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Power Supplies for Big Multi-Camera Rigs

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Offline JC

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Power Supplies for Big Multi-Camera Rigs
« on: 02 / September / 2017, 22:03:41 »
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I could use some help with power supplies.  I have an array of 66 cameras (Canon A3400 and A4000s) arranged in 11 arrays of 6 cameras.  I currently have them powered by separate power supplies that replace the batteries ( Kapaxen PA-CADC-10k-CN  4.3V/1.5A) to each camera.  I would like to either have one power supply for each array of 6 cameras or one power supply for all cameras.  What spec do I need for this power supply?

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Offline waterwingz

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #1 on: 02 / September / 2017, 23:46:16 »
tl;dr : large single power supplies not a good idea - sorry.

Big power supplies.   In some ways, the holy grail of mulitcam rigs. Get rid of all the individual 5"x2"x1" battery eliminator power packs with their 4' AC cords.  (sorry for the American units). 

But here's the problem.  For 66 cameras you would be looking for a power supply that can put out 100 amps at 4.3V! Even if such a thing existed commercially, it might seem like overkill as surely not every camera will be drawing maximum power at the same time? Maybe - but when you shoot with a multicam rig, they will all be moving motors, charging flash units, shooting, and saving to the SD card at the same time.  Their times of maximum power consumption will all be synced. Bad news that.

And there is an even more important consideration.  The interconnecting low voltage wiring.  Simple Ohm's law - as the current goes up, so does the voltage drop down any connectors.  So to make this work,  you either need a set of 66 power cables all leaving the power supply in parallel, or less conductors shared between cameras that must be of a much thicker gage. And it does not end there.  Each power cable is effectively a transmission line, with its own resistance, capacitance, and inductance.  When you are only powering one camera that does not matter a lot.  But when you have multiple cameras in parrallel, it counts and can cause nasty interactions between cameras as high frequency current variations start to take effect. Sorry to say that I've been there, done that, got the t-shirt.

And then we need to talk about grounding.  And ground loops - something you need to deal with even with 66 separate power supplies.

Complicated stuff - I've been dealing with this sort of problems for a very long time.

So my advice? Keep it to your arrays of six cameras that are located closely together ( max 5') on a single supply.  Use a power supply that can push out at least 10 amps peak at 4.3V.

A better solution might be small DC-DC converters mounted at each camera that can reduce a shared 9VDC-24VDC (the higher the voltage the better as current drops are reduced that way) to 4.3V at each camera.  If you get  DC-DC convertors that can handle 12V DC input then you can probably hook up 20 or so cameras safely to the same bulk DC supply.  Just my gut feel here BTW.

Grounding is another challenge.  Once you decide on power sources, we should dicuss that too.  Doing it wrong here can result in anything between intermittent cameras shutdown issues and strong to fatal electrical shocks.

I know your were hoping for a link to a web site with a power supply that would solve all your problems.  I don't think such a thing exists. And even if it did, the interconnecting cable issues and  grounding problem would shut you down anyway.

Sorry.


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Offline JC

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #2 on: 03 / September / 2017, 00:17:43 »
Please explain the grounding issue.  I have groups of 6 cameras with 6 power supplies into a power strip, the power strips are then connected to another power strip with a 3 prong grounded plug (US), which is connected to a wall supply.  We have not noticed any ground loops or odd behavior of the cameras.  Should I be concerned?
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Offline waterwingz

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #3 on: 03 / September / 2017, 00:35:21 »
Sounds like you have a good setup on the AC side of your rig. No issues there that I can see.

How do you have the low voltage / USB connections wired to your PC and grounded?  That's usually where the problems lie.
« Last Edit: 03 / September / 2017, 16:55:14 by waterwingz »
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Offline Hardware_Hacker

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #4 on: 03 / September / 2017, 20:44:31 »
Quote from: JC on 02 / September / 2017, 22:03:41
@ JC ... I could use some help with power supplies.  ....
I currently have them powered by separate power supplies that replace the batteries ( Kapaxen PA-CADC-10k-CN  4.3V/1.5A) to each camera. 
I would like to either have one power supply for each array of 6 cameras or one power supply for all cameras. 
What spec do I need for this power supply?

Ref:- @ ww "...can cause nasty interactions between cameras as high frequency current variations start to take effect..."
Ref:- @ ww "...can cause nasty interactions between cameras as high frequency current variations start to take effect..."
There may be other, separate and more complex, multi-cam power supply issue's.
Simply put there is a lack of certain filter components, at a certain low frequency band, at or above the (very) Hi Audio range.
But if this issue proves to be true, then how to simply and cheaply solve this potential multi-cam P-S issue.

I am currently looking at a (cheap) solution to the above issue re; multi-cam power supply's, but the details are about 4 to 8 week's away.
So what's your time frame for the replacement power supply's.

Also do you have a spare Kapaxen power supply's to be used for some, low voltage, experiments.
or alternatively any detailed photo's of your multi-cam rig and/or the Kapaxen power supply's.
And do you have access to any measurement equipment.
How do you currently sync your cameras.

H-H
« Last Edit: 04 / September / 2017, 20:36:47 by Hardware_Hacker »
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Offline JC

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #5 on: 04 / September / 2017, 00:55:25 »
Quote from: waterwingz on 03 / September / 2017, 00:35:21
Sounds like you have a good setup on the AC side of your rig. No issues there that I can see.

How do you have the low voltage / USB connections wired to your PC and grounded?  That's usually where the problems lie.

Power supplies are connected to each camera via the battery pack replacement. 
We have USB cable to each camera  connected to a Manhattan USB hub (no external power), we are using 4 manhattan hubs which are then connected to another 4 port hub connected to a computer (server).
 
