Thread: BMMCC 14.8V Battery Module by RADIOPROEKTOR

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  1. #51  
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    thats kind of interesting

    so what they are saying is if you are using same power source for both monitor and camera where they are connected via SDI (applies to HDMI also?) you DON'T want isolated grounds for the two connections, and they should actually share a ground?
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  2. #52  
    Senior Member shijan's Avatar
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    Stelvis, all grounds are connected but if you connect monitor to camera, turn them on and measure voltage between monitor DC ground and HDMI cable ground, you will see some very small voltage there (average 0.06V). I have no idea why.
    I found that this voltage leak depends of HDMI cable quality. Branded cables with better isolation leaks 0.01-0.02V. Highly used cheaper OEM China cables leaks 0.06-0.15V. This ground voltage leak exists even if you power camera and monitor from separate batteries.
    If you turn off any device there is no voltage leak between HDMI and DC grounds.

    Not sure if i understand the thing but i have a theory that it may be due both electrostatic damage and due ground loop same time. Without ground loop when you touch the camera, electrostatic voltage splash from your body goes away somewhere to camera body and next somewhere to outer ground. But when there is a ground loop with HDMI/SDI, electrostatic voltage splash may go to electronic circuit and damage HDMI chip. This is explains why those damages are so random. I used single battery setup about the month without any problem and once upon a time i turned camera on and no HDMI signal.
    beside electrostatic voltage splash this also could be a moment when you insert cable into the battery and produce small electric spark and due ground loop it somehow may damage HDMI circuit.

    I don't believe that average measured 0.06V potential between different grounds may somehow actually damage HDMI chip. Ground loop cause hum, noise, interference, but how so low voltage can damage electronic chips?

    Maybe we need to look for some kind of electrostatic protection instead of isolated grounds? But i am not so advanced in electronics so this is just a guesses.

    UPDATE:
    I found that same small voltage leak is present even if you measure between grounds on both HDMI cable ends. (Cable must be connected to the camera and monitor and both devices must be turned on)
    Last edited by shijan; 10-09-2018 at 03:16 PM.
    All my custom made accessories for BMMCC/BMMSC now available here https://lavky.com/radioproektor/
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  3. #53  
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    I think a small DC Offfset is very unlikely to be the problem - but transient voltage spikes on connection or disconnection is the likely culprit
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