An odd bms reading

Hi everyone!

Im installing my first bluetooth bms unit to my 18s lipo pack. The bms can be used up to 24s.

At the moment I just finished the main leads and connectors for the unit itself. I will wire up and connect the individual cells/turn on wires etc. to it soon. At the moment the bms is practically bare except for main wires.
I had a question about something that seemed odd.
The 18s pack was sitting at 73V or so before I added the bms. After adding the bms to the battery side, the voltage says around 23V when I tested the C- end which goes to the controller/charger.

All wires/bms connectors are removed from the bms except the large thick B- to battery negative and C- to controller/charger negative.

Does the bms need to be turned on in order for full voltage to pass through it? I assumed the full voltage would flow through it whether its on or off but maybe i misunderstand how it works.
Thanks!

The BMS does not enable the main power circuit unless the sense wires are connected and the cell values are within spec. You can sometimes read an arbitrary voltage on the power leads when they’re cut off, but there’s no power there.

Balmorhea said:

The BMS does not enable the main power circuit unless the sense wires are connected and the cell values are within spec. You can sometimes read an arbitrary voltage on the power leads when they’re cut off, but there’s no power there.

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Hi! Oh thats very interesting