I had thought to use a Triac because ...

1. The price is significantly cheaper than a relay (This is my number one consideration I am quite poor).
2. Current levels needed to trigger the relay were higher (Though if I end up using an opto coupler this might not be an issue)
3. Triac doesn't seem to be as bulky.

"at those level of current and voltage"

Is there something about 24 VAC and .35 Amps that would make a relay a good alternative where some other current and voltage level it wouldn't be?

Once again thanks for all your help,
Z

 

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You may have to reduce the values of those two resistors if you are using 24V instead of 220V.

It would be better for your understanding if you search for "SCR quadrants" instead in Google and read the material that turns up.

Posts back if you have questions about the information in them.

I'm having a lot of difficulty figuring out what value and wattage rating those two resistors should be. I'm doing something wrong. Any help would be appreciated.

 

Hello,

Are you still looking for the connection of the 24 Volts AC for the sprinklers?
In the link I gave you some time ago there are calculations for the resistors.

For 24 Vac line, the triac will turn on with the 100 ohm and 180 ohm resistors, but I think the initial turn-on cycle will be 'late', at 13 V max (but I think it stays on once turned on). A resistor value better suited is:
24 x 1.414 = 34 V, so R = 34 V / 1 A = 34 ohms minimum. Round to 33 ohms for a standard value.
The max triac turn-on voltage will be:
R x IGT + VGT + VTM = 33 ohms x 50 mA + 1.3 V + 3 V = 6.0 V.

Greetings,
Bertus

 

Bertus --

Yes thank you . I've read over it repeatedly. There are a few problems.

1. The schematic for the one they reference is for a non-inductive load. Correct me if I'm wrong but the coil in a sprinkler solenoid is inductive.

2. I'm not using the same triacs they are using. My specifications aren't the same so I need a better understanding of what they are doing to figure out what I need to change.

3. Calculating wattage for the resistor is a problem. They state...

Measuring the voltage across the resistor when the triac is on showed a 5 mA pulse for about 50 us every half cycle of AC. Apparently, this is when the triac is switching, and draws current on the gate.

I'm not sure where this 5mA pulse every 50 us is coming from. I don't know if my triac will give the same result .

4. Even if we go with 33 ohms for the small resistor. The large resistor will be in series with the capacitor when the opticoupler is off. If I'm calculating the wattage dissipated by this resistor when the optiocoupler is off correctly (I'm probably not) the wattage is going to be quite large even if I make the resistor smaller by a factor of ten. I'm not really sure what the proper way to calculate the value of this resistor is.

Regards,
Z

 

So any help on understanding this?

 

Hello,

I found an aplication note (attached) on using a triac in combination with an opto coupler.
There is a drawing for inductive switching.
The reistor is divided and a capacitor is added.

The resistor should be ca. 18 Ohm each in your case (24 V AC).

An other alternative could be a CPC1979 opto relais.
See attched dataheet.

Greetings,
Bertus

 

1584Bertus--

Thank you so much for trying to help...

An other alternative could be a CPC1979 opto relais.

At over 15 bucks it's outside my price range for this project.

The resistor should be ca. 18 Ohm each in your case (24 V AC).

How did you get this? And what wattage should I use. It seams to me while the thing is off the cap is going to let AC current pass and you are going to have a huge current through the 18 ohm resistor. Am I missing something? Maybe 60 Hz is low enough frequency that the cap will block it?

Robert

 

Hey,I'm doing one of the project in my university about soft starter (3 phase induction motor). I'm thinking of using 3 triac. I'm wondering using the schematic provided by http://www.nalanda.nitc.ac.in/industry/appnotes/Intersil/an6182.pdf or www.fairchildsemi.com/an/AN/AN-3004.pdf. Do you have any suggestion? One of the biggest problem I'm facing is I do not know the dc logic circuit but I'm thinking of using 8051 microcontroller. Please give advise. Thanks.

 

Dear all
''Can you help me , How to control 50W lamp and Fans with Triac ''

 

From the web..................
Search for dimmer circuits.

 

Dear all
''Can you help me , How to control 50W lamp and Fans with Triac ''

Full ON/OFF or phase control?
Max.