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Author Topic: Strange current draw readings  (Read 5746 times)

DavidTurner

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Strange current draw readings
« on: July 31, 2016, 06:28:48 PM »

I had an unusual situation last night that I'm trying to figure out.

The club we were playing had only one three phase 400 amp disconnect so we had to run lights, video and audio all on the same service. Lighting was all led and movers. Sound was a small rcf line array with 6 subs all self powered plus my rig - two digital consoles, iems and backlne.

We were connected to the service in this order:
Disconnect- video distro, lighting distro, sr pa distro, sl pa distro, my distro which powered our console, backline and a few of the movers.
During soundcheck we made sure to run everything up full while I observed the ammeters to insure that we wouldn't exceed capacity since the movers we carry were powered by my distro.
The ammeters on my motion labs distribution unit showed periodic jumpin current draw on one leg only. This jump on the ammeter was accompanied by a corresponding jump in voltage on the neutral. After soundcheck I continued to monitor current draw to see what might becausing this jump. The strange thing is that the current draw on that leg continued to periodically jump from zero to 24 amps with nothing running.

I disconnected all backline and monitor rig cables fed by that leg yet the periodic current burst continued. I tried a different cabe/quad box for monitors as well as unplugging items im racks one at a time - nothing changed! I moved monitors to another circuit on a different leg as a precautionary move and then the current burst would alternate between legs 2 &3.

I would add that the ammeters I was observing were on my distro that was the last in line. The video distro, first in line, showed a similar burst. The other distros had no ammeters installed. We checked at my end with an inductive ammeter and confirmed that my ammeter was accurate.

We played the show with no ill effect, yet I am still puzzled about what may have been causing this anomaly.
« Last Edit: July 31, 2016, 06:48:11 PM by DavidTurner »
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Stephen Swaffer

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Re: Strange current draw readings
« Reply #1 on: July 31, 2016, 10:14:02 PM »

Define "nothing running"?

Since moving the monitors chnaged the symptom, I would say you were getting warm.
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Steve Swaffer

DavidTurner

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Strange current draw readings
« Reply #2 on: July 31, 2016, 10:21:02 PM »

Define "nothing running"?

Since moving the monitors chnaged the symptom, I would say you were getting warm.

 As in the power drop to the monitor rig disconnected, the only stage circuit on that leg also disconnected, no music playing through the pa, nothing on the video screen and no lights illuminated.
« Last Edit: July 31, 2016, 11:07:48 PM by DavidTurner »
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Mike Sokol

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Re: Strange current draw readings
« Reply #3 on: August 01, 2016, 08:44:12 AM »

As in the power drop to the monitor rig disconnected, the only stage circuit on that leg also disconnected, no music playing through the pa, nothing on the video screen and no lights illuminated.

I wonder if the monitor amps were going into some sort of ultrasonic oscillation as described in this other thread? http://forums.prosoundweb.com/index.php/topic,160189.0.html

And when you say "periodic" was it a repeatable time? So every 10 seconds, or 30 seconds, or 2 minutes or what? Or was it more random, sometimes every 30 seconds, sometimes every 5 minutes? For instance, I once had seemingly random noise bursts on my PA in a bar that seemed to be more frequent after each dance song and when we took a break. After much troubleshooting we found that all the outlet grounds on  stage were tied together along with the outlet for the cash register. However, the outlet grounds were never bonded to the service panel ground so they were all floating together. When the patrons were done with a fast dance they all ran to the bar for a drink, and every time the cash register made a sale the old-school solenoid on the drawer put a voltage spike in the outlet ground, which went right in my PA system ground and produced a big pop and buzz noise. It appeared to be random, but the noise burst was tied to another non-random event. I've also been in a few old bars with flickering neon beer lights on the wall, and every flicker would make my guitar player's amp buzz with a quick noise burst.

Now imagine any of these cases creating ultrasonic noise bursts feeding big amplifiers. And if you were metering them you would see a big current spike. 

My point is that documenting the period of an event can give you a clue as to its source. There are very few truly random events. Most of them are caused by something we haven't observed directly which confuses us. Consider that before Nicolaus Copernicus  stated “We revolve around the Sun like any other planet.” there were a lot of crazy calculations required to explain why the planets seemed to move in strange ways, sometimes appearing to go backwards. Early astronomers didn't have the concept of the sun being the center of the solar system, with all the planets orbiting about it. 

Troubleshooting problems is getting to be a lost art since it takes time we often don't have. But it's time well spent.

« Last Edit: August 01, 2016, 09:43:09 AM by Mike Sokol »
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DavidTurner

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Strange current draw readings
« Reply #4 on: August 01, 2016, 11:13:54 AM »

The burst continued with the monitor rig completely disconnected from the distro. At first it seemed to go away when I disconnected the monitor rig. That's when I tried a new cable/quad box combo - then disconnecting things in the rack including the ups and power strip. Then it came back while the entire monitor rig was unplugged as well as the backline on that leg.
The bursts were frequent, but seemingly irregular. I did not think to time them. They were, perhaps, 10 to 20 seconds apart.

