Contactor Triac Power Supply Problem

[ibwev]

Please reference the attached circuit. What is causing the voltage to increase when the switch is closed?




Triac Datasheet
https://www.electro-tech-online.com/custompdfs/2013/02/BTA2008W-600D.pdf

Voltage Regulator Datasheet
https://www.electro-tech-online.com/custompdfs/2013/02/LM317M-DPDF.pdf

 

[cowboybob]

Why such an elaborate circuit for triggering the triac?

 

[ccurtis]

You're overdriving the gate of the triac (assuming the triac terminals are all connected properly, not labeled on your diagram). Recommend a 560 ohm resistor in series with the switch, using your attached circuit topology. Can't say how that explains the voltage rise for sure, but it's a good place to suspect what's causing the problem.

But, yes, why not just connect the switch with a series resistor between the gate terminal and the T2 terminal of the triac and forget the power supply?

 

[ibwev]

Why such an elaborate circuit for triggering the triac?

I am attempting to figure out the power supply for a circuit that will eventually include a pic, leds and a buzzer. The pic will perform a series of test before sending a signal to the triac.

 

[ccurtis]

Whoa, there's something amiss too, because there's no reference for the gate voltage. The way you are doing it is not proper.

 

[cowboybob]

Design your PS circuit to power the PIC, LED and buzzer (I'm assuming all are 5VDC) as a separate unit from the triac.

Then use an output of the PIC to drive, for instance, an opto-isolator triac such as this:

https://www.electro-tech-online.com/custompdfs/2013/02/nte3048.pdf
for switching the contactor.

 

[ibwev]

You're overdriving the gate of the triac

I was able to connect a few resistors in series to give me 590 Ω. This reduced the voltage to about 6.2. So I experimented further and found that about 3.2 K ohm resistance works nicely. It brings the voltage to 5.0 and still triggers the gate. However, the voltage is about 13.4 where the gate pin of the triac meets the resistor. Please see diagram.

1) Should the gate pin read 13.4 volts?

2) How do I calculate the required resistance value for the gate pin of the triac?

 

[ccurtis]

It might work, but the circuit is not proper for controlling the triac using a PIC. What you are reading is the average magnitude of an AC waveform that is alternating in polarity and developed between the gate of the triac and an arbitrary node. That is not the gate voltage you are reading, from the standpoint of what gate voltage means to triac operation anyway. You must reconsider your entire circuit topology if you want to be successful.

 

[ibwev]

as a separate unit from the triac.

1) Does this mean I can not use the 24 VAC power source of the contactor to power the pic that will control the triac?

2) If not, could I use the 120 volt power source of the transformer that controls the contactor to power a pic that will control the triac that will operate the contactor? (see diagram) (toe bone connected to the foot bone, the foot bone connected to the ankle bone......tehehe)

 

[cowboybob]

!. You could, but:

I'd go with 2. The contactor, being inductive, is going to generate a substantial, reverse current inductive "kick" once released. No need to have that flying around the more sensitive analog/digital power buss(es), even if you can snub most of it out.

 

[gerty]

You should have filter/stabilizing capacitors on input and output of regulator.
You show a 40Ω resistor between output and adjust, data sheet shows 240Ω.
Look at data sheet it has a world of useful info.


edit: The above will help on your voltage regulation

 

[ibwev]

Gerty,

Thanks for the information. I have a couple of questions.

Look at data sheet it has a world of useful info.

I tried to follow Figure 1 of the datasheet.

You should have filter/stabilizing capacitors on input and output of regulator.

The fine print asterisk on page 1 implies it is not necessary. Should I instead follow Figure 6 Ripple Rejection Test Circuit?

You show a 40Ω resistor between output and adjust, data sheet shows 240Ω.

40Ω and 120Ω resistors are more readily available with higher precision and wattage. I took the formula in Figure 1 to mean that the size of R1 may be altered. Using the 40Ω and 120Ω resistors produces 5 volts but would 240Ω and 720Ω resistors make the circuit more stable?

Again, thanks for the help.