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Powering BDR through the RS port on the Alexa

Alexa BDR

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#1 Bryan Fowler

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Posted 07 November 2012 - 10:46 PM

Has anyone else had problems powering the BDR through the RS port on the Alexa?

We were using the M1, and Anton Bauer batts on the back.

It was stopping halfway through the calibration cycle, and just clicking. I backed the torque all the way down, and it would finish calibration, but then it would fail (pause for 5-10sec, then start recalibrating) when I tried to make a moderately fast focus move.

The lenses were not stiff.

We ended up using a D-tap from an external battery to power the BDR, and all worked fine.

Just wondering if others had this problem? We didn't test it with 24v.
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#2 joe mcnally

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Posted 08 November 2012 - 12:34 PM

Hi Bryan, Ive used mine a few times via the Alexa RS port and dont recall any problems. Not even sure if the RS port is 24v or 12v but all seemed to work fine. I think optimal performance is with 24v though so if its available thats the voltage to choose
All best Joe
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#3 Bryan Fowler

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Posted 09 November 2012 - 08:36 AM

It's the 2nd time I've had issues with the BDR and RS port on the Alexa, but the first time was during a feature, and we didn't really have time to troubleshoot. This time was during prep, and so I could play around with it more. But I didn't have a 24v power source, so that might be an easy fix.

I wonder if the fSTOP guys might know?

I'd like for it to work, so we could use it for handheld, or jib work...any number of things.
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#4 Kar Wai Ng

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Posted 09 November 2012 - 09:07 AM

Never had a problem running the BDR off the Alexa RS port, driving a Preston DM-1X. Even with fast racks (and the 1X is fast!) never had any issues. I wonder what the current draw is on the digital M1 motor?

What onboard batteries are you using, the HC's? The current output on the RS ports are limited by the power source. HC's can do 10 amps, but the camera has to take that 14V power and upconvert to 24V anyway. Since the RS ports are limited to 2.2A total @ 24V, presumably that means the current draw could be something like 3.7A at 14V of peak current. Add that to the current the camera is drawing, plus maybe a monitor powered off the MON power, and it is not difficult to go over the current limit for an onboard batt.

Are you running any other accessories off the RS ports? Normally we try to power the Alexa off a block batt, and use a power cable with a Y split at the end that gives you a RS breakout, so that any high current accessories bypass the camera internals entirely. This is my practice with any camera, not just Alexa.
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#5 Victor Lazaro

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Posted 09 November 2012 - 09:49 AM

I also have some issues when powering the Epix and Bartech from the same battery. The camera shuts down when I switch on the Bartech. There seems to be a peak when you turn it on. (It's also discussed in another thread)

Edited by Victor Lazaro, 09 November 2012 - 09:50 AM.

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#6 John atkinson

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Posted 09 November 2012 - 08:57 PM

I had trouble powering Bartech with M-one, when racking focus the camera stopped rolling and the motor went into calibration mode. Use the D-tap from D-tap sandwich plate.

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#7 Peter Hoare

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Posted 10 November 2012 - 04:36 PM

The RS port is 2amp max (thats between both of them) so depending on the motor and the stiffness of the lens, you may or may not go over 2amps. We have had this problem with our system too, I always try and make sure people power off a Dtap....
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#8 Barry Strickland

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Posted 29 July 2015 - 05:22 AM

I haven't had any trouble with my BFD using the MKV FMG 6 motor. Don't know the amp draw difference from the M One... Will have to look into it.
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