Depower the system in sailboat

[DeBommel]

Hey,

This winter I'm will be installing my 8S LFP-battery. As I'm not living on the boat, I would like to be able to switch off the SBMS0 completely when I leave the boat. I can disconnect the flatcable every time, but that's not practical.

The 12-wire-flatcable uses wires 2 - 10 for voltage sensing. Wire 1 is for SBMS0 Power Negative and wires 11 + 12 are for SBMS0 Power Positive. 

I would imagine that disconnecting wire 1 and wires 11+12 using a double-switch would completely depower the BMS, cutting consumption to zero. I *think* I can combine wires 11 + 12 on a single pole of the double switch. I even *think* I could only use a single -pole-switch do disconnect wires 11+12.

I found a thread with the same question (from 2020) and there it was suggested to use a 7-pole-switch for a 4S battery. Which, if translated to 8S, would mean a 11-pole-switch. 

Can de SBMS0 be (safely) powered down using the double-pole-switch (wire 1 and wires 11+12) or even by a single pole-switch (wires 11+12)?

Cheers,

Leonard

[Dacian Todea (electrodacus)]

Leonard,

Yes you can power down the SBMS0 by just disconnecting the 11+12 wires but there will still be some small self consumption as the BMS IC will still be able to power itself trough the cell monitoring wires.

The SBMS0 uses in normal operation around 0.3W with WiFi OFF and 0.8W max with WiFi ON so over a say 6 month period it can use between 0.3*24*180 = 1.3kWh  and 0.8*24*180 = 3.4kWh and if wires 11+12 are disconnected it will use less than 0.01W but that will still add up to 0.01*24*180 = 43Wh plus probably more from battery self discharging.

So please make sure you leave the battery fully charged or very close to fully charged before you disconnect.

But if you have access to SBMS0 back it will just be easiest to disconnect the 12pin connector especially if this just happens once a year. Could be less work than to install a switch to disconnect the 11+12 wires.

[DeBommel]

Thanks, that answers my question! 

Op maandag 16 juni 2025 om 18:32:26 UTC+2 schreef electr...@gmail.com: