I have heard that aluminium clad resistors can damage a drive, is this true?
As we know a dynamic brake resistor is connected directly to the DC link on a drive, this is the main reservoir of power for the drive. You can imagine that shorting this connection can have catastrophic results for the input rectifier of a drive.
Some aluminium resistors are manufactured in such a way that in certain failure modes can cause them to short the DC terminals to the Earthed case, causing the drive fail. REO Aluminium resistors utilize a superior construction method to minimize the likelihood of this happening.
Resistor coils manufactured from Copper-Nickel (Constantan) or Nickel-Chromium, which have resistance values that are constant over a wide range of temperatures. Several coils are con¬nected in parallel which means that the load does not rely on a single winding.
The windings are surrounded by quartz filler which provides mechanical stability, short circuit protection and provides self extinguishing properties which are important from a safety and re¬liability point-of-view. This also assists with the efficient transfer of heat from the resistor windings to the inner surfaces of the aluminium housing.
Further electrical isolation is provided by insulation sheets that are inserted between each wind¬ing and between the resistance winding assembly and the sides, top and bottom of the extruded aluminium housing.
For further isolation and to provide high ingress protection ratings of up to IP67 the resistor as¬sembly is encapsulated within the cavity in the aluminium extruded body by the use of a silicone sealant at both ends. The sealant is then protected by cover plates that are screwed to each end of the aluminium housing.
- The extruded aluminium housing acts as a heat-sink and quickly dissipates the thermal energy generated by the resistance windings to open air. Special grades of aluminium finishes are used to give long term durability to all types of atmospheric conditions, including salt-spray.