Triac burn out

Thread Starter

Amir19997

Joined Jun 13, 2022
9
Hello
I used the attached circuit for controlling the motor in the gate opener control board. we mass produced this device.
Some customers report Triac failed at the starting moment(about 5 percent). I can't burn Triac in our lab.
I attached my EMI filter too. someone says not placing at the output of line filter can make this problem.
Can anyone help me with this problem?
 

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Ian0

Joined Aug 7, 2020
6,281
What is the locked rotor (stall) current of the motor?
Are there any mechanical latches to keep the gate in the position that it is in before the motor starts?
 

MaxHeadRoom

Joined Jul 18, 2013
25,976
That appears to be a zero crossing Triac, possibly it may be better to use a phase angle type where you can use a simple ramp-up circuit at switch on?
 

Alec_t

Joined Sep 17, 2013
13,147
Are your capacitor voltage ratings AC RMS? The 250V rating seems rather low for 220V mains and might be exceeded by inductive spikes.
 

Thread Starter

Amir19997

Joined Jun 13, 2022
9
What is the locked rotor (stall) current of the motor?
Are there any mechanical latches to keep the gate in the position that it is in before the motor starts?
The motor current is not changed in a locked rotor situation.
No, All the Triacs burn out instantaneously. we test this case many times.
 

Thread Starter

Amir19997

Joined Jun 13, 2022
9
That appears to be a zero crossing Triac, possibly it may be better to use a phase angle type where you can use a simple ramp-up circuit at switch on?
As I mentioned in another post, I think using zero-cross switching is safer.
single phase motor control | All About Circuits
This board was tested for about 4 months, if there is a problem in the switching method expect it to happen in our lab too and have more fails.
we recognize most failures happened in small cities so we guess the power source could cause this problem.
another one reported this problem too:
Broken Triac: What Went Wrong? - CR4 Discussion Thread (globalspec.com)
I conclude maybe the EMI filter not working well enough. What's your idea?
 

DickCappels

Joined Aug 21, 2008
9,295
Triacs are sensitive to fast changes in voltage between Main Terminal 2 and the Gate electrode. Quickly changing voltages can cause the triac to turn on, sometimes resulting in the destruction of the triac. A type of circuit that limits the volts per second change across the triac is referred to as a "snubber".

1658925106213.png

Some are more sensitive than others -ST Microelectronics makes a series of triacs that are very robust, referred to as "Snubberless" triacs (if you can afford to use them).

There are people here who are experts in this area so now that I have mentioned the subject I will be quiet.
 

Thread Starter

Amir19997

Joined Jun 13, 2022
9
We buy snubberless triacs from a Chinese company(yzpst). I put snubber cap parallel to Triac too. at least 500 of these boards are installed and 95 percent of boards give errors at the first time they used.
 

Danko

Joined Nov 22, 2017
1,440
Capacitor, connected in parallel to triac, discharges every half of period through triac
with current up to hundreds amperes. These pulses kill triac.
It is why snubbers contain resistor in series with capacitor, which limits
discharge current at level no more than I max of triac.
 
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Thread Starter

Amir19997

Joined Jun 13, 2022
9
Capacitor, connected in parallel to triac, discharges every half of period through triac
with current up to hundreds amperes. These pulses kill triac.
It is why snubbers contain resistor in series with capacitor, which limits
discharge current at level no more than I max of triac.
We used a zero-cross driver(moc3063) so capacitor voltage at the turn-on moment is zero. We test this board hundreds of times to burn out Triac and it was unsuccessful. why does this problem not occur in our lab? why do most of the faults happen in small cities?
 

Danko

Joined Nov 22, 2017
1,440
We used a zero-cross driver(moc3063) so capacitor voltage at the turn-on moment is zero. We test this board hundreds of times to burn out Triac and it was unsuccessful. why does this problem not occur in our lab? why do most of the faults happen in small cities?
Low quality mains lines (sparking connections etc) can provide many random zeros during half of period.
It may happens even in time, while plug will pushing in receptacle.
And capactor parallel to triac, without series resistor is nonsense in electronics design.
51 Ω resistor in series with capacitor solves this problem.
 

MisterBill2

Joined Jan 23, 2018
13,108
Hello
I used the attached circuit for controlling the motor in the gate opener control board. we mass produced this device.
Some customers report Triac failed at the starting moment(about 5 percent). I can't burn Triac in our lab.
I attached my EMI filter too. someone says not placing at the output of line filter can make this problem.
Can anyone help me with this problem?
The statements make no sense at all. Not placing What? Where?? We see partial circuits with not enough information as to what is connected where.
 

DickCappels

Joined Aug 21, 2008
9,295
Is the motor located very close to the controller board, or is there a long cable in-between?

In some areas the power mains are pretty trashy -my guess is that the impedance of the lines in small villages may be high and loads being switched in one part of the grid can show up a distance away. That might result in large voltage spikes on your triac and possibly cause problems.

Is the BTA08 the triac that keeps burning? If so, you might want to place small inductors between the motor connections and the capacitor/triac combination to keep noise from the motor or the motor's wiring from getting back into the traic.

Not being able to reproduce the problem on the workbench means it will take a while to really know when the problem is solved.

1. Surmise cause of problem
2. Apply probably fix
3. Apply design in production
4. Wait for reports of field failures
5. If still failing, go to step 1, else continue shipping and hope for luck.
 

MisterBill2

Joined Jan 23, 2018
13,108
The two snippets of circuit in post #1 do not provide enough information for an adequate analysis. The one detail that is obvious is that indeed the voltage rating of the one capacitor connected across the triac does seem to be rather close. But it seems a bit unlikely that a shunt capacitor should cause a failure, unless it was able to supply a burst of current enough to cause an over-current failure. What sort of failures were they? Short circuited, opened, or just unable to trigger?
Triac failures are usually caused by either excess current or excess voltage, either to the gate or through the device, and if they happen at the moment of turn on application it is most likely not overheating.
An evaluation of the actual circuit may lead to an understanding of the cause.
One more question is about the failures: Did the problem start after some change, such as different part supplier, new PCB material, alternative component? New motor model? or some engineering revision? Or has this been an issue for some time?
 
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