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Offline JC

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #6 on: 04 / September / 2017, 01:05:04 »
Quote from: Hardware_Hacker on 03 / September / 2017, 20:44:31
Quote from: JC on 02 / September / 2017, 22:03:41
@ JC ... I could use some help with power supplies.  ....
I currently have them powered by separate power supplies that replace the batteries ( Kapaxen PA-CADC-10k-CN  4.3V/1.5A) to each camera. 
I would like to either have one power supply for each array of 6 cameras or one power supply for all cameras. 
What spec do I need for this power supply?

Ref:- @ ww "...can cause nasty interactions between cameras as high frequency current variations start to take effect..."
Ref:- @ ww "...can cause nasty interactions between cameras as high frequency current variations start to take effect..."
There may be other, separate and more complex, multi-cam power supply issue's.
Simply put there is a lack of certain filter components, at a certain low frequency band, at or above the Hi Audio range.
But if this issue proves to be true, then how to simply and cheaply solve this potential multi-cam P-S issue.

I am currently looking at a (cheap) solution to the above issue re; multi-cam power supply's, but the details are about 4 to 8 week's away.
So what's your time frame for the replacement power supply's.

Also do you have a spare Kapaxen power supply's to be used for some, low voltage, experiments.
or alternatively any detailed photo's of your multi-cam rig and/or the Kapaxen power supply's.
And do you have access to any measurement equipment.
How do you currently sync your cameras.

H-H

I do have basic measurement  - multimeter, no scope
Replacement is needed as soon as possible; so if we are 4-8 weeks then OK, but 2 weeks would be ideal.

I will work on getting photos but probably not til next week.
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Offline waterwingz

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #7 on: 04 / September / 2017, 09:57:57 »
Quote from: JC on 04 / September / 2017, 00:55:25
Power supplies are connected to each camera via the battery pack replacement. 
We have USB cable to each camera  connected to a Manhattan USB hub (no external power), we are using 4 manhattan hubs which are then connected to another 4 port hub connected to a computer (server).
That's an acceptable way to get things to work reliably. Each camera's power input "floats" (assuming the Kapaxen power packs are properly isolated) and the GND ground pins on the USB connectors all have a single path to ground via the USB hubs to your the PC.



While you won't get ground loops from such an arrangement, your path to ground is through tiny 22 gage wires.  I can't find the reference right now but somebody posted on this forum about getting electrical shocks from just such a system.  I don't know how it was resolved - I suspect they had a one or more power supplies that "leaked voltage" and inadequate grounding (i.e. just the USB GND wires) to safely shunt that leakage voltage away.

In any case, if you switch to shared power supplies, make sure you use heavy gage wires for the DC connection to the cameras.  And the longer the cables, the heavier the wires need to be. Make sure the DC negative connection is "earthed" (or connected to building ground) at each power supply output.  The use of ferrite beads or toroids (like you will see on the DC side of many laptop power supplies) can help filter current spikes from causing interference between cameras but I don't have any design criteria for using such devices.

Note : the ideal way to do what you want is probably to use a big 9 to 12 DC power supply to provide a DC power line and then use little DC-DC converters at each camera to get down to 4.3 volts at each camera.   But this takes a little bit more assembly work and is extra cost.


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Offline Hardware_Hacker

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #8 on: 04 / September / 2017, 21:01:49 »
Quote from: waterwingz on 04 / September / 2017, 09:57:57
Quote from: JC on 04 / September / 2017, 00:55:25
Power supplies are connected to each camera via the battery pack replacement... 
...The use of ferrite beads or toroids (like you will see on the DC side of many laptop power supplies) can help filter current spikes from causing interference between cameras but I don't have any design criteria for using such devices.

Note : the ideal way to do what you want is probably to use a big 9 to 12 DC power supply to provide a DC power line and then use little DC-DC converters at each camera to get down to 4.3 volts at each camera.   But this takes a little bit more assembly work and is extra cost.
Using, ferrite beads or toroids and any design criteria, this is part of what I intend to look at in much more detail.

Using little DC-DC converters at each camera this may not solve the basic problem for several reasons:-
a/ A Possible NEW EM-NOISE source.
b/ A recent post on another forum suggests that they may not be capable of supplying the necessary peak currents.

An alternative is to use local Low Drop-out linear voltage regulators with local de-coupling/filters at each camera.
This has less power efficiency, and is probably more costly, than using little DC-DC converters at each camera but has the major advantage of widely distributed multiple de-coupling/filters. So the Possible EM-NOISE source's have very reduced common mode signal path lengths.

Also the AC Mains wiring should be physically separate to the DC-Power and Control wiring.

And this gets to the cause, effect and measurement of this type of potential problem and is another part of what
I intend to look at in much more detail.

If there is a simple and low cost way to do measurement's then it becomes much to solve potential EM-NOISE and related issues.

H-H
« Last Edit: 04 / September / 2017, 21:12:19 by Hardware_Hacker »
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Offline ottokar

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Re: Power Supplies for Big Multi-Camera Rigs
« Reply #9 on: 22 / September / 2017, 05:09:57 »
I would just add, I have used those little dc-dc convertors, they're cheap and do the job fine, with no interference problems, in my experience.

 However, I just have these bare boards hanging off my cameras, and that is bad because I feel I have to treat them with kid gloves whenever I touch them. In the future I want to be able to take my setup down, transport it somewhere and set it up again, and I need something that's physically more robust.

 It would work as it is, I would have to be so careful and delicate when disassembling and reassembling it, but i couldn't trust a helper to do it, I would have to do it myself to make sure it was done ok.

 So I would say if you want to prototype something at home cheaply, they work, but I would not use them for a real use system,

andrew
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