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Problem in triac circuit

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gowtham velusamy

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Hi

I have used three BTA 24(TRIAC) for switching three loads via microcontroller. MT2 terminal of each triac are commonly connected to the PHASE of the 230VAC. Also, i have used manual switch for each load for the purpose of switching the loads ON/OFF instead of the MCU.

I have 1xMain and 3xmanual switch. The main switch controls the Phase in for the triac, so that when the main switch is OFF, the loads do not ON/OFF via the triac. The manual switches are the ones are for turning on/off my loads manually when i dont use my triac (consider the switches on a switch board) Please refer to the diagram in the attached image.

Coming to the problem.
When my main switch is OFF, the entire 3 triacs must be useless, and i get to turn ON the load only by means of the manual switches and not the triac. But in my case, say, when i turn ON load1 using the manual switch and trigger the gate of the triac1, it gets to turn on my other loads also inspite of the main switch being OFF. How can i overcome this problem?
 

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Its a very unusual circuit layout. Normally all the triacs are commoned to the neutral line with the loads commoned to the live with the triacs switching pulling the ends of the loads down to neutral.
i think the problem is with the Dv/Dt of the manual switch. Its firing off the other triacs via their internal capacitance. Try a lower value gate resistor.
Frank
 

Your main switch has no effect on your 1st triac and load but it has on others .
Are U sure dont turn on other triacs?because when U turn on triac1 and manual switch1 the line voltage from MT2 of triac1 goes to MT2 of triac2 & 3 and only thing that can switch on other loads is turning gate of triac 2 & 3
 

You can do this. Watch the change in the image.
(...Or something like that. Anyway I would try using Double Throw switches).triacs switched edaforum1.jpg
 
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The circuit is not symmetrical. Move the main switch closer to the line (then it will match your description). Also put a 0.01 -0.1 uF capacitor in parallel to 390R so prevent spurious triggering.
 

Normally all the triacs are commoned to the neutral line with the loads commoned to the live with the triacs switching pulling the ends of the loads down to neutral.
Frank

In your point of view live are directly connected to the one end of the Load,That way neutral can be bypassed via Triac .But line directly to the load and neutral via switch is not the proper method for wiring .Line are bypassed via switch for safety purpose.
 

Neutral or hot connection of the triac switches isn't the point, I believe. That's more or less arbitrary and doesn't really matter when using opto isolation and connecting to a 230 V wall outlet without dedicated neutral.

The problem is that the manual switches can be bypassed by triacs by design. If this is a problem, e.g. safety-wise, you have to design the circuit differently, using a multi-pole "main" switch or a respective contactor. Simple and obvious.
 

In your point of view live are directly connected to the one end of the Load,That way neutral can be bypassed via Triac .But line directly to the load and neutral via switch is not the proper method for wiring .Line are bypassed via switch for safety purpose.

You did not understand correctly. You need to shift the load, along with the capacitor-resistor snubber, to the line just above. In other words, the loads should be connected to the line side and not to the neutral side.

The manual switch must be shifted parallel to the triac. When the manual switch is on, the triac will be bypassed.

You need to put a capacitor in parallel to 330R to prevent spurious triggering.

The opto-isolator is also wrongly connected. The trigger voltage must be applied between the gate and neutral.

The main switch must be connected directly after the line and not as shown.
 

Hi,

There is no explicit error in your circuit. All the drivin circuit is correct.

The problem is that there is an unwanted current path.

Triggering the the upper triac generates a high dV/dt in the other triacs, causing to switch ON the other loads.

Here your schematic.
Green is the wanted current path.
Red is the unwanted current path.
Triac boardErr.JPG

Maybe a snubber across the triacs can help.

I try to find another solution.

Klaus

- - - Updated - - -

**
What about moving the snubber circuits (away) from the load to the triac.

Klaus
 

It's unclear if the OP complains about unwanted triggering or the possibility to get a load switched on through triacs with "main" switch off. Unwanted triggering can be probably avoided by state-of-the-art snubbers, intentional switching can't be blocked without using multi-pole switches.
 

What about moving the snubber circuits (away) from the load to the triac.

Klaus

I have tested the snubber across the Triac,There is no problem for inductive load but in resistive load when i connect less than 5W means it is continuously glowing without Triac being ON.Then I measured the output voltage of Triac when it is being OFF,It shows 230V.
 

Hi,

Measuring a high impedance voltage is meaningless.

For sure a 100n has a known impedance, causing limited current to flow.
For low current loads use low value capacitors.

Klaus
 

Does high impedance voltage affect,when any one touch it?.
A triac switch won't be recognized as safety switch in any case, in so far the question isn't actually relevant. The circuit behind the triac must be considered as hazardous contact voltage, no matter if the triac is on or off.
 

Does high impedance voltage affect,when any one touch it?.

It depends; the final damage is caused by the flow of current and not really the voltage.

If you receive 12V via an intravenous injection needle, it can be fatal (if the return path is also low resistance).

On a dry winter day, standing on a set of dry glasses (acting as an insulation), you can be charged to 25KV without feeling any effect. You will get a shock only when the charge is discharged.

1mA flowing directly via the heart is *very* dangerous. The heart always provides a parallel low resistance path to current.

5mA current flowing through your body (dry skin) is very dangerous. Leakage currents in triacs will be in uA (100s) but you will get a shock. If there is a snubber, that can be dangerous (because it can store larger energy).

Common neon lamp testers (for line level voltages) allow about 1mA to flow through the body. It is very important to respect high voltages.
 

hi,
I have used SPDT switch instead of both manual and main switches. Now i can switch the load either manually or via controller. Thank you to all.
 

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