A quick update here – just to add an addendum to the LifePO4 series. No-one who is following this blog for travel reasons will find this interesting, but it’s an important point as I know several people use a 7713 as a main relay in their systems.
There was an annoying bug where if I turned off the battery bank and turned it on again, the discharge relay (a Blue Seas 7713) wouldn’t turn on, and I had to connect a laptop and do a soft reboot. This is because it was looking for 12+v on the switching wire – but for that to happen, the BMS had to power up first. Having both of them come up at the same time didn’t work.
Anyway, even the soft reboot stopping working so that finally got me off my arse to fix it. I did so by adding in an additional switch. It’s in-between the P-Channel MOSFET (which takes the pulling-to-ground signal of the BMS and inverts it to +12v) and the 7713.
Now if I need to reset the system, I can just power off the system, power it back on, wait two seconds and then flip the discharge switch from on to off to on again. Simple.