Lifetime Examination Of A Pwm Control - ABB SA/S 12.16.6.1 Product Manual

®
ABB i-bus KNX
4.3.5 Lifetime examination of
a PWM control
158 2CDC 505 056 D0207 | SA/S
Planning and application
If a PWM cycle time of 15 minutes has been selected, this means that 4
switching operations (switching on/off) occurs each hour, 96 in a day and
3000 in a month. This amounts to 36,000 switching operations a year. With a
5
relay life of 10 switching operations, this means a Switch Actuator life of
less than 3 years.
If however, the cycle time is set to just 3 minutes, this means in about
150,000 switching operations annually. This means the Switch Actuator life
would be less than a year.
This observation assumes an AC1 switch loading (almost exclusively
resistive load) at rated current. If the maximum number of switching
operations for a purely mechanical relay loading is assumed, the life of the
Switch Actuator is extended. This has an inherent risk: the contact materials
can wear prematurely and cannot safely guarantee conduction of current.
In the following, conventional cycle times for control of various heating and
air-condition systems are listed:
Heating system
Water heating
Supply temperature 45...70 °C
Water heating
Supply temperature < 45 °C
Underfloor/wall heating
Electrical underfloor heating
Electrical fan heating
Electrical convection heating
Control type Cycle time
PWM 15 minutes
2 step –
15 minutes
PWM
PWM 30...20 minutes
PWM 30...20 minutes
2 step –
PWM 10...15 minutes
2 step –