BMS not balancing cells...

mathewhgreen

New Member
Joined
Apr 5, 2021
Messages
27
Hey

I built a 4s100p 270aH Lithium Ion Pack.
I installed a Daly 4s35A 12V BMS and wired it up.
It appeared to be working perfectly for about 6 weeks with daily use then the inverter kept randomly rebooting.
I checked out the pack and found this...

Top pack - near the positive - was 3.63V
Second pack was 4.2V
Third pack was 3.94V
Fourth pack was 3.99V

i have been charging my individual packs with my B6 charger on 1s to bring the voltages in line with each other and about to put it back together.
What's your thoughts about the BMS? Is it faulty? Could there be any other issue?

I did find a single cell which was hot and have removed that. Once it cooled down it's voltage was around 0.25v.
Could that affected the BMSs ability to keep the packs in balance?

Thanks in advance...
Mat
 

JeepDaddy

Solar Addict
Joined
Feb 1, 2021
Messages
245
Location
Kent, WA
The balance feature is passive and uses about 30mA and only balances above 4.18v at the default settings. That's not much to keep your 400 cells in shape. Your second pack was the only one in range to actually balance.

I'm more familiar with LFP, but match the tested cell capacity and internal resistance as best you can. Top balance and keep an eye out for bad cells like you already found. Maybe an additional active balancer would be in order.
 

mathewhgreen

New Member
Joined
Apr 5, 2021
Messages
27
The balance feature is passive and uses about 30mA and only balances above 4.18v at the default settings. That's not much to keep your 400 cells in shape. Your second pack was the only one in range to actually balance.

I'm more familiar with LFP, but match the tested cell capacity and internal resistance as best you can. Top balance and keep an eye out for bad cells like you already found. Maybe an additional active balancer would be in order.

I'm not 100% certain what you mean by only balancing above 4.18v?
 

mathewhgreen

New Member
Joined
Apr 5, 2021
Messages
27
A BMS will only balance above a certain voltage - 4.18v default in this case. There is no balancing happening under that voltage.

View attachment 50550

Ah I see... So this BMS will only manage charging balancing and from what I have found at 35ma...?

I was only charging it to about 80% capacity then draining to about 40% capacity as my solar was keeping it topped up...
That would mean it was never hitting a high enough voltage to start balancing?

Is there a better solution?
 

Substrate

Solar Addict
Joined
Apr 28, 2021
Messages
675
Location
SoCal
STOP! 4S100P "li-ion" 270ah battery and just slapping a DALY bms on it and crossing your fingers?

Not specifically stating your chemistry (lfp vs non)?
Not knowing what balancing means above 4.18v? (I'm now suspecting non-lfp, but not sure if YOU know)

Trying to charge your individual 100P pack-cells with a SkyRC Imax B6, just to make them a little equal in some random voltage?

Dude - I'm going to be harsh. Your system is a danger to yourself and others. Lack of knowledge shows - which can be remedied, but right now, you are playing with a pile of trash that is a danger to yourself and others.

At this level, one can't just throw things at the wall to see if it sticks, or if one of us has the magic formula to turn your trash into gold, without you having to do your homework first.
 

MurphyGuy

GOD ALMIGHTY
Joined
May 20, 2020
Messages
1,036
35ma of balance current on a 270aH pack? ROFL..

That's like using the brakes from a 10speed bike on a 50,000 lb concrete truck and expecting it to stop.

Daly BMS's are desgined for electric scooters.. and even then, I wouldn't want that scooter charging anywhere near combustibles.

Go get a Batrium or a REC BMS.
 

vk2emp

Solar Enthusiast
Joined
Mar 2, 2020
Messages
87
You can use a daly with LFP as there is no danger of fire. I would never use one on lithium ion. Too dangerous (in fact I don't have any home made lithium ion packs).

A 270Ah lithoum pack like yours, when it goes off, its going to be like a fire in a fireworks/munitions factory. Get a proper BMS for that bomb.

Yes we are all being harsh, but we don't want to hear months down the track "My daly bms didn't do its job and my house burn't down".

Anyway the BMS is the LAST RESORT. You should be top balancing your pack, then setting your charge controller to stop charge at 4.1V per cell, and cease discharge (by programming the inverter) to shut off at 3.4v per cell (if I recall correctly).
 

mathewhgreen

New Member
Joined
Apr 5, 2021
Messages
27
STOP! 4S100P "li-ion" 270ah battery and just slapping a DALY bms on it and crossing your fingers?

