problem regarding ac load

Hi all

I am controlling a relay through a CARD which is basically a usb device. When i make the digital output of the usb device high then the transistor conducts and energizes the coil of 12 volt SPDT Relay. On the normally open contact i have connected an AC solenoid valve . As the coil of the relay energizes the relay actuates and AC supply is provided to the Solenoid valve and the valve opens. But when i make the digital output of USB card low then the valve closes but it hangs my USB  CARD. Why every time my usb CARD hangs when i shuts off the AC valve.

Circuit image is also attached

Do you have a diode across the coil of the relay?

Since the contacts on the relay are completely isolated from the coil the fact that you are switching AC voltage shouldn't cause an issue.

However, not have a diode on the relay coil will cause the power supply to short out when the relay shuts off and can lock up the hardware on the card. 

Yes i have placed a diode across the coil of the relay to provide ground to the back e.m.f.

But still it is giving the problem.

Can you post the diagram?

Does it work properly if you disconnect the solenoid?  What about if you replace the solenoid with a light?

Hi

I have tested Solid State Relay with the solenoid valve , it works perfect but still i can not understand why the normal SPDT relay gives the problem

The only other thing I can think of, if you diode is connected properly, is that that the contact switching in the relay is generating noise that is picked up by the coil and brought to the DC side.  Have you put an oscilloscope on the DC power supply and watched it as you turn the relay on and off?

It's very common to use an opto isolator between low voltage DC and high voltage AC - I would bet that the solid state relay is using one. 

There are a few tests you can do - like disconnecting the AC voltage and seeing how the system performs.  If it works fine with no load then you can assume the load is generating noise.  If the problem still exists, but doesn't happen with the solid state relay, you can assume the coil of the relay is causing your problem.