Lithium TN 110ah charging problem.. (1 Viewer)

[andy63]

Hi I'm just going to describe a recent issue I've had and see what anyones thoughts on it are.. be much appreciated
Visited the van after a 7/8 week lay up in storage..
I have 280w solar through an mppt controler.. two of the above batteries in parallel... a Stirling 60 amp battery to battery and a dedicated lifepo4 20 amp mains charger..
The only load on the leisure would have been a Stirling battery master device keeping the start battery topped.. and the solar connected to the leisure batteries..
The growler alarm was active and whatever other small loads are associated with the vehicle electronics..
So when I checked it the leisure batteries were reading 12.5 volts.. the start battery 11.7v.. the engine just started and I watched to see what the battery to battery would deliver..
My solar appeared to be supplying nothing.. I put that down to the conditions but later found a dodgy fuse connection to be the likely cause.. and possibly why the battery voltage had dropped so low..
It's been sat 4/weeks before with no issues..
The voltage rose to 14.5v from the btb charger but no current flow....
Took it for a drive about half hour and still no change to those readings so I connected a generator to the hook up and switched on the mains charger..again voltage rose to 14.4v but no current flow....
The following day I got the van home and removed the batteries..
With a multimeter they each had 12.7 v on the terminals..
I tried a victron charger on each one but again it's as if the charger was seeing full batteries.. Good voltage but no current flow into the batteries..
I briefly tried a small load on each battery and it was still supplying current ..I didnt want to load them to much till I could see what was going on..
So..the batteries hadn't shut down but wouldn't accept a charge..
Anybody offer an explanation..

Andy

 

[Raul]

If you still have warranty on TN power, I would take this with the seller. It looks like BMS inside is playing up, or protecting for further damage.

 

[Two on Tour]

What's the temperature up where you are, has the BMS kicked in doing it's job ?

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[SandraL]

Could the bms in the lithium battery think that it was full and decline to accept a charge, hence no amps flow?
Or was the battery temp low and bms declines to charge?

 

[Raul]

When the voltage rises immediately, indicates that bms disconnects the charge, hence you see the charger voltage free floating

 

[Raul]

There is one more think you could try. Bring batteries to warm environment. Since is been down to 12,5v that’s 3,125v er cell. It may not take full current to go back up, or it may have a protection built in to prevent big current on low cell voltage. I was suggesting a low amp charger like a 2-4a charge on individual battery and see if voltage rises.

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[andy63]

If you still have warranty on TN power, I would take this with the seller. It looks like BMS inside is playing up, or protecting for further damage.

thanks..yes they still are in their warranty period and I have contacted them..they have been helpful but without been able to say for sure what is going on..
I should say that I have now managed to charge both batteries but im not sure what action resulted in them eventually accepting a charge..there were a number of things I had been playing around with ...they are both now fully charged and it took about 110ah th charge them both indicating they were only about 50% discharged..
ill be running then down and recharging to see what happens before/or if they go back into the van..
Andy

 

[Raul]

Something is not right, 12,5 is not 50% SOC. Maybe low temp protection kicked in? I wold keep a eye on voltage and try not to go below 13v for few cycles. Could be unbalanced cells, and every time you charge they will balance from about 13,6v up.

 

[andy63]

What's the temperature up where you are, has the BMS kicked in doing it's job ?

Could the bms in the lithium battery think that it was full and decline to accept a charge, hence no amps flow?
Or was the battery temp low and bms declines to charge?

the temp according to the car was around 2 to 4 deg the day I went up to the see the van..
one of the things I did do when I got them home was bring them into the house..so they did warm up before they took a charge
but id also had them connected to an ancient little 4 amp 6/12v charger I have so wasn't sure which action had made the difference
Andy

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[Googlebot]

They shouldn’t accept a charge in low temperatures. I wonder if the BMS kicked in and stopped the charge.

 

[andy63]

Something is not right, 12,5 is not 50% SOC.

the 12.5v was the battery monitor reading.. I measured 12.7 with the multimeter when I got them out and separated..
the supplier said 12.7v would equate to 50% soc ..because I had pointed out to them that I was surprised that it only took about 110ah to bring them back to full
Andy

 

[andy63]

little update...
its a time consuming process testing batteries
ive discharged both batteries using an 11/12 amp load and taken them down to 11 volts before disconnecting the load...
The data sheet says the over discharge protection activates at 10 volts..but the voltage does drop quickly once you get into the low 12 volts region..
both batteries were then charged with the Victron 20a charger until full... the Victron app showed both batteries accepted around 105 amp hrs of charge.Indicating they were well discharged..
ive then paralleled the batteries and discharged them again using a 15amp load and taken them to 11volts before disconnecting the load...
Just finished the final charge using the victron 20 amp charger with the two batteries paralleled and again according to the app they have accepted 205amp hrs of charge..
So in spite of the glitch of them not accepting a charge the other day they appear to be fine now..
As most have indicated it was most probably a low temp cut off but it certainly wasn't below 0 on the day I discovered this..
Ill try and get some actual figures for the various safety features the bms is responsible for from the supplier who have been helpful when I've managed to get through..
Andy..

