Got yet another explosion, this time with heating resistor. It was ARGOL 10 ohm 25 watt heat sinked resistor, and the problem was that if i tried to go above 200 celcius, there was "explosion", with one cap of the resistor blown out.
Maybe should try to drill out the center stuff, and use resistor wire, and fill with some non-exploding cement (any suggestions what would be good cement?)
I suggest you use sodium metasilicate silencer cement - the kind sold for auto repairs. In a thick mass it will take a fair while to dry out though. Even high-temperature epoxy won't like the conditions close to the wire, but metasilicate is ok at over 1000C. The brand below is good. If you plan to keep the resistor submerged for a long period I would use a little silicon bath seal to keep water out- just a smear over each end of the package. But only use the silicon AFTER you have dried out the cement.
After putting your heater wire inside I would suggest drying the cement out at around 60C for 24 hours, then ramp it up to 200-250 (if your oven goes that high) for at least 2 hours.
Got yet another explosion, this time with heating resistor. It was ARGOL 10 ohm 25 watt heat sinked resistor, and the problem was that if i tried to go above 200 celcius, there was "explosion", with one cap of the resistor blown out.
Maybe should try to drill out the center stuff, and use resistor wire, and fill with some non-exploding cement (any suggestions what would be good cement?)
Just to get a rough picture....for what do you use this resistor for?
I have made many resistors with ceramic cement and Kanthal. Up to 1500 W, glowing orange hot.
For many purposes, bare, open-coiled Kanthal is sufficient and cools better. The coils can be wound with care on a threaded rod in a drill. A lathe is safer if you can use one. Wear safety goggles and gloves.
This link will enable you to calculate the dimensions and wire sizes necessary for any coil (within reason). It is exceptionally accurate and reliable.
Got yet another explosion, this time with heating resistor. It was ARGOL 10 ohm 25 watt heat sinked resistor, and the problem was that if i tried to go above 200 celcius, there was "explosion", with one cap of the resistor blown out.
Maybe should try to drill out the center stuff, and use resistor wire, and fill with some non-exploding cement (any suggestions what would be good cement?)
First of all, the name is ARCOL, not ARGOL as you can see from the text on the resistor.
But that is the product name, not the brand name which is Ohmite.
For these type of resistors Ohmite states :
Heat Dissipation
Heat dissipation: Whilst the use of proprietary heat sinks
with lower thermal resistances is acceptable, uprating is not
recommended. For maximum heat transfer it is recommended
that a heat sink compound be applied between the resistor
base and heat sink chassis mounting surface. It is essential that
the maximum hot spot temperature of 200°C is not exceeded,
therefore, the resistor must be mounted on a heat sink of
correct thermal resistance for the power being dissipated
So it means that if your environment temperature is 200 C, you are not able to dissipate any power in the resistor since that would bring the possible spot temperature above 200 C.and will destruct your resistor.
An open coil resistor, wound yourself from Kanthal vape wire, can withstand 1200 C for a while, and 800 C almost indefinitely.
I brought several alumina power resistors to glowing hot for a short while, but they fired out liquid (molten) glass when they popped so I won’t repeat that.
If one knows how hot they want, a convection-radiation calculator can tell you how many watts a cylinder of a given size needs to reach a certain steady state temperature. From there, one works backwards to supply a coil resistance and length that matches the physical size desired and power level. I was able to do this within 5% on the first try. I underestimated how much power could be put to the resistor, but the temperature per power in was pretty much as designed.
Here is an image of a home made resistor cylinder at 1100 C.
Here is a home made resistor with a hot spot, seconds before total failure of the coil. The spot sort of wiggled around, grew white hot and then dimmed out.
