How much does zero-crossing extend appliance's life span?

[alphacat]

Hey.

Have you encountered any resarches that investigated by how many percents the zero-crossing capability (powering on/off the appliance and zero-voltage) extends the appliances' life span?

Thanks.

 

[Nigel Goodwin]

Unlikely, as it doesn't extend life - except perhaps of incanescent bulbs.

Zero-crossing is to prevent mains interference, soft-starting is what's used to prevent the high current surge at switch-on causing problems.

 

[alphacat]

Hey,

This mains interference you mentioned, like a voltage spike (sudden change from 0V to ±110V/220V) could damage the appliance in the long run?

For example, if the load is inductive, and the voltage starts off with -220V, then since the current should follow the voltage (and not backwards), the current would fall down quickly from zero to a very negative value (with amplitude larger than its steady-state amplitude).

Dont such cases damage the appliance? (at least in the long run).

 

[kpatz]

Dont such cases damage the appliance? (at least in the long run).

Not likely. In the case of a motor, that surge will be absorbed by the windings (and capacitor, if present) like it wasn't even there. The inductance of the windings would reduce the current flow during the initial surge. The surge of current needed to start the motor puts more stress on the windings than a non-zero crossing turn-on.

For electronic devices, the transformer and/or the filtering capacitors in the PSU will swallow the surge like candy.

Like Nigel said, it might extend the life of incandescent bulbs, slightly. But it's more the rapid heating/expansion of the filament that causes bulbs to burn out when switched on than a non-zero crossing spike.

Zero-crossing switching is more to reduce noise/interference on the lines.