BMS cut off , one unbalanced cell

HRTKD

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Ah Ok now i understand, would you say something like 13.7v or 13.8v would be ok?(it trips at about 13.9V).
Thanks

The lower the charge voltage, the longer the BMS _may_ have to get things balanced. Start as low as you want, but something just over the voltage at which the BMS starts to initiate balancing.
 

MisterSandals

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If you don't mind me asking what are your settings for charging(absorption) and float?
My charge profile is pretty conservative. I charge to 13.8V and float just below where they settle (3.35V x 4 = 13.4V) so they don't micro-cycle (repeated charge, settle, charge...). So i float at 13.2V.

Others that use their RV's full time have great success floating much higher since they have a lot of continuous loads (fridges, phone chargers...).

The good news is that you can experiment a little and easily make adjustments to get it to work best for YOUR use case. I would try NOT to get into cases where your BMS cuts out because this can be hard on it and i suspect if that goes, its game over.
 

maydayone

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Others that use their RV's full time have great success floating much higher since they have a lot of continuous loads (fridges, phone chargers...).
Is there a way to work out what the optimal float V is? I'm planning to live in the camper full time and will have fridge running 24/7 and other appliances as well? Is it only about keeping the cells at given voltage(the voltage they "settle at" and avoiding them getting them constantly recharging? How do you achieve that if you have a constant load/discharge not always of the same magnitude?
 

maydayone

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Is there a way to work out what the optimal float V is? I'm planning to live in the camper full time and will have fridge running 24/7 and other appliances as well? Is it only about keeping the cells at given voltage(the voltage they "settle at" and avoiding them getting them constantly recharging? How do you achieve that if you have a constant discharge and intermittent charge not always of the same magnitude?
 

MisterSandals

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Is there a way to work out what the optimal float V is? I'm planning to live in the camper full time
The victron profile for lifepo4 had slightly lower settings -14.2 absorption and 13.5 float which I also tried with the same outcome.
Think of float voltage as a "minimal state of readiness" setting. Being a full timer with continuous loads, I would want a HIGH state of readiness as you're always using it. I think the default Victron 13.5V is good. This will keep your batteries at 95% SoC so i'd try this and see if you notice anything that needs fixing. (unlikely i think).

Similarly, i'd try 13.8V as max charge and see if that gives you enough battery power without the BMS disconnecting.
 

SteveCA

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It sounds like Sterling is using poorly matched cell. That is a big imbalance and that should not happen with properly matched cells. There will be some imbalance but .37 volts is a lot IMHO. I dont know if you can get to the cells, but if you can, I would try using a Heltec active 5 amp balancer. It would likely reduce the imbalance to allow charging to at least 14.2 volts or so.
 

mikefitz

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a brand new Sterling 120ah lifepo4 battery and one cell seems to be quite severely unbalanced.
May I ask how things are going with your issues?

I am trying to help someone who has a problem almost identical to yours and getting nowhere with Sterling. I am in email contact with Sterling but have had no useful response yet.
This is showing the BMS shutdown at just over 14v charge,
BMS Q.jpg

It's either out of balance cells or a faulty/mis calibrated BMS, I understand the BMS is a Daly product.

I know the answer may be to perform a top balance, but unless the battery case is cut open thus voiding warranty (a supposed 5 years) this cannot be done.
If anyone else has had issues with the smart Daly BMS reporting incorrect cell volts and can offer advice it would be useful.

Mike
 

maydayone

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Well, i got the battery replaced, the second has exactly the same issue plus it came in with misconfigured BMS ( completely wrong max discharge and charge limits), not detecting anything going in or out of the battery if it's less than 5A . As it is right now i have one runner cell which hits 3.71V which causes the BMS to shut down at 13.9V, the remaining cells are at 3.4V. Of course I was assured that they sold thousands of those batteries and this has never happened before. Initially trying to blame my charger - even after showing them a screenshot with the BMS disconnected charging.

I've measured the battery voltage with the external multimeter and this checks out with the sum of what the BMS shows for the cells individually. So unless the BMS somehow shows lower voltage for some cells and higher for others so the sum adds up then to me it's a balancing issue or a faulty cell. Give that i had two batteries with the same issue plus sounds like I'm not the only one, to me there is a pattern here...

I will be returning the battery as i had enough of this circus.
 

maydayone

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It sounds like Sterling is using poorly matched cell. That is a big imbalance and that should not happen with properly matched cells. There will be some imbalance but .37 volts is a lot IMHO. I dont know if you can get to the cells, but if you can, I would try using a Heltec active 5 amp balancer. It would likely reduce the imbalance to allow charging to at least 14.2 volts or so.
I agree almost 0.4V delta is huge! You could balance cells this way or in many other ways but for that you need an access to the cells. Since this is a sealed unit there is not much I can do -that 35mA of balancing from Daly BMS won't do much in this century. This should have been done at the assembly stage - that's why I paid premium for it.
 