Not specifically stating your chemistry (lfp vs non)?
Not knowing what balancing means above 4.18v? (I'm now suspecting non-lfp, but not sure if YOU know)

Trying to charge your individual 100P pack-cells with a SkyRC Imax B6, just to make them a little equal in some random voltage?

Dude - I'm going to be harsh. Your system is a danger to yourself and others. Lack of knowledge shows - which can be remedied, but right now, you are playing with a pile of trash that is a danger to yourself and others.

At this level, one can't just throw things at the wall to see if it sticks, or if one of us has the magic formula to turn your trash into gold, without you having to do your homework first.

Hi

They are 18650 cells. Lithium Iron cells.
I bought 400 of them with capacities of between 2600mAh and 2900mAh.
I used rePackr.com to make my 4 packs as equal as possible.
I checked all the voltages of each cell and they were all 3.7v.
I put them in 100 cell packs and used nickel strips with a spot welder - battery operated - to put them all in parallel.
I then charged them up with my Victron smart charger at 6A to 14.6 volts over about two days through the BMS.
My understanding of the BMS was that is balanced the packs on charge and discharge. I was wrong about that!

I have taken my 4 packs apart and used my B6 charger to bring the voltages upto the same level so I can put it back together again and monitor it. It's taking a couple of days to get them balanced but I;m nearly there.

I have bought voltage monitor circuits with displays to keep an eye on things instead of using my Digital Voltmetre. I will calibrate the circuits with this as they are not exactly the same.

I do have missing knowledge!

I only draw between 5amps to 10amps max so between the 400 cells is only 0.025amp per cell. All the cabling is capable of handling it and I have fuses in place.

I am open to suggestions. I am willing to learn! I did a huge amount of watching of videos and reading on forums to get the pack designed and built in the first place. Nothing is overheating and it's sitting next to me as it charges so I can keep an eye on it! It's very low amps going in so all is good!

I understand it might seem I have thrown it together but I haven't! :)
Just want to fix the balancing issue!

I've been reading on here this evening and have come across ISDT P10 400W 16A as a possible solution as its DC powered which I would connect to my MPPT controller but I am not sure if that is possible or if there are any issues with that idea??

Anyway if you have any pointers I'll read anything!! :)
 

vk2emp

Solar Enthusiast
Joined
Mar 2, 2020
Messages
87
Its never going to balance if you are only charging to 14.6v. They are lithium ion cells, full voltage is 4.2v. Thus full for the 4S pack is 16.8V. I know you may only be charging to 14.6 to stay inside the voltage range of a particular piece of gear in your setup, but the balancer of the daly will never kick in at 3.65v.

It seems you are using Lithium Ion cells for a task where Lithium Iron Phosphate cells would be more suitable?
 

mathewhgreen

New Member
Joined
Apr 5, 2021
Messages
27
My Epever charge controller is programmed to stop charging at 16.1V as I wanted to maximise the number of cycles I could get out of my pack by not charging to 100%. I have also programmed my Inverter to cut off at 15.25V. The whole system was working great until the other week. It probably coincided with a week of bad weather? Not sure...

I will program the charge controller to 16.8V again and monitor it daily. I will also order a Batrium or REC BMS? Is that the best way forward?
Any suggestions where from? I am in the UK and cannot find any over here in the usual places...

Thanks for the info... :)
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
5,589
Location
Rural NE Ontario Canada
Chargery will not do NMC Chemistry.
That is not the correct chemistry to use for ESS (Energy Storage), the voltage ranges are outside of standard specs supported by most solar equipment or just at the "edge threshold". NOTE, Each Lithium Chemistry has its specific needs and voltage curves and they vary a lot. A poorly assembled NMC Pack with mismatched cells can be a very serious risk as imbalances lead to failures that result in thermal runaway situations. It only take ONE CELL to go bad and runaway and NASA you have problems.

PLEASE Ensure that you have a large enough PROPER Chemical Fire Extinguisher on hand.
For best results dowsing a Li-ion fire, use a foam extinguisher, CO2, ABC dry chemical, powdered graphite, copper powder or soda (sodium carbonate) as you would extinguish other combustible fires.

