Tesla S Battery Bank for Solar

[Maddog55]

Talking to a Victron sales rep. He is suggesting one 48/8000 inverter and one VICTRON 120/240V 32/100A autotransformer to share a common neutral between the two 120v legs.

Assuming 4 panels of 24v 300 watt solar panel array can generate 35 amp hrs / 100 watts / day = 420 amp hrs / day * 24 volts = 10,080 watts / day. If the math is correct, it seems I’m limited by the solar specifications.

The thought process is to match the system specification to its capability parameters. Assuming the numbers are correct, I would have to live within those power parameters and break out the generator if I run out or need more power an any given day. At 20% drain parameter, I would have less than 8000 watts/day. As long as I don’t run the air conditioner or the furnace, I should be okay. The water heater can run on propane.

For the battery bank, 48V * 300 amps = 14,400 watts * .77 drain and top of specification = 11,088 watts. So a 48V 300 amp LiFePo4 would be a good fit based on solar panel capabilities.

On the other hand, the question of “is the juice worth the squeeze” is a totally separate question. Is $27,000+ worth 10,000 watts of power/day?

LiFePo4 batteries, solar panels, and inverters can be pricy. I think I will limit myself to under $10,000 and try to configure the best system possible. Tesla S batteries figure into that equation. Power, reliability, value, and weight are primary considerations.

[alanhenson]

I talked to victron and he said your average installer won't be able to install an auto transformer because of the floating ground. He warned me not to get one.

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[DaveMatthewsBand]

Warranty is good.

My apologies for being obtuse but I can’t imagine Tesla honoring the warranty since it’s been removed from one of their (wrecked) vehicles and is not being used for it’s intended purpose. Hey if I’m wrong, maybe I’ll get one too.

But if Tesla isn’t honoring the warranty, then I assume the company selling the battery is offering one?

Can you post a link to reference that warranty?

All 4 of my Battle Borns combined weigh 116# which is awesome and significantly less than what 8 AGM would weigh, but if they didn’t have at least a 4 year warranty I probably wouldn’t have spent $925 each on them.


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[Maddog55]

My apologies for being obtuse but I can’t imagine Tesla honoring the warranty since it’s been removed from one of their (wrecked) vehicles and is not being used for it’s intended purpose. Hey if I’m wrong, maybe I’ll get one too.

But if Tesla isn’t honoring the warranty, then I assume the company selling the battery is offering one?



Can you post a link to reference that warranty?

All 4 of my Battle Borns combined weigh 116# which is awesome and significantly less than what 8 AGM would weigh, but if they didn’t have at least a 4 year warranty I probably wouldn’t have spent $925 each on them.


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I was saying your warranty is good. Used batteries from a wreaked Tesla doesn’t have any warranty. Although some Ebay offers did have a 6 month warranty. Obviously not as good as a factory warranty like Battle Borns.

As for weight:
Battle borne 12v * 100 amp hrs * 4 = 4.8kWh @ 116#’s & $4,000
Tesla 24v * 232 amp hrs = 5.5kWh @ 55#’s & $1,200

Used Tesla has no warranty for sure but it is over engineered and will never be truly taxed to its capabilities in a TT. The combination of power to weight and power to cost ratio looks might attractive. Just trying to figure out the best combination of power, reliability, value, and weight for the dollar.

[Maddog55]

I talked to victron and he said your average installer won't be able to install an auto transformer because of the floating ground. He warned me not to get one.

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Did he, the Victron rep, have an alternative recommendation?

[DaveMatthewsBand]

I was saying your warranty is good. Used batteries from a wreaked Tesla doesn’t have any warranty. Although some Ebay offers did have a 6 month warranty. Obviously not as good as a factory warranty like Battle Borns.

As for weight:
Battle borne 12v * 100 amp hrs * 4 = 4.8kWh @ 116#’s & $4,000
Tesla 24v * 232 amp hrs = 5.5kWh @ 55#’s & $1,200

Used Tesla has no warranty for sure but it is over engineered and will never be truly taxed to its capabilities in a TT.
The combination of power to weight and power to cost ratio looks might attractive.
Just trying to figure out the best combination of power, reliability, value, and weight for the dollar.

Thanks for the clarification.
Some food for thought, since you haven't yet purchased your batteries...
To be fair, mine are $949 each not $1,000 each, unless you're referring to the new GC2 model.
Still, $3800 is definitely more than $1200.
Keep in mind also, you have to factor in how much a 10 year warranty is worth, because that does have value.
Also, mine came with an advanced BMS and you're not factoring that into the cost you posted above.
Can you go into any detail on the BMS you'd use for the Tesla setup and it's cost?
I can't imagine it costing much, but I'm curious if it offers the same level of protection, and that has value.
Lastly, were you going to have your trailer wired to be 24v? and if so what advantages are there to that over 12v?

