I've noticed that many systems utilize a high current switch to isolate inverters and charge controllers from the battery. I assume the idea is to disconnect the batteries from the entire system to prevent issues in case of a malfunction without blowing the battery fuse. However, the downside is that introducing a switch adds another potential failure point. Plus, quality switches can be quite pricey, while cheaper options from Amazon have been known to be unreliable. Most Battery Management Systems (BMS) come with an electronic switch function that can be activated easily with a small toggle. Has anyone experienced problems when using the BMS for battery isolation? Of course, I know that physically disconnecting the battery is necessary for maintenance work related to the battery system.
2 Answers
It’s actually a requirement to have a power disconnect at any source of power! If you're unsure about installation standards, it’s better to learn the regulations or hire a professional. Otherwise, you might be playing with fire, literally!
For my setup, I use quality Blue Sea disconnects for both the batteries and inverter, along with DC breakers on the inputs and outputs of my MPPTs, plus Class-T fuses on each big battery at the terminal. There’s also the concern that FETs on LiFePo4 BMSs might fail and not disconnect properly. I prefer having a mechanical disconnect switch; I wouldn’t trust the BMS on its own for disconnections.
I’m aware of that regulation but my question is specifically about whether a BMS-based disconnect suffices or if a physical switch is absolutely necessary. I checked the ANSI/RVIA LV standard but didn’t find anything about battery disconnects specifically. Do you know of any standards that say RVs need a physical disconnect?