Paralinx fried by Alexa

[Walter F. Rodriguez]

Beware of power Tereadek using non-Teradek 2pins lemo.

Teradek tech should be addressed this issue.

All of our accessory which powered by 2pins lemo are following standard wiring code.

pin1 is positive; pin 2 is negative.

 

Teradek is reversed. Pin 1 is negative.

 

So, if you use 2pin-lemo cable, you will fry your device.

I was lucky, PRO has 3 circuit breakers to protect.

It popped out and saved my day.

That's when I found out Teradek Pin1 is negative.

Always bring along a voltmeter with you.

 

Cheers,

 

Ken Nguyen.

The pin selection Teradek uses also happens to be the same as Preston and Sniper.

[Alan Rencher]

It looks like this setup has the camera being fed by two batteries in series, which actually connects the positive of one battery to the negative of another. I would bet that the P-Tap isn't connected to a regulator, so what they might be doing is just using one battery of the series as an unregulated 12V. The problem then may be that when you connect the two grounds together via the SDI, you are actually shorting positive in one battery to the ground in another. Normally, that would be protected on an Arrow-X, but the short is bypassing the power input protection circuits and actually backfeeding through the SDI board. Just a guess.

[Alan Rencher]

This is a more common problem than you might think. Any sled that has a switch that puts the battery plates from parallel (12V) into series (24V), but doesn't either use a regulator or use an isolated third battery to output to the 12V line has a chance of causing a short through coaxial lines. Here's the basic principle:

 

• When you have a sled in parallel mode, all positives and grounds are tied together, respectively. This doubles the power capacity while keeping the voltage the same.
• When the system is switched to series, the positive of one battery is connected to the ground of another battery, just like when you stack AA batteries in your remote control. This doubles the voltage while keeping the power capacity the same.

Here's where that bit about needing a regulator or an isolated third battery comes in. When you have a system that is wired in series, the proper way to get 12V is to take the 24V from both batteries, and step it down to 12V with a regulator OR, you need to use a third battery that isn't part of the series. The sleds that are creating shorts in 24V are actually creating the short with how they achieve 12V.

These sleds achieve simultaneous 12V and 24V by connecting to the positive and negative of just one battery in the series. This won't cause a problem if you are isolating the 12V and 24V devices, but if you tie the two systems together (like through a BNC cable), you are actually shorting the positive of the 24V system with the ground of the 12V system.

There's an easy way to test this with a multimeter:

• First, take the negative probe from your multimeter and find the ground pin on your 3-pin 12/24V output on your sled
• Second, test each positive output with the positive probe of your multimeter. On fully charged cells, you should read ~32V on the 24V line and ~16V on the 12V line. This is normal and fine.
• Third, find the short! if you place the negative probe on your 12V line and the positive probe on the 24V line, an interesting thing happens, you will read ~16V!

The reason this happens is because the positive wire of the 12V line is tied to the positive terminal of the one battery in the series and the positive wire in the 24V line is tied to the positive terminal of the other battery in the series. BUT if you pay attention to how series wiring works, the positive wire of the 12V line is ALSO tied to the ground terminal of the second battery in the series.

Therefore, just as you did with your multimeter probes in the test I described. when you connect a BNC line from the camera being powered from the 24V line to the device being powered from the 12V line, you are shorting the second battery in the series directly to its own ground terminal.

The tricky part with coaxial lines (both coaxial power and coaxial video) is that they are not usually isolated from chassis ground. This is where a short can travel through the whole system, even if you think two systems are not connected together. This is also a problem with having working P-Tap ports on battery plates in a system that can switch to series wiring.

[Jess Haas SOC]

What you describe happens if you pull 12v from the second battery in the series but if you pull it from the first then the 12v and 24v lines are sharing a ground so there should be no voltage potential between properly grounded BNC terminals of sled powered components. I would assume that most sleds are wired this way. Mine is and I have had zero problems with using 2 12v batteries to supply both 12 and 24v.

