Daly BMS 24V 8S 100A - poor balancing + charging and discharging prematurely stopped

Marten

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Since it is a different cell each time I recommend stop charging at 27.0 volts and stop discharging at 24.0 volts. I believe you are still getting most of the energy out of the battery. If the cell delta at the top is able to equal out after a month or two then increase the charging voltage to 27.5 and see what goes.
24-27 V is too little power to operate a wheelchair. Even conventional lead-acid batteries would have a longer range.
 

Marten

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Is there any better BMS that does balancing battery cells even when discharging? (without Active Balancers)
I think Daly BMS is a bad product for me. Too small balancing currents and it balances only when charging. Should the balancing be active in discharging, there will be no difference in hitting 2.5 V.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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Please understand that at 3.65V the cell is at Max Allowable Voltage, it is beyond full.

LFP Nominal Voltage is 3.200, The full working voltage is 3.000-3.400, and typically we look at 2.900-3.450 and the 90% we want to use, because this is where the majority of the power is.

Charging above 3.500 is for all intents & purposes a waste of energy because you can charge your cells, to 3.65V and 100% SATURATED meaning taking <1A, stop charging and the cells will settle to 3.500 within an hour. Above 3.500 and below 2.900 the voltage curve is very short and only represents about 5% total capacity.

Now another Solution that actually may be the cause of your problem with overdriving the cells, is your charge profile. If charging to 29.2V you're overdriving the cells. 3.500V x8 cells = 28.0V
I've done testing including extreme hard-edge limit Thrash Testing with Grade-A Matched, & Bulk cells as well as EV Grade LFP cells and came up with a profile that works well.
NOTE: LFP only requires CC (Constant Current) which will charge the pack to 90% or so and CV (Constant Voltage) with decreasing amperage to finish the last 10%. Technically they do not require Absorb and they NEVER need Equalization by a charge controller (which is for Lead Acid only).
This is my Charge Profile that I use with a Midnite Classic-200 Solar Controller. My Samlex Inverter has identical settings.
All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

** Coulumbic Efficiency for LFP is 99%
NOTE that ABSORB (which is Bulk) is at 28.2 / 3.525Vpc,

Try adjusting your Solar Controller settings to match the above and you may see better results as it "should" not overdrive the runner and allow the other cells to top up more.

Regarding Active Balancers: (Consider only AFTER changing charging profile & testing that for 3 days of good sun - charging weather.)
There are many types and some are chemistry specific and various features. You want Active Balancing of at least 5A or more... Higher Amperage = Higher cost of course.
There are a vast amount of them out there. They are very specific and quite "quirky". Many are junk !
Known Good are:
QNBBM by Deligreen, Deligreen / Alibaba link
Heltec, Heltec / Alibaba Link
Hankzor, (is a VAR Value Added Reseller) Hankzor Alibaba / Link

Hope this helps.
Steve
 

ken morgan

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May 11, 2021
Messages
392
its simply a fault in how they represent what is charging vice discharge.. will they refund? I highly doubt it. it al works minus the simple + vs - in the description. the unit works with out any kind of output if you have the battery indicator (sorry names changes weekly) it has the Led display to show charge and a single button to turn on. everything works except the simple plus vs minus.. so I would bet they tell yo to pack sand as it works for everybody else. you want cheep? learn to deal with the idiosyncrasies of other languages.
 

GXMnow

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Jul 17, 2020
Messages
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Have you actually tried to do a real capacity test? LFP cells are a bit odd in that they all hold a very close voltage for the middle 70-80% of their charge/discharge range, but then as they hit the top or bottom knee, one or more cells will run fast. So your cells may actually be very close to balance. If it was always the same cell, then I would say it is more likely a balance problem, but if it is a different cell each time, then it could just be the drift that makes one cell hit the knee first at random. In either case, the BMS is doing it's job and keeping you from trashing a cell.

Charge the pack the slowest you can. Maybe try putting a light bulb in series to lower the current of your charger. Let the DALY balance for a while and hopefully the lowest cell will be able to get over 3.45 before the top cell hits the 3.65 cut off. Then discharge it and time the amp hours you get before the lowest cell hits the 2.5 volt cut off. If you are getting better than 90% of the cell rating, you are doing just fine.
 

Zwy

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Joined
Jan 3, 2021
Messages
1,049
A random battery cell of 8 pieces stops charging and discharging when it hits the highest or lowest point. (Daly BMS doesn't balance right)


Daly BMS 24V 8S 100A (R16A-GA14) Software version/Firmware: 20201205-1.01G

(sorry for my poor English)

Charging:
Once one cell hits 3.65V, then the Daly BMS stops charging. Balancing is also stopped. The other 7 cells have: 3,451 . 3,454 . 3,398 . 3,389 . 3,399 . 3,395, 3,401

You are in the knee area for SOC and have one runner cell. I read thru the responses already and you said at first you top balanced in parallel but not quite, you used a resistor/light bulb to draw down the top cells during charging. This is not a top balance in parallel to 3.65V per cell. Source a PSU and do it the right way.


7 battery cells have low voltage :-(

Discharge:

Once one cell hits 2.5V then Daly BMS stops discharging. The other 7 cells have: 2.864 . 2,902. 2,901, . 2.872. 2.861 . 2.845. 2.862.

No balancing while discharging. This is not a defect in one battery cell, it is always a random cell that hits the upper or lower boundary before the others

Any ideas?

