• Please visit and share your knowledge at our sister communities:
  • If you have not, please join our official Homebrewing Facebook Group!

    Homebrewing Facebook Group

PWM question

Homebrew Talk

Help Support Homebrew Talk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

clay9_24

beerganeer
HBT Supporter
Joined
Dec 19, 2009
Messages
110
Reaction score
1
Location
Comanche
looking into building a PWM controller to compare it to my pid box. Ideally an analog output from the plc could control the PWM but that is another story.

My question is for SSRs what is the frequency range that they should be ran at? Most of their data sheets do not give max switching speed or control frequency max(at least on the ssr that i have looked up thus far). If the ssr has built in zero crossing, would that limit the frequency.

I understand that i am just heating water and it probably doesn't matter that much but am curious on what frequency you guys are building your PWM boards.

:mug:
 
SSR can be switched as fast as you want, however like all SCR's or Triacs, once they are switched on, they don't turn off until current stops flowing. In the 60Hz world you can switch them 120 times a second, but for heating water a period of 2 seconds seems to be the norm around here (totaly of 2 seconds, so on-time plus off-time).
 
SSR can be switched as fast as you want, however like all SCR's or Triacs, once they are switched on, they don't turn off until current stops flowing. In the 60Hz world you can switch them 120 times a second, but for heating water a period of 2 seconds seems to be the norm around here (totaly of 2 seconds, so on-time plus off-time).

Not necessarily.
There are basically 2 kinds of SSR's: Triac/scr based, and transistor based. Most transistor based SSR's today use MosFet transistors.

In both cases, there's a maximum frequency at which the SSR can be operated, defined by the minimum rise time of the components used.
In the case of the triac/scr based SSR's, as Bjornbrewer accurately said, the operating frequency will be, in practice, limited to twice the grid frequency (or exactly the grid frequency for scr based units, as scr's are polarized), as the triac/scr will stay latched, after being activated, until the voltage crosses the "0V" mark.
In case of transistor based SSR's, the manufacturer should provide a maximum operating frequency. Those SSR's, while more expensive than triac based units, will allow you to use much higher switching frequencies, which in time will translate in a better temperature control (in case you need it), and in a longer element life. Either way, if you know you have a transistor based SSR, you can safely use it within the audio frequency range. Most of them (that I know of) work well up to several MHz.
 

Latest posts

Back
Top