Because heat is removed from a component in two principle ways, convection and radiation, Ohmite have investigated the latter with a view to fanless, power saving operation.
Radiation is an electromagnetic phenomenon generated when heat is removed from charged particles within atoms, so Ohmite applied Planck’s law of radiation which says “If the object is a black body in thermodynamic equilibrium, the radiation is termed black-body radiation. The emitted wave frequency of the black body thermal radiation is described by a probability distribution depending only on temperature”.
In situations where a fan is used, the heat removed via radiation is negligible compared to the heat removed through convection. Customers using forced air can marginally reduce costs by using the degreased, non anodized version.
New TO247 resistor from Ohmite has a 100W rating
The development of a new heatsink which aids low thermal resistance has enabled Ohmite to push the power ratings of their TO-247 resistors to new levels, resulting in the new TEH100 which is rated at 100W at a 25⁰C case temperature.
Ideally suited to power supply applications, the thick film, non-inductive power resistor is totally encapsulated and insulated and attaches to the heatsink with a simple, single screw mounting. Environmental issues are addressed by the totally moulded housing.
The TEH100 has a maximum working voltage of 350V and is available in stock resistance ranges of 0.05Ω to 1MΩ. Resistance tolerances are ±1%, ±2%, ±5%, ±10% and the linear derating is 100% at 25°C to 0% at 175°C.