Boxx transmitter causing battery shutdowns when piggybacked in 24V configuration with video signal connections

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2012Video Assist and Video Accessories forum

14 years old. Gear and prices may have changed since.

DisputedParticipants disagreed and reached no conclusion. Read the findings as positions, not as an answer.

When a video transmitter is powered from a battery in a series 24V setup and video signal cables are connected, the video ground can create an unintended current path that causes battery breaker trips and potential overvoltage damage to connected devices.
Operating a 12V video accessory via battery piggyback in 24V mode while connecting BNC video cables creates a ground potential difference issue where devices may receive 24V instead of intended 12V.
The problem occurs because batteries connected in series establish different ground potentials, and connecting video cables bridges these potentials together, causing backfeeding and shorts.
Powering a video transmitter via cable from an external power supply rather than battery piggyback eliminates the ground potential difference problem.
Running the video transmitter from the monitor battery only or using an inline power supply avoids the issue.
In three-battery configurations, mounting the transmitter on the dedicated 12V accessory power battery is safe.

The exact voltage overage received by affected devices was not measured with instruments.
Not all sled configurations may exhibit identical behavior due to different internal wiring designs.
The issue was observed with multiple transmitter models but the underlying mechanism was not definitively confirmed through testing.
Some participants disagreed on whether the BNC carries power, voltage, or acts as ground.
The risk profile in specific configurations like the MK-V remains unclear.