TRIAC or relay

[Cristi_Neagu]

Hello.

I working on an application that needs to power 3 paint guns at once. The guns are powered with 230VAC, @0.4A each. They need to be just turned on and off.

Space is a bit of an issue... I guess I could fit a relay in the housing, but i'd rather not start drilling holes for them, or even design some kind of attachment system. TRIACs are just easier to use, since they go on a PCB.

On the other hand, on the same PCB that the TRIACs will be placed, I'll have low voltage signal lines (5V), so I do realize that some measures of protection need to be taken.

Also, I'll be using a basic PWM DAC with a low pass RC filter. Do I need to take any major precautions agains 50Hz interference, or will everything be ok?

So... should I use a TRIAC to control them (obviously using something like a MOC3041 or the likes), which would make for easier and faster implementation, or should I use a relay, in which case I need to figure out how to mount the thing?

Thanks.

[Soeren]

Hi,

Also, I'll be using a basic PWM DAC with a low pass RC filter. Do I need to take any major precautions agains 50Hz interference, or will everything be ok?

That depends on layout and circuit impedance. With a sensible layout, where the low voltage part is isolated from the mains side with the legally required distance or more and the low voltage circuitry is kept as low impedance as possible it should be fine.


PWM, 3 paint guns... I smell a "dial-in" CMY multicolor paint gun project
(If I'm right, you might consider adding a 4th. gun for black).

I made plans for an air brush equivalent (based very loosely on the Paasche Turbo principle) twenty-some years ago

So... should I use a TRIAC to control them (obviously using something like a MOC3041 or the likes), which would make for easier and faster implementation, or should I use a relay, in which case I need to figure out how to mount the thing?

You can get small PCB mounted relays able to switch mains voltage, but if you prefer TRIAC's, go with them - If the paint guns are the least bit inductive loads (which they probably are), use 600V TRIAC's and don't forget snubbers. Relays will need snubbers over the contacts as well, or they'l be eaten up in no time.

Another thing to note with inductive loads is, that the zero-cross switching in the MOC30nn-series are voltage zero-cross and to switch noiseless with an inductive load you need current zero cross (due to the phase difference). Whether it means anything in your app or not, I cannot tell - snubbers will help.

The MOC30nn's have different current requirements to trigger the IR-LED, which may be nice to know if there's little current to go around:
MOC3040, 30mA
MOC3041, 15mA
MOC3042, 10mA
MOC3061, 15mA
MOC3062, 10mA
MOC3063,  5mA
(The above are all voltage ZX switching, but not all of the MOC30xx have ZX-switching).

[Cristi_Neagu]

PWM, 3 paint guns... I smell a "dial-in" CMY multicolor paint gun project

Well... no. I'm working on a rig for penetrant liquid defectoscopy (that sounds weird in English...).

Anyways... I was afraid there were some hidden dangers related to the TRIACs. I was somewhat correct, because I didn't know about the snubbers.

Thanks for the reply.

[Soeren]

Hi,

Well... no. I'm working on a rig for penetrant liquid defectoscopy (that sounds weird in English...).

Not at all, but when Googling it, most pages originates from Russia and Ukraine, with a few from India and the former East Germany and I didn't find any clear explanation, just a bit here and there, so maybe I have a rough idea of what it is or perhaps I'm  just guessing.

Anyway, good luck with it

[Cristi_Neagu]

I didn't find any clear explanation, just a bit here and there, so maybe I have a rough idea of what it is or perhaps I'm  just guessing.

The principle is the following (more or less):
After you pass a part through a process (welding, molding, etc), micro cracks could form. To detect them, you first apply a penetrant liquid to the surface of the part. This liquid, as the name implies, penetrates those micro cracks. After washing away the excess liquid, you add a developing liquid, which usually is white. The result is that you would end up with a white surface with red spots where micro fissures are on the part.

Anyways, for this project I'm mainly taking care of the automation side of things. Some other people are taking care of the actual process.

[Soeren]

Hi,

The principle is the following (more or less):
After you pass a part through a process (welding, molding, etc), micro cracks could form. To detect them, you first apply a penetrant liquid to the surface of the part. This liquid, as the name implies, penetrates those micro cracks. After washing away the excess liquid, you add a developing liquid, which usually is white. The result is that you would end up with a white surface with red spots where micro fissures are on the part.

Anyways, for this project I'm mainly taking care of the automation side of things. Some other people are taking care of the actual process.

Thanks a lot for the clear picture - my guess was a little off then