so why do the triacs make that noise?
is there a way to stop it? or maybe make less noise?
thanks!

 

noise?

I'm guessing you are swiching some decent power (10kW+) and have a switching freq in the audiable range?

 

I don't think he is talking about acoustic noise.
Problem is with the way power is sliced and diced during thyristor
and/or triac operation. Only pure sinewave form is clean.
Any other shape or sudden change in gradient is source of harmonics
and that's where the noise comes from.

Your hairdryer or toaster are not going to be impressed but if you are watching TV and certain channel is noisy, you will change the channel
or go fishing. But can you imagine what happens when little
noise induced in the power lines of your PC that corrupts the data
your CPU is processing? It is going to crash the system in most
unpredictable way. Now what if this is not a PC or TV but some
industrial controller operating bunch of robots?

Why would computers and other electronics be so sensitive?
The SCRs and triacs are used in power applications, harmonics
are strong enough to create malfunctions and errors in puny
little sensitive electronic devices. Think about it.
Your PC you use right now probably has CPU running on ca
1.2-1.5V (current draws is significant - it's in the 60Amp range or so
but the voltage is low).
Now what are the signal levels defined as "0" and "1" if the power
to chip is only 1.2V?

 

well, i am talking about acustic noise.
i used the triac (BT136-4Amps, 600V) for switching like 25W @12V. it was making some acoustic noise. i guess low frequency.
i also used it for controlling some lamps powered from the mains(150W, 250W). it makes a bigger noise.
now, you know those potentiometers for light, that you put them in place of the normal switch? those make noise too. and use triacs as well.
and the noise gets annoying....i stay somewhere close to the switch. and if it is quet in the room, i don't like the noise.
so.....why do they make this noise and can it be stopped?

 

thought you were talking abt acustic noise, just wrong on the power level.

Well it will make some noise because you are switching power and silicon power devices do make a noise.

Try and firmly mount the Triac down. If it is leaded in a TO220 package and hte case in in the air that will resonate. It needs to be tied down flat to stop any internal (to the package) kicking off any more and making the package vibrate.

otherwise try slowing down the switching of the device (ie turn-off and turn-on time) that way any potential to cause audiable noise will be reduced since the turning on/off isn't as snappy. This comes at a price of increase switching losses tho.

What are you using to drive your Triacs?

 

well, i will try to mount them on a pcb and a small heatsink on each.
the time i tested i used them 'in the air', yet on a heatsink.
so.....just one more question
there was a website used to calculate the heatsink charactersitics based on dimensions and shape.....i lost the address. you might know where it is?
and anoter thing....
how do i calculate how big the heatsink should be ?
the triacs i will use are rated 4amps at 600V and i will not use them for more than 1A.
i will use them to control the light in my room....hopefully.....i am still thinking about this project. i want to be able to control the lights(i have 5 bulbs conneted 2 and 3), probably use a remote control, and the normal switch that you find in a room. also i want to be able to control the intensity....

 

oh....and you asked what i drive the triacs with....well...an optocoupler....driven...by an ic.

 

Well I never could detect any sound from the triac or SCR.
Load - yes (inductive), but not the semiconductor.
You can try to dip the circuit in some compound like epoxy or so.
That's what I do with coils so the windings will not vibrate.

:roll:

 

hm...oky
im still looking for that website about the heatsinks....anyone knows where it is?

 

I can't help you with the heat sinks, but you could try increasing the switching frequency to get rid of the noise. I'm not sure exactly how you're setup works - if you switch on/off once or twice per 60Hz cycle or more like pulse width modulation. If it's the former, then you'll get a nasty 60 or 120Hz humm. But if it's the latter, you could increase the frequency to above 16kHz so you can't hear it.

Look where you got the triacs from; they might have some suggestions for heat sink sizes. Good luck.

 

thanks guys..!!!!