Daly BMS (200A) with 2x Tesla Model S Battery Modules

[mckinleytabor]

Greetings All,

I’m seeking advice on trouble shooting a battery I am building. I know that the Tesla battery modules have fallen out of DYI favor due to the need for caution with the Li-ion chemistry, but these two Tesla Model S battery modules are what I have to work with at the moment.

I’m have a 13s Daly 200A BMS that I’m trying to use to protect and balance these modules. I also have 2 Stealth EV BMS adapter boards on the modules to give me a cleaner pinout to the individual cell strings.

My issue is that on the Daly BMS my cell string voltages are VERY incorrect. My understanding is that the Stealth EV boards (and indeed the Tesla wireless themselves) will not give me individual string voltages, but rather ADD the voltages up as I move down each string. So string 1 gives me 3.8v, string 2 gives me 7.7v, string 3 gives me 11.4v, etc, etc up to string 12 which is 45.6v. I know that my strings are not balanced, so the numbers here are examples.

That having been said, the Daly BMS shows me 12 strings, but with voltages that do not correspond with my manual measurements. Presuming that I can calculate cell string voltages with subtraction working backwards from the last cell string, my voltages are between 4v at the high end and 3.8 on the low end. (Like I said, I know the pack is out of balance). On the Daly BMS, my cell string voltages are 5v at the high end and 1.5v at the low end, and there isn’t even a clear correlation when comparing my manual readings vs the Daly look for which cells are “high” and which cells are “low”.

Oddly the total voltage on the pack from the BMS DOES match my total voltage as measured manually, and the average cell voltage from the BMS pretty much matches a manual average. (Which makes sense given 12 cell strings and the matching total voltage)

I’m taking my manual readings from the balance lead end that plugs into the BMS so as to verify the lead, Stealth EV board, and all the various connections.

The Daly shuts down after a few seconds, which I am presuming is the unit cutting off in accordance with its safety features as 1.5v and 5v are way outsize the protection limits. I have to apply or disconnect a 48v charger in order the get the BMS back up momentary to work with it. I’ve tried setting my cell string voltage high and low limits up and down to see if it is the protection system shutting down the BMS, but the values I input for those fields are not saving. Values for other fields such as total pack amp hours, amp discharge protection, etc, etc are being saved, just not the “high” and “low” cell voltages, which may be because the values I’m entering as so wrong.

Also at no point am I getting more than 21v out of the battery via the BMS, and that value does not change if the BMS is on or off. Again, I’m guessing this is the protection features at work. When I check the voltage at the battery terminal it is correct for the pack based on the series voltage of the cells.

Am I dealing with a bad BMS, or is there some settings that I’m missing? I’ve gone though all the main settings in the IOS Bluetooth Daly app and they all “look” correct. Are there additional settings worth looking at via USB and the Windows application?

Is this Daly BMS unsuitable for Tesla battery modules given the battery’s accumulating cell string voltages?

Thanks

 

[curiouscarbon]

Dear @mckinleytabor,

sorry that you’re experiencing this challenge.

Many a time I have read of people experiencing these weird shutdown or battery voltage monitoring issues with high amp Daly BMS units. Unfortunately I don’t have sage advice on how to ameliorate the behavior of the unit.

From what I have read, Daly designs the low amp BMS they sell, but the high amp ones are a two module combo where one part is daly one part is not, and sometimes things get hairy.

Anyways, if it does get to the point of new BMS, I have been using JBD BMS 4S so far and the voltage monitoring and digital communication have been very reliable so far.

hope this helps, again sorry that it’s not working well today

 

[jwu_cc]

Are you sure you can use Daly 13S BMS with a 12S battery ? It may not be functioning correctly as it's expecting a 13th cell voltage. Also just want to confirm that your BMS is configured for Li-Ion and not LiFePO4.

 

[mckinleytabor]

More Data....

The Daly 13s BMS does have an option in settings for "collect board settings" in which "board 1 cell num" can be adjusted. This was set to 12 in my testing. Yes, I also had already set the option in "cell characteristics" for "type of battery" to Li-ion.

As an additional test, I hooked cell tap line 13 to the overall positive terminal of the pack just to see if that made a difference, and something did change. Now my cell string voltages are better, but still do not match my manual readings. I say "better" in so far as the voltages are closer to reality, with a "high" still of 5v and a "low" of 2.6v. I reset the "cell volt low protect" to 2.5v from 2.7v and now the BMS stays on... Progress?

It looks like "cell volt high protect" is capped at 5v, can't adjust the value any higher than that. (I was trying to just it earlier to 5.1v)

Also the "Dischg MOS" ointmental switch indicator on the main screen show on, which I believe shows that the BMS is allowing power from the battery, and indeed I'm now getting full pack voltage from the P- line.

Now that the BMS is staying on, I've hooked it to a 54v 2a power supply to see if I can trickle any power into the battery and see what changes happen. Sadly though, the current indicator is still reading as 0a (even after setting current to zero with the power supply disconnected).

 

[jwu_cc]

Do you have a link to your Daly BMS ? Also, did you leave the 13th cell tap open ? If the BMS does indeed support variable number of cells, it should indicate how to handle the extra cell taps in the manual. Generally it would leave some of the middle cell taps open, instead of the most positive one, but that's just based on my own experience with Ant and QUCC BMSes so I'm curious if Daly BMS is doing something different.
Would you be able to hook up a single 18650 cell temporarily in serial to the 2 tesla modules and connect the 13th cell tap to it, just to see if you'll get the correct voltage readings ? Make sure you are not charging/discharging if you attempt this though, as the capacity of a single 18650 cell is going to be far less than the cell groups in a Tesla module and could easily over-charge / over-discharge the cell.