Low profile braking resistor, optimized design for high energy to heat conversion
When designing a motor controller, which has to be as compact as possible, every engineers challenge is to deal with the heat dissipation which is being generated when braking the motor. Using the BRK-series of Isabellenhütte as a braking chopper, you're able to resist high energy loads. It's ideal for use on Inverters, EV pre-charging & current limiting applications.
When braking a three-phase motor driven with an inverter or servo controller, the flyweight of motor and moved external mass acts as a generator via the motor winding whereas the resulting electric energy in large drives is fed back into the mains. This is not possible for small drives from a few hundred watts to the 10 kW range for economical reasons, which means that the generated energy has to be converted into heat. In this case the „generator“ loads the intermediate circuit up to a maximum voltage (usually 750 V). When the preset limit value is exceeded, the braking resistor is connected directly between the intermediate circuit voltage and ground (see figure in the attachment). If the transistor is opened only for a set time, this process is repeated more or less rapidly to the end of the braking process – this is called a braking chopper. During the braking process which is limited to approximately 1–3 seconds, a relatively high braking power of up to 3 kW is generated, which needs to be converted into heat within the resistor and dissipated by its own heat sink. Because of the limitation of successive braking cycles the average power is usually much lower than the peak braking power.
Load capacity up to 3 kW
This requirement is met by the design principle of the ISA-PLAN® braking resistors. The resistor components are constructed in the proven ISA-PLAN foil technology, i.e. etched from relatively thick rolled MANGANIN® foil and electrically insulated with a high thermal conductivity adhesive on a solid 2 mm thick copper base. The high mass of the resistance structure ensures the very high energy load (up to 100 Joule) in the short term range. The sound thermal conductivity of the ceramic-filled adhesive reduces the internal thermal resistance to 0.1 K/Watt and, together with the large Cu mass of the substrate, allows a braking power of up to 3 kW for several seconds, which is extremely high considering the size of the component. Continuous power is mainly determined by the heat transfer to the external heat sink. The values specified in the data sheet are reference values and far higher loads can be accommodated with careful assembly and an effective external heat sink.
- Compact size
- High pulse load capacity
- Very good thermal conductivity
- Easy assembly
- UL-listed materials
- Load capacity up to 3 kW