No Spam wrote:
On Sat, 04 Dec 2010 11:44:55 -0800, Richard Clark wrote:

On Sat, 4 Dec 2010 18:22:21 +0000 (UTC), No Spam
wrote:

I used a carbon watercleaner cartridge to build my term resisor :-)
! ! ! !

This demands more discussion.

73's
Richard Clark, KB7QHC

Sure!
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.

/****/
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.


Electrodes from an carbon arc light or pencil leads can also be used for
a non precision resistor.

Carbon "suppressor" ignition wire

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

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)