[Maddog55]

Thanks for the clarification.
Some food for thought, since you haven't yet purchased your batteries...
To be fair, mine are $949 each not $1,000 each, unless you're referring to the new GC2 model.
Still, $3800 is definitely more than $1200.
Keep in mind also, you have to factor in how much a 10 year warranty is worth, because that does have value.
Also, mine came with an advanced BMS and you're not factoring that into the cost you posted above.
Can you go into any detail on the BMS you'd use for the Tesla setup and it's cost?
I can't imagine it costing much, but I'm curious if it offers the same level of protection, and that has value.
Lastly, were you going to have your trailer wired to be 24v? and if so what advantages are there to that over 12v?

Victron BMS runs about $118.00. Battle Born stock BMS is redundant.

Potential power:

12v 200 amp = 2.4kWh
24v 200 amp = 4.8kWh
48v 200 amp = 9.6kWh

You’ll need a buck converter to step down from 24v/48v to 12v. But at the end of the day you have more storage capacity for your TT power.

[gbkims]

I was wondering about the differences between Tesla 24V modules, Battle Born 12V LFP, Victron LFP and how a BMS would work for the Tesla monitoring its cells.

Sounds like the BMS monitors each cell within the battery.
Victron LiFePO4 batteries says 4 cells for 12.8V battery, 8 cells for 25.6V battery, & the BMS protects each individual cell

Battle Born LiFePO4 12V 100Ah - didn't see how many cells per battery on their site.
The BMS protects the cells against excessively high or low voltages, high currents, short circuits, and excessive heat or cold
https://battlebornbatteries.com/are-...-bms-built-in/

Tesla Model S Lithium Ion Battery 18650 EV Module - 22.8 Volt, 5.3 kWh - http://www.evwest.com/catalog/produc...roducts_id=463
The packs contain 444 cells.
Tesla cells - nickel cobalt manganese aluminum oxide cathode and a graphite silicon anode.
http://media3.ev-tv.me/TeslaModuleController.pdf

Is there a BMS like the EVTV Tesla Battery Module Controller or https://hackaday.io/project/10098-model-s-bms-hacking that works with the module's cells.
96 cells or 444 cells per module?
The 85KWh pack contains 16 modules, each of which is a 6s 74p array of 18650 cells, 96 series cells total. Each 6s module communicates with a master BMS via an isolation barrier, the master BMS talks to the ECU and charger and controls the main contactors. https://hackaday.io/project/10098-model-s-bms-hacking

edit: Tesla battery module cell config. Used info from https://marinehowto.com/lifepo4-batteries-on-boats/ to help me understand it a bit better.
74p6s cell config = 74 cells in each voltage cell(parallel connected) and six of these voltage cells in series = 444 cells in a module.
The Tesla 6s module monitors the 6 74p voltages.

Tesla BMS battery monitoring printed circuit board is mounted on one end of each battery module.
It measures the voltage of each individual voltage cell(74p) and the temperature of positive and negative module terminals.

[alanhenson]

Did he, the Victron rep, have an alternative recommendation?

Two inverters.

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[alanhenson]

I was wondering about the differences between Tesla 24V modules, Battle Born 12V LFP, Victron LFP and how a BMS would work for the Tesla monitoring its cells.

Sounds like the BMS monitors each cell within the battery.
Victron LiFePO4 batteries says 4 cells for 12.8V battery, 8 cells for 25.6V battery, & the BMS protects each individual cell

Battle Born LiFePO4 12V 100Ah - didn't see how many cells per battery on their site.
The BMS protects the cells against excessively high or low voltages, high currents, short circuits, and excessive heat or cold
https://battlebornbatteries.com/are-...-bms-built-in/

Tesla Model S Lithium Ion Battery 18650 EV Module - 22.8 Volt, 5.3 kWh - http://www.evwest.com/catalog/produc...roducts_id=463
The packs contain 444 cells.
Tesla cells - nickel cobalt manganese aluminum oxide cathode and a graphite silicon anode.
http://media3.ev-tv.me/TeslaModuleController.pdf

Is there a BMS like the EVTV Tesla Battery Module Controller or https://hackaday.io/project/10098-model-s-bms-hacking that works with the module's cells.
96 cells or 444 cells per module?
The 85KWh pack contains 16 modules, each of which is a 6s 74p array of 18650 cells, 96 series cells total. Each 6s module communicates with a master BMS via an isolation barrier, the master BMS talks to the ECU and charger and controls the main contactors. https://hackaday.io/project/10098-model-s-bms-hacking

People have used the REC cms with Tesla batteries with his success.
You're not really comparing Apple's to apples when comparing battle born 12v batteries to Tesla. You have to compare Victron 24v 200ah batteries to Tesla. Tesla weigh 54 lbs and victron weighs 120lbs. Tesla can discharge at 1000amps. Victron at 270amps. Victron can charge at recommended 54amps with high current at 180amps. Tesla can charge at 300+ amps. Victron is $4000 vs $1200 for Tesla. Battle Born cannot charge or discharge as fast. They're not nearly as powerful because they're 12v. They really don't compare. Victron doesn't either and they cost nearly 4x as much. Tesla are superior in nearly every way except warranty. You just have to ask yourself if that warranty is worth $3000 which it isn't.

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