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[Raul]

In a discharge test you start with a full battery and measure the discharged energy, not the charging energy. It’s a difference. But your test is still conclusive enough. I would of not had any doubt and not gone through the discharge. At least you got peace of mind. Anything below 3v per cell (12v)should be avoided, there’s not much left in there, and you cut valuable cycle life each time you deep in there. The low temp cut of, like I said, victron settled for 4C deg. I have my charger set at 3C deg and the hysteresis is 1deg. My batteries do not have low temp cut off so I rely on the charger.

 

[andy63]

In a discharge test you start with a full battery and measure the discharged energy, not the charging energy.

Cheers for the observations Raul..
I did actually monitor voltage and load current hourly..and taking an average current over the test durations gave an amp hour discharge very similar to the chargers estimation of amp hours replaced..
The 11v discharge figure in the tests was a result of a discussion with the supplier..
And my back of a fag packet graphs do show a very rapid drop of in output from around the 12.5 volt Mark..

 

[Raul]

That’s a nice feedback, I appreciate your effort to share, thank you.
I have my inverter set for low voltage disconnect at 12,6v, anything below that is reserved for 12v loads until my alarm kicks in at 12,2v. I know after that there is not much left or worth to exploit.
A friend of mine does 48v battery packs and bottom balances the cells. That involves a bit of equipment ( cell log) that’s capable of discharging single cells and set at 2,6v. Then it stops. It charges the pack and the cells stay balanced within 0,001v. But never brings the pack to 3,6vpc otherwise it ruins the bottom balance. This protects at low voltage, in unattended off grid application, without bms communication. Our integrated bms, it balances at the top (top balance), so you have a higher degree of protection at charged voltage, top voltage. As you discharge, the lower you go the more imbalanced they become. Hence stay away from bottom knee. The cells are never equal, and you can only balance top or bottom, each with their advantage and draw backs. The incorporated bms can only balance at the top when it enters absorb phase at around 3,45-3,5vpc it starts to balance.

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[andy63]

That’s a nice feedback, I appreciate your effort to share, thank you.
I have my inverter set for low voltage disconnect at 12,6v, anything below that is reserved for 12v loads until my alarm kicks in at 12,2v. I know after that there is not much left or worth to exploit.
A friend of mine does 48v battery packs and bottom balances the cells. That involves a bit of equipment ( cell log) that’s capable of discharging single cells and set at 2,6v. Then it stops. It charges the pack and the cells stay balanced within 0,001v. But never brings the pack to 3,6vpc otherwise it ruins the bottom balance. This protects at low voltage, in unattended off grid application, without bms communication. Our integrated bms, it balances at the top (top balance), so you have a higher degree of protection at charged voltage, top voltage. As you discharge, the lower you go the more imbalanced they become. Hence stay away from bottom knee. The cells are never equal, and you can only balance top or bottom, each with their advantage and draw backs. The incorporated bms can only balance at the top when it enters absorb phase at around 3,45-3,5vpc it starts to balance.

Cheers Raul..im trying to follow your post..ive heard of this top and bottom balancing but never really got in to understanding it..
Andy

 

[Raul]

I will try to explain as best I can.

A- top balance, achieved by bms, and it detects first cel at 3,65v it shuts of, if current exceeds the capability of the balancer to shunt it, or resistor to bleed it. The balance is done in two ways: bypass current to next cell (active balance), or resistor bleeding of until others catch up. When you discharge a top balanced pack the first cell to reach 2,5v ( smaller capacity) will trigger the bms to shut of, there is no balancing on discharging. Cell drift will be automatically dealt with by the bms, and you will notice reduction in capacity. The capacity always will be dictated by the weakest cell.
Advantage: ease of use, fit and forget, perfect top balance and max capacity use.
Disadvantage: failure of bms LVD when first cell reaches 2,5v. If this happens, nothing can protect your pack for reverse polarity, partial charged cells to discharge in the empty and create thermal runway. It will ruin the pack, or even fire, depends on energy left.
That’s why I use the bms as a fail safe and have the loads shut way before it can interact.

B- bottom balance, you start with empty 2,5v cells ( a known common point), and charge as a pack, until first cell hits top voltage 3,65v as example. Most go to 3,5v max; once first cell hit top, record pack voltage. That is HVD for that pack. Each pack will be different, depending on how well are the cells matched. The better are matched the more use of the capacity. Cells can drift as well with use. A new 102ah in 3-400 cycles can be 98ah so new balancing is needed.
Advantage : great protection against LVD failure, if cells come down even, there is no reverse polarity, because they are balanced at the bottom.
Disadvantage; HVD failure, car run the risk of cell overvoltage. Sure fire.
As you can see the bms option are more suited for inexperienced and does the job for you. On the other hand bottom balance if charged low enough so you never hit top voltage, is bullet proof, IF you have reliable high voltage disconnect. Usually a relay in cascade as a redundancy with the chargers it works. This is for ppl that really know how to exploit cells without bms, and have the means to prepare such pack.
Finally;
C- not used as every day method, is a middle balance, it wastes a lot of capacity, at the top and at the bottom. This is only adopted temporary, set with very conservative voltages, until other bits are added to the system.
I hope this helps.