Charging a battery 50 times to test the Daly balancing function

I'm re-visiting the Daly BMS. As we know from previous test, the Daly BMs only balances while charging, Furthermore, it only balances while the app is showing a charging current. That is a total flaw in design!
I cycled a 4s battery 50 times with a Daly BMS connected to measure the success in balancing.

Here is what I found....

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[tenoirab]

Hi Andy! With the PC-Software (search for "Sinowealth BMS Tool V0.1) connected via USB <-> Uart (Serial) to the BMS, you can set the threshold of the charge and discharge current to be shown. Factory setting is 1000mA (they call it "DiftterCur" in the Software under the "System" Tag) So as long as the Charge- or Discharge Current is below 1A, the App shows 0A. And while charging with less then 1A -> no balancing, as you figured out! I reduced it to 100mA, so the balancer keeps balancing if the charge current is bigger than 100mA. But perhaps you have to calibrate the bms amp-meter (can be done in the "calibrate" Tab). My BMS showed constantly +300mA when there was absolutly no current flowing into the battery. So the SOC (State of Charge) rised, even when no charger was connected to the battery :-o I guess if you don't give a sh... on the SOC Gauge, you could "miscalibrate" the BMS-Amp meter so it shows constantly +300mA when it should show 0mA. Set the threshold to 100mA so it keeps balancing with it's ridiculous 30mA at least when you are above your selected 3.5V start balance voltage. Aber ich geb dir recht, verglichen mit den anderen BMS'sen die du getestet hast, ist das Daly was das Balancen an geht, ich sags direkt auf Deutsch: Kacke! :-) Grüsse nach Australien!

[teardowndan]

In principle, if you run batteries as a pack, the entire pack is seeing the exact same charge-discharge cycle and the only balancing that should ever be required is to offset differences in the batteries' self-discharge current. LiFe batteries should have a self-discharge rate under 2.5%/month, 2.5% of 300Ah is 7.5Ah/month of balancing, so you shouldn't need to balance more than about 0.22Ah/day. You just need to take a break from your unhealthy obsession with balancing voltages to at all times, let cells settle at whatever voltages they want to as long as they remain within comfortable limits.

[PowerPaulAu]

LOL... this was fun to watch, and I'll be amused to read the buildup of comments. As we know, people have a love/hate relationship with Daly, just like Aussies are (or at least used to be) Holden or Ford people.

I agree with just about everything you found. The balance current is terribly low, and for large batteries it seems impossibly low. But the results I've had have been positive. I do of course top balance properly, and that's the first step to a good battery. I also agree that the balancing is annoying to only happen during charging, however that does ensure that a faulty cell won't bring down an entire pack while just sitting there doing nothing. In practice the start voltage does prevent that from happening in most of the balancers/BMS's though. I have mine balance from a much lower voltage too, mine start at about 3.0v, so it does a little bit for a long time. It's a different way of doing a similar job, and that's where just transferring settings from different balancers sometimes doesn't work well.

Tenoirab makes a good point about the current sensing. It's one of my biggest gripes with the Daly BMS. That 1000mA threshold is to get rid of noise or spurious readings from the current sensor. It can be tweaked to be more accurate, but there's still a threshold.

Thanks for providing an awesome unbiased technical review of this feature, it's always good to see someone do this without just trying to prove their own point.

Some of the newer models of Daly BMS actually do 200mA balance current, I think it's the ones with a fan, but I haven't looked into them yet.

[michaelwilkes]

In my experience, once the pack is fully charged, if you let it rest for 30 minutes, it is back to just a few mV deviation. My pack only gets substantial deviation when approaching full charge while being charged. Walk away and come back later and the pack is once again balanced.

[sr]

Thanks Andy! I don't have a Daly as a preface but I do use a bms with 310 ah batteries that only balances while charging. It's for a rv setup and after a good top balance it stays balanced. I don't feel the bms balancer does a whole lot but this setup just works.

[xntr]

I use a Daly BMS in my 24V House Battery since 18 Month, running them from 100%-20% 24/7. So far they are perfectly balanced.

