I am currently planning a system based on Nissan Leaf cells and have ordered some pcb’s to test out diybms as it seems ideal for this.
One question I had was around the use of a pre-charge relay when using a main contactor. Has anyone implemented this with diybms and if so are you able to connect the resistor before the main contactor is closed?
the best and easiest way to do this is to install a resistor in series with a momentary switch in parallel with the main contactor. then before flipping the main switch, you push the precharge momentary switch for a second and you’re good to go.
As far as an automatic way, that I do not know. it would need to involve a delay circuit of some sort and sounds complicated.
My question is, how often do you really need to precharge your system?
If you are doing some maintenance or something short, then just power down the system PRIOR to disconnecting the power and the capacitors will stay charged enough to not even need a precharge. this is how I do it. I have had it disconnected for a weekend and still had no spark.