[Alan Rencher]

That's incorrect. The problem is not from the shared ground. It comes from the positive lines. I'll do a video follow up when I have time. A bridge rectifier on the 12V line would probably fix the problem.

[Jess Haas SOC]

But the 12v and 24v lines never come in contact with each other. Its not like a 24v device runs its SDI line at line voltage or anything. They both run to SDI spec. I've been running 24v and 12v power this way for 10 years with zero problems. My monitor has always been 12v. Not as much as a spark on the BNC.

[Ken Nguyen]

But the 12v and 24v lines never come in contact with each other. Its not like a 24v device runs its SDI line at line voltage or anything. They both run to SDI spec. I've been running 24v and 12v power this way for 10 years with zero problems. My monitor has always been 12v. Not as much as a spark on the BNC.

 

Just be caution with this technique.

Make sure you connect all SDI connections BEFORE powering up your rig.

 

Cheers,

 

Ken Nguyen.

[Alan Rencher]

Jess, As you can see in the video that Will and Brian posted, it can happen with certain rigs. Using anecdotal evidence as a blanket argument is not in the best interest for people who have experienced this problem. The SDI line doesn't send 12V or 24V, but rather a much lower voltage; if you have a floating ground in one of the positive lines, you'll cause a short when it meets the positive from its source battery. That is what's happening in that video.

[Jess Haas SOC]

From their video it looks like the p-tap at the base is wired to the second battery in the series. They are getting exactly the results I would expect in that situation. Also powering from the d-tap on the battery plate for the second battery in the series would have the same result.

 

My "anecdotal evidence" was to show that when wired properly 12 and 24v from only two batteries is not a problem and no fancy voltage converters, etc are necessary. It surprises me that the pro is wired that way. Nothing should pull from the second battery for 12v when in 24v because as they have seen it can fry things.

[Jess Haas SOC]

In a previous post in this thread I mentioned my Bolt being fried. Turns out the insulation to the postive wire in my Anton Bauer to XLR adapter (AB SO-XLR) had broken down and was energizing the casing of the XLR plug causing current to flow and bad things to happen.

[Alan Rencher]

If you look at how series wiring works, you will see that no matter if you derive 12V from the first or second battery, you will be connecting to both a positive and negative terminal. A rectifier should filter out the problem.

 

I don't know why you're arguing with me. It's like you trying to Fletcher me, or something. What I am talking about is specifically the P-Tap in the CineLive. The short that is happening in the video is exactly what I described in my post; there is no questioning that.

[chris fawcett]

Manufacturers need to make people aware of this problem. We've been discussing it here since 2009:

 

http://www.steadicamforum.com/index.php?showtopic=10918

 

At least Tiffen blocks the D-Tap on the second battery plate on their rigs, but this in itself is not foolproof. Transvideo also warns specifically about this problem in their Titan HD manual, but it's still an easy mistake to make in the heat of the monent.

 

Chris

[Jess Haas SOC]

I never said there wasn't a problem with the p-tap on the cinelive. It should not be used in 24v mode.

 

Yes you can fix the problem with all sorts of circuitry or you can do what my sled and Tiffens sleds do and not pull 12v from the second battery.

 

You are the one telling me I am incorrect but if your 12v and 24v lines share a negative then there is no problem. End of story. If both devices have their BNCs connected to this same negative even if one runs at 12v and the other at 24v then there is no voltage potential between the BNC shields because they are tied together. Even the 12/24v lemos on most rigs use a single pin for ground for both voltages.

[Alan Rencher]

Again, Jess, it's not a problem with the shared ground. The problem is when you are using the positive terminal on the first battery without filtering out the ground from the second battery. If you do that, and the two system's respective positive lines come in contact, even when regulated, the floating ground from the second battery will short with the power coming from the 24V line.

[Jens Piotrowski SOC]

ceasefire, thx guys