Need higher power resistors, or heaters, as we like to call them? Build them yourself. Matseng hand-wound 6 meters of 38AWG wire to build 12 ohm resistors. He used a pencil and some kapton tape as the base for the resistor.
I needed two power (just ~1 watt) 12 ohm resistors for a project and I only had a bunch of 1 ohm 5w resistors and some random other values that I couldn’t use so I wound two resistors by hand for the first time in my 40 years of electronics tinkering.
Via the forum.
I doubt this would have inductance properties and would be inappropriate if used in some AC applications.
Just wind half clockwise and half counterclockwise. Then the fields cancel and you have a non-inductive power resistor.
Right said. You reminded me the physics lesson of my part1 syllabus. But practically both part will never have a equal opposite winding unless you’re using a special machine. But this indeed is a good DIY job. I remember some 10years ago I had coiled such resistor(inductor) and added it in series to a 0.1uF cap to the output of an amplifier and got better quality audio.
If you have an idea of how much wire is needed to start with, cut that first, fold it in two, twist them together slightly (hand drill or electric drill on the end), then wind as one bifilar strand. That way you’re guaranteed exactly the same number of CW and CCW turns. Also, since the strands are twisted, they should cancel out inductance pretty well.
Wouldn’t you have a huge impedance with such systems ?
These will only be used for led lightning in my microsope. The leds will be pwm controlled but only at 100 Hz or so, with a bit of luck the inductance won’t matter here.
Maybe I should for fun build the http://dangerousprototypes.com/2012/10/10/7400-competition-entry-4049-inductance-meter/ and actually measure the inductance….
When you only need a temporary high-power load, you can immerse power resistors in a cup of water and run them somewhat over 100% rating (at least until the water boils dry!)
don’t for get copper has a terrible temperature coefficient, if it is 12R @20’C it’ll be ~13R@40’C
Hm… Didn’t think about that.
Luckily the tempco of copper is positive so it won’t cause a thermal runaway where the resistance is decreasing when it getting warmer causing more current to flow and more heat to be generated causing more current to flow…….. :-)
Yup, @Lindsay Wilson has the right approach, Re: Bifilar Windings. See here:
https://en.wikipedia.org/wiki/Bifilar_winding
The Ayerton-Perry bifilar winding is a useful approach for a bifilar winding where you want an axial instead of radial component (like the original poster). However there are trade-offs, sometimes a radial bifilar air-wound resistor is preferred over an axial-wound resistor when mounting to a PCB, to keep parasitics from the PCB ground plane. Sometimes not.
https://en.wikipedia.org/wiki/Ayrton-Perry_winding
See this page for a rather clear depiction of the difference between the standard bifilar and Ayerton-Perry bifilar winding:
http://www.resistorguide.com/wirewound-resistor/
Then there’s the Tesla approach; spiral wound bifilar. Google will pop up a lot about this from Tesla Coil Hobbyists. Also the spiral wound bifilar inductor is a go-to for 2D designs on PCB’s, microwave substrates, and in integrated circuit layouts.
Enjoy, David in Jakarta