BTW: All iems - no power amps.

At any rate, tomorrow is a different venue. It will be interesting to see if the anomaly returns.
« Last Edit: August 01, 2016, 12:16:16 PM by DavidTurner »
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Ike Zimbel

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Re: Strange current draw readings
« Reply #5 on: August 01, 2016, 12:14:48 PM »

The burst continued with the monitor rig completely disconnected from the distro. At first it seemed to go away when I disconnected the monitor rig. That's when I tried a new cable/quad box combo - then disconnecting things in the rack including the ups and power strip. Then it came back while the entire monitor rig was unplugged as well as the backline on that leg.
The bursts were frequent, but seemingly irregular. I did not think to time them. They were, perhaps, 10 to 20 seconds apart.

BTW: All iems - no power amps.
I wonder if it was something happening elsewhere in the building. Years ago, I ran into a problem at a three day folk festival that I was mixing FOH for. Every year, on the last day, towards the end of the day, the PA would cut out for a second or so, seemingly at random, but usually more often as the day wore on. This one took at least a couple of years to track down, with a few red herrings along the way that looked like they might be the issue but weren't. Ultimately it turned out to be the air conditioner on one of the rented trailers being used backstage for offices. By the 3rd day of people constantly going in-and-out of this trailer, the compressor on the a/c unit would ice up, and every time it tried to start up it would cause a voltage sag to the whole power distribution for the stage area. In that case, the key to finding the issue was having someone with some knowledge and some spare time wandering around backstage trying to track down the fault.
iz
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DavidTurner

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Re: Strange current draw readings
« Reply #6 on: August 01, 2016, 12:19:29 PM »


I wonder if it was something happening elsewhere in the building. Years ago, I ran into a problem at a three day folk festival that I was mixing FOH for. Every year, on the last day, towards the end of the day, the PA would cut out for a second or so, seemingly at random, but usually more often as the day wore on. This one took at least a couple of years to track down, with a few red herrings along the way that looked like they might be the issue but weren't. Ultimately it turned out to be the air conditioner on one of the rented trailers being used backstage for offices. By the 3rd day of people constantly going in-and-out of this trailer, the compressor on the a/c unit would ice up, and every time it tried to start up it would cause a voltage sag to the whole power distribution for the stage area. In that case, the key to finding the issue was having someone with some knowledge and some spare time wandering around backstage trying to track down the fault.
iz

I wondered about that. The three phase service had been recently installed at the request of the production company. Allegedly there were no other loads on it.
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DavidTurner

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Strange current draw readings
« Reply #7 on: August 01, 2016, 12:21:34 PM »

I wonder if the monitor amps were going into some sort of ultrasonic oscillation as described in this other thread? http://forums.prosoundweb.com/index.php/topic,160189.0.html

And when you say "periodic" was it a repeatable time? So every 10 seconds, or 30 seconds, or 2 minutes or what? Or was it more random, sometimes every 30 seconds, sometimes every 5 minutes? For instance, I once had seemingly random noise bursts on my PA in a bar that seemed to be more frequent after each dance song and when we took a break. After much troubleshooting we found that all the outlet grounds on  stage were tied together along with the outlet for the cash register. However, the outlet grounds were never bonded to the service panel ground so they were all floating together. When the patrons were done with a fast dance they all ran to the bar for a drink, and every time the cash register made a sale the old-school solenoid on the drawer put a voltage spike in the outlet ground, which went right in my PA system ground and produced a big pop and buzz noise. It appeared to be random, but the noise burst was tied to another non-random event. I've also been in a few old bars with flickering neon beer lights on the wall, and every flicker would make my guitar player's amp buzz with a quick noise burst.

Now imagine any of these cases creating ultrasonic noise bursts feeding big amplifiers. And if you were metering them you would see a big current spike. 

My point is that documenting the period of an event can give you a clue as to its source. There are very few truly random events. Most of them are caused by something we haven't observed directly which confuses us. Consider that before Nicolaus Copernicus  stated “We revolve around the Sun like any other planet.” there were a lot of crazy calculations required to explain why the planets seemed to move in strange ways, sometimes appearing to go backwards. Early astronomers didn't have the concept of the sun being the center of the solar system, with all the planets orbiting about it. 

Troubleshooting problems is getting to be a lost art since it takes time we often don't have. But it's time well spent.

On second thought, could have been one of the pa amps. We didn't disconnect them as they were fed up stream of my distro
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Stephen Swaffer

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Re: Strange current draw readings
« Reply #8 on: August 01, 2016, 12:50:36 PM »

I wondered about that. The three phase service had been recently installed at the request of the production company. Allegedly there were no other loads on it.

