120volt photo cell energizes 120volt coil on contactor but will not de energize

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Matt Mckenzie

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I tried 2 different new 120 volt photo cells on a 120 volt parking lot lighting contactor with 120volt coils. Photo cell would energize contactor but not turn off. Mechanical clock would turn contactor on & off no problem. Any idea
 
Matt Mckenzie said:
I tried 2 different new 120 volt photo cells on a 120 volt parking lot lighting contactor with 120volt coils. Photo cell would energize contactor but not turn off. Mechanical clock would turn contactor on & off no problem. Any idea
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Guess: If you were testing it in bright sunlight, whatever you put over the photocell to simulate darkness was not dark enough e.g. light would shine through your hand. Black tape usually works well.
 
Coppersmith said:
Guess: If you were testing it in bright sunlight, whatever you put over the photocell to simulate darkness was not dark enough e.g. light would shine through your hand. Black tape usually works well.
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I think you mean the opposite since he says that the photoeye would not turn off the contactor. When sunshine was available.
Possibly did not wait long enough (approx 3 minutes) for photoeye to switch state or does not have photo eye and timer connected correctly to give proper results.

power to timer......then to eye......then to contactor.
set timer ON early morning so eye takes control durring daylight hours (this will allow lights to come on durring inclimate conditions/eclipses/evening) then timer OFF at desired time of night you don't want lights to operate.
 
Photocells usually do not immediately turn off their output power. It sometimes can take several minutes for them to 'react' to sensing lack of light.

Also, black is usually the input, red is output. If you swap them, sometimes it can cause this problem.
 
Matt Mckenzie said:
I tried 2 different new 120 volt photo cells on a 120 volt parking lot lighting contactor with 120volt coils. Photo cell would energize contactor but not turn off. Mechanical clock would turn contactor on & off no problem. Any idea
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One of the most popular designs uses a normally closed contact - so the output is "on" immediately when you energize it. The presence of light on the cell allows current to flow through a small heating element which in turn operates a bimetal strip which has one side of the contact attached to it. Absence of light lets the strip cool and close the circuit again. Time is needed for both heating and cooling of the strip, usually at least a minute but sometimes up to five minutes.
 
Its not a mechanical latching contactor, is it? When you turn off the power to the photocell, does the contactor open?
 
steve66 said:
Its not a mechanical latching contactor, is it? When you turn off the power to the photocell, does the contactor open?
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growler said:
He did say it's parking lot lights. A mechanical latch would be common to protect the contacts.
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First thing I thought of too. The time clock has a Form C contact, so one contact closes to turn it on (Latch coil), then other closes to turn it off (Unlatch coil). The photocell has only one state.
 
Jraef said:
First thing I thought of too. The time clock has a Form C contact, so one contact closes to turn it on (Latch coil), then other closes to turn it off (Unlatch coil). The photocell has only one state.
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Which is why there are products on the market (or build your own with time delay relays) which provide two momentary contacts on state change from a simple continuous on or off input.
 
Just a thought. Drop out current is usually far less than pull-in current. Maybe it it isn't getting below drop-out current?
 
170918-2000 EDT

Some simple tests and measurements should solve the problem.

Test a photocell in the shop and see how it works.

Measure current and voltage at various points in the field and see what the results are.

.
 
gar said:
170918-2000 EDT

Some simple tests and measurements should solve the problem.

Test a photocell in the shop and see how it works.

Measure current and voltage at various points in the field and see what the results are.

.
Click to expand...

Also close circuit path of photocell contacts and then open that path, both with photocell disconnected, and see what the relay does!
 
Don't know much about this circuit are the lights are 120 or 240 volt?

But all depends on the circuit, some times using a 120 volt switching device on 240 volt
light circuit will cause a feedback through the other line light loads and cause the lighting contactor not to drop out.
 
ronaldrc said:
Don't know much about this circuit are the lights are 120 or 240 volt?

But all depends on the circuit, some times using a 120 volt switching device on 240 volt
light circuit will cause a feedback through the other line light loads and cause the lighting contactor not to drop out.
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You can tap 120 volt controls off a 120/240 circuit, but is a good idea to make all controls 120 to prevent possible unintended backfeeding from causing such problems.

Keep all relay coils or other control loads at 120 volts or provide relay isolation if 240 volt items are necessary for some reason
 
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