[squizwiz]

I want to update on my DALY. I installed the program on my computer that allows for me to make changes to the DALY. I mapped the gain function with respect to the current shunt. I programmed the current shunt to see 5x what current is actually going into the pack. This allows me to trick the DALY into thinking that I am charging at 1A, while I am feeding the pack 200mA. I also changed the balance delay to 0 seconds so there is no delay in activating it. These settings together allow for FAR more time to balance the pack on the daily basis. I have a 78AH pack composed of 6ah cells; 16s 13p configuration. I have the solar charge controller charging up to to 55.3v (3.456v/cell), and programmed to sit in the absorb cycle for 3 hours @55.3v (my system of packs need this for multiple reasons). The DALY is set to trigger balancing at 3.46v, and the balance open diff volt set to 0.010v. I am now on 36 cycles, and it finally appears to be doing its job. The pack in this video is very small compared to what I have, and I calculated it would take a whole year to balance my pack at the settings the DALY was shipped with. With the modified settings, it seems to get at least 15x more time to balance with these settings changed. After composing this pack, I balanced it the best I could, but alas, it wasnt good enough. Cell row 4 was considerably off from the others. Cell ro 4 is not at cell row 11's voltage, the next row in line to show the highest voltage. Just a note for anyone who is making a pack like mine: each of the 13 cells in parallel have their own tape behavior. Its never recommended to charge the whole pack to 3.65v/cell due to the variances! IF YOU CHOOSE TO DO SO< ENSURE THAT YOU CHARGE IT TO THIS VOLTAGE STEP-WISE LITTLE BY LITTLE WITH THIS BMS, AND APPROACH THE MAX CHARGE VOLTAGE SLOWLY. This is still not recommended, because you want the pack to balance at the votage settings that you're planning to use every single day! Good luck to everyone, this will be the last DALY BMS i'll ever purchase, even for small packs! The discharge function is sim[ply not powerful enough for anything bigger than cell sized 3200mAh in a single cell-row configuration. I have to stick with this BMS due to funds and the work it would take to replace it isnt worth the time. Use my setting, and figure out the gain settings in the PC app (real fun I'll tell you).

[Muppet_Interfector]

Andy, I think that the balancing on the Daly is achieved by placing a resistor across the cell that has too high a voltage. At 30 mA it requires approx 110 Ohm resistor. The resistor needs to burn off about 105 mW. That is probably consistent with a surface mounted resistors heat handling capacity. I therefore think that the reason they have such low balancing current is simply due to the capacity of the surface mounted resistors they are using. The other issue where capacity might be a problem is the current handling of the FET used to switch in the resistor, this would be secondary as the internal resistance of the FETs will be very low if they can be turned hard on. They can claim they have a balancing function which places them ahead of those without balancing however it is of limited value if you are trying to balance a couple of Amphours of difference in the cells. It would take about 30 hours to burn off One amphour of capacity difference, as long as you keep the charge current above the threshold charging current.

[henrikjanum]

Your configured balance turn-on voltage difference is 0.02 volts, not 2 milli-volts (0.002 volts) as you say in the video. This explains what you call the 'late turn on' of the balance function. See your video at 3:38 to see the configured value.

[felaxchow]

I think the Daly BMS is really good for cells that are well matched and top balanced before they're put in service. Charge and discharge at a 0.2•C rate is perfectly fine for that type of BMS, however what gets us in trouble over time is the relatively flat charge curve of LiFePO4 compared to the traditional NMC variant where the curve is fairly linear. The "smart" bms is really a NMC variant BMS with top balancing and LiFePO4 is just an afterthought. Once it hits the 3.5 volt mark, the current rapidly drops and the voltage sharply spikes up to the upper limit of 3.65 volts. At 30 ma bleed off resistors don't really have a chance to bleed off the extra charge until the others play catchup. The charge curve datasheets on NMC cells I've looked at are quite linear so it can play catchup with each other without too much difficulty.

I guess you can use a basic bms to protect the cells and have an external active balancer monthly maintenance balancing if they drift too far apart.

[diysolaradventures]

Wow watching this particular video i got my Daly bms to actually turn on and work i been up all night watching your video much appreciated

[dig]

Thumbs up and subscribed! Thanks for demonstrating the unique function of a Daly BMS! That was beer money good, thanks again!

