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Solar Phase 2: The Tesla Battery

Solar Phase 2: The Tesla Battery

After getting the solar panels on the roof and connected to our existing batteries in Phase 1 it was time to upgrade the system with a bigger better battery. We opted to install a Tesla Battery Module in our RV. 

We did lots of looking into different battery options trying to figure out what would give us the best performance and bang for the buck. 

Most RV batteries are deep-cycle 12 V lead acid batteries that, honestly, are a pain to maintain.

We finally settled on lithium ion batteries, but new they can be crazy expensive.  That’s when we started to think about getting a used electric car battery.

Reusing Electric Vehicle Batteries

​​After doing some research, we found that electric cars that have been wrecked are a great place to get big inexpensive lithium ion batteries.  Once we decided on using a used battery it then came down to picking which one. 

The options at this time we could use were Chevy Volt, Nissan Leaf or Tesla Model S batteries.  There are other out there but these are the easiest to get our hands on.   ​

After some careful consideration we decided to use a Tesla Model S battery module.  You can learn all about the battery we chose in this video we put together about it:

Overview of the Tesla Lithium Battery Module We are Installing in our RV - EV Battery Hack!

So after we had purchased the battery it was time to figure out how to use it and a few big hurdles stood in our way. 

Our RV (and most RVs) primarily operated on 12V DC but this battery is a 24V battery.

We went with a 24V battery for many reasons the first of which was that we got an awesome deal on our Victron Multiplus 24/3000 Inverter that is a 24V unit. 

Also, after getting the inverter we installed a Victron MPPT 100/50 Solar Charge Controller that is limited to 12 or 24V battery systems (although it can handle over 100V from the RV solar panels).   

Ideally, I would have gone with a 48V system but 24 is still better than 12 when you are talking big power usage.  This is primarily because you can use much smaller wires and the inverters tend to be more efficient.   

This is the schematic of what we ended up installing.  See the link below for a full resolution PDF.  

MOTM 24v Tesla battery wiring diagram

!! IMPORTANT !! 

Before reading further, the design in this article does not meet new requirements I have learned of about the BP220,  During design of this 2 years ago, there was no information about reverse charging with the BP.  We got away with it for a long time but this could be a fire hazard, read more here

DISCLAIMER

While Tesla batteries are a very high quality and safe when handled and run within operating characteristics, if something goes wrong they can be quite dangerous.  It is your responsibility to fully understand and make sure the system is safely programmed and installed if you choose to install a Tesla battery in RV.  

Furthermore, this build is not endorsed or supported by any manufacturers of the components used in this build, and they may not provide support on an install like this if you run into trouble. I am not able to provide individual support on these builds. You might be able to find community support over in the Second-Life Batteries Facebook Group.

UPDATED DESIGN

*This design has been updated – check out the update here.


After we got it all figured out, we went ahead and installed it! 

This video walks you through the installation of this battery and integration with our existing 12V system. 

PHASE 2 SOLAR - Installing the Tesla Battery and converting the RV from 12V to 24V

Be sure to check our our Phase 3 post where we install the Victron Multiplus hybrid inverter and power up our 120V AC system. 


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AkashaK

Wednesday 15th of July 2020

How did you connect your Battery up to the tenergy 5 in 1? Is there a specialized connector or?

GSenthil

Monday 12th of August 2019

Is it possible to charge the tesla modules with a constant volatage AC-DC (or DC-DC) converter and a relay that shuts off charging when the voltage reaches 24.5V?

Mickie Davis

Saturday 10th of August 2019

Hi, Thanks for all your posts. I have the Tesla Module at BMS Rev B with the 15 pin cable on my module. I was going to buy a standard JST-XH 6s cable and connect the wires as Neg, 2,3,4,5,6 on the JST cable (got the cell numbers from the EVWEST diagram) in order to connect it to the Tenergy 5-in-1 Cell Meter. Next come then install. My Victron 24/3000 in on the way. Still a bit a bit confused about the BP220. I only have 1 of those, but we have no solar yet. Were just going to start out with Honda 2000 charging when necessary. We have a Truck Camper.

Mickie Davis

Saturday 10th of August 2019

In Our solar home, we wired the Solar Charge Controller into the batteries. However, in the schematic, the Solar and the batteries are on the bus bar. Why a bus bar? Thanks.

David

Wednesday 17th of July 2019

Lee... If you are using the Victron Inverter, you could wire your Water Heater to the Aux AC out terminals. These terminals would then only send power to your water heater when you are plugged into Shore Power, thereby eliminating your need to switch off the Breaker.

Lee

Wednesday 17th of July 2019

David, Since I went with the Victron 24/2000 instead of the 24/3000 Multi-plus I don't have that option. The 24/2000 does not have an aux AC output. And my power panel configuration won't allow me to connect it to the input side of the inverter.

Lee

Wednesday 17th of July 2019

Lloyd, I just returned from a weeklong trip with several days of overcast and little sun. If I only used the microwave and coffee pot sparingly, run the water heater snd fridge on propane, and minimize inverter/DC loads; I can go 3+ days before needing to charge. I only ran my 2000W generator for about 2-3 hours the whole trip. But I was also running the fridge off the inverter when towing my trailer. And even though it was overcast/raining I did get some solar which was enough to do a bit of charging when I was away from the RV. With the Tesla battery it takes a charge fast from the generator. And if I don't fully charge it, that's okay, the battery is just fine with a partial charge. The main reason I needed to even run the generator at all was forgetting to turn things off when not needed, or forgetting to turn the water heater breaker off. My switch for the electric water heating element is right above the kitchen counter and can get easily bumped and turned on, causing me to use a LOT of power, so I turn the breaker off to prevent "accidental" water heating.

David

Wednesday 17th of July 2019

Lloyd... If you are boondocking, and you don't use your 120v appliances (and you have LED lights), you should be able to run your RV for 6 to 10 days on just the Tesla Battery alone. Where you begin to shorten your days on battery alone are when you run your Furnace, that thing is simply a power pig. Previously, I tested my RV (previous rig) and I calculated my 12 volt usage at 100 amp hours for a 24 hour period, this is with running the furnace at 70 degrees (F) overnight. Based on this experiment, I figure the Tesla battery alone ( approximately 500 amp hours at 12 volts) would keep us comfortable for 3 to 4 days without any charging when the nights are cold. Any 120 volt usage would shorten that time period and any Solar charging would lengthen that time period. By design, I sized my Solar system to be larger than would be necessary, to accommodate for cloudy days and low Winter Sun angles. Consequently, with 1200 watts of Solar and panels that are designed to utilize low irradiance , I don't anticipate using my Generator. I might need to use the Generator if we get caught in some very hot weather and need to run the Air Conditioner for more than an hour or so ( my Tesla Battery and Solar should run the A/C for a couple of hours in the afternoon if needed). PS: if you are interested I chose Canadian Solar panels for their 11% better performance in Low Irradiance conditions.

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