Fun with USB and Followspots

[StradivariusBone]

Running Light Factory with two Enttec USB DMX Pro dongles. We turned on our 575W Strong HMI followspot last night and both dongles stopped blinking and output froze. We use one for input from an Express and it too stopped showing any signs of life from the console which was working fine.

I was able to replicate it this morning and whenever the lamp was striked (struck?) both USB dongles winked out. LightFactory would still run like normal, but when you tried to exit the program it would lock up as it tried to shut down the DMX processor (conceivably because it was locked up, but still attached).

It turns out that the follow spot was plugged into the same circuit as the computer, unbeknownst to us initially as we thought they were separate. Once we put it on a different circuit the problem went away.

I'm just curious as to the mechanism that would cause this to happen? I understand that the ballast draws the most current when the lamp strike happens and if there's already two clip lights, a computer, two monitors and a lighting console on the circuit, it might overload that circuit briefly.

The lighting computer is on a UPS, but I don't know how those behave with power dips. In any event the alarm never made a sound when we tried the followspot.

It's all working happily now, but made for some tense moments late last night during a tech run.

 

[JChenault]

The enttec is getting power from the computer. I have seen issues where a marginal power supply would make the enttec device quit working. Once it quits you have to reinitialize the device by ( for example ) re starting your control program. It is likely the power drop made the output power momentarily drop causing the issue.

I would suggest that for some cheap insurance, get a powered USB hub. This injects power for the enttec and has been more reliable in my experience.

 

[derekleffew]

Either, or a combination, of: a) Inrush current causing voltage drop, but too fast and short for the UPS to react, and/or b) striking an arc lamp emits massive amounts of momentary RFI which can travel up the line and "contaminate" all other electronics on the circuit or power source.
Ever hear the noise a ringing cellphone makes next to a Clear-Com beltpack?

 

[JD]

And the winner is: Derek!
The amount of RF energy backfed into the supplying circuit from an arc-strike is mind-numbing! This has always been the case. I can remember back in the 80's when a sound tech grabbed his power off of the line feeding our Altman Satellite I (575 HMI) and toasted his board out on strike. I later put a scope on one at the shop and found the backfeed during strike to be in excess of 400 volts peak-to-peak. Now, modern spots don't kick up as much noise, and modern electronics have better filtering, still, I would never want the source of power to be shared.

 

[Amiers]

And USB Powered speakers. I know when I'm getting a text from the speakers before my phone even goes off. It's kind of fun to scare people who walk in ur office and your speakers make the noise and you say your getting a text or a call.

 

[JohnD]

I sometimes miss the fun of the cell phone on the desk next to the CRT monitor, oooooohhhhh pretty lights.

 

[PeteEngel]

Always keep your followspots on separate circuits. Never share followspot circuits with anything else. Clean power is happy power.

 

[StradivariusBone]

I agree! We thought they were separate until last night. We don't find ourselves using followspots frequently and this was the first time since we moved the computer up there. They are now veritably separated.

 

[Matthew Symons]

I have an Enttec dmx pro (for some reason it broke, the input still works). I had a RF fog machine remote, and for some reason when ever I triggered the remote, the DMX dongle would cut out, and I would need to unplug the USB and re plug, I feel as if these dongles must be sensitive to outside noise. I now just use etc nomad/gadget.

 

[n1ist]

I also had issues with the DMX pro and a small AC desk fan. Using a powered USB hub cleared up my problem.
/mike

 

[NewChris]

Always keep your followspots on separate circuits. Never share followspot circuits with anything else. Clean power is happy power.

My high school had two Altman 1000Q, a sound board. Light board, and CRT monitor all on one outlet..... Only blew a fuse once though.

 

[JD]

My high school had two Altman 1000Q, a sound board. Light board, and CRT monitor all on one outlet..... Only blew a fuse once though.

The 1000Q is not an arc lamp so should not be a problem. It is the lamp ignition system that causes all the problems.

 

[PeteEngel]

As JD noted, the Altman 1000Q is not an arc lamp that has a rather high inrush current at lamp strike. But even so, you should take some time to consider your high schools circuit loading as it relates to what you wrote. If you have a standard 15a breaker, you have 1800w load capability. If you have a 20a breaker you have 2400w load capability...
2 1000w followspots = 2000w
1 sound console (unpowered, 16 channel) = 100w +/-
1 light console (small NSI console, 1.8a) = 200w +
1 CRT Monitor (17") = 100w to 200w +/-
or
1 flat screen monitor (17") 40w to 70w +/-

you have a load of 2340w to 2500w.

Just a little math.