Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

"Jim Lux" wrote in message
...
Copper sulfate in water makes a nice resistor, too. It's used a lot for
"energy dump" resistors in pulse power applications.

From a theoretical standpoint, copper sulfate solutions should increase
their resistance with frequency more rapidly than the sodium and ammonium
chloride solutions used in the ARRL article. This is mainly due to ion
mobiity in solutions.

The power limiting thing on resistors like this is the packaging. If
you put it inside PVC pipe, then the thermal resistance of the PVC
limits how fast you can get the heat out (and the maximum temperature,
too)

Heat transfer was the primary reason for using transformer oil or mineral
oil in the old Heath Cantenna. Without the oil, the Globar carborundum
resistor would rapidly overheat. With the oil, the resistor could could
dissipate 200 watts continuously. If you started with room temperature
mineral oil, it could dissipate a kilowatt for about a minute before the
oil got too hot and reached the flash point. Medicinal mineral oils have
an open-cup flashpoint between 171 and 221 ºC depending on the specific
manufacturer, while that of technical grade oils is somewhat lower. Of
course, Heath suggested removing power to the Cantenna when it reached 60
ºC [the temperature at which the can is too hot to touch continuously].
At the time the HN-31 was produced, transformer oils generally contained
polychlorinated biphenyl (PCB) additives which reduced their
flammability. This is why Heath rated the Cantenna at 1 KW for ten
minutes or less when it was filled to the proper level with transformer
oil.

I have a Bird dummy load rated at 1 kW continuous. It has a larger
resistive element, still immersed in oil. However, the case is finned to
help dissipate the heat.

Jim is quite correct about the PVC pipe limiting the heat transfer. I
would suggest using power chip resistors. Digi-Key carries Bournes chip
resistors rated at 50 ohms and 100 watts for less than $8 each.

73, Dr. Barry L. Ornitz WA4VZQ

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

Nordic Breeds WA4VZQ wrote:
"Jim Lux" wrote in message
...
Copper sulfate in water makes a nice resistor, too. It's used a lot for
"energy dump" resistors in pulse power applications.

From a theoretical standpoint, copper sulfate solutions should increase
their resistance with frequency more rapidly than the sodium and ammonium
chloride solutions used in the ARRL article. This is mainly due to ion
mobiity in solutions.


Copper sulfate is popular because it is compatible with copper
electrodes, too. Sodium chloride tends to corrode the electrodes.

There might also be some difference in solubility, which would affect
the range of resistances available.

http://home.earthlink.net/~jimlux/hv/rwater.htm has a discussion of
building water resistors for HV applications.

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

On Mon, 06 Dec 2010 16:52:21 -0500, Nordic Breeds WA4VZQ rearranged some
electrons to say:



Jim is quite correct about the PVC pipe limiting the heat transfer. I
would suggest using power chip resistors. Digi-Key carries Bournes chip
resistors rated at 50 ohms and 100 watts for less than $8 each.

73, Dr. Barry L. Ornitz WA4VZQ


Amen on the thick-film chip resistors. I built a 200W dummy load using
two 100 ohm 100W devices in parallel.

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

On Dec 5, 8:13*pm, "Nordic Breeds WA4VZQ"
wrote:
"No Spam" wrote in message

...



I have dremmel-tooled open a used dried-out water filter cartridge from
my fridge that contained a hollow carbon shaft about 10" long and 3" in
diameter with a 3/4 inch hollow inside diameter. The end to end
resistance was about 600ohms. The carbon shaft is a bit soft and
crumbles
under the pressure of tools. This was how I destroyed the first unit I
played with in trying to make it 480ohms by trimming the ends.

Using another filter, I encapsulated the carbon shaft inside a sewer
tube. (Denser PVC and hopfully more impervious to heat) I attached
conductors to the ends using flat washers with springs and left vent
holes in the PVC end caps when I attached them to push it all together.
I
did not attempt to trim the resistance by shaving the length. The
modules
finished resistance measured ~590ohms.

Since this WAS a used water filter, I ran some HV through it to heat it
up a bit to see if it would vent gas or smoke. The resistance decreased
a
bit as it heated but returned to near 600ohms when it cooled. I kept
the
power to less then 100w using my bench HV power supply. After about 1
minute, the PVC started to feel warm but no smoke was seen though it
did
stink a bit.

The whole PVC module I made sweeps out flat from 1Mhz (bottom of my
test
gear) to ~40Mhz where I think my wiring started having some effects. I
had to use springs on the ends to push the contact washers up against
the
carbon shaft and suspect I need to come up with something better here.
Also, the pressure of the springs and end caps varied the resistance
about 20 ohms.

