ECN Forum Forums General Topics of the Trade General Discussion Area blinking photo cell

hi all
happy holidays.
i have a problem with photo cell for a sign.
it keeps blinking in the day time.i have put 3 different typs in and still blinks...anyone have a answer????
thanks

Permit me to walk myself through this situation. Perhaps it will spur some connection with someone else and then they can find the solution. Photocells usually fail so as to leave the lights ON. If it was a night-time problem it would be reflected light causing the blinking. Since it happens in the day, assuming its not in some real dark place, it should leave the lights turned off. When the lights are first turned on, the photocell takes some time to respond to daylight, and the lights are turned off. If there was a loose connection, it would cause the photocell to turn on the lights erratically, not "blinking". If you have only one fixture in the sign, then it could just be a problem with the fixture ballast overheating and tripping out thermally..over and over again. But the light wouldn't be on in the first place if the photocell was working ok. If it is multiple lights..then I'm stumped! Not likely a mis-application of photocells, since the sockets are keyed for the operating voltage, but if it is hardwired in, perhaps someone else replaced it with the wrong voltage rating, and everytime you replace it it gets toasted because of too high a voltage. That would leave the light turned on, and the resulting blinking might just be a ballast problem, as I mentioned earlier....

Just a guess:

if the photocell sees any light from the sign direct or reflected it will think it's daylight and shut off. now that it's dark, it will comeback on and so on and so on.

Photocells sometimes have 5 min delays built in so if it's happening evey 5 min or so, this could still be.

Good luck.

If this photocell is connected with its supply run through a time clock first, the PC will come on for a short period when the time clock makes.

i could understand if it were doing it at nite but it does it in the day time.
i want to say the sign has atleast two ballasts and works fine without the cell in the circuit.i got the same type on the roof sign and it works fine.
i dunno i'm stumped on something so simple...

Are you near any trees? Maybe even an airport? When you say blinking, do you mean on off on off repeatedly every few seconds; or on for a few seconds, off for a few minutes?

Obviously the sign is receiving power in some way so only three scenarios that come to mind. First--Defective photocell. Did you try three different manufacturers or three different photocells from the same manufacturer? Sometimes, bad batches of product are shipped.

Second--Good photocell, combinations of temporary shade and settings on the photocell are causing it to close.

Last--Somehow there is a short occuring around the photocell. Maybe a skinned conductor is on each side of the j-box and the j-box is not grounded.

Actually another far reaching idea comes to mind--induced currents on the load side of the photocell. This is probably not the problem but just in case there is some strange configuration of signs and conductors together.

Good luck.

Just had this problem 3 days ago!!! If you are using a twist lock type photocell, try putting a new base in. We received a batch of bases that the contacts didnt line up quite right in the base and caused an intermittant connection. Thus causing are fast acting Tork photocell to turn on and off in intervals. Hope it helps.