Hi to all,
while i know well that this argument has been discussed more and more times, i have some questions because i don't understand NOTHING about elettronic stuff (well, i love programming and i'm playing with arduino
For my project i initially choiced some 9v bistable electrovalves (that open when power flows in one direction and close when they got it inverse) and i'm controlling them using a TB6612FNG.
Now i want to try to control solenoid valves for many reasons, the most important is that they are faster and i can use PWM to control how much open the valve and how much faster open it.
Solenoids i want to use need 24VAC and 300mA to work, they will be powered by a 230vac to 24vac transfomer
For this reason (PWM) i can't use a normal relay, looking over the web (and arduino forum) i founded many many people talking about:
- Triac + Optoisolator;
As far i understand the SSR (Solid State Relay) works similarly like a Triac+Optoisolato based cicuit but i don't understand which is the difference between these two (well the SSR is self-packaged and don't need other stuff, but apart this?)
As far i understand, like the VDC solenoid controlled by a mosfet, i need a diode, which diode i should use? As far i understand, i should put a diode on the AC line, this is right or is a non sense? And, if yes, which is the direction of the diode on AC? (on DC it make a sense put the diode between vcc and gnd, but on AC?)
More, reading on the web it seems that may happen that because of a "zero crossing stuff" (really, i don't know what it means, it refers to the no power phase of AC?) the circuit (SSR or Triac+Optoisolator) may turn on on his own, i read about using a "snubber" (as far i understand a simple snubber could be composed by a resistance and a capacitor) to avoid these kind of activations, could someone give me more info?
I've founded this threadhttp://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1230333861/all
And as far i understand, this circuithttp://lh4.ggpht.com/_liDL5ZFNsxs/SmUcmP5y9iI/AAAAAAAADw8/kXMf-cm_5aU/s800/ac_control.png
does exactly what i need, but it's for 120vac 60hz while i need for 24vac 50hz (well, i don't know which transfomer i'll use but it should maintain the frequency ... by the way i just need to fix the code if the frequency change) ... the only part i don't understand is in the lower right corner:
- there is an F1 (3A refers to 3 ampere?) that i don't know that it is, i don't recognize the symbol;
- what means ACN?
May i use 1/4 WATT resistences for that circuit? It's powered at 24v so it should be fine, right?
What i should change if i need to run that circuit over a 230v? I don't know yet, but there is the possibility that i need to control a water pump and to avoid pressure problem i want to be able to dimmer the power to reduce the output pressure.