Fluorescent lights inrush current, and equipment malfunctioning.

[JHAnd]

Hi,

We have a music studio room at work, where some people claim that when the lights go on the output sound of the sound card/audio interface stops or starts to output a bit crushed type of distortion. Restarting the computer seems to solve the problem.

Lights are connected to a motion detector, so if you sit still in the room the lights go out after a while, and then if you move your arms the lights switch on again... and then the problem above reportedly happens to some users.

I have not been able to recreate the problem after several tries, but there have been several reports.

My working hypothesis is that either:

1. The soundcard stops working at the same time the lights switch on by coincidence and the user interprets this as being the cause, but in reality there was just a bug with the sound card driver or computer.

2. The inrush current when switching on the fluorescent lights cause a voltage drop on the mains, dropping the voltage on the sound card to a level that it can't handle, and it to misbehave for some reason. However I find it strange that I can't reproduce the problem.


What do you guys think?

[Jwillis]

How many fluorescent lights do you have on the circuit.  Can you put the computer on a different circuit than the lights?  What type of ballast is used? Cheap ballasts don't have much current limiting or with zero voltage crossing.

[JHAnd]

How many fluorescent lights do you have on the circuit.  Can you put the computer on a different circuit than the lights?  What type of ballast is used? Cheap ballasts don't have much current limiting or with zero voltage crossing.

I think there are maybe four or five lights?

Only two outlets in the room. Not sure the one with the studio equipment is sharing with the lights but possibly. The only other outlet in the room sits on a panel with auto/off switches for the lights so I would assume this outlet is sharing circuits with the lights.

I have not looked inside the lights, but yes I would assume that they are cheap. Would switching to LED alleviate the problem?


I had a thought just now on why perhaps I can't reproduce the problem. The mains voltage can vary slightly. Perhaps this problem only occurs when the mains is lower then usual, say it is 207V instead of 230V at a particular moment. If someone put the lights on and the mains is low, then the voltage sag because of the inrush current could lower the mains more then the sound card can handle.

So perhaps I could reproduce by putting the studio equipment on a Variac and lower the voltage to 207 V. Then try turn on the lights.

[Jwillis]

Sounds like you need line conditioners and surge protection for your equipment. You can do this with either a UPS or a dedicated line conditioner. I say UPS loosely since theirs a difference between a standby UPS system and a Line-Interactive & On-Line UPS System.

[Doctorandus_P]

If this happened to several people (different customers, independent of each other) then you have a pretty high confidence the problem is real.

And a music studio in which the audio is not reliable is enough to scare away customers, and then they probably won't come back.

For the solution, There is a bunch of options. You could go measure what the real problem is, and then fix it (The amount of noise is likely very much dependent on the phase angle at the moment the lighting turns on). Or you can (semi) randomly try some things that probably work. Is it possible to put the lighting on another phase then the PC? A UPS should work, but is overkill. Maybe a few mains filters? Or just don't switch the lights at all but leave them on.