Triac wont switch off

Thread Starter

Garydwall

Joined May 16, 2019
11
Hello, sorry I know this is very basic but I want to understand the problem.

I have an output on a boiler circuit board which feeds the ignition. Normally a small 550 watt ignition is connected directly to the output and switches on and off correctly.
The output is controlled by a triac.

I have fitted a larger ignition 1600 watt and have wired the output to a 230 volt coil of a contactor and fed the ignition from a separate supply so as not to damage the circuit board.

The problem I have is the contactor does not switch off as the triac still outputs approx 40 volts when the circuit is switched off by the circuit board.
What is the best solution to dissipate the 40 volts and allow the contactor to de energise. ??Screenshot_20210203-090230_Drive.jpg

Thank you very much.
Gary
 

drc_567

Joined Dec 29, 2008
1,111
... A generic guess, but you might place a snubber circuit in parallel with the triac, to prevent erroneous triggering. Try a 47 Ω resistor in series with a 10 nF capacitor for the snubber. ... Values may vary depending on power factor involved.
 
Last edited:

Thread Starter

Garydwall

Joined May 16, 2019
11
... A generic guess, but you might place a snubber circuit in parallel with the triac, to prevent erroneous triggering. Try a 47Ω resistor in series with a 10 nf capacitor for the snubber. ... Values may vary depending on power factor involved.
Thank you
 

Alec_t

Joined Sep 17, 2013
12,080
the triac still outputs approx 40 volts when the circuit is switched off by the circuit board
Does the triac still work correctly to switch the smaller ignition unit on and off? If not, it's possible the triac has been damaged trying to drive the larger unit and now has a short between its main terminals.
 

Thread Starter

Garydwall

Joined May 16, 2019
11
Does the triac still work correctly to switch the smaller ignition unit on and off? If not, it's possible the triac has been damaged trying to drive the larger unit and now has a short between its main terminals.
Thank you yes it works correctly with small ignition
It does not switch off when connected to a1, a2 of a 230volt contactor coil
 

LesJones

Joined Jan 8, 2017
3,188
Could it be the reactance of C65 being low enough to produce 40 volts across the coil of a small contactor. (What is the value of C65 ?) You could put a capacitor of similar value to C65 in series with a 47 ohm resistor across the contactor coil to see if that improved the situation. You may have to experiment with capacitor values as some values could form a tuned circuit with the inductance of the contactor coil.

Les.
 

Thread Starter

Garydwall

Joined May 16, 2019
11
Could it be the reactance of C65 being low enough to produce 40 volts across the coil of a small contactor. (What is the value of C65 ?) You could put a capacitor of similar value to C65 in series with a 47 ohm resistor across the contactor coil to see if that improved the situation. You may have to experiment with capacitor values as some values could form a tuned circuit with the inductance of the contactor coil.

Les.
Thank you Les
 
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