LED bulbs flickering with time lag switch

[ariemich]

I live in a condominium with a staircase lit by 9 LED bulbs of 10-11 w each. The bulbs are controlled by a time lag switch produced by Hager Electro, with 3-wire connection. Several months ago the lights started flickering, or even fading for several seconds and then