Can you combine Tesla S batteries (5.3 kWh w/ 5.2 kWh) for 48v parallel bank?

[Standardtribe]

Question:
I have an off-grid application leveraging “Tesla Model S, 24V, 250Ah, 5.3kWh, 444 Panasonic” batteries. Currently, I am using two of these and am curious whether I can combine two additional Tesla batteries; specifically; Tesla Model S 85 battery module block, 24V, 250Ah 5.2kWh. One set is 5.2 kWh and the other is 5.3 kWh. Could those two batteries be combined in a 48v parallel? (Schneider 4048 inverter/charge controller)

Appreciate your advice.

 

[sunshine_eggo]

Optimal 48V NCA chemistry is 14S.

Tesla module are 6S, so you're at 12S. If your hardware can handle that range, then it's fine.

You would have an operating range of 36-50.4V. If you want the cells to last, you'll be limited closer to 42-48.6V utilizing 50-60% of their capacity.

I assume you already have or will have functional BMS for each 6S module and that you'll ensure the modules are balanced before putting them in series.

 

[Ampster]

I was considering Tesla modules. The main reason I did not go down that path was the scalability. Each 48 volt increment was going to require another BMS.

 

[Standardtribe]

Optimal 48V NCA chemistry is 14S.

Tesla module are 6S, so you're at 12S. If your hardware can handle that range, then it's fine.

You would have an operating range of 36-50.4V. If you want the cells to last, you'll be limited closer to 42-48.6V utilizing 50-60% of their capacity.

I assume you already have or will have functional BMS for each 6S module and that you'll ensure the modules are balanced before putting them in series.

I am quite new to upgrading my off-grid system which was set up three years ago with Tesla batteries. I have a 48v set up with a Schneider inverter and Outback charge controllers. What BMS unit would you recommend (any brand)? Appreciate all the help you can provide. Also, if you email me directly I can provide more information for your consultation. (matovu@hotmail.com).

 

[sunshine_eggo]

I never recommend the use of Tesla modules. Brand new LFP cells are safer and cheaper.

 

[Jennifer]

I was considering Tesla modules. The main reason I did not go down that path was the scalability. Each 48 volt increment was going to require another BMS.

Why would you "increment" in 48 volt steps, that would be a new system is that what you mean, then yes... but for those of us using these modules, the EVTV BMS works great and allows us to scale up to 32 modules so your comment about lack of scalability is not correct, it's very scalable. In fact, Jack (RIP) makes a version of the BMS which allows the use of a complete pack from either a Model S or 3.

For more information, check out @dougbert 's great thread at this location:

Something I built DIY back in 2000 - my path from Trace to Xantrex to XW Pro inverters

You hit an item that's been driving me crazy, how do we interface our JITB's to our systems, there's can and 485 but I've not seen anything about hooking it up to Schneider or Victron which is a disappointment as I run my system in Victron's DCC mode and BMS control would be nice. I'll have SOC...

diysolarforum.com

Jen

 

[Ampster]

Why would you "increment" in 48 volt steps, that would be a new system is that what you mean, then yes...

Each Bank of two 24 volt modules would required a separate BMS every time I wanted to add two modules. I already had an expensive BMS and did not want to buy another. I simply went with another option that was more cost effective.

....... for those of us using these modules, the EVTV BMS works great and allows us to scale up to 32 modules so your comment about lack of scalability is not correct, it's very scalable. In fact, Jack (RIP) makes a version of the BMS which allows the use of a complete pack from either a Model S or 3.

Not correct? Correct or not, it was not scalable in the context of my parameters. Jack is dead and even when he was alive, I never had confidence that he would continue to support the Tesla BMS based on years of watching EVTV and his evolution from EVs to solar inverters. As you explained his last iteration was to a complete pack from a Model 3 because the Model 3 no longer had the 24 volt modules like the Model S and Model X. I am glad it is working for you. I am a Tesla Fanboy, but I found a better value with DIY LFP cells where I could use my existing BMS. I already have two Teslas in my driveway and have been driving Teslas since 2016.

 

[Jennifer]

Each Bank of two 24 volt modules would required a separate BMS every time I wanted to add two modules. I already had an expensive BMS and did not want to buy another. I simply went with another option that was more cost effective.


Not correct? Correct or not, it was not scalable in the context of my parameters. Jack is dead and even when he was alive, I never had confidence that he would continue to support the Tesla BMS based on years of watching EVTV and his evolution from EVs to solar inverters. As you explained his last iteration was to a complete pack from a Model 3 because the Model 3 no longer had the 24 volt modules like the Model S and Model X. I am glad it is working for you. I am a Tesla Fanboy, but I found a better value with DIY LFP cells where I could use my existing BMS. I already have two Teslas in my driveway and have been driving Teslas since 2016.

1: Disagree but I thought I was wrong once but was mistaken so I could be again.
2: You're owning 2 Tesla's is not relevant or give your opinion any weight nor authority but congratulations none the less, I own 2 BMW M5's that doesn't make me an expert in BMW's. That said, your comments I disprove in the videos below, clearly negate any of that increased knowledge you elude to.