Normal for commodity cells. If you want perfectly balanced cells, you will have to pay to get them.

Batteries are new from brand manufacturer. (8 x 110Ah LiFePo)

Daly BMS 24V 8S 100A (R16A-GA14) with BT/UART + CAN/485. Software version/Firmware: 20201205-1.01G . BTW: Where can I get new firmware?



--------------------------------


Problem number two:


When charging, the Smart BMS application on the first page shows " minus " ( for example " -4A " ) Once discharged, it does not show a minus. ( for example " 4A " ) This should be reversed, minus must always be displayed when discharging. But it's not. What's the problem?

Normal, charging shows as a negative number and discharge shows as a positive number. I use a seperate Columb meter and it displays the same way.


I think a top balance in parallel to 3.65V would ease your concerns. Reality is that once you get into the knee area, you will always find a cell that is a runner using commodity cells. The solution is to set your charger to a max of 3.50V per cell, in the case of a nominal 24V pack that would be 28.0V. This will not only extend the life of cells, but allows some balancing to take effect over time and not overcharge a cell unless you have a runner that can't be controlled well.

I would wager within a few minutes of stopping the charge, the cells will settle all around 3.4V. Mine do in a very short time. Those few Ah's you get from 3.4V to 3.65V don't amount to squat.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
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Location
Rural NE Ontario Canada
LET ME MAKE IT SIMPLE:

Bulk Commodity Cells will only provide a reliable 90% of their Label Rating. Simply put a 280AH Bulk cell will GIVE you 250AH without issues, above that runners will take over and result in Cell Hi Volt disconnects. These most often will test out between 260-275AH when run through a proper test cycle with test equipment. These can & will deviate through their operating cycle. This deviation is generally most notable during Charge Cycle above 3.350 and can see cells deviate by as much as 1mv per AH of cell capacity... Meaning that a 280AH cell can deviate by as much as 280mv.

NOTE: MANY BMS' also have a cell differential cutoff in the even that the cells deviate too much which can result in other problems. These problems are less "hazardous" with LFP than with other chemistries.

Matched/Batched/Binned cells will ALWAYS deliver the AH Label rating PLUS ! For a 280AH Grade-A Matched Cell you WILL get 280AH no problem. These DO test out at 285-290AH sometimes even higher. These also stay fairly close in IR (Internal Resistance) throughout their operating range, typically no further apart than 30mv, most often less.

There is NO POINT in charging LFP above 3.525Vpc it IS a waste as your in the Cliff Climb Knee and even with that it will settle to 3.500 or slightly lower which is normal. Also consider that cells at a Hi State of Charge (meaning above 80%) for long periods is harmful to LFP.

The 10%-90% Window for max lifecycles and optimal lifepan IS 2.900-3.450 VPC where the "official working voltage" is 3.000-3.400.

Vpc = Volts per cell.

Why do folks think they'll get a Rolls Royce when they buy a used VW Bug I dunno... Hopefulness and unrealistic expectations ?

Simple Rhetorical Question:
Just why on earth do people not equate why EV Car Batteries are so damned expensive ?
Because of High Tolerances & "Perfectly Matched & Batched" cells (regardless of chemistry used). Matching & Batching is time-consuming and expensive to do, this also produces many B-Grade & Grey Market cells because they don't "cut it".
 

Just John

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Aug 15, 2020
Messages
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Charging:
Once one cell hits 3.65V, then the Daly BMS stops charging. Balancing is also stopped. The other 7 cells have: 3,451 . 3,454 . 3,398 . 3,389 . 3,399 . 3,395, 3,401

You didn't do a proper top balance with a difference that large. There are no shortcuts.
when properly top balanced, the limited balancing is perfectly adequate to account for slight differences in self discharge. 3.65v is NOT what you should be charging to, that is an extreme you should only use when top balancing. 3.0v to 3.45v is the range you should be using.

Discharge:

Once one cell hits 2.5V then Daly BMS stops discharging. The other 7 cells have: 2.864 . 2,902. 2,901, . 2.872. 2.861 . 2.845. 2.862.

Looks like you bottom balanced.

If you want matched cells, they cost extra. I paid a little over $500 USD including shipping for 8 Eve 105AH cells. They come with test reports and are even throughout the range, they are not commodity cells.

The cells you are complaining didn't all reach 2.5v simultaneously, have less than an amp hour remaining at those voltages. Pretty good bottom balance, actually.
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
2,411
Is there any better BMS that does balancing battery cells even when discharging? (without Active Balancers)
I think Daly BMS is a bad product for me. Too small balancing currents and it balances only when charging. Should the balancing be active in discharging, there will be no difference in hitting 2.5 V.
What is wrong with an active balancer? I recommend it if you are have trouble at the top. Do you have a way to charge the low cells to 3.65 volts? Do them one each day after the cut off.

Get the top correct. Don't worry about the bottom as it is best not to go to 2.5 volts unless something extraordinary is needed. 2.8 to 3.0 volts minimum. If you regularly go lower consider getting more capacity.
 

Drago

New Member
Joined
Jul 18, 2021
Messages
6
Is there any better BMS that does balancing battery cells even when discharging? (without Active Balancers)
I think Daly BMS is a bad product for me. Too small balancing currents and it balances only when charging. Should the balancing be active in discharging, there will be no difference in hitting 2.5 V.
A balancing when discharging is an additional battery discharge. Why ? Set the lowest limit for any cell and discharging will stop. When charging a cells will be balanced.
 
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