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Powering Alexa


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#1 Victor Lazaro

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Posted 10 April 2015 - 09:58 PM

Hi, 

What is the difference between powering an Alexa from:

- 2pin connector in 12v

- 2pin connector in 24v

- XLR cable to SO-XLR dummy battery

Thanks,

V. 


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#2 William Demeritt

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Posted 10 April 2015 - 10:17 PM

In my understanding, the cable itself is wired for 24v, not 12v, so the "positive" receptacle inside the cable has 24v power, and the ground is ground. The CAM power ports have 3 pins: 12v, 24v, and ground. When your sled is in 24v mode, the 12v receptacle has no load and the 24v receptacle has 24 volts, and the ground is always ground. 

 

The Arri 2-pin power cable only takes power from the 24v line (since that's the only power connector that's wired), and ground is connected to ground. 

 

12v mode = the power cable ground connects to the ground on the battery, but no power is supplied because the power receptacle is not connected to the system (it's 24v).

 

24v mode = the 24v pin is powered with 24 volts, so the power cable has 24v power and ground connected. 

 

Assuming your XLR power cable is wired for 12v as well, that means it will only connect to the 12v line and only give power when the sled is in 12v. If the sled is 24v, the cable has no power because it's connected to a dead pin (the 24v pin, which has no power). Also, in the best of my understanding, the Alexa takes only 12v power on the battery connector (or the SO-XLR plate in this case). 

 

So, with the XLR cable to SO-XLR plate, it's giving 12v power to the plate and 12v power to the camera (as if a 14.4v battery was present). If you set the sled into 24v mode, nothing happens because the 12v XLR cable doesn't touch the 24v lead, so no power supplied. 

 

... I think?


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#3 Jess Haas SOC

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Posted 10 April 2015 - 10:33 PM

If you wire an XLR cable to provide 24 on what should be the 12 pin an Alexa will happily run from it.If using the Amira the D-tap will then be outputting 24 as well so you have to be careful to not fry anything on it.

The Alexa will also happily run off 12v on the 2 pin power connector as long as the camera is not set to shutdown below a certain voltage above that (it's in the menus)

If you hook up multiple power sources to the camera (12v battery and 24 on 2 pin for example) it will run off the higher voltage and hot swap if necessary.

That's how I understand it atleast. Usual disclaimers apply (double check before doing anything silly)
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#4 Victor Lazaro

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Posted 10 April 2015 - 10:53 PM

Thanks. 

So if the camera works off 12v, even on the 2pin connector, what is the point of running it in 24v?


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#5 Jess Haas SOC

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Posted 10 April 2015 - 11:19 PM

It's more efficient in 24v. You are cutting the amp draw in half so there is less resistance and voltage drop on your sled wiring, etc... End result is batteries should last longer in 24v mode.
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#6 Alec Jarnagin SOC

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Posted 11 April 2015 - 12:38 AM

I've always run the Alexa off of 24 Volts, in part because all my cables are wired that way, but it seems to make sense since you are cutting the amperage in half.

 

Another note, Will, you wrote:  "When your sled is in 24v mode, the 12v receptacle has no load and the 24v receptacle has 24 volts, and the ground is always ground. "  This is actually not the case with a PRO sled.  Your 12 Volt pin still carries 12 Volts so, even in 24 Volt mode, you can power 12 Volt accessories off a camera power port providing you use a 12 Volt cable. Obviously when in 12 Volt mode, your 24 Volt pin is not hot.


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#7 Alan Rencher

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Posted 11 April 2015 - 03:37 PM

Also, if you are feeding the Alexa 12V, it's built-in distro (24V outputs) boosts that voltage to 24V instead of passing the unregulated voltage along.
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#8 Jens Piotrowski SOC

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Posted 11 April 2015 - 05:30 PM

to my knowledge there no regulated power supply (DC 12V to DC 24V) build in, so you get out what you put in....


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#9 Alan Rencher

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Posted 11 April 2015 - 05:53 PM

From Alexa manual SUP 11.0
Attached File  uploadfromtaptalk1428792806556.jpg   62.37KB   26 downloads
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#10 Jens Piotrowski SOC

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Posted 11 April 2015 - 06:37 PM

This is news to me, my info is directly from Arri, head of technical support. Unclear.
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#11 Jens Piotrowski SOC

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Posted 11 April 2015 - 07:18 PM

From Arri,

Jens,

12V is regulated, the two RS ports are whatever you plug in (voltage range 10.5-32V). Actual voltage range is actually 10.5-34V, but high end is cut off at 32V. Something to be careful with as some 3rd party accessories might not be protected for these voltages.

Sincerely,
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#12 Brian Freesh

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Posted 11 April 2015 - 09:41 PM

That's weird Jens, my understanding has always been that the camera converts incoming 12v to 24v, I know we talked about it here on the forum.  I remember there being a discussion that it's best to run the camera at 24v because it is a 24v camera so it won't have to convert the 12 to 24.  And Greg Bubb recommended powering 12v from an XCS sled because the sled is native 12v and will not have to convert to 24v.

Those may have been slightly different discussions, and I may not be remembering 100% accurately. Cause time and age and all that. ;)

I can definitely confirm that when feeding 12 or 24v, I've never seen a problem when powering something from the RS ports.  I cannot however confirm that any of those accessories wouldn't be perfectly happy with 12v. For example, Preston recommends an MDR be powered 24v, but it will take the 12v just fine.

Now I want to meter an Alexa...


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#13 Alec Jarnagin SOC

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Posted 12 April 2015 - 01:59 AM

Jens, I too was always told what Alan and Brian said.  RS ports are up-converted to 24V when supplied with only 12V. 


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#14 Jens Piotrowski SOC

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Posted 12 April 2015 - 09:36 AM

The info i posted is from Stephan at Arri and also my personal experience in the field.

 

I was originally unable to power up an early BOXX version and was only feeding 12V (14V) from my XCS sled into the Alexa and the RS port was giving out the input voltage...


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#15 Victor Lazaro

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Posted 12 April 2015 - 10:13 PM

One more question: 

Would it be OK to power an Alexa with the SO-XLR from the LEMO 0B.303 (The smaller connector on the front of the CineLive box, not the CAM PWR) or is that too much power for the connector size? I have a LEMO 0B.303 to 4Pin XLR cable made for my Zephyr already and a last minute shoot coming where I would love to fly without a battery without burning anything down. 


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