K2634 TRIAC Switch Card problem - output stays on

I am facing following problem with my K2634 board:

Quickly switching the outputs works ok, but if I keep one of the outputs powered for some time, then I can not get the power off, even when disabling it via its corresponding input control (led off). Looks like the triac output stays “connected”. Only way to reset from this state is to temporarily remove the load from the output. Then the output again listens to the input signal.

Anyone a clue about the cause and work-around?

Thanks a lot in advance, Patrick

Most likely due to the load.
What load are you using?

On two outputs I connected water pumps. On a third output I connected a 75W UV lamp.
(My application is a swimming pool controller)

N.B. One of the two pumps takes quite some power, so I replaced the triac of that output by a similar type with higher max current. On that output I did not see any problems (yet). Don’t know whether that’s a lucky shot, or due to the different triac type of different pump type.

These triacs are not suited for inductive loads. Furthermore, they are not equipped with a snubber network.

Pumps and lamps are inductive loads? Why is one output working ok and others not?

On a different forum I read something about snubber networks: capacitor and resistor in series.
Could that be a work-around? How big should capacitor/resistor be? Is there some formula/way to calculate?

A pump is a motor. Motors are inductive loads.
An UV lamp is most likely a capacitive or inductive load.
One works because as you mention you have replaced the triac with a different one.
A typical snubber network is a 220 ohm/1W resistor in series with a 100nF/400V cap, in parallel with the load.

Did you check the dissipation of the triacs? As you say that quickly switching works, heat might also be a problem.
Careful: Do not touch the triac while they are live, as they are not isolated from the mains.

Heat shouldn’t be the issue because the I also have the problem with the 75W lamp.
I will try the snubber network, and replace all triacs with higher power versions.
Thanks so far, Patrick.


would a BT137 be bether suited for the 220v/50hz/55w inductive load of an single phase AC motor ?
(probably a PSC type but not sure, its a domestic table fan with a four speed selector and a thick 1,5uF Condenser inside)

what values for the R and C of a Snubber network should I use for this kind of load ?


Mostly, the resisotor = 100 ohm, capacitor = 0,1µF (=100nF) but must be an X2 type. (250V AC or 400V DC)


what about the triac?
I have some BT137
should I use the TIC206M included in the kit or use the BT137?

Difficult to say, please experiment.
Please note that with most low power motors, the snubber network can cause them to run continuously.
In that case, choose a smaller cap.