FlexWatt Help

[Will]

So I'm cleaning all the shelves tonight and I start hearing this buzzing sound when wiping off the heat tape. Turns out that when I put my hand across the heat tape I can hear a faint buzzing sound, kinda like the sound a current would make. This was somewhat troubling. Probably not the safest way to find this out, but it makes no electrical "buzzy" feeling when I do this, but if the room is totally quiet and you put your ear right next to the tape, you can hear this buzzing. I'm sure I can hear it, although it is really faint.

I'll describe what I have, but I've also got photos, since those are more useful. I connected the tape using O-ring connectors and drilling a screw into the melamine shelves. I completely sealed the screws in silcone sealant and taped everything up - both ends of the flexwatt. The flexwatt is held down using foil tape, and the thing is, is that the sound only occurs when touching the 2 strips of foil tape, not when touching the two sides that aren't covered in foil tape. Is it possible for the foil to be drawing a current through the flexwatt's plastic coating...? I covered over the flexwatt's metal conductor strips, even though there shouldn't be anything exposed there, but it still buzzed when I put foil tape back on. I double checked all possible exposed ends(don't worry, I unplugged it all first ;)) and made sure the foil tape was nowhere near anything that could be exposed, and made sure the plug connection was totally insulated and still with the buzzing... :confused:

I dug out a digital multimeter, but I haven't played with one of those since Grade 12 Physics, and I really question my focus in that class to begin with. I played with all the settings, but got some sort of reading on only one of those settings, so I snapped a pic of it, figuring someone here'll know what that means :D

Anyways, here's some photos, maybe someone here can help...

Here's the whole length of shelf. Again, I can only hear the buzz when I touch the two sides of foil tape, and I only got the reading on the mutimeter on the foil, not the other uncovered strips.
http://www.ssnakess.com/photopost/data/500/2033Untitled-2-med.jpg

Here is a closeup of the plug connection with most of the elecrical tape taken off.
http://www.ssnakess.com/photopost/data/500/2033Untitled-3-med.jpg

Photo of the multimeter. I played with most setting and in various spots. This was the only reading I got. Again, I can't feel anything, but could hear a buzz, so I dug this out to give me something else to work with.
http://www.ssnakess.com/photopost/data/500/2033Untitled-4-med.jpg

This is kind of dark, and I'm not sure if this helps any, but here is exactly how the rubbermaid sits on the shelf. It only covers 1/2 of the tape.
http://www.ssnakess.com/photopost/data/500/2033Untitled-1-med.jpg

[ChristinaM]

this is what I got from hubby:

1. How are you taking the readings with the meter? Where are you putting the probes?

One probe needs to be grounded, the other on the place you are testing. If anything is leaking, it will be AC Volts...( the selection on the meter directly to the right of the off)

2. In laymans terms, hydro makes noise. It is possible that when you are pressing the foil tape, the sound is amplified ( the hydro making the tape vibrate )

HTH

[Stockwell]

Your installation looks fine.
The noise you hear is the result of the chopped waveform you're feeding it from a dimmer.
You didn't say you had a dimmer, but I bet you do right? And it's probably set about half way right?
This is the same type noise you hear when you sometimes dim lights. In that case the filament is resonating.
In this case the heat tape is resonating and the wood its on and surrounding tape is acting like a baffle and acoustically amplifying the sound. If you turn your dimmer up and down, the amplitude and frequency will change.
See dimmers work by chopping the AC waveform, and that chopped current has very fast rise and fall times, and that can actually cause the load to "sing"

Cheap dimmers cause this trouble more than the full range 20 dollar ones, but don't worry about the noise. If you turned the dimmer up full it would go away.
You could try a more expensive dimmer or just live with it.

[Will]

1. How are you taking the readings with the meter? Where are you putting the probes?

One probe needs to be grounded, the other on the place you are testing. If anything is leaking, it will be AC Volts...( the selection on the meter directly to the right of the off)

I just had one probe in each strip of foil tape, so I may not be doing it the right way to find anything out.

Stockwell:

Yes, I am using dimmers I bought from Home depot although they are set down near off, maybe 1/8 of the way up. If that's the case though, why is it that I only hear it when I make a connection between trhe two strips of foil tape...? If I do it on the spots w/o foil, I get nothing. This is what worried me in the first place as it seemed to me that if it were onky between two pieces of conductive materials(foil) I thought there was some sort of curcuit I was closing with my hands, which could lead to a risk of a short.

Thanks for your help guys.

[crazyboy]

its prolly the dimmer because they make noise. that was the first thing that came to mind when i was reading your post.

[Stockwell]

Hey Will, connecting the tape other than through the internal silver side foil buss runners doesn't provide power to the entire strip, therefore less current flows, and that would naturally result in less sound because most of the heat tape wouldn't be connected.

When properly connected, current flows across the black conductive ink from one silver buss runner to the other.

The black stuff is conductive graphite ink and is the resistive heater and fairly high resistance, so you never want to make your primary connection by penetrating the black part, as it will remove 120 from the rest of the buss runner and restrict flow to the rest of the tape, reducing the overall wattage and heat .
If you connect that way, you might remove the noise, but you wont have much heat either.
All of the black runs(the zebra stripes) must see 120v across them at all points along the tape. This is accomplished by only making connection to each opposite internal foil buss.(at one end only& insulate the other end)

By the way, you wont be able to correctly read that voltage with a meter if the dimmer is controlling it , as the chopped waveform from the dimmer will screw up your reading. AC Meters are designed to read sine waves only. A meter is of little use here.

You need to be careful using foil duct tape to hold down your heat tape because it's electrically conductive, and is a potential shock hazard if you accidentally connect it to line by screwing through it.
Your connection looks OK in the pic, but realize that the stick down tape must never inadvertently make contact to any exposed live parts.
Make sure you don't screw through anything other than the silver buss inside the heat tape. This connection should never be made through the duct tape if it's conductive.
Using standard fabric non conductive duct tape is actually much safer, and it should just cover the edge enough to hold it down.

Try hooking it up as described and turn the dimmer up full to remove the chopped waveform.
If the sound disappears, it's as I described earlier, and there is little you can do about it, other than try a more expensive dimmer.
Another thought is you might try repositioning the tape so that it only contacts the outside margin without overlapping onto the black part so much. It's the black part that is resonating, so anything contacting that might be adding to the "speaker effect"

The 20-30 dollar full range slide dimmers have better electronics and better RF hash filters than the cheaper 6 buck jobs. You might find it makes a difference, but I can't guarantee it.

The other advantage to using the more expensive dimmers is that they will restart after a power outage.
When you get yours set up for the correct temp, try unplugging it and plugging it back in. If you are using it less than 40%, and it's a cheaper dimmer, you'll find it wont turn back on until you turn it up....This little glitch leaves lots of herps cold after even 1 second power failures.
Using the slightly more expensive "full range" dimmers will prevent this. Ie they come back on after a power failure, even if set down near zero

regards