Thread: BMMCC with a v mount converter?

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  1. #81  
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    I know with AC you can use transformers to actually mechanically isolate different circuits

    I googled this and with DC there are lots of articles on isolated grounds to remove signal noise - eg by using optocouplers and the like (this transmits the signal over a small gap using light instead of electricity) or by using diodes or even transistors, and special IC packages to manage what direction current can flow or capacitors to manage spikes sand noise but most of these solutions are designed for signal level voltages and current (ie 5v and less than amp or so) - the don't generally seem to be designed for power supply isolation

    In fact I struggled to find any articles at all on power supply isolation for low voltage DC circuits, and all the articles that discussed grounding in a signal quality context seemed to stress how non obvious and potentially tricky this stuff was

    I guess I'm still skeptical that these "BDS systems" do anything beyond add a fuse in appropriate places or maybe a voltage regulator (though I guess voltage regulators themselves might be be isolation devices but not necessarily)
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  2. #82  
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    eg if I google rectifier:

    https://en.wikipedia.org/wiki/Rectifier

    the entire article is about transforming AC into DC not isolating multiple DC outputs from a single DC source
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  3. #83  
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    Yes, rectifier was a bad choice of words, and is normally used to convert AC to DC, before “switching” type power supplies came out.

    I never opened up a BDS and took it apart, but all you see is a circuit boards, and fuse connections. All I know, is the original BDS brand units advertised having isolygrounds in the output, and if yiu messure the voltage potential across the ground connections, is was “0”.

    Whatever you use, just use a meter first to check if there is any voltage leaks across the ground connections. If none, you should be good to go.
    Cheers
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  4. #84  
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    Quote Originally Posted by Denny Smith View Post
    Looks good, but be careful powering both the monitor and camera with a splitter type cable. This could lead to a ground loop situation in the HDMI to camera to monitor connection. A better idea is to use a BDS between the battery and camera/monitor that has isolated ground connections on the power tap outputs. There have been a ver reports of HDMI piers getting fried. Also connect cables to camera send monitor first, HDMI next and batter connection last.
    Cheers
    Hello Denny!
    Thank you for your mention!

    I saw your post about ground loop on other thread.
    So I got paid insurance for my equipment. This is not fundamental solution but I think it will help a bit.

    Btw, I like your Bolex style micro that you posted on other forum (maybe official forum?).
    I'm so excited to see your new micro rig
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  5. #85  
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    Thanks, trying to get it together now. Will get some photos posted soon.
    Cheers
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  6. #86  
    Junior Member Antithese's Avatar
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    I just tested how long my v mount battery setup works for my Micro Cinema Camera and Video Assist today.

    - - - - - - - - - -

    In theory.

    Micro Cinema Camera - Max 10W
    Video Assist - Max 9W

    Source of information
    http://bmduser.jp/admin/f_img/最大消費電力・給電方法一覧.pdf


    Juicebox V-Mount Battery and Charger (95Wh)

    Calculation

    95 / (10 + 9) = 5 hours

    - - - - - - - - - -

    In actual fact from my test

    5.5 hours (60fps)

    - - - - - - - - - -

    It is almost same time as theory.
    Thank you!
    Last edited by Antithese; 11-30-2017 at 08:52 AM.
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  7. #87  
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    Quote Originally Posted by Stelvis View Post
    see I never understand this idea- and it may very well just be me being ignorant - but how do you exactly 'isolate grounds' when they will end up at the same contact terminal on the battery one way or another?

    can someone explain how this works in more detail?
    I don't think it really matters, the idea of isolated power falls apart once the two devices are interconnected with copper. Both my micro camera and monitor are chassis grounded and the IO connectors are chassis grounded as well, once they are interconnected they share a ground, not to mention the ground they share through the cage and arm. So even fiber would not provide ground isolation unless the 2 devices were electrically isolated.

    For a quick test I ran both devices off of dedicated batteries, the only difference I got was what battery system I was testing. Using a meter I went from the hot side of the V-Mount camera battery to the monitor chassis and got 16v, going the other way I'd get 8V. The idea that you can isolate grounds is a myth.
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  8. #88  
    Senior Member shijan's Avatar
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    BMMCC expansion port also use one common ground for all power and signal connections. That ground also connected to camera body and to D-Sub connector shell
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  9. #89  
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    Yes, you are not really “isolating the ground connection per se, from what I understand, you are isolating any potential voltage leak between the various grounds in use, on the different power connections to them. Once a camera, monitor, etc are all connected up, even with different battery sources, you still end up with a common ground connection coming together on the camera. The. I do ca era DB15 has several ground connection pins that go to a common buss, so yes, they are interconnected, but on,y one ground wire is connected to any given ground pin on the connector.

    What a BDS tries to do, is have the various power taps electrically act like separate battery connections.

    I house or AC mains wiring, you can have a so-called isolated gound outlet installed by an electrician for your computer system, (hospital blue or red outlets are this type). But are they really isolated, no, even the ground and neutral connection are not really isolated, all these connections come together in the main panel and are connected to a ground rod in the ground. By isolating the ground, a AC circuit just has a dedicated (not shared by another outlet) hot, neutral and ground run directly to the sub or main panel circuit breaker. This reduces the chance of a cross over voltage leak between the neutral and ground which creates what is called a “ground fault”. Stray voltage between various ground connections in a DC circuit is also similar to a ground fault, in that there is a voltage leak somewhere causing this.

    A BDS tries to reduce the potential for this to happen, eliminate crooks connection issues and reduce audio (and video) noise issues caused by power connection issues. Is it 100-percent effective? No, not always, but every precaution you take helps. See: http://remoteaudio.com/products/power/bdsv4-bdsv4u/
    Cheers
    Last edited by Denny Smith; 11-30-2017 at 02:15 PM.
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  10. #90  
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    thanks for the link Denny

    going from AC to DC you can definitely separate different application using separate transformer windings - I believe this is for example how PC power supplies work where they provide different core voltages for various bits inside a pc (eg 12v, 5v, 3.3v) - but thats not quite the same thing as we're discussing...
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