After over a year of working with these systems, I have refined my recommendation on equipment and build a little.
While our original Tesla battery install is working great I have had the opportunity to install a few more of these systems and get tons of questions about it.
These systems can be constructed with numerous different components and can work with many different designs, however to keep costs down and make a safe system the following is a recommendation on one way to build a safe, cost effective Tesla Install.
Do note that 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 take on an install like this.
Furthermore, this build is not endorsed or supported by any manufacturers of the compenents used in this build, and they may not provide support on an install like this if you run into trouble.
I also 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.
Recommended Changes from the Original System
The following is an update to the way I originally installed my battery. This is not necessarily the best install option, but it is cost-effective. This install does not utilize a full-time BMS but if you are interested in using one Batrium is coming out with a new watchmon 5 (or watchmon plus) and should be a great solution for integrating Tesla packs with a full supervisory BMS solution at a cost-effective price. You can learn more about the Batrium BMS here.
The main component changes in my system involve the exterior voltage and temperature monitoring to control battery shutdown. The Victron BMV 712 was not available when I built my system, but is a far superior product to the BMV 702. This device has the capability to control an external relay on temperature, high voltage and low voltage. It can do even more, but these three features simplify the install if we use it to control the battery disconnect. The below schematic shows how I recommend using this as the primary disconnecting means for battery charging.
The intent of operation of this install is to have the Inverter and charge controllers be programmed to not overcharge the battery. I usually program the absorb and float to 24.00V and 23.98V or 24.5V and 24.48V respectively. I use the 24 V setting for general usage, but in the dead of winter I push it a little to 24.5 to get a bit more power out of it for cloudy days and long nights . These settings will appropriately charge the battery, but in the case that something went wrong with the chargers or the settings got changed we need a backup to prevent overcharging the battery (one of the most dangerous conditions) That is where the BP220 input disconnect is used with the relays from the BMV712 to take the battery offline. I program the BMV712 high voltage relay setting to 24.8V
The battery temperature should also be managed externally and can be done with a heating pad and a controller or I have seen some have success using these tank heating pads.
These devices should keep the battery warm, but in the case that the battery is too cold it should not be charged and thus the relay in the BMV again can be set to switch on temp. I set the low temp switch to 42 degrees (because at that temp something is wrong with my system) but you can use whatever you feel is safe for your setup. The BMV712 has a temperature sensing option that is connected off the shunt and sends temp info back to the head unit.
The only trouble with using the BMV712 relay to disable charging is that you actually need two relays for this system as the inverter charge can be disabled using one of the inputs. ( you need to program the inverter to use an input as a charge disable, for victron this is done with a external BMS assistant). To get two inputs from the one relay output on the BMV712 we use a DPST relay and hold the coil closed. This is a fail safe configuration that will open and shut down charging in a failed state.
Of course when commissioning a system like this be sure to test the system by setting temps and voltages too low and letting the BMV disconnect the system to make sure everything is working properly.
The rest of the system is pretty similar to how I have it drawn out in the previous posts. You can connect the AC side from the inverter however you want but if you are connecting to a 50A 240V split phase RV a new product that might assist your install is the AM solar smart ATS. This allows you to use a hybrid inverter automatically on a 50A system. The only drawback to this is if you have a built in dual leg single phase generator as it will half the power output from the gen. I have talked with them about this and they may fix it in future versions.
List of Components
For those looking for a list of components, here it is:
Again this is not complete and you can swap components for your system, but this is what I have used.
*This charger will limit the system to 1400W
*This charger will be good for solar up to 2800W
I recommend the use of busbars, they help keep installations clean and distribute power well
*If needed can get the 70A version that has lugs and is adjustable voltage
*This is not used as a “BMS” just to periodically check and balance the batteries, You need to adapt XH connectors to the battery cells to use this device. Do not leave this plugged in as it will unbalance the battery.
*These are optional but provide extra protection for the batteries during installation and handling from a short
*These are installed at battery on lugs. If battery is shorted this will protect battery internal fuses from destroying battery
*This is just a relay that turns one signal into two… we cannot put the two devices in series due to how their circuits work.
just a suggestion. Make sure its true 1/0AWG, not international wire standard
I have heard of people having good luck using these tank heaters.
As in the previous posts this system does not utilize a full BMS but rather relys on periodic testing of the battery to check balance with a tenergy 5-1 cell meter. To use one of these with a tesla pack you need to either buy a pack that has standard JST-XH connectors adapted to it already or you will need to adapt it yourself.
Dave posted a comment on my prevous post about having to adapt his battery to work with the tenergy 5-1. Below is his recommendation and it sounds about right.
If you received your Tesla Battery with the BMS Board still attached, I recommend you immediately remove it. My BMS Board was “electrically” warm when I received my Tesla Module.-Dave
The Tesla BMS wires on the Module are numbered 0 to 6, with 0 and even numbers on the top and the odd numbers on the bottom. the 0 wire is attached to the negative terminal of the battery and 1 – 6 address the different cells. Electrically, each BMS wire is additive, i.e.: between 0 and 1 is 3.5v and between 0 and 2 is 7v and 0 – 3 is 10.5v, etc. (your voltages will vary). The Tesla BMS uses two JST XH connectors, one is a 5 pin connector and the other is a 7 pin connector. I purchased a set of JST XH extension cables from Amazon, the set consisted of 2 cables each with 3, 4, 5, 6, and 7 wires. I took a 7 wire connector and a 5 wire connector and removed the male ends from each connector, I then inserted the pins from the two female connectors in a 0 – 6 sequence into the male connector. The two female connectors were attached to the two BMS leads from the Tesla Battery Module, the key to sequencing the female connectors is that Tesla used every other pin on these two connectors. So, what you wind up with is: Male pins 0 – 6 as follows: (# 1 pin top) then (# 1 pin bottom) then (# 3 pin top) then (# 3 pin bottom) then (# 5 pin top) then (# 5 pin bottom) then (# 7 pin top). The male 7- pin connector then fits right into the Tenergy BMS.
You can also purchase these packs already modified from Jason Hughes at 057 tech. Jason is also working on a simple BMS solution that will balance the packs and possibly have an alarm output. It is not available yet but conceptual drawings are out and it looks great! Keep an eye out for it at https://057tech.com/
If you are considering using Tesla packs in a mobile application I hope this helps you out and gives you an idea of one way to do it. If you want to learn more about this and other systems be sure to join us on our Second Life EV Facebook Group!
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