Cressall Resistor's HP and ES series braking resistors

Cressall Resistors' HP series of high-performance dynamic braking resistors (DBRs) are suitable for use on cranes, winches, conveyors and test loads, as well as on lifts and elevators. These compact, ready-boxed DBRs are protected to IP20 and make virtually no noise when subject to inverter braking currents. Their low inductance open-wound element construction allows high-power dissipation in a small space. It is these two factors that make the HP series useful for lifts and elevators, where noise and heat dissipation are both significant issues. The braking resistors can be used with any make of inverter drive.

The range is divided into HP1, HP2 and HP3 units, which have continuous power ratings of 1.5kW, 3.0kW and 4.5kW, respectively. These continuous power ratings can be exceeded when power is applied for less than 100 per cent of the time and the extent to which this can be done is calculated using a simple equation.

Also available is Cressall Resistors' range of low-noise ES braking resistors, which has recently been expanded with the addition of 1.0kW and 2.0kW models. These new ratings complement the existing range, which includes 0.6, 1.5, 3.0 and 4.5kW versions with resistance values from 3.9ohm to 330ohm. The new 1.0 and 2.0kW sizes are used where there is a need to cope with high levels of regenerated energy in a compact space. This includes motor control on elevators, VSD control and use on conveyors, cranes and winches, as well as test loads. Like the HP series, these robust IP20 units produce negligible audible noise.

Both sets of resistors are manufactured using high-grade nickel-chrome wire, which means the resistance value changes negligibly over the temperature range of the element. CP Automation's director Tony Young states: "This is a significant factor because a design using lower-grade stainless steel could increase in resistance by as much as 50 per cent - resulting in impaired braking."