BMPCC 4K Ground loop ? "Is it safe?"

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aknittel

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BMPCC 4K Ground loop ? "Is it safe?"

PostThu Jul 23, 2020 12:34 am

After extensive reading, I am totally on board a V – mount battery solution for the BMPCC 4K.

v-mount batteries (98W) with TWO d-taps should power the camera and a monitor (specifically SmallHD focus 7).

If I'm running a gimbal I can totally offload the weight on the gimbal or camera with a v- mount waist belt. When I’m on a stick, should be easy to rig the camera and v-mount battery with a passive v mount plate off the rig or tripod. Since there are no batteries needed plugged into the monitor, weight comes off the monitor as well.

So to build that flexibility, I'm considering the following.

SOONWELL B98-V 98Wh 14.8V Lithium-Ion Battery

Cheap passive V mount plate just for rigging the battery off a cage, rails, or waist belt

A dummy battery FOR THE SMALL HD that powers the monitor from the ONE of the D-TAPS on the
https://www.bhphotovideo.com/c/product/ ... ml/reviews

4. The OTHER d-tap ON THE BATTERY goes straight to the BMPCC D-TAP port

The BMPCC requires 22 watts when recording raw to external drive. So, I would guess the math is simple. If you have a 98 watt-hour battery, and the camera is drawing 22 watts + the monitor draw of 11 watts = 33 watts. 98/33 gives max almost 3 hours.


I've read these reports concerning issues with powering multiple components from ONE battery. Seems across the industry (BMC, Arri, etc.)

viewtopic.php?f=2&t=101481&p=596189&hilit=bmpcc+ground+loop#p596189

https://www.newsshooter.com/2020/02/15/ ... i-outputs/

viewtopic.php?f=2&t=107642

Seems like it’s just a matter of training oneself to plug the POWER taps in first, THEN the HDMI out from the BMPCC to the monitor. You can buy special “isolation” adapters for d-Taps but these seem expensive.

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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostSat Jul 25, 2020 12:27 am

Bump. ANyone? BlackMagic?
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostSat Jul 25, 2020 5:40 am

The only way to be safe from a ground loop is to separate power or use a power distribution battery plate like the Wooden Camera battery distribution system.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostMon Jul 27, 2020 12:02 am

That a $600 answer -- not great for Independent Filmmakers that just bought a $1200 camera and are spending $1000 just to rig it with acceptable power and a decent monitor.

I get we're supposed to rig the camera -- that's a bare bones solution, but I wish BMC would be a little more forthcoming with official statements about ground loops.

I've contacted TWO dual d-tap v mount battery suppliers -- Soonwell and IDX. Are they supposed to be able to answer for BMC if the power coming directly off their D-TAPS is also isolated and wont cause ground loops?

I can't believe the industry hasn't solved this as a standard for ANY camera -- RED, ARRI, whatever. "Solved" meaning it's a no-brainer issue and its fail safe and consumers (or prod) can't get themselves into trouble frying equipment just by plugging in rigs one way ot the other.

BMC can you PLEASE make a statement? Just tell us what we're supposed to buy, do, or avoid.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostSat Aug 15, 2020 9:24 pm

Can we have a STATEMENT from BMC?

Just trying to keep my equipment safe and need a surefire procedure to power from ONE V-mount dtap monitor and camera. What is the best practice in workflow given this rig configuration.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostSun Aug 16, 2020 4:27 pm

Can anyone from BlackMagic Design shed some light on this?

Can I raise a support case?
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostSun Aug 16, 2020 5:13 pm

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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostWed Sep 16, 2020 12:08 am

Yes. The CORESWX solution is on the right track, but doesn't really solve the issue. A dummy battery is just that -- it STILL makes a connection direct to the camera.

I was watching this review of the SmallHD focus monitors:



Look what he is doing starting at 2:10.

I had the revelation that although there are TWO batteries involved here, the one that powers the monitor CAN BE FED and kept charged up by a V-MOUNT battery – basically a battery to battery connection via a D-TAP to DC input connection on the CORESWX NPF Flat pack.

https://www.coreswx.com/store.coreswx/product/npf-shd/

So I called CORESWX – they are local – and got a tech support guy who will tell me if this setup inherently avoids a ground loop, because i THINK it would effectively isolate the monitor from the V-Mount battery's other connection to the BMPCC connector.

Anyone care to comment if this is true?

So then I would choose a V-Mount with two D-TAPS, or one that mounts to a plate with two D-TAPS: one to the NPF Flat Pack battery that in turn powers the monitor and the other straight to the BMPCC.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostThu Sep 17, 2020 7:48 pm

I was just about to create a thread asking a similar question because I recently ran into a power issue, and someone I know said it could've been a ground loop problem even though it wasn't the HDMI ports that were the victim, but instead my batteries. I figured it would be good input to this thread since I also prefer to power everything from one battery.

