Static relay vs ZVS commutation

[BenoitR]

Hello,

Application is room heater. Resistive load switched on MAINS.

Focus on the switch. I have to choose. EMR or SSR ?

SSR is able to switch at MAINS ZVS. As, in my application, the switch will be turned ON only few times per hour, considered as not repetitive disturbance, then not triggering at ZVS has no impact on conducted noise (EN55014).

I'm right ?

If yes, there are others reasons to switch at ZVS ? (protect the load maybe, but it helps to fullfil an another specific standard ?

Thanks in advance for your help,

Benoit

 

[betwixt]

SSR is more reliable and silent in operation. For a heater load the ZVS is not important but be aware that a heater typically draws high current so there will be some losses in an SSR which will will make it heat up to some degree.

Brian.

 

[BenoitR]

Thank you Brian,

Few SSR are mentionned: "With integrated ZVS for resistive load". (for exemple SIEMENS SSR).

That's why I would like to know if it is integrated too fullfil a specific standard ?

 

[betwixt]

I suspect the "ZVS for resistive load" has something to do with the zero crossing detector and how it handles phase shift between the voltage and current. For your application it doesn't matter whether you have ZVS or not. The only advantage it would have is reducing EMC but it would be very small and more related to the operation of a mechanical relay than the power it is switching.

Brian.

 

[BenoitR]

Once again, thank you Brian,

Then no standard to fullfil that should say that a triggering at ZVS is mandatory (as in my application this is not a repetitive triggering but only about once per 10 min...).

 

[FvM]

Most heaters are switched by contactors. Cheaper, less power dissipation, surge resistant. Calculate expectable lifetime based on datasheet and see if it's acceptable for your application.

 

[betwixt]

Then no standard to fullfil that should say that a triggering at ZVS is mandatory (as in my application this is not a repetitive triggering but only about once per 10 min...).

None at all. ZVS is a system that ensures the switch operates as the AC crosses zero voltage and therefore is less likely to cause interference or stress on some parts. It is only important for some applications and in any case when the switching occurs much faster than every few minutes.

FvM is correct, a contactor is a mechanical relay though so it's up to you which to use. The only drawback to an SSR is that when it conducts it drops a small voltage, it isn't a perfect short circuit like a mechanical switch. The voltage drop is probably insignificant to your heating element but it will cause some heating in the SSR itself which you may need to conduct away. Look at the SSR specification, it will tell you the voltage drop, then multiply the voltage by the current through your heater to find the power the SSR will dissipate.

Brian.

 

[BenoitR]

Thanks,

Yet, we also often see room heater driven by Triacs or hybrid relay (Triac + EMR in parralel).

Then, the ZVS seems usefull for this application (even if it triggers only few times per hour). That's why this question.