SteveCA

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Interesting. One would not expect a commercial battery to be that unbalanced. Clearly there is a QC problem at Sterling. You would think they’d cycle the battery before sending out another dud.
 

maydayone

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Yeah, you would think that they will test the replacement thoroughly before sending out. The first battery i had was bought from a supplier, not Sterling directly, was actually better than the second one which was swapped directly by Sterling.

Two batteries with one cell off - makes you think , either the don't top balance when they assemble the battery or they mix and match cells they know are different.

I'm kind of leaning towards a QC here since the second battery which came from Sterling directly had an incorrect BMS settings as well. Some of which I can change through the Bluetooth app, like max discharge and charge rates, some of them i can't, for instance the BMS is not reporting any load in or out if it's less than 5A. For this as far as I know you need to connect the PC which i can't because it's a sealed unit.
 

maydayone

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The other thing which i wonder is how many people who buy a commercial battery actually check if it works as advertised? Wouldn't most people just connect it and if the light comes on then they're happy?
 

HRTKD

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The other thing which i wonder is how many people who buy a commercial battery actually check if it works as advertised? Wouldn't most people just connect it and if the light comes on then they're happy?

You're right, most people won't know to check it or how to check it. Ask them if they connected to the BMS and they'll respond, "What's a BMS?"
 

maydayone

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You're right, most people won't know to check it or how to check it. Ask them if they connected to the BMS and they'll respond, "What's a BMS?"
Yeah and as few people on this forum suggested if on every single charging cycle the BMS cuts in(this is a safety feature not a "normal" way of operation) , it might eventually fail, and that is not good.
 

Hedges

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How about bleeding off charge from the one high cell until it reaches same voltage as others?
Ideally, hold battery at a voltage below BMS disconnect with suitably adjusted charger, so other cells are part way up knee of curve.

With cells top balanced, they should remain reasonably balanced at a lower battery voltage so you can have SCC terminate charging without BMS disconnect. There will be some imbalance that BMS needs to tolerate at voltages other than fully charged, but shouldn't be as far apart as you see.

So you get cell voltage divergence while charging. After you stop charging with one cell at/near 3.75V, to what voltage does it immediately drop (and what imbalance between cells)?
Poor contact with a cell will show up as high voltage during charging, low voltage during discharge.
 

maydayone

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Hedges, since it's a sealed battery and still under warranty, I think maydayone is reluctant to open it up to get access to the cells.
Yep, the battery is going back to where it came from - no doubt about it. I'm getting 280ah cells and a BMS and building it myself - something i had hoped I can save some time on by buying ready made unit. Where I live i can get 4 x 280ah cells for about 800 pounds plus about 150 for a BMS. If i wanted to buy a proven alternative to Sterling - something like relion or victron I'm looking at 1K for a 100ah so it's a no brainer in my opinion.
 

Hedges

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Hedges, since it's a sealed battery and still under warranty, I think maydayone is reluctant to open it up to get access to the cells.

Yes, there should be a voltage he can set SCC to that doesn't cause disconnect. I think cells have diverged too far with other cells < 3.4V, ought to have remained balanced up to maybe 3.5V so SCC could be set for 3.5V per cell (14V). If not meeting published spec for charge voltage, should be replaced/serviced under warranty.

If warranty isn't an option, then break out the can opener and do the manufacturer's job for them.

I've dug into stuff and found manufacturer used components outside their specs. After warranty up. Boss though we should have them re-engineer the product and I though we should fix it ourselves. He opted for replacing failed components and continuing to use them out of spec. Cooling system for a laser. My solution would have been change a resistor so operated within spec RPM, and replace hose disconnects with lower backpressure ones.

Yep, the battery is going back to where it came from - no doubt about it. I'm getting 280ah cells and a BMS and building it myself - something i had hoped I can save some time on by buying ready made unit. Where I live i can get 4 x 280ah cells for about 800 pounds plus about 150 for a BMS. If i wanted to buy a proven alternative to Sterling - something like relion or victron I'm looking at 1K for a 100ah so it's a no brainer in my opinion.

Is that 800 British Pounds = $1096?
Unless those are superior quality cells, sounds to me like twice the price people here have been paying.
Double-check on that.
Also, make sure about trustworthiness of supplier, since with many there isn't a practical return option. (Maybe that's the price difference you see?)
 

RCinFLA

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With 3.4v on other three cells you are very close to full charge. There is not much difference in state of charge when all cells are above 3.4v. The high cell should continue balance bleed after bms cutoff. It should come into balance. May take a few bms cut off cycles before it does.

Leave a little bit of time after bms reconnects to continue its high cell bleed before starting charge again. Usually balance bleed enable requires a cell to be above 3.4v.

How you got that way may be due to not being used for a while with variations in cell self discharge rate, or high discharge/charging current rate will drive faster divergence in cell balance. Also only repeated partial charging may never enable balancing due to cell not exceeding 3.4v.
 
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