I posted a video explaining what happened (originally posted on Reddit, hence the "hey Reddit" at the start):
[I will update this with a link to the video when my account is allowed to post URLs. In the meantime, Googling "2 Gold Mount Batteries Died Out of Nowhere. Can anyone help me troubleshoot?" should yield the links to the two Reddit threads where I asked this question. One is under r/bmpcc and the other is under r/cinematography]

I recommend you watch it get the full picture of the issue and to see what my set-up looks like, but in short, what happened was that my 190wH D&O Lighting battery completely died during a shoot when I connected my IndiPro Tools Gold Mount plate to the monitor via the plate's d-tap. The cable used was a Lanparte d-tap cable. The camera was already connected to the plate, and the HDMI was already connected between the camera and the monitor. The monitor was the last thing that I had to connect and power. When I plugged in the d-tap cable from the plate to the monitor, the battery died.

Thinking this was a battery issue, I e-mailed D&O and asked for a replacement. They sent it to me, and all went well for one shoot. While prepping for the second shoot with the new battery, it completely died when I connected the 2 pin cable from the plate to the BMPCC4K. (Note: on this second occasion, the monitor was not yet connected via d-tap. So on the first occasion, the battery died when connecting the d-tap from the plate to the monitor. And on the second occasion, the battery died when connecting the plate to the camera).

I've posted this video on Reddit and gotten different answers to what the potential issue may be.
Here are the links to the threads in case you want to see what others had to say:

Thread 1:
[I will update this with a link to the thread when my account is allowed to post URLs. In the meantime, Googling "2 Gold Mount Batteries Died Out of Nowhere. Can anyone help me troubleshoot?" should yield the links to the two Reddit threads where I asked this question. One is under r/bmpcc and the other is under r/cinematography]

Thread 2:
[I will update this with a link to the thread when my account is allowed to post URLs. In the meantime, Googling "2 Gold Mount Batteries Died Out of Nowhere. Can anyone help me troubleshoot?" should yield the links to the two Reddit threads where I asked this question. One is under r/bmpcc and the other is under r/cinematography]

In summary:
- Someone said it's a damaged battery and that D&O batteries are unreliable and that I should use more reputable brands. Keep in mind that I used the first battery for a year with no issue, and then the replacement lasted only one shoot because it died during prep for the following shoot.
- Someone said the plate seems to be the culprit.
- Someone said the HDMI or d-tap cables I used could be the culprit.
- Someone said the battery fuse is gone, and it could've been a short in the d-tap terminals.
- Someone said it's a ground loop problem, but instead of my HDMI frying, my batteries did, and that I'm better off powering monitors separately from the camera (which I really don't want to do because I like having one battery powering everything, and I don't want to carry a bunch of different types of batteries).
- Someone said that I should always have everything connected BEFORE putting the battery on the plate because it can cause power spikes. This is something I never did, and think it could've honestly been the main problem, not the equipment itself, but my procedure....or it could be a mix of any of these suggestions. I don't know. I don't have the greatest electrical knowledge. I'm holding off on buying a new battery or a new plate or new cables until I have a better idea of why those two batteries died. Last thing I want is to buy a new battery and have it die on me, and be down a few hundred bucks.

Anyway, if someone knowledgeable could offer input into what I did wrong or where they think the issue lies, that would be greatly appreciated. And hopefully to anyone that stumbles upon this thread, they get some good insight when building out their BMPCC 4K.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostFri Sep 18, 2020 7:46 am

If the battery died quickly, it surely is not a ground loop problem, or your monitor and camera would be totally fried. If it is a short, your battery plate did a nice job protecting.

Just a month ago I put three Eneloop AA batteries in a doorbell. I put one the other way around. The plastic casing was on fire in under a second.

Now imagine what happens with a 15V (?) 190wH battery ...
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostSun Sep 20, 2020 5:09 pm

BUMP!

Anyone from BMC want to comment on my "solution" with CORESWX? Is a seperate battery for the monitor in turn charged from the same V-Mount battery that is using the power input in the BMPCC avoid a ground loop?

Why is this so hard to get engineers to comment from BMC??? Doesn't it behoove you to test these configurations since it's so obvious that people have to rig the BMPCC for more power for any professional use?

Don't you want to avoid warranty claims?
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostWed Sep 30, 2020 11:44 pm

aknittel wrote:BUMP!

Anyone from BMC want to comment on my "solution" with CORESWX? Is a seperate battery for the monitor in turn charged from the same V-Mount battery that is using the power input in the BMPCC avoid a ground loop?

Why is this so hard to get engineers to comment from BMC??? Doesn't it behoove you to test these configurations since it's so obvious that people have to rig the BMPCC for more power for any professional use?

Don't you want to avoid warranty claims?