TIP, IF you wish to remain with 18650 NMC then I HIGHLY Suggest building a fire-proof box to house the battery packs. Yes, first instinct is metal, well it won't do much with a Li-Fire, the cells will melt any metal. You can build a Battery Box or Cabinet even that can really resist a serious fire without extreme difficulty. By using Magnesium Oxide Board which is Fire/Water/Insect proof (beyond std cement fireboard at 1/2 the cost) you can build a safe containment box. In the USA a Common Brand Name is DragonBoard LINK: https://dragonboard.com/ and it should be available at Lowes, HomeDepot and such as well. FYI, it's Heavy Stuff, and get a cheapo "toss away" circular saw blade (carbide tipped though) to cut the sheets and Wear a MASK (the dust is evil) Experience talking, I've used mag-O Boards for years, for tile base & fireplace backing etc.

Hope it helps, Good Luck
 

mathewhgreen

New Member
Joined
Apr 5, 2021
Messages
27
UPDATE

I balanced my packs within a 0.09v range and have charged/partially discharged over 4 days and the range is still the same without a BMS. No overheating of any cells.

I did find a blackened cable end going into my inverter on the positive cable which I’ve cut back and now have zero issues with my inverter disconnecting due to a Low Voltage error. Anyone any ideas what would cause this? Photo attached with a freshly cut cable for comparison.

I’ve installed a Bluetooth temperature sensor in my case for any temperature changes.
 

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mathewhgreen

New Member
Joined
Apr 5, 2021
Messages
27
And I’ve now installed the BMS again… going to continue testing pack voltages etc :)
 

Sanwizard

Photon Sorcerer
Joined
Feb 2, 2021
Messages
1,358
UPDATE

I balanced my packs within a 0.09v range and have charged/partially discharged over 4 days and the range is still the same without a BMS. No overheating of any cells.

I did find a blackened cable end going into my inverter on the positive cable which I’ve cut back and now have zero issues with my inverter disconnecting due to a Low Voltage error. Anyone any ideas what would cause this? Photo attached with a freshly cut cable for comparison.

I’ve installed a Bluetooth temperature sensor in my case for any temperature changes.
Are you using bare wire into the inverter? if not, how did you get the cables out of the lugs?
 

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,440
Hi

They are 18650 cells. Lithium Iron cells.
I bought 400 of them with capacities of between 2600mAh and 2900mAh.
I used rePackr.com to make my 4 packs as equal as possible.
I checked all the voltages of each cell and they were all 3.7v.
I put them in 100 cell packs and used nickel strips with a spot welder - battery operated - to put them all in parallel.
I then charged them up with my Victron smart charger at 6A to 14.6 volts over about two days through the BMS.
My understanding of the BMS was that is balanced the packs on charge and discharge. I was wrong about that!

I have taken my 4 packs apart and used my B6 charger to bring the voltages upto the same level so I can put it back together again and monitor it. It's taking a couple of days to get them balanced but I;m nearly there.

I have bought voltage monitor circuits with displays to keep an eye on things instead of using my Digital Voltmetre. I will calibrate the circuits with this as they are not exactly the same.

I do have missing knowledge!

I only draw between 5amps to 10amps max so between the 400 cells is only 0.025amp per cell. All the cabling is capable of handling it and I have fuses in place.

I am open to suggestions. I am willing to learn! I did a huge amount of watching of videos and reading on forums to get the pack designed and built in the first place. Nothing is overheating and it's sitting next to me as it charges so I can keep an eye on it! It's very low amps going in so all is good!

I understand it might seem I have thrown it together but I haven't! :)
Just want to fix the balancing issue!

I've been reading on here this evening and have come across ISDT P10 400W 16A as a possible solution as its DC powered which I would connect to my MPPT controller but I am not sure if that is possible or if there are any issues with that idea??

Anyway if you have any pointers I'll read anything!! :)
Just make sure you have a fire alarm mounted above the battery, please.
 

ereams65

Solar Addict
Joined
Feb 10, 2021
Messages
293
Sounds like you didn't top-balance these cells either so you're just starting to experience why that's important. The SOC of each pack varies greatly. Sometimes the difference between 3.71 and 3.74v is substantial, as it applies to state of charge. Even when you go into the BMS and change the Balance setting, your BMS won't be able to keep up until you get these packs all top balanced.
 
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