Triac model question

[qtommer]

hi

Im looking to switch AC loads using a triac and optoisolator. I have found a site
SimpleIO - TriacOut Schematic Notes
which recommends the triac model BTA08-400B used together with the MOC3041 optoisolator.
It is mentioned that the triac ratings are 400V/8A. The 8A rating is in rms.

The power ratings in my area are 240VAC/13A
Hence, I guess that I would have to look for a model which can support 13A? Are there any recommendations?

Also,this model has an isolated tab. What is the purpose of having an isolated tab vs not having one?

Thanks

 

[crutschow]

Im looking to switch AC loads using a triac and optoisolator. I have found a site
SimpleIO - TriacOut Schematic Notes
which recommends the triac model BTA08-400B used together with the MOC3041 optoisolator.
It is mentioned that the triac ratings are 400V/8A. The 8A rating is in rms.

The power ratings in my area are 240VAC/13A
Hence, I guess that I would have to look for a model which can support 13A? Are there any recommendations?

Also,this model has an isolated tab. What is the purpose of having an isolated tab vs not having one?

The Triac rating is for the load you are driving, not what the power line can supply.

The tab is for attaching to a heat sink, which is likely needed for loads over a couple amps. The isolation of the tab means there is no voltage on it. Without isolation there would be 220V on the tab.

 

[qtommer]

thanks for the quick reply!

totally get your explanation crystal clear

in your experience, would you recommend the models I've mentioned or have any better models in mind?

 

[crutschow]

How large an electrical load do you need to switch?

 

[Mr RB]

I recommend you buy a solid state relay.

 

[qtommer]

How large an electrical load do you need to switch?

I would be switching domestic appliances. Nothing requiring large currents. I'm actually connecting the triac to a power strip. Thanks

I recommend you buy a solid state relay.

That would be ideal but cost is a factor for me

 

[Roff]

I would be switching domestic appliances. Nothing requiring large currents. I'm actually connecting the triac to a power strip. Thanks

You have to consider the total load of all appliances plugged into the strip.
Be aware that 240VAC can be lethal if you come in contact with it. I am leery of noobs working on mains circuits.

 

[qtommer]

sorry if I didnt explain much. I am employing a triac switch for each individual outlet. In my country, domestic appliances are rated to a max of 13A tops. Hence, I would need a 240VAC/13A for each outlet. Although not many appliances go as high as 13A in my country. It's just for safety purposes. Because in a power strip, we cannot foretell what EXACTLY is going to be connected (what exactly the LOAD is) but we can generalize a maximum rating

any recommended tried and tested triacs used before for this purpose?

 

[qtommer]

anyone?

btw how hot can a triac get with heat sinking? if placed within a plastic enclosure, would the radiated heat from the heat sink cause the plastic to melt? (no ventilation)

 

[Roff]

A device's max allowable temperature is specified in the datasheet. It is the job of the heatsink, and ventilation, to keep the temperature below that limit. The higher the dissipation and ambient temperature, the bigger the heatsink must be. If you put a heatsink in a well-insulated enclosure without any ventilation, you are just delaying the inevitable by a few seconds or minutes. And yes, the plastic may melt, but that depends on several variables.
A heatsink provides more surface area, which allows the heat to radiate away from the device. However, if it radiates into an enclosed space, it heats up the air and anything else in the space. The enclosure's external surface will radiate some of the heat, but possibly not enough.