage ramps up so quick at the end of the charge cycle?

I just set my charger to 13.8v for absorption and float based on Current Connect's website stating 13.8v float. I'll see if that cell starts to balance out after a couple days of a float only charge.

For what it's worth, when I got the batteries the app showed 0% charge. I charged with a Victron Blue Smart 15a charger on the LifePo setting.

I also emailed the company this afternoon, I'll post any updates I get.
 
Here's an update on my batteries.

SOK replied their batteries would self balance and there's no need for an active balancer (I had asked if warranty wise they would allow me to install one). They kept stating the battery will self balance but it wasn't happening after sitting for a couple days. They sent some documentation and if I set my Multiplus to match their stated 14.4v absorption and 13.6v float I would get BMS disconnects.

They asked if I had done a capacity test. I had with two batteries in parallel. My Victron BMS 712 showed 212ah before one of the battery BMS shut down. This was when charged with the Multiplus set to 13.9v (if I recall correctly).

I was getting the felling our conversations were going to go around and around without any acknowledgment of the issue. So, I took the cover off and used a 1ohm 25w resistor to bring down the high cells down to the lowest cell's voltage. I had to do this with three of the four batteries I have.

I used a 10a bench supply to charge to 14.4 and no cells went over 3.7v. I had this supply buried in the garage, had I remembered before putting the batteries back together I would have done a top balance when the cover was off the batteries... Anyways, after charging I let each battery to sit for a couple days and they eventually balanced to .005 to .007v, depending on which battery (I'm also assuming because the voltage dropped a bit after a couple days).

After doing this I can set my Multiplus to 14.2v absorption and charge all batteries with no BMS disconnects but I can't set the Multiplus to 14.4v as the documentation SOK sent me states. I'll still have a cell in a battery that runs away towards the end of the charging cycle, BMS disconnects and charge voltage goes over 15v and the others disconnect.

The Multiplus likes to overshoot the set absorption voltage. I have it set to 14.2 but the BMS 712 measures the peak at 14.39. I have the V Sense of the inverter hooked directly up to the battery which I thought was supposed to help with this but maybe it's contributing to the higher than set charge voltage.

I don't know if I'll nit pick this any more; I've learned a lot about LifePO4 while switching form AGM batteries in my trailer. I'm not loosing much capacity not charging to 14.4v. From what I read and in my limited capacity test, even charging to 14v I wouldn't loose much. Plus I don't want to leave a full charge on my batteries if I don't use the trailer for three weeks? I figured I'd leave them around 80% and if we're planning a camping trip top them off before we leave.
 
Did you check for loose connections? Can sometimes be an issue if one cell begins to act up.
 
Here's an update on my batteries.
.......................
The Multiplus likes to overshoot the set absorption voltage. I have it set to 14.2 but the BMS 712 measures the peak at 14.39. I have the V Sense of the inverter hooked directly up to the battery which I thought was supposed to help with this but maybe it's contributing to the higher than set charge voltage.
.........................
With that said, when you set the Multiplus to 14.2 volts, it functions as if were set to 14.39 (basically 14.4).
In my opinion, you have set the charger to 14.4 as directed by SOK and the SOK batteries perform properly.
 
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With that said, when you set the Multiplus to 14.2 volts, it functions as if were set to 14.39 (basically 14.4).
In my opinion, you have set the charger to 14.4 as directed by SOK and the SOK batteries perform properly.
Yes, but not until I opened them up to somewhat balance them, I just wasn't expecting to have to do that.

But, I can say I'm glad I got a battery I could open up to do this with. Being able to monitor the BMS is also nice, otherwise I might not have known why my Victron was going over voltage while charging at the end.

Overall I'm happy with them and it's been a good learning experience for me.
 
in fact, this is very normal.... hard believe you get the 108ah and 111ah capacity....
 
Have you ever tried to charge each battery up *individually* BEFORE putting them into parallel service to cut down on the variables? Recommended to do so. At the very least, it provides a better diagnostic for any problems later.

Heck, this applies to lead-acid as well. I know, most of us want the bms to wave the magic wand, but sometimes you have to give the individual components a fighting chance to get along better with each other.
 
With that said, when you set the Multiplus to 14.2 volts, it functions as if were set to 14.39 (basically 14.4).
In my opinion, you have set the charger to 14.4 as directed by SOK and the SOK batteries perform properly.
If the victron is going to charge at 200 mV higher than specified I would be reducing to 13.6 or 13.8 and verify peak voltage both with the victron and at the SOK cell level.
 