I have run about 400w avg for several minutes into the load under voice
and so-far the damn thing is still hanging on the T2FD antenna and
loads
just fine. In usage, the resistance varied about 50ohms upward in the
last several months of tracking it. I hope to remove the resistor
shortly
and inspect if there is any chemical reaction with the steel washers
and
the carbon rod ends. I need some better way to make this contact and
also
some way to increase the surface area of the contact to stabilize and
perhaps reduce the resistance. I'm thinking copper pipe endcaps heated
up
and cooled over the ends either on the outer diameter or on the inside
hollow part of the carbon shaft.

/****/
Another idea I just had is perhaps having someone with a ceramics oven
paint on the endcaps with ceramic glaze. It would look like a giant
ceramic resistor! *But then again, I would guess that as the resistor
heated up, it would crack. * Never mind...
/****/

I now have another filter module to dissect. I hope to come up with a
better way to mount contacts to the carbon shaft and some way to assure
a
nice airflow around and hopefully through it to allow for higher power.

In retrospect, with the amount of time and work I've put into this
resistor project, I would have been better off purchasing the buxcomm
resistors for $25. (I have one) * But then again, I had fun playing
with
this too! If anything, ideally, I hope to come up with something that
weighs half the weight of the buxcomm resistor so my T2FD antenna looks
more graceful under the burden of the resistor. :-)

The water cleaner cartridge is activated charcoal with a small amount of
organic binder. *It is not graphite as graphite will not function to
clean the water. *Activated charcoal has an extremely large surface area
which adsorbs contaminants. *Depending on how it is produced, a gram of
activated charcoal can have from 100 to 1000 square meters of surface
area.

Your idea of a metallic ceramic glaze will not work as the glaze is a low
temperature melting glass (usually a lead glass) with fine metallic
particles in it. *Once fired, the glass melts, but the metallic particles
are still insulated from each other.

You can buy conductive copper, nickel, and silver based paints for
repairing printed circuit boards. *GC Electronics sells small bottles of
silver print paint (Part No. 22-024 1 troy oz. Bottle) which has a
surface resistivity of 0.1 ohms per square, and nickel print paint (Part
No. 22-207 2 fl. oz. Bottle) which has a surface resistivity of 5 to 6
ohms per square. *Be extremely careful when diluting these paints. *Use
only chemically pure solvents as any oil or other such material in the
solvent will serve to insulate the particles from each other. *GC Part
No. 10-4102 Polystyrene
Q-dope thinner (toluene) might be suitable. *I would suggest the nickel
print paint as the silver print is quite expensive. *Heed the warnings in
the respective MSDS's for these products.

Another alternative is to have the ends of the activated charcoal rod
electroplated. *A thin copper flash film applied to each end, followed by
a thicker conventional electroplate would give you contacts that could be
soldered to. *If there is someone in your area that does electroless
nickel plating, this would also be suitable.

An entirely different approach would be to use a conductive liquid for
the resistance. *An old QST article in June, 1965, entitled "Aqueous
Dummy Loads" by Alexander Marion, W2CUE (now a silent key, I believe),
should give you some ideas.

* * 73, Dr. Barry L. Ornitz * * WA4VZQ

Yes, I had a friend who was in the Navy during WWII, he described how
they used buckets of salt(sea) water for dummy loads. The further you
put the electrode in the bucket the lower the resistance.

Jimmie

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

On Dec 8, 12:25*pm, Jim Higgins wrote:
On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No Spam
wrote:

Another idea I just had is perhaps having someone with a ceramics oven
paint on the endcaps with ceramic glaze. It would look like a giant
ceramic resistor! *But then again, I would guess that as the resistor
heated up, it would crack. * Never mind...

I'd guess the high heat used to fire ceramics would simply cause the
carbon to burn up.

In the Navy, the shipyards all have a device called a Load Bank. It's
a
large metal tank on an insulated vehicle. The tank is filled up with
salt water and electrodes lowered into it to test the output of the
ship's
generators. Any chance that it has ham applications? I intend to try
it
first with an antenna analyzer and then, if it looks promising, my rig.

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

On Dec 9, 12:42*am, "Sal M. Onella" wrote:
On Dec 8, 12:25*pm, Jim Higgins wrote:

On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No Spam
wrote:

Another idea I just had is perhaps having someone with a ceramics oven
paint on the endcaps with ceramic glaze. It would look like a giant
ceramic resistor! *But then again, I would guess that as the resistor
heated up, it would crack. * Never mind...

