Rheostat Definition and Construction
A rheostat is a type of variable resistor, but is generally defined by having a high power rating. These power ratings available in the APR rheostat range are available from 25 watts up to 500 watts. When working with high power rheostats it is important that the quality of the device and its construction are of the highest standard to ensure reliability of operation over many years. Key design features of our rheostat range include:
- Toroidally wound resistance element on a solid ceramic former
- Coating of the resistance winding to maximise dissipation of heat from the element.
- Minimisation of wear of the wound resistance element by use of a graphite brush wiper assembly. This is extremely important and low cost manufacturers of rheostats often use inferior wiper technology resulting in intermittent operation and reduced operating life.
Applications Of Rheostats
Application 1. Linear high current battery charging unit. Rheostats lend themselves well to limiting current in high power battery charger applications, using ‘standard’ linear battery charger design techniques. A client has been using the 50 watt APR50 rheostat in their linear battery charger, with reliable operation, for over 15 years. The design of the charger calls for a constant voltage output, 13.8 volts in this instance, but requires the output current to be controlled, which is where the rheostat is used. The rheostat is installed into the battery charger, via the 9mm threaded mounting bush and wiring onto the rheostat is via quick connect terminals.
Application 2. Motor Control. The photo finishing industry uses many a.c. motor controlled inspection benches to visually inspect printed rolls of photographic paper. To control the speed of the drive motors on the inspection benches, they employ 150 watt rheostats to limit the current to the drive motor. The inspection process often spans 2 shifts per day, so the rheostat can be used for more than 12 hours per day so high reliability and the ability of the rheostat to have a high mechanical life is critical.