[camro]

It's a very good point.

My Overkill/JBD BMS can balance *either* while charging or discharging (not charging, to state it better), but unfortunately not both. In light of that, my (limited) testing with my 2p4s EVE 280ah battery has shown it to be more useful to balance while NOT charging in my case, but of course still above 3.45v or so.
1- The effect of the tug of war between charge current and balance current on the cell voltage seems to make the balancer a bit less effective, since it bounces back and forth as the balancer hits the voltage differential threshold and turns on/off.
2- The best charger for my application unfortunately only has pre-defined charge profiles, and the closest one to what my preferred settings would be charges to 14.5v. In my case, there are plenty of times where the battery will get fully charged and then have no loads applied for quite a while. So by balancing while discharging (aka, not charging), I can also use the balancing to more quickly bring the cell voltages back down to the flatter area of the curve.

[jasondevine]

Thanks Andy. You will get a bashing from the Daly fanboys. As some others have pointed out these BMS are really only good for ebikes and such that have long chargers overnight on wall chargers. Thanks for this practical demonstration, great use of your tester!

[jackoneil]

Thanks for the test Andy, tough duty but someone has to do it right?
I concur with your assessment Andy, and that it makes more sense to get a BMS with active balancing for solar power applications.
My use case is a little different and wanted to test the Daly BMS units for a possible production run of EV power packs because they are compact, durable, weather resistant, cheap and available.
I recently bought a pair of cheap 16S, 20amp Daly BMS units (non-UART) to test on a pair of 4S, 6ah LFE cell packs, and after doing some high-current discharge tests and charging at 6amps, saw up to 120mv imbalances, After dropping the charge current to 2amps, brought the imbalance down to about 40mv as slow charging gave it more time to balance.

I spoke with an engineer at the large volume Daly supplier, and for large packs and fast charging he recommended adding an active balancer (they sell a lot of Daly BMSs and Active balancers.

As as I plan to use these packs on low-power inverters that have a low voltage cut-off above the minimum safe discharge pack voltage, I may bypass the BMS for output, use a fuse for short-circuit protection, and use the Daly BMS for over-charging protection, add passive balancing If needed, and use the charger's 'Full Charge' LED to activate the active balancer.

[Dabobeans]

I used to really look forward to new episodes on this channel, the battery build and all of the pieces and parts to make the system work. Seems like anymore we are down into the weeds about topics only the most nerdy viewers care about. It's no longer an enjoyable watch for me, but it's not my channel and as long as Andy is having fun, I understand.

[aatdekwaast]

in the settings you have put 20mV diff Volt instead of the 2 mV you thought That's why balance didn't kicked in at time stamp 17:25 minutes

[JerrePictures]

Hy Andy, your videos help me in to constructing my overlander. I also ordered a Daly BMS. And I get your point. BUT and here is the big BUT. We do agree charging and discharging is energy. And that is now the point. Long talk short we need to balance but balancing is charging and discharging mostly it are 1 til 2 cells that need more attention so these gonna be charging more than the other it is energy...but these will fail quicker it is like humans they work fysicaly harder and will die faster. Balancing need to be done!! Bit not to much! In my case I also buyed a 5-8amp active balancer that will react only if there is a difference of 5mV while charging or discharging...but still doubting if I will use it maybe I put a switch on it. But remember in order to have a longer lifespan for your battery do balancing only when it is highly recommended...

[keyem]

Two things that crossed my mind regarding that implementation of balancing.
1) Balancing a pack is not a goal in itself. The reason why we want it balanced is that we want to avoid early shutdowns due to a runaway cell.
Having that in mind, it makes sense to stop balancing when not loading, since there is no risk anymore of a cell running away.
2) This saves every as much as possible. Every balancing burns energy so not balancing is the efficient choice.

Unfortunately, the balancing current is way too small to make a difference, but that is true for all balancers. If you charge with 40A no balancer in the world will stop a cell from running away.

[vaneay]

it is just that dally BMS are very conservative BMS they try not to discharge the battery when there is no charge current to conserve maximum state of charge of the pack when it is iddle or discharging.
Maybe you should start balancing at 3.45v or 3.4v with the dally bms