BMPCC 4k, power question.

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LGrane

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BMPCC 4k, power question.

PostSun Oct 27, 2019 2:17 pm

Hello i have a bmpcc 4k and i use a cheap gold mount battery plate whit 5-7,2-12-16v outputs to power the camera. Sometimes i use a hdmi monitor.
Today i read that i could damage the hdmi port if you power the camera and monitor from the same source :?

I have used my setup since i bought the camera in the spring and so far nothing bad has happened.
I use the 12v to the camera and the 15v to the monitor.
Should i stop doing this? :oops:
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Robert Niessner

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Re: BMPCC 4k, power question.

PostSun Oct 27, 2019 3:25 pm

LGrane wrote:Today i read that i could damage the hdmi port if you power the camera and monitor from the same source :?


Who said that and where?
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LGrane

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Re: BMPCC 4k, power question.

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Robert Niessner

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Re: BMPCC 4k, power question.

PostSun Oct 27, 2019 5:44 pm

Oh - THAT guy. Who already fried HDMI ports on several other cameras and doesn't know anything about electronics but recommends a power cable with a ferrite - well ah yeah, sure.
He doesn't give any technical details about what he did exactly do and which components he exactly used.

Please don't just believe what some random YouTubers are telling you to get their views.
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LGrane

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Re: BMPCC 4k, power question.

PostSun Oct 27, 2019 5:51 pm

Yes the cable thing sounded weird, but is there any ground loop issues whit the bmpcc 4k?

Its very convenient to use one battery for the whole rig 8-) but is it safe?
Is it better if i only use the non regulated 15v or dtap port on the battery plate?
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LGrane

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Re: BMPCC 4k, power question.

PostThu Feb 20, 2020 5:28 pm

To be sure i installed an isolated DC/DC converter for the monitor. Before i had a 0,2v ground-loop from the hdmi to the - on the battery and now is down to 0,0v. So i suppose i am safe now

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Kristian Lam

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Re: BMPCC 4k, power question.

PostThu Feb 20, 2020 11:31 pm

The first thing I would check is the HDMI cable to make sure both connecter shields are connected. Lots of cheap ones on Amazon, Ebay etc and we had a customer repeated fry his monitor (Feelworld) with a similar setup. We got the entire setup back including the HDMI cable he was using. Turns out the cable is out of spec and not grounded correctly.

The HDMI port has overvoltage protection, but repeatedly sending it large surges due to poor grounding will wear the protection down.
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LGrane

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Re: BMPCC 4k, power question.

PostFri Feb 21, 2020 4:33 pm

The hdmi connector on the camera-side fells a little bit warm (not hot), but i think i measured the cable and the grounding was good. Any specific brands of cables to search for?
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Re: BMPCC 4k, power question.

PostFri Feb 21, 2020 5:01 pm

My short hdmi measures 1,6ohm, and my long 8,4ohm in the grounding
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Re: BMPCC 4k, power question.

PostFri Feb 21, 2020 6:16 pm

Are you measuring the individual pins connected to the shield? (See the pinout description in the right-hand column https://en.wikipedia.org/wiki/HDMI). Or are you measuring between the metal frames on the two connectors of the HDMI cable?

8 ohms is a bit high.

Also, to verify that the cable can actually carry this loop current, connect the HDMI cable to the monitor, then measure the resistance back to the power ground input, or outer ring of the barrel connector of the power cable if that's what you're using. Repeat the same exercise except with the camera.
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LGrane

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Re: BMPCC 4k, power question.

PostFri Feb 21, 2020 7:38 pm

Metal frame to metal frame
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Re: BMPCC 4k, power question.

PostFri Feb 21, 2020 10:18 pm

On my Pocket 4K, I got a good connection between the negative terminal of the 12V input and either the top or bottom 1/4-20 screw mount. Not very good connection to the lens mount.

Of course I don't have your monitor to test the equivalent points. I think that negative terminal of the camera to the negative terminal of the monitor with the HDMI cable connected would be a better measurement.
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Re: BMPCC 4k, power question.

PostSat Feb 22, 2020 4:08 pm

LGrane, i see that that opto-isolator inside your box outputs 12V 1300ma. This is 15.6W and sometimes it may be not enough for Pocket 4K camera which consumes up to 22W at maximum resolution/framerate/brightness. Hope it will work for you.

HDMI cable shields are very different. I checked a lot of different cable models and cheapest no-name cables always have voltage leak between grounds. Same timev oltage leak on quality cables always was very close to none.

Take attention to this article https://www.newsshooter.com/2020/02/15/ ... i-outputs/ and this forum thread viewtopic.php?f=2&t=107642 It seems we have now a real explanation what exact cause HDMI damage when camera and monitor are powered from same battery:

From the ARRI article:
"This damage to the SDI connection can occur when connecting an unshielded power cable to an accessory that is already connected to the SDI output of the camera. If the plus pin is contacted before the negative pin, the BNC cable will close the current circuit resulting in the fatal damage of the included SDI driver chip which itself is not designed to handle such high currents. "

If simplify worlds - to avoid damages, you should always connect (-) DC power cable pin before (+) DC power cable pin.

Actually it is not so easy to do in real life until you have dedicated switch on positive wire of DC cable, or specially designed DC connector which 100% always connects (-) pin before (+) pin.
All my custom made accessories for BMMCC/BMMSC now available here https://lavky.com/radioproektor/
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Re: BMPCC 4k, power question.

PostSun Feb 23, 2020 12:38 am

Dmitry Shijan wrote:LGrane, i see that that opto-isolator inside your box outputs 12V 1300ma. This is 15.6W and sometimes it may be not enough for Pocket 4K camera which consumes up to 22W at maximum resolution/framerate/brightness. Hope it will work for you.


I only power my monitor thru the isolator, and it only uses 4-600mA :)

But is this cheap/bad cable issue only affecting when you power camera and monitor from the same source/battery? Or is even if you use separate battery or opto-isolator?

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