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telling Alexa which batteries to use

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#1 richard bellon

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Posted 28 January 2012 - 04:31 AM

hi all

ive got a shoot tommorrrow on Alexa,
and i was wondering....

is there a setting on camera to tell it to use the onboard battery first
and when that dies kick over to my sleds batteries?

i was wondering if this is possible as i would like to plug it into the sled
and not have it use the batteries except when hot swapping the onboard batteries
without having to plug/unplug and have the cable stuck/dangling next to camera body

i didnt get a chance to check it out yesterday at the g/check as there were other issues
that were being dealt with

thanks in advance
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#2 Fabian Roesler

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Posted 28 January 2012 - 05:10 AM

7.1 Power Management
When using the BAT connector and one or more onboard battery adapters
simultaneously, the camera power management ensures that the power
source with the highest voltage level is used. When the voltage level of one
power source drops below the level of the other, or a power source is
disconnected from the camera, the power management automatically
switches to the other power source, avoiding shutdown of the system.
So as an example, one could use a 12 V onboard battery as backup for the
main 24 V battery, or power the camera from the 24 V battery while on a
tripod and use the 12 V battery for fast switching to handheld mode by just
unplugging the power cable.
When using two onboard battery adapters with batteries in parallel (one on
top and one on the back), they are treated as one source by the camera.
This allows combining small batteries with less load per item into one strong
power source.

hope this helps

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#3 Brant S. Fagan SOC

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Posted 28 January 2012 - 08:50 AM

Sadly, there is no simple way to have this work without some help from a voltage regulator. If you are using an onboard battery, that will tie up the A/B or V-Lock plate and force you to supply 24 volts to the 2-pin Fischer connector. Once you do that, the Alexa will draw power from that until the low voltage cutoff level is reached. Upon hitting that threshold, the Alexa will draw from the onboard battery plate source. This would be simple if there was a separate 12 volt connector on the body which then would allow what you are attempting.
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#4 Benjamin Treplin

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Posted 28 January 2012 - 10:56 AM

Hi Brant,
you can use the 2-pin Fischer connector to power the camera with a 14.4V battery. In fact the camera accepts from 10,5V to 34V on the 2-pin Fischer. You just have to adjust the cameras low battery warning in the menu: Menu -> System -> Power
The simple solution is to rewire a regular Arri 24V cable on the sled side and make it a 12V cable. This way the Alexa draws from the onboard battery until the voltage drops below the voltage from the sled. Sled voltage is likely to be lower for certain time due to voltage loss of the centerpost cable.
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#5 Ken Nguyen

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Posted 28 January 2012 - 01:48 PM

There is no way to tell Alexa to draw power from the on-board battery first.
Alexa will look for the power from the external power port first. It is its priority power source.
It then compares with the on-board power.
Which has a higher voltage will be drawn first from Alexa.

If your sled power is 24v, or 2 x 12v batteries in parallel, and the on-board is 12v, your sled power will be priority.
If the on-board is 24v, chance is it still drawing power from your 24v sled if the on-board battery voltage is dropped down below yours.

Your only chance is power the camera with 12v from your sled. And the on-board battery must be 24v.

My solution is, in your case, not to connect the sled power into the camera.
Having the power cable in your pocket, and only plug in when needed to hot-swap the on-board battery.
It alway works for me.

Safe fly,

Ken Nguyen.
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#6 richard bellon

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Posted 28 January 2012 - 02:23 PM

hi all

thanks for all the answers, its what i suspected :(
but some excellent ideas though which i'm def gonna look into for next saturday,
as i have another job also on Alexa :D

kindest regards
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#7 richard bellon

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Posted 15 February 2012 - 05:39 AM

hey all

just a thought...

if u select 12v power from sled and power the alexa do u think it would use the on-board battery first because of voltage drop up the post?
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#8 richard bellon

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Posted 15 February 2012 - 08:31 AM

i think i awswered my own question while reading another post about the codex
thanks all
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