A new transformer/meter/disconnect or just a new 3 phase disconnect?  We often view power systems in buildings as isolated-but they are far from that.  Most utilities have fairly stringent rules on motor size to prevent customers from affecting others-rules that often really can't be enforced.  That said, I could see an outside/upstream event causing voltage fluctuations-but a 24 amp current draw is pretty significant and it would have to go through some piece of gear on your setup.  A missing leg or even a bad connection on a leg (not unheard of on even a new setup) can cause imbalance and unusual neutral readings and current.  A bad/missing neutral connection can cause the same symptoms.  The real danger being that they can cause an overvoltage on a piece of gear and ultimately damage something.
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Mike Sokol

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Re: Strange current draw readings
« Reply #9 on: August 01, 2016, 12:55:19 PM »

I wonder if it was something happening elsewhere in the building....

By the 3rd day of people constantly going in-and-out of this trailer, the compressor on the a/c unit would ice up, and every time it tried to start up it would cause a voltage sag to the whole power distribution for the stage area. In that case, the key to finding the issue was having someone with some knowledge and some spare time wandering around backstage trying to track down the fault.


This is exactly my point. In order to troubleshoot a problem you have to look beyond the immediate area. For instance, I would sometimes have the circuit breakers trip during my live church-sound seminars. In at least a few of the cases the kitchen staff had plugged their big 1,800 watt coffee urns into the same outlet that was feeding my video projector. And you guessed it, without cool down time one of my $600 projector bulbs blew up. Ugh... 

Temp and wind can also play a factor. In one of my day jobs as an engineer we had the alarm system tripping on a random basis. This went on for weeks until the security guys got mad enough to call in engineering. It seemed to happen more when it was hot outside, so by logging the time and temp of each occurrence I was able to zero in on the problem. It was indeed heat, but only when the wind was blowing. I guessed that a wire was pinched somewhere in the million square foot warehouse, and we finally traced it down to a wire run between a support I-beam and the sheet metal on the outside of the building. When it got hot outside the metal expanded enough to pinch the wire insulation nearly through. At that point a strong wind could now short it out momentarily and set off the alarm. Took a few month to figure this one out, but the fix was to re-run that piece of signal wire properly and apply a little e-tape.   
« Last Edit: August 01, 2016, 12:59:47 PM by Mike Sokol »
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DavidTurner

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Re: Strange current draw readings
« Reply #10 on: August 01, 2016, 01:59:00 PM »

A new transformer/meter/disconnect or just a new 3 phase disconnect?

We traced the install all the way to the pole. It all seemed to be brand new conduit. There had only been single phase service at this club before. That would seem to indicate a new transformer as well.

Quote

A bad/missing neutral connection can cause the same symptoms.  The real danger being that they can cause an overvoltage on a piece of gear and ultimately damage something.

I watched the production company connect his tails. He gave each a good tug to make sure they were secure. We went back to each cam lok junction and made sure that each was securely tightened. I also kept an eye on the volt meters. They hovered between 115 and 121.

I moved the monitor rig to another circuit on a different leg leaving only the bass player's wireless, the tracks rack and the drum thumper on leg three thinking that we could continue the show without any of those things. After moving the monitor supply, the surge would alternate between the legs...
« Last Edit: August 01, 2016, 03:08:45 PM by Mike Sokol »
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Ike Zimbel

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Re: Strange current draw readings
« Reply #11 on: August 01, 2016, 04:06:14 PM »


We traced the install all the way to the pole. It all seemed to be brand new conduit. There had only been single phase service at this club before. That would seem to indicate a new transformer as well.

I watched the production company connect his tails. He gave each a good tug to make sure they were secure. We went back to each cam lok junction and made sure that each was securely tightened. I also kept an eye on the volt meters. They hovered between 115 and 121.

I moved the monitor rig to another circuit on a different leg leaving only the bass player's wireless, the tracks rack and the drum thumper on leg three thinking that we could continue the show without any of those things. After moving the monitor supply, the surge would alternate between the legs...
That should rule out a problem with your connections, but I have seen issues with compression fittings between the transformer and the mast either go bad, or not be made properly in the first place. Likewise, any connection inside the panel upstream of where the tails tie in could be loose. I think that if any piece of your gear was causing 24 amp voltage swings, it would have blown up already. I would guess that it might be difficult to isolate all the equipment used on this gig and power it up the same way at another location (like the production company's shop), but that would be one thing to try. Failing that, I would recommend that the installation be inspected thoroughly, from the pole to the stage.
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DavidTurner

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Re: Strange current draw readings
« Reply #12 on: August 01, 2016, 05:17:39 PM »

Thank you all for your replys. It is unlikely that we will play this club again this year. We are at a different venue 800 miles away tomorrow. I will, at least, keep a watchful eye on mu gear to see if the issue repeats.
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DavidTurner

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Re: Strange current draw readings
« Reply #13 on: September 15, 2016, 06:56:43 PM »

Update: Since starting this thread we have played a variety of venues - clubs, fairs, festivals, theaters - the issue has never recurred. I suppose we can rule out any of my gear
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Re: Strange current draw readings
« Reply #13 on: September 15, 2016, 06:56:43 PM »


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