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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Just in case anyone else may be interested, I found out that the CPVC pipe I have is "Harvel Corzan 4120". (I believe this stuff is the common type of cpvc found at most hardware and plumbing supply stores).
The manufacturer's data sheet specifies the dielectric loss as a "power factor" of 0.007% @ 1 kHz:
This number seems very low to me...almost too good to be true; especially given that some data sheets for apparently similar material specify the dielectric loss to be more than two orders of magnitude higher:
Because of this, I wrote to the manufacturer, Harvel, asking for a confirmation, i.e., that their number is not a misprint (e.g., should be 0.007 rather than 0.007%), and also asking if there is any data at any higher frequencies.
While waiting for a response, I decided to do a quick test by putting a piece of the cpvc pipe (weighing about 2 ounces or so), into an 1100 watt microwave oven, along with a cup containing about 4 ounces of water.
After about 45 seconds at full power, the water was near boiling (too hot to touch), while the cpvc was just barely warm to the touch...almost imperceptibly, maybe a few degrees above room temperature.
So it may actually be that this particular type of cpvc pipe made by this particular manufacturer is an almost ideal material for bobbins/coil-formers for any kind of high frequency inductor application.
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
1kHz is a pretty low frequency, I think most plastics should have a low loss at that frequency.
With high frequency power transformers, I thought the issue is more in the loss of the magnetic core material.
Edit: Did a quick literature search. This file is probably subscription locked, but it discusses dielectric properties of CPVC:
The takeaway is that for frequencies under 100kHz and temperatures under about 340K, the loss tangent should be under 0.01 for pure CPVC. The loss increases quite a bit with temperature after that point. The loss also steadily increases with frequency to .02 @ 1MHz @ room temp.
They also studied CPVC stabilized with cyanoguanidine, which had quite a bit more loss, starting at .05 for 10kHz 300K, and .02 for 100kHz 300K.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Hello Mattski,
I'm not sure how much you can generalize about the frequency dependence of dielectric loss in plastics.
I've seen data sheets for various plastics suggesting that losses don't vary all that much with frequency. In some cases, IIRC, the dielectric losses actually decrease.
For example, here's a DuPont PVC with dissipation factor specified as 0.060 @ 1 KHz and 0.072 @ 1 MHz; so for this material, a three order of magnitude increase in frequency results in a 20% increase in dielectric loss.
In any case, what I specifically want to know, is: Is it possible that Harvel Corzon cpvc might actually have a "power factor" as low as 0.007% @ 1 KHz? (BTW they didn't reply to my query yet).
If this is the case, this material might be the ideal material for Tesla coils, for example.
Edit:
I've given up on trying to get any information from the manufacturer...they simply refuse to respond to my several queries.
In any case, I did a possibly more useful microwave test by comparing cpvc to pyrex, as the two materials have a similar specific heat capacity.
I put two roughly similar sized pieces of pyrex and cpvc in the microwave for 30 seconds, and compared the temp. rise.
The pyrex was significantly warmer than the cpvc, so I guess I can say that the DF @ 2.45 GHz is somewhat less than 0.005; maybe in the range of 0.003 to 0.004. If cpvc is like pvc in the sense that its DF is significantly lower at microwave frequencies than at audio frequencies, then it's possible that it could be in the range of 0.006 to 0.008 in the freq. range of interest. In light of this reasoning I think the data sheet value of 0.007% is a misprint, and it probably should have been stated as 0.007.
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Dielectric Loss in CPVC