Put an active balancer and be done. I don't know why they have such a bad rep, both Will and Andy seem to hate them but I never had an issue. I have made 2-3 batteries with rando cells and it brings them all up to 3.63v.

Its the one with the red capacitors and sells for like 25 bux on aliexpress.
 
Put an active balancer and be done. I don't know why they have such a bad rep, both Will and Andy seem to hate them but I never had an issue. I have made 2-3 batteries with rando cells and it brings them all up to 3.63v.

Its the one with the red capacitors and sells for like 25 bux on aliexpress.
I guess you do not understand Andy's logic on how active balancers take cells out of balance if left on all the time and how they can top-balance cells if switched on only as battery approaches 100% SOC.
 
Or maybe Andy doesn't understand. The active balancer shuts off once the cells are with in 0.01 volts of each other. It just doesn't decide to say well I think I'll just throw a monkey wrench into this and mess the cells up.

The reason he has an imbalance is because during discharging his cells can have a situation where the are more than .1V difference amount the cells hence turning on the balancer. Now some say this is good because if your cells are not all the same capacity the healthier cell can Help the weaker ones by sending current to them, there by giving you more usable capacity (other wise your capacity of your pack is limited to the lowest capacity cell in your pack). Grade B cells will have this happen more often then grade A cells.

Other say it is creating an imbalance and balancing should only happen at the top end, which again would not be an issue if all the cells were matched when the pack was created.

I say, it doesn't matter, when you charge the battery, the active balancer will bring all cells to the same voltage regardless. And if you look at a video he posted recently, all 3 of his battery banks came into perfect charge. I very much doubt the difference between the cells is more than 2-3 amps if even that.

An active balancer works far better than the built in BMS balancer, its like 20x faster.

But the whole notion that an active balancer will intentionally dis-balance a perfectly voltage balance pack is not true. If you have mismatched cells then it could potentially do it because during discharging you can have a situation when 1 cell is weaker and has a big enough voltage delta to trigger the active balancer.

Overall, just keep it on its cheap insurance.
 
Or maybe Andy doesn't understand. The active balancer shuts off once the cells are with in 0.01 volts of each other. It just doesn't decide to say well I think I'll just throw a monkey wrench into this and mess the cells up.

The reason he has an imbalance is because during discharging his cells can have a situation where the are more than .1V difference amount the cells hence turning on the balancer. Now some say this is good because if your cells are not all the same capacity the healthier cell can Help the weaker ones by sending current to them, there by giving you more usable capacity (other wise your capacity of your pack is limited to the lowest capacity cell in your pack). Grade B cells will have this happen more often then grade A cells.

Other say it is creating an imbalance and balancing should only happen at the top end, which again would not be an issue if all the cells were matched when the pack was created.

I say, it doesn't matter, when you charge the battery, the active balancer will bring all cells to the same voltage regardless. And if you look at a video he posted recently, all 3 of his battery banks came into perfect charge. I very much doubt the difference between the cells is more than 2-3 amps if even that.

An active balancer works far better than the built in BMS balancer, its like 20x faster.

But the whole notion that an active balancer will intentionally dis-balance a perfectly voltage balance pack is not true. If you have mismatched cells then it could potentially do it because during discharging you can have a situation when 1 cell is weaker and has a big enough voltage delta to trigger the active balancer.

Overall, just keep it on its cheap insurance.
The problem is that the voltage isn't a good indicator of SoC when the voltage is "between the knees". If you balance in the middle region of the curve then you could unintentionally be unbalancing cells that were already balanced. Based on Andy's testing this does in fact happen.
 
The problem is that the voltage isn't a good indicator of SoC when the voltage is "between the knees". If you balance in the middle region of the curve then you could unintentionally be unbalancing cells that were already balanced. Based on Andy's testing this does in fact happen.
I have watched a few of those videos and while perfect top balance might be lost I have not seen a test where total capacity was lost.
The last video I saw Andy had to increase his normal charging voltage well into the knee to demonstrate loss of balance.
Andy seems biased in this area.
 
In your case I would do the following:
Stop all charging, and use the batteries untill you get to a low voltage (below 3v per cell).
Then charge the batteries separately with a decent amperage up to about 80-90% SOC (3.4v per cell). Then charge them SLOWLY (still separately, say no more than 1A), up to 100%. This slower charging at the top should allow the balance current to keep up with the charge current. I'm not sure what the balance current on the SOK is, but maybe you will need to go even lower on the charge current.
 
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