Joined
·
78 Posts
I've been looking all around for a concrete answer about parallel wiring at the module level with Tesla modules and I have gotten all kinds of answers. So I figured I'd make a post about what I've figured out so far and what I'm still trying to figure out.
Let's start with where I started: reaching out to EV West. On the page where they sell Tesla modules, they suggest that they can be arranged "2p5s for a total of 53kWh of energy with a total of 10 modules." So I reached out to them by email and they said that they've had customers that use 5 in their conversions and then want to increase their range so they will parallel another 5 in while still using just one BMS. But then again, EV West often doesn't even use BMSes with lithium batteries, which I find to be honestly idiotic and dangerous.
Next, I decided to contact Orion, who makes the Orion BMS 2 that I intended to use. They pointed me to Evolve Electrics, who sent me these two PDFs: this one on parallel strings and this one on setting up parallel strings with the Orion BMS.
What I know for certain at this point:
Let's start with where I started: reaching out to EV West. On the page where they sell Tesla modules, they suggest that they can be arranged "2p5s for a total of 53kWh of energy with a total of 10 modules." So I reached out to them by email and they said that they've had customers that use 5 in their conversions and then want to increase their range so they will parallel another 5 in while still using just one BMS. But then again, EV West often doesn't even use BMSes with lithium batteries, which I find to be honestly idiotic and dangerous.
Next, I decided to contact Orion, who makes the Orion BMS 2 that I intended to use. They pointed me to Evolve Electrics, who sent me these two PDFs: this one on parallel strings and this one on setting up parallel strings with the Orion BMS.
What I know for certain at this point:
- You need a BMS for each parallel string
- Each string needs to be very close in voltage to not cause issues
- In the first document, it recommends using a separate contactor for each string and essentially treating the two parallel strings as separate packs. This seems like it could lead to imbalances at the module level and I would think that this could be potentially more dangerous than just having them both connected to the same contactor.
- That document also warns against leaving the parallel strings permanently connected, saying, "Never leave two lithium ion strings permanently paralleled or leave multiple strings paralleled without monitoring systems and a means of automatic disconnection. As always with any safety critical circuit, always use multiple redundant and independent shutoff systems." Why would it be dangerous to leave two parallel strings connected? Of course, more safety disconnects is always better but what makes parallel inherently more dangerous than series when left connected?