Question:
What are the differences between spring-operated and permanent magnet brakes? How are they influenced by free-wheeling diode and spark suppressors?
Answer:
- The spring-operated brake normally opens at approx. 20 V and closes at approx. 3 V (values depend on size and spring type)
- A permanent magnet brake opens at approx. 20 V and closes at approx. 16 V => this may cause the brake to close in case of voltage fluctuations
- Free-wheeling diodes and spark suppressors protect the switching contact in case of switching on the DC side (for 24V brakes)
- If free-wheeling diodes are used, inductive voltage peaks are decreased. This is not the case with spark suppressors => 6 to 10 times of the brake closing time if a free-wheeling diode is used (compared to spark suppressors)
- If permanent magnet brakes are used the immense time difference is not really perceptible (closes at 16 V) - unlike spring-operated brakes, as the voltage decrease to 3 V takes considerably longer.
This means that the closing time of permanent magnet brake and spring-operated brake is different if free-wheeling diodes are used. Therefore, spark suppressors should be preferred together with spring-operated brakes (in the Lenze Brakes catalog a spark suppressor for 24 V is defined - one type for all brake sizes).
