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Alexa won't power through sled. Why?


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#1 Dan Coplan

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Posted 23 February 2012 - 03:29 PM

I have a PRO rig and brand new HC batteries. Putting these batts on the plate on back of the camera - no problem. But when I put them on my sled and ran the cable to the fat 2-pin connector on the back of the camera - nothing. Not even a blip. I tried two of these cables and I know they're good because I've used them in the past with no problem. Switched between 12 and 24 on the sled. Nothing.

Apologies if you all have been through this before. I searched the forum for the answer to this but didn't find anything.

Dan
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#2 Eric Fletcher S.O.C.

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Posted 23 February 2012 - 03:29 PM

Pro HD or earlier Pro?
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#3 Brian Freesh

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Posted 23 February 2012 - 03:52 PM

Crazy random thought from someone who does not own a pro (me).

When you were in 24v mode on your sled, did you make sure the Alexa was enabled to take 24v from that port? It's in the menu somewhere. If it is only enabled for 12v, it will not accept the 24v from from your sled.

I don't know how pro camera power connectors are wired, but I imagine that cable you have will only accept 24v from your sled because it was wired to be used with a 235, 435, 535, ST, or LT, all 24v cameras. Unless you had it specially made. If you want to use 12v off your sled, you'll need a different cable or to re-wire what you have.
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#4 Lawrence Karman

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Posted 23 February 2012 - 07:38 PM

I have a PRO rig and brand new HC batteries. Putting these batts on the plate on back of the camera - no problem. But when I put them on my sled and ran the cable to the fat 2-pin connector on the back of the camera - nothing. Not even a blip. I tried two of these cables and I know they're good because I've used them in the past with no problem. Switched between 12 and 24 on the sled. Nothing.

Apologies if you all have been through this before. I searched the forum for the answer to this but didn't find anything.

Dan



Correct jumper on the front of the PRO base? Also in the camera menu you can set the minimum voltage it will accept before shut down on the 12v plate an on the 2 pin Lemo input. Perhaps it is set too high?
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#5 RonBaldwin

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Posted 24 February 2012 - 09:29 AM

I assume you have tried a volt meter on the cable to make sure power is making it to the camera? The breakers can take a pooper at the most convenient times (so don't use them as a switch) did you give the cam/aux breakers a jiggle to see if power was intermittent?
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#6 Dan Coplan

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Posted 25 February 2012 - 09:34 PM

Thanks everyone for all your feedback. Unfortunately I was just on this one day so not able to apply your thoughts to the issue at the moment, but I'll keep all this info in my notes for the next Alexa shoot which may actually be pretty soon. Will report back.

For the record: Pro 2, not Pro HD. Did not check to see if the cam was enabled for 24v from that port. Didn't even know that was an option. But yes, my cables were designed for film cameras so maybe you're on to something there. Yes, correct jumper but did not check the minimum voltage setting. But since it worked fine on the body, would there be a difference coming into the power plug? Unless you're suggesting you can set the min voltage for both taps separately. Did not take a volt meter to the cables but would be very, very surprised if it was a cable issue as I'm super anal about my gear and I have more than one cable as backup. Did not jiggle the breakers with respect to this issue.

Dan
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#7 William Demeritt

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Posted 25 February 2012 - 10:02 PM

Dan: you can set the voltage warnings for the two items separately.

I was working with an Alexa a few days ago whose owner has not yet updated the software (anamorphics with no desqueezer was fun for him on the monitor, but my Cinetronic worked out with a manual aspect ratio). In the menus, though, I did find voltage warnings for the battery and for the plug.

Further, I couldn't actually find where to specify what kind of power for it to accept over the Arri 2-pin power port. I only have Arri 24v power cables, and when I plugged it in and set my sled to 24v power, the Alexa turned right on. Obviously, when I tried that with the sled set to 12v, it didn't power on. Noteworthy: it didn't power on and give me an "under voltage" warning, but it just didn't power on.

That's because the sled makes 24v power and sends it over 1 of the 2 pins in the Arri 2-pin power connector. Maybe correlated somehow?
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#8 Brian Freesh

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Posted 25 February 2012 - 10:21 PM

After thinking about it , I'm not sure how valid my information is. I remember hearing about that when it first came out. If it was true then, it's not true now. Shoulda had Will google that for me.

From the FAQ:

ALEXA will accept any input from 10.5 to 34.0 V DC on any power input. Most 14.4, 24 and 26 Volt batteries and power supplies will work fine, as long as they can supply at least 100 W. While most 12 V batteries will work, they can quickly discharge below the 10.5 V limit and thus are not recommended. While most 30 V batteries will work, they will supply above the 34.0 V limit when fully charged and thus are also not recommended.

How hot are those brand new bricks right off the charger? if they are at all over 17v each, two of them in series will be over the 34v limit. Might explain the issue.
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