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Powering an Alexa


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#1 David M. Aronson

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Posted 19 August 2012 - 10:36 PM

Okay, so my first Alexa job is coming up and the camera owner got in contact with me asking if I'm going to power from my rig. He can supply dionic 160s for powering the camera/sled since I only have 90s. He wants to know because he's had steadicam ops fry 3 camera bodies before(over 16 years, but still) I have a master series and I have the little 24v converter thing. I also have the arri 2 pin fischer cable, but it's an older one designed for the film bodies. Wlll it work? Should I run 24v to the camera? Is it better to have the batt on the back of the camera and just use 90s on the bottom? The shoot is a tour of some civil war battle ground and they want to it in as much of one shot as possible. There's going to be a "park ranger" (actor) walking and addressing the camera. HELP!
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#2 Erik Brul

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Posted 20 August 2012 - 04:45 AM

In my humble opion, just run the camera from it's own battery on the back..

Cheers,
Erik
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#3 Afton Grant

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Posted 20 August 2012 - 06:35 AM

Yup, that 24V converter on the old Master Series sleds won't be able to give the Alexa what it needs in terms of power. Quite frankly, it won't be able to give a lot of cameras what they need in terms of power. When you get some time, I'd recommend changing that out for a 2nd battery plate so you can have true 24V, rather than upconverted 24V. For this upcoming shoot, you might have to live with a battery on board. Dionic 160 isn't small. If you can get some Dionic HC's you'd be in much better shape, otherwise the camera will get heavy on you very quickly.
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#4 RonBaldwin

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Posted 20 August 2012 - 07:13 AM

The 160 is 3.4 lbs. I love them...but on the sled. The alexa will run fine off a 90
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#5 John Ritter

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Posted 20 August 2012 - 07:58 AM

Definitely Run The Camera with it's own battery,
The Dionic 160 should safely give you an hour+ Run time
(if it has anywhere near full capacity if it is older than 1 year do not expect over 80% capacity subtract about 10% for each additional year).
Battery Date codes: T=2006, U=2007, V=2008, W=2009, x=2010, y=2011, z=2012, 2 digits before the "S" is the month 01=January and so on

Power everything else separately.

A full set up with monitor,Focus, zoom, remote, wireless can top out at 140 watts plus.

John
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#6 James Davis

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Posted 20 August 2012 - 09:20 AM

In my humble opion, just run the camera from it's own battery on the back..

Cheers,
Erik


Thats what I do, much less hassle :-)
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#7 Eric Fletcher S.O.C.

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Posted 20 August 2012 - 09:39 AM

If your worded run the Alexa off of a HC. The Alexa's input voltage is 10.8-36 volts so it will run off of 12 volts just fine if you can't do 24
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#8 David M. Aronson

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Posted 20 August 2012 - 11:43 AM

The dionics I have are the non HC model, and they put out 5.5 amp hours last time I checked. Anything I should know about mounting it?
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#9 Matthias Biber

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Posted 20 August 2012 - 04:12 PM

Watch out for vibrations. Especially with a heavy battery on the back of the camera.
Use a bracket that locks down the back Sony style hook.
e.g. cam-jam.de
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#10 Mark Schlicher

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Posted 20 August 2012 - 08:25 PM

David,

You could be in trouble with a single Dionic 90, even if it's only powering the camera body and recording to SxS. The specs say 85W with camera body, viewfinder and SxS recording. So...maybe 80w without the viewfinder?

In a nutshell, you not only risk short runtimes, but you can damage your battery and reduce its overall service life. John Ritter can confirm this. Essentially, the Dionic90 were designed for a maximum sustained current load of 50W. AB stated that they could handle up to 90W with reduced service life (which means your batteries will wear out far sooner than the normal 3 years).

In practice, if you run the camera for long periods on a Dionic 90 you might get away with it, or you might trip the battery's internal thermal protection fuse. Either way, you will be cooking your battery.

As far as runtime, you may get 30-45 minutes off of a Dionic...so if you decide to risk it, have plenty of batteries because they will take awhile to recharge!

I agree that HC's are the way to go. They are designed for high current draw. Rent some HC's or better yet, some HCx's (which are only 1/2 pound heavier than a Dionic 90 or HC). Don't fry your personal Dionic 90's.
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#11 Mark Schlicher

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Posted 20 August 2012 - 08:28 PM

And a big thumbs-up to Matthias' bracket. Solid, reasonably priced, and a very clever design.
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#12 Andrew Ansnick

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Posted 20 August 2012 - 08:57 PM

I've run Alexa's off of Dionic 90's from the rental house on several occasions and never had issues. Yes you will have shorter run times but at least your batteries won't be getting cycled. I say use their batts, whatever size they may be.
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#13 Twojay Dhillon

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Posted 20 August 2012 - 08:58 PM

I, personally, love heavy cameras. The 160 is awesome for the Alexa (from my experience). Depending on the lenses used, it may very well get the focal plane right over -- or very close to -- the center of the post. If you are using Pana Anamorphics, this will almost always get the FP over the center of the post (using an LMB-5 with one filter and a Cinetape with read-out mounted on the side of the LMB-5).


Have fun w/ the best non-film camera!
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#14 Mark Schlicher

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Posted 20 August 2012 - 10:03 PM

Andrew, just be aware you may be damaging the rental house's batteries for the next guy, who might suddenly discover he's got 15 minutes of runtime. Unless it turns out you are the "next guy", in which case you might get stuck with batteries with the "last guy" cooked. That's happened to me, and it's not pretty.

Yes, I try to avoid using my own Dionic 90's on high-current cameras, but there are both practical and karmic reasons to use HC or HCx batteries, even when they are rentals. Rental houses around here are mostly small businesses, as I suspect they are in many markets. I don't want to deliberately crap in anyone's yard.
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#15 Andrew Ansnick

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Posted 20 August 2012 - 10:21 PM

The way I see it is that if the rental house supplied the batteries and the camera, then they intend them to be used in combination with one another. Now if they happen to provide HC's (and more often then not that's what they provide) I'd be more then happy to use those as well.
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