programming cc and connecting powerwalls?

[Mcmullen7242]

I have the 45amp tristar mppt controller and two of the 48v powerwalls from bigbattery.com (https://bigbattery.com/product/48v-li-ion-powerwall/). These powerwalls each have one anderson sb50 port so i was going to make two y connectors, one to parallel them and another to go from the batteries that are connected to the inverter i have and the charge controller (similar to this but with 6 awg wires https://www.techdirectclub.com/ander...llel-cable-36/). I have the dipswitches set on my charge controller but have not hooked it up to my computer yet as i do not know what values to enter for things like absorption, float, and what not. If any of you can provide some insight, that would be appreciated.

Thanks

[Ampster]

........ I have the dipswitches set on my charge controller but have not hooked it up to my computer yet as i do not know what values to enter for things like absorption, float, and what not. If any of you can provide some insight, that would be appreciated.

Tell us about the specs of those batteries, any numbers you can share?
Chemistry - LFP or NMC?
number of cells in series? ( that will enable you to go from cell voltage to pack voltage settings. Probably something like 12 or 14 for a 48 v pack )

[Mcmullen7242]

the only specs i know are right on that link but ill write them here.
Nominal Voltage: 52.5V
Voltage Range: 42V ~ 58.8V
Capacity: 3.8kWh
Configuration: 12S
Chemistry: Li-ion
Maximum Charge Current: 65A
Maximum Discharge Current: 130A
Cell Over Charge: 4.20V
Cell Over Discharge: 2.75V
Breaker: 63A

[Mcmullen7242]

have you heard of anyone hooking bigbattery's powerwalls in parallel?

[Ampster]

have you heard of anyone hooking bigbattery's powerwalls in parallel?

Yes, they are doing it with $120 BMSs. Daly, Ant and Chargery are some of those BMSs that I believe come in 12S varieations. There are some YT videos out there. I am only a casual observer of those and do not have much in the way of helpful knowledge. I will take a stab at your battery settings above.

https://www.youtube.com/watch?v=R_fuEP_LDkc

[Ampster]

.......
Nominal Voltage: 52.5V

This number seems too high. Do you have a voltage for what your pack measures at its current state of charge>

Configuration: 12S

This is a critical number to remember in order to translate pack voltage, charging and other settings into per cell numbers.

Chemistry: Li-ion

That is a generic term that includes LFP NMC and others. Most likely this is NMC which has per cell ranges that I will discuss later.

Maximum Charge Current: 65A
Maximum Discharge Current: 130A

Good to know for determining wiring size and breaker sizes. Since you will be putting these in parallel those numbers could double but you probably won't be able to charge at that rate and probably don't need to discharge at that rate.

Cell Over Charge: 4.20V

This is the biggest clue that the chemistry is probably NMC which is the same as my Nissan Leaf modules and similar to my Teslas. I set the Absorb voltage on my Leaf pack to 4.05 per cell which translates to 48.6 volts on your charge controller for Absorb.
Temporarily I would set the high voltage disconnect at 4.1 per cell or 49.2 for HVD as it is sometimes abbreviated. Later these voltages need to be coordinated with your BMS so you have a backstop in case one system or the other fails. More on that when you program your BMS.

Cell Over Discharge: 2.75V

I usually set this conservatively at 3.5 volts per cell or 42 volts.
Let us know when you hook up your BMS and we can walk through those settings. With a used pack I am always careful as I cycle the battery to make sure any of the 12 cell groups in series are close to the same voltages. If not you will have to try some methods to top balance that can be discussed later.

[Mcmullen7242]

Thank you very much, I’ll check the voltage on the batteries shortly and let you know. Also I don’t need to buy a new bms correct? Can I program the one that the batteries came with? I thought to put them in parallel I would just need to make two Anderson y connectors putting two positives together and two negatives to one Anderson sb50

[Mcmullen7242]

Just checked the batteries, one is at 57.4 and the other is at 58.3

[Ampster]

Just checked the batteries, one is at 57.4 and the other is at 58.3

57.4 volts is 4.75 volts per cell. Either that is way over charged, cell count in series is incorrect or that is some Lithium chemistry I am unaware of. It is consistent with the numbers they published. Perhaps it is 14S, in which case those cell voltages are consistent with NMC and the set points I gave you earlier are all wrong. How many BMS wires are there? I will answer the questions in your other post in a subsequent post.

[Ampster]

..... Also I don’t need to buy a new bms correct?
Can I program the one that the batteries came with?

I don't know anything about that BMS. You will have to see what luck others have had. I lot of people have purchased those batteries and have experience with them that I don't have.

I thought to put them in parallel I would just need to make two Anderson y connectors putting two positives together and two negatives to one Anderson sb50

Yes that works or Andersons to a common buss bar where your fuses or breakers are to protect the wire. A lot of people like breakers to disconnect for diagnosis. Blue Sea makes a good AB switch also.

[Sunking]

You cannot connect lithium battery packs in parallel.

[Mcmullen7242]

57.4 volts is 4.75 volts per cell. Either that is way over charged, cell count in series is incorrect or that is some Lithium chemistry I am unaware of. It is consistent with the numbers they published. Perhaps it is 14S, in which case those cell voltages are consistent with NMC and the set points I gave you earlier are all wrong. How many BMS wires are there? I will answer the questions in your other post in a subsequent post.

I am not sure because everything is enclosed in the case and I’ll have to take it all apart to check. The only things showing outside the case is the port for the Anderson sb50 connector, the voltage meter, and breaker.

[Mcmullen7242]

You cannot connect lithium battery packs in parallel.

Are you sure about that? When I bought them I specifically told them I will be paralleling them and they said that’s not a problem, also they advertise that they can be put in parallel on the website

[Ampster]

You can connect Lithium batteries in parellel if you understand the issues. I prefer to do it at the cell level, but with low cost BMSs many DIY users are getting low cost storage with used batteries like the above.
For another opinion go to diysolarforum.com

[Sunking]

Are you sure about that? When I bought them I specifically told them I will be paralleling them and they said that’s not a problem, also they advertise that they can be put in parallel on the website

I do it professionally. I am not DIY.