Plug-in AC noise filter?

[Anonymous user]

I recently installed another SUA1500 in my living room to sit between my entertainment center and the incoming AC power. I have had the first SUA1500 in my network/server rack in my basement for a couple of years now. Anyway, the living room SUA1500 began emitting a very loud buzz a few hours after I plugged it in and plugged my loads into it. After some investigation, I discovered that the UPS only buzzed when plugged into line power and only when the exterior lights were turned on (a string of 27-watt compact fluorescent bulbs on an electronic time switch). When the house was built, the electrician put the exterior lights on the living room circuit instead of pulling a separate circuit.

Anyway, due to the way the wires are run (all in exterior wall cavities -- packed with insulation and not easy to access from below or above), I cannot easily run a new circuit to the area behind my entertainment center, nor can I get a new feed to the exterior light switch box, so I am faced with only one option -- noise filtering.

Does anyone know of a (relatively inexpensive) product that I could plug in between my living-room UPS and the receptacle it is plugged into? I tried putting an APC SurgeArrest in-line, but there was no change. I don't know if those surge strips even do filtering anyway. I'd like to avoid spending any more than $50 or so on this -- I just didn't know if any of the ones you can find at Smarthome.com or similar places would do what I need.

Here's an example of a 15A plug-in filter. It is intended to improve X10 signal distribution, but would it also filter out noise generated by electronic ballasts?

http://www.smarthome.com/4845acf.HTML

Thanks,
Chris

[TheNotoriousKMP_apc]

Hello,

As far as upstream Noise Filtering, I would recommend APCAV products, however, I don't really think that would solve the problem. I think to solve the issue of the filtering, you're going to have to go, as you pointed out, towards the route of the Smarthome filter. However, pertaining to the ballasts, I am not sure that it would work in conjunction with that, since the ballast is what's causing the problem, where the filters are filtering noise from other appliances. Is the UPS at least three feet away from the equipment? Is there a possibility of electromagnetic distortion that could be causing this?

[Anonymous user]

It appears the electronic timer + CFL is causing half-wave rectification, therefore adding a 2nd harmonic(DC bias) on the line which will cause the transformer to hum. Consumer grade electronic timers often advise you against using anything but a regular light bulb with it.

* Try bypassing the electronic switch with a regular one.
If that doesn't fix it..
* Try changing ALL the CFLs with regular light bulbs.

There's a good chance both electronic switch + regular bulbs or regular switch + CFLs would fix the problem.

You can either then just live with it that or have an electrician put in a commercial grade timer switch approved for fluorescent lights if you really want to use CFLs. You'll likely need an electrician to do it for you, as fluorescent rated switch often requires a neutral to be run to the switch box.

Let us know how it turns out.

[Anonymous user]

That's what I was afraid of -- the combination between electronic ballasts and the timer. I don't think EMI is a factor since the UPS and the receptacle it is plugged into are 25+ feet away from the nearest outdoor light and 30+ feet away from the switch.

Interestingly enough, the timer is intended to control fluorescent lights, but it is only a residential timer. I do, however, have neutrals in all of my switch boxes, so I could install a higher-grade time switch if the in-line filter doesn't stop the buzz. I don't want to switch to incandescent because I really like the CFL's for their light quality and energy use properties.

Hopefully the in-line noise filter will do the trick -- I know I'm using it in the reverse of the way it is intended, but if it is actually an isolation transformer, then it shouldn't matter, correct?

If not, I believe I will try to pull a separate circuit for the AV stuff. I don't understand it, but devices on other circuits aren't experiencing the noise, suggesting that the panel is actually blocking the noise from being transmitted to the other circuits.

Thanks for the help,E

[TheNotoriousKMP_apc]

I wasn't suspecting that it was anywhere near the lights or the switch. I was shooting more towards being near a high-quality television/monitor, or audio equipment.

[Anonymous user · Accepted solution]

In Europe, they have a law that prohibits appliances that produces excessive harmonics. There is no filter that will remove harmonic distortion and short of eliminating the source, you can't correct it. This is why power companies don't like it.

As I said before, bypass the timer switch with a mechanical switch and verify that this corrects the problem. Residential two-wire electronic switch maybe rated for fluorescent, but they often don't work well with electronic ballasts.

Order a 3 wire (one with neutral) commercial grade timer switch after you verified the above corrects your problem.