I'd guess the high heat used to fire ceramics would simply cause the
carbon to burn up.

In the Navy, the shipyards all have a device called a Load Bank. *It's
a
large metal tank on an insulated vehicle. The tank is filled up with
salt water and electrodes lowered into it to test the output of the
ship's
generators. *Any chance that it has ham applications? *I intend to try
it
first with an antenna analyzer and then, if it looks promising, my rig.

Yes they did the same with transmitters, often all you need was a
metal mop bucket and a piece of copper pipe.

Jimmie

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

On 12/9/2010 7:56 AM, JIMMIE wrote:
On Dec 9, 12:42 am, "Sal M. wrote:
On Dec 8, 12:25 pm, Jim wrote:

On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No
wrote:

Another idea I just had is perhaps having someone with a ceramics oven
paint on the endcaps with ceramic glaze. It would look like a giant
ceramic resistor! But then again, I would guess that as the resistor
heated up, it would crack. Never mind...

I'd guess the high heat used to fire ceramics would simply cause the
carbon to burn up.

In the Navy, the shipyards all have a device called a Load Bank. It's
a
large metal tank on an insulated vehicle. The tank is filled up with
salt water and electrodes lowered into it to test the output of the
ship's
generators. Any chance that it has ham applications? I intend to try
it
first with an antenna analyzer and then, if it looks promising, my rig.

Yes they did the same with transmitters, often all you need was a
metal mop bucket and a piece of copper pipe
Jimmie

A water load bank is good for hundreds of KW at 60hz.

For use with a pair of 6146's we used to wire a lamp to a coax
connector. We had a load as well as visual indication of the relative
power output.

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

On Dec 9, 1:51*pm, Jim wrote:
On 12/9/2010 7:56 AM, JIMMIE wrote:





On Dec 9, 12:42 am, "Sal M. *wrote:
On Dec 8, 12:25 pm, Jim *wrote:

On Sun, 5 Dec 2010 21:28:56 +0000 (UTC), No
wrote:

Another idea I just had is perhaps having someone with a ceramics oven
paint on the endcaps with ceramic glaze. It would look like a giant
ceramic resistor! *But then again, I would guess that as the resistor
heated up, it would crack. * Never mind...

I'd guess the high heat used to fire ceramics would simply cause the
carbon to burn up.

In the Navy, the shipyards all have a device called a Load Bank. *It's
a
large metal tank on an insulated vehicle. The tank is filled up with
salt water and electrodes lowered into it to test the output of the
ship's
generators. *Any chance that it has ham applications? *I intend to try
it
first with an antenna analyzer and then, if it looks promising, my rig..

Yes they did the same with transmitters, often all you need was a
metal mop bucket and a piece of copper pipe
Jimmie

A water load bank is good for hundreds of KW at 60hz.

For use with a pair of 6146's we used to wire a lamp to a coax
connector. We had a load as well as visual indication of the relative
power output.- Hide quoted text -

- Show quoted text -

I built a wattmeter of sorts around a circuit like that. After tuning
up the transmitter to light bulb dummy load I would measure the
resistnace of a photo resistor exposed to the light then see how much
60Hz AC voltage and current took to light the lamps to the same
brillance.

Jimmie

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

Yes they did the same with transmitters, often all you need was a
metal mop bucket and a piece of copper pipe
Jimmie

A water load bank is good for hundreds of KW at 60hz.

For use with a pair of 6146's we used to wire a lamp to a coax
connector. We had a load as well as visual indication of the relative
power output.- Hide quoted text -

- Show quoted text -

I built a wattmeter of sorts around a circuit like that. After tuning
up the transmitter to light bulb dummy load I would measure the
resistnace of a photo resistor exposed to the light then see how much
60Hz AC voltage and current took to light the lamps to the same
brillance.

Jimmie

if you were really good you could estimate the power from the brightness
in real time. it did take a lot of practice.

Ho-made non-inductive resitor WAS: Folded Dipole Antenna
 

On Thu, 9 Dec 2010 19:21:48 -0800 (PST), JIMMIE
wrote:

I built a wattmeter of sorts around a circuit like that. After tuning
up the transmitter to light bulb dummy load I would measure the
resistnace of a photo resistor exposed to the light then see how much
60Hz AC voltage and current took to light the lamps to the same
brillance.

Hi Jimmie,

An excellent example of the concept of a transfer standard. This
method is one of the oldest and most robust methods of accurate
measurement. It removes a lot of variables (by, ironically, not
changing them) that would be exceedingly difficult to determine their
impact upon an accurate measurement.

73's
Richard Clark, KB7QHC