I'm with you. My camera is at Blackmagic right now because my v-mount fried the AC port, smoke out of the camera and everything. I asked if I could be put in contact with the techs but they only referred me to the forums to ask what other users are doing. Check out my thread called "AC port on my bmpcc4k fried today"

I have absolutely no idea why my camera went up in smoke, and I have no idea if when I get the camera back and I plug everything back in that it won't immediately happen again. I wish they had some kind of diagram or approved list of ways to do this because powering these cameras via v-mount is extremely common.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostThu Oct 01, 2020 3:37 pm

If the techs at BM don't know, how can they assume the forum will know ?

There should be an official document describing best practice and what not to do.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostFri Oct 02, 2020 2:50 am

Available options are:
Use separate battery for monitor. Safest and simplest option.

Use special splitter box with opto-isolator chip similar as described here viewtopic.php?f=2&t=101481&p=596189#p596189 Very rare, expensive and low wattage solution. opto-isolator is very rare thing. It is NOT the same as voltage regulator or step up/down converter used in most battery plate splitters..

Somehow connect all (-) wires before (+) wires. Disconnect all (+) wires before (-) wires. It is possible with some custom made on/off switch on positive (+) wire of DC cable or with build-in ON/OFF switch on some batteries. More info described in this thread viewtopic.php?f=2&t=107642 Still risky option.

Use quality HDMI cables. Damaged or low quality insulation may produce voltage leak and in some critical moment may damage HDMI chip.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostFri Oct 02, 2020 6:15 am

The problem is, when connecting battery to a device there can be a current spike as the capacitors load etc. also long cables can have capacitance and cause voltage/current spikes when connecting.

Normally this is not a problem, it has been taken into account when designing the device.

For some reasons it seems that the engineers have not always taken into account the situation when more devices are connected to the same battery. They really should consider this quite normal situation. I am not sure if this is the case with P4K, maybe it is just fine regarding this also, and it would be good to get BMD comment on this.

The Problem can be, if HDMI is connected between camera and monitor, camera external power is already connected, and same external power is used for the monitor. On this situation when connecting the power tab to the monitor, if + pin connects first, the the GND is already connected via HDMI cable, and all the current will go trough the HDMI cable before the GND pin is connected on the power connector. Just the fraction of the second can be enough to burn the HDMI GND connection, if it is not designed to take this.

There is the above mentioned solutions, but really I would hope the design engineer take this into account when the device is on design phase, and:

- design the HDMI etc. GND connections strong enough to take the connection current spike.
- isolate the GND so that it is not a problem
- use power connector that makes sure GND is always first connected.
- have some smarter system verifying GND is properly connected, before connecting the power to the device.

Otherwise if using same unisolated power source for multiple devices, like connecting one V-lock battery to monitor and camera directly, is just an accident waiting to happen.

The question I have is, is the P4k designed so that it can handle the ground loops?

Ps. This is what happens when connecting a power cable to a device that has empty capacitors. In this case it is very clear as the capacitors are big and this is a 50V bicycle battery, but the same happens in smaller scale with smaller batteries and capacitors. If that current goes on a route it is not designed to go...



Pss. There can be also other problems related to ground loops, like disturbance on video or hum on audio.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostFri Oct 02, 2020 8:13 pm

aknittel wrote:BUMP!

Anyone from BMC want to comment on my "solution" with CORESWX? Is a seperate battery for the monitor in turn charged from the same V-Mount battery that is using the power input in the BMPCC avoid a ground loop?

Why is this so hard to get engineers to comment from BMC??? Doesn't it behoove you to test these configurations since it's so obvious that people have to rig the BMPCC for more power for any professional use?

Don't you want to avoid warranty claims?


Have you contacted BM directly? When I have a question, that's what I've always done and never had a problem getting a helpful reply. Though BM does get on these forums this isn't a direct support site for questions, it's a user site to gather information from other users.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostSat Oct 03, 2020 8:23 pm

I am curious. Has any one had this issue when they had all the cables hooked up before turning on the power on their battery plate?
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostMon Oct 19, 2020 7:28 pm

As far as contacting BM, can someone use a support request for that WITHOUT buying the camera first?

Im happy to do that.
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Re: BMPCC 4K Ground loop ? "Is it safe?"

PostTue Oct 20, 2020 7:23 am

lost_soul wrote:I am curious. Has any one had this issue when they had all the cables hooked up before turning on the power on their battery plate?

If on/off switch in your battery plate wired to (-) cable, soon or late it will cause permanent HDMI damage when you turn battery on. I personally damaged HDMI port on BMMCC in exact same way when experiment with my early battery enclosure prototype connected to camera and monitor. In final version of battery enclosure i changed cables layout and place on/off switch to (+) wire. So negative always connected before positive when you turn battery on.

It is unknown if all battery plates from other manufacturers use on/off switch connecterd to (+) wire.
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