why the lights stay ON

[Ponchik]

A friend of mine had installed 4 motion sensor lights and instead of using incandescent bulbs he installed CFL. However, ALL of the lights were staying ON 24 hours a day regardless if it was dark or if they saw motion. I suggested to replace the bulbs with incandescent and that has solved the problem.

Now I like to know why incandescent solved the problem. How were the CFLs over riding the motion sensor and the photocell?

Thanks for your input.

 

[augie47]

There may be a better explanation than this, but I have found some motion sensors that require a minimum load to work properly.

 

[Smart $]

A friend of mine had installed 4 motion sensor lights and instead of using incandescent bulbs he installed CFL. However, ALL of the lights were staying ON 24 hours a day regardless if it was dark or if they saw motion. I suggested to replace the bulbs with incandescent and that has solved the problem.

Now I like to know why incandescent solved the problem. How were the CFLs over riding the motion sensor and the photocell?

Thanks for your input.

Possibly has thyristor (TRIAC) output control and no snubber for reactive circuit loads.

 

[steve66]

TRIAC's are finiky devices. Once they are turned on, they will not turn off until the current flowing through them goes to zero. (That is, they won't turn off until the current flowing to the load goes to zero.)

That normally happens 120 times per second with an incandescent light bulb, or with a resistive load. With that type of load, the current follows the voltage. The voltage crosses zero 120 times per second, and so does the current.

But with a compact fluorescent light, the load is the ballast. And a ballast can do funny things to the input current. My guess is that the ballast has some filtering that keeps the current from going to zero.

 

[GoldDigger]

Possibly has thyristor (TRIAC) output control and no snubber for reactive circuit loads.

Another potential problem is that many motion detector circuits deliberately incorporate a function to override the motion detector if a series switch is turned on, off, then on again. Capacitor charging currents and arc discharges inside the CFL from the very low current the motion detector relies on while sensing could cause the sensor to think that the switch is being constantly flipped.
If you look very closely in the dark, you may see the CFL flashing at a low level.

 

[Smart $]

TRIAC's are finiky devices. Once they are turned on, they will not turn off until the current flowing through them goes to zero. (That is, they won't turn off until the current flowing to the load goes to zero.)

That normally happens 120 times per second with an incandescent light bulb, or with a resistive load. With that type of load, the current follows the voltage. The voltage crosses zero 120 times per second, and so does the current.

But with a compact fluorescent light, the load is the ballast. And a ballast can do funny things to the input current. My guess is that the ballast has some filtering that keeps the current from going to zero.

Been many, many years since I've had any interaction with triacs on the component level, but as I recall, the voltage and the current must have simultaneous zero crossings to turn off. That's why a snubber is needed for reactive circuits.

 

[GoldDigger]

Been many, many years since I've had any interaction with triacs on the component level, but as I recall, the voltage and the current must have simultaneous zero crossings to turn off. That's why a snubber is needed for reactive circuits.

If there is no current drive to the trigger electrode, then the triac will turn off when the current goes through zero. And necessarily at that point the voltage across the triac is also zero.
What is happening to cause what Smart $ is referring to is that the control current through the trigger of the triac is usually derived from a time/phase-shifted version of the waveform applied from hot to neutral or hot to load rather than the instantaneous voltage across the triac itself. The current into the trigger electrode has to be zero at the same time the current through the triac goes through zero.

 

[hurk27]

Could be the design of the motion detector circuit, I have several installs where I have 26 watt CFL floods on motion detectors and never had a problem?

It could be the caps they have on their power supply keeping a voltage on the output of the triac in the motion detector???

 

[GoldDigger]

Could be the design of the motion detector circuit, I have several installs where I have 26 watt CFL floods on motion detectors and never had a problem?

It could be the caps they have on their power supply keeping a voltage on the output of the triac in the motion detector???

And I have had the opposite experience with two 8-watt LED floods in a motion detector fixture. The motion detector never turned on the LEDs from motion, only from flip-flopping the wall switch, while with normal 50-watt incandescents it worked fine.

If you have a motion detector rated only for use with incandescents and add in CFLs or LEDs not rated for use with a dimmer or motion detector, all sorts of bad things can happen.
One quick experiment you can try if they are two-bulb fixtures is to replace just one of the CFLs with a small (20-watt or less, maybe even 4-watt nightlight) bulb and see what happens.

 

[Little Bill]

Could be the design of the motion detector circuit, I have several installs where I have 26 watt CFL floods on motion detectors and never had a problem?

It could be the caps they have on their power supply keeping a voltage on the output of the triac in the motion detector???

And I have had the opposite experience with two 8-watt LED floods in a motion detector fixture. The motion detector never turned on the LEDs from motion, only from flip-flopping the wall switch, while with normal 50-watt incandescents it worked fine.

If you have a motion detector rated only for use with incandescents and add in CFLs or LEDs not rated for use with a dimmer or motion detector, all sorts of bad things can happen.
One quick experiment you can try if they are two-bulb fixtures is to replace just one of the CFLs with a small (20-watt or less, maybe even 4-watt nightlight) bulb and see what happens.

I've heard several poeople say that you can't use CFL bulbs in a light with motion sensor and dusk to dawn features.

It may be a brand thing because I had one up for 5 years and it worked fine until the motion sensor went out on it. It also had the function of coming on half bright at dusk and going to full bright on motion. All of that worked fine with the CFLs.

It was cheaper to buy a new light then to try and replace the motion sensor.
I did however put in regular Par floods in the new light.
I like the light output better on the incandescent. Plus the CFLs take longer to come on, especially when it's cold.
The CFLs were bought by mistake since they look like regular floods on the outside.