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Re: [TCML] Concrete Form Secondary Resistance Measurements



Hi Jeff, All,
I would like to know how the Sonotube fairs. I think they make a thick and thinner version in the 22-24" sizes. DC Cox say he removes a layer of the inside tube to get rid of the release agent coated paper.
I would be real interested in your findings!
Jim Mora
-----Original Message-----
From: "Jeff Larson" <jeff@xxxxxxxxxxxxx>
Sent 4/1/2008 8:42:27 PM
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Subject: [TCML] Concrete Form Secondary Resistance MeasurementsI did some resistance measurements on a cardboard concrete form tube
from Home Depot.  Home Depot's brand is "Quick-Tube".  I used a Megger
MIT 430 for the measurements.  It uses up to 1100 volts DC to measure
the resistance.   It was at that voltage for all these measurements.
To do the test I used a caliper set at 0.1 inches lightly scribed 3
pairs of lines on the inside the tube, 3 pairs on the outside where
there was no black ink, and 2 pairs on the black ink.  I made sure that
the caliper did not scrape the ink or surface away as I wanted to be in
contact with it.
I did the test twice.  First test was done about an hour after the tube
had been brought in from the garage where the temp was about 45 degrees
F and 50% humidity.
The second time I did the test the tube had been sitting in the lab for
about 5 hours at 75 degrees F with much lower humidity.  I am assuming
that the tube dried some after sitting in the lab for 5 hours since most
of the values went up.
Here are the values.  The letters indicate the test area.
1st test  after 1 hour inside.
Outside of tube, no ink            Outside of tube on black ink
Inside of tube
a)    4.5 gigohm                              d)  14.5
gigohm                                f)   7    gigohm
b)    8.5 gigohm                              e)   25  gigohm
g)  3.5  gigohm
c)     11 gigohm
h)  2    gigohm
2nd test  after 5 hours inside.
Outside of tube, no ink            Outside of tube on black ink
Inside of tube
a)  20 gigohm                            d)   27
gigohm                                    f)      9.6    gigohm
b)  60 gigohm                            e)   26  gigohm
g)     16    gigohm
c)  30 gigohm
h)     30   gigohm
It seems that the inside has quite low values as compared to the
outside.  The coating on the inside seems to be
heavier.  Humidity seems to have a pretty big part in the values, but
there are a few that changed little where as others changed a lot.  The
ink vs no ink does not show up in this test.  Maybe more data points are
needed.
The same tests should be done with the "Sono-Tube" and the Menards tube.
Jeff
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