After over a year of working with these systems, I have refined my recommendation on equipment and build a little.
I will most likely be replacing mine with a relay.
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.
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 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.
*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.
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.
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/
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