Photocell controlling an 120V relay

[powerplay]

I have come across a K121 photocell controlling an Bronnen 120V 30A relay (black cube with quick connects sticking out) that switched two lighting circuits. I was informed that it had been working a long time, so simply replaced the parts which worked for a day but now does not shut off again. What would cause the relay to fuse ?? Does the photocell have issues switching a solid state relay ?? Would changing the magnetic light ballasts to electronic ballasts have an effect?

Thanks again!

 

[480sparky]

Is the load impressed on the contacts far in excess of their rated capacity? If they're 10a contacts, and the load is 25a, they may simply weld themselves closed after a couple arcs.

 

[wireguru]

look carefully at the ratings on the relay. Those types of relays while having a 30a general purpose rating, the rating for lighting use is much smaller. I am looking at one with a 40a @ 277v rating, but its only good for 10a @ 120v for tungsten lighting. This is why we use lighting contactors for lights, and why these contactors are so huge compared to the relays. The relays weld themselves closed with the filament inrush current.

 

[wireguru]

oops, i didnt read your whole post. Is this a solid state relay? The 'inductive kick' (i dont know the proper term) from magnetic ballasts can fry them. There are ways to fix this with caps and an inductor.

 

[IMM_Doctor]

If you replaced the original electro-mechanical contactor with a solid state power switching device, you probably will need some sort of loading resistor across the "gate" (control input) of the solid state power switching device.

The off-state leakage of the photo-cell is higher than the turn-off voltage/current of the SSR.

 

[powerplay]

thanks for all your feedback....the funny thing is that I was told it worked fine for years, but lately that it changed...perhaps they just didn't notice the 24 hour lighting.

 

[sawdust454]

Different solid state relays may have a higher cutoff voltage to it's "coil". If you replaced it chances are it is not the same brand or model number.
As IMM_Doctor said you may need to add a load to the coil terminals and since it is an ac ssr a simple pilot light may work. Also as wireguru and 480sparky said check the actual load to see if it is in excess of what the ssr can handle.