Jack's intent to go to full packs was CLEARLY stated in NUMEROUS of his videos (samples below to time stamp) and it has to do with the higher current / heat when running in lower voltages than in the higher full pack voltages. Not once did I hear him say it was related to lack of 24 volt modules.

That said we'll agree to disagree, I'm glad you found a solution but please don't knock ours because of incorrect knowledge, people are here to learn facts, not fiction, especially when they are trying to get knowledge about an item that CAN be so dangerous if not implemented correctly or they commission a system based on bad guidance some here seem to share (see comment about videos), have a great day.

(Please no jokes about his voice, this was one of his last videos before passing away).

 

[Jennifer]

I never recommend the use of Tesla modules. Brand new LFP cells are safer and cheaper.

Agree, if I had to do it again I would use LFP as well, I bought in and paid for the EVTV BMS and bought lots of modules before the price drops / popularity of LFP..... agree with you completely, but I'm committed now so just need to build accordingly (ala concrete battery bunker).. LOL

 

[Ampster]

2: You're owning 2 Tesla's is not relevant or give your option any weight nor authority

It was simply to give some context and explain that I have a lot of respect for the engineering that goes into any Tesla battery and that my comment was not because I was biased against Tesla. I have evolved through two pack configurations since that decision three years ago. I just made a change in inverters as well.

 

[Ampster]

I'm glad you found a solution but please don't knock ours because of incorrect knowledge, people are here to learn facts, not fiction,

No knock intended or implied. I simply made a different decision and shared my reasons, consistent with the concept of knowledge sharing on forums like these. As I mentioned above, I have a lot of respect for the engineering that goes into Tesla batteries.

 

[Jennifer]

For others interested, what @Ampster is referring to with the modules being different is that instead of having numerous individual modules like in the model S, the model 3 has the following:

• The modules are much larger than in the S or X. They are long narrow logs of cells with 23 cells in two of the modules and 25 cells in the other two.
• The two 23 cell modules are at each edge of the pack and 67 1/2 inches long, 11 1/2 inches wide and 3 1/2 inches thick and weigh 191 lbs.
• The two 25 cell modules are located in the middle of the pack and 73 inches long, 11 1/2 inches wide and 3 1/2 inches thick and weigh 207 lbs.

The Tesla Model S modules feature a dedicated stack monitoring BMS board on each module, securely wired to the individual cells and two temperature sensors. This board uses a Texas Instruments cell stock monitoring board that is designed to link vertically using an SPI bus (Serial Peripheral Interface).

The modules feature what is basically a six foot long flexible printed circuit board with copper runs insulated by a translucent insulating layer and connecting to each “brick” or “cell” of the battery pack plus a couple of temperature sensors. There is one of these copper run “tapes” running down EACH edge of the module. The bricks or what Jack calls “cells” are actually made of 46 cylindrical cells 21 mm in diameter and 70mm long.

They are nominally 3.6v at 5 amp-hours capacity with the 46 connected in parallel. So 3.6v x 230 Ah per cell and 25 cells for 90 volts on the long ones and 23 cells for 82.8volts This gives us a nominal pack voltage of 345.6volts at 230 Ah for a total capacity of 79,488 watt-hours. It has been LISTED at 80.5 kWh elsewhere and that COULD be true if the amp hour capacity were 232.92 Ah indicating 5.0636 Ah per cylinder.

So while the battery is not as amicable to DIY use (at least as far as modules are concerned, as opposed to the use of the full pack, which is easier), it's use of 21700's and other changes, sure seems to have made progress in other areas.

Tesla Model 3 batteries show impressive fire resistance despite damage from high-speed crash

A high-speed accident involving a Model 3 crashing into a pole recently provided an impressive look at the fire-resistant capabilities of Tesla’s batteries. Despite major damage to the vehicle and two of the battery modules being breached from the violent impact, none of the Model 3’s 2170 cells...

www.teslarati.com

 

[Ampster]

Those modules pictured are also higher voltage than the Model X and S modules. Since there are four in a 400 volt pack I assume they are each 100 volts each. The evolution continues and the emerging trend is for structural packs where there are no modules. Therefore the new packs most likely will not be friendly for DIY disassembly. The good news is a former Tesla employee has formed a company to recycle used packs and got a grant to built a factory in Nevada.

 

[Jennifer]

Those modules pictured are also higher voltage than the Model X and S modules. Since there are four in a 400 volt pack I assume they are each 100 volts each. The evolution continues and the emerging trend is for structural packs where there are no modules. Therefore the new packs most likely will not be friendly for DIY disassembly. The good news is a former Tesla employee has formed a company to recycle used packs and got a grant to built a factory in Nevada.

Yup, grab your model S modules now if you want them kids Ampster's spot on..... but as @sunshine_eggo mentioned, now there are far better/safer options if just starting down that road. The prices have fallen out on these modules, when I bought my first set of 5 I paid well over $1200 each, I bought 3 more this week and am paying less than 700 shipped, but with nations around the world (and the EU) banning petroleum cars, I expect prices to skyrocket again, we need more model S crashes to cover that shortfall.. LOL

EU parliament votes to ban sale of petrol car by 2035

Member states have already approved the legislation and will now formally nod it into law.

www.lemonde.fr