Triac/Optoisolator combo - why won't it turn off?

[krp_eee]

I bought a solid state relay (made of triac with zero crossing detected optocoupler), it turned on/off sine wave AC of Line by 5 volt dc. But it didn't turned off UPS voltage(square wave), it remains always on.

 

[FvM]

But it didn't turned off UPS voltage(square wave), it remains always on.

Yes, this sounds reasonable. A ZC detector SSR doesn't work with square wave. You need at least a sufficient low impedance snubber to reduce dv/dt. But it may not work at all.

 

[krp_eee]

I tasted it in AC Line of pure sine wave 50Hz, 220V, but when it off, it gave 40V ac on load, why? i tested a triac in same line, but it's ok. (And load current is too small <1A. So di/dt is not problem here)

 

[FvM]

The measurement setup isn't very clear. A residual voltage with high impedance or no load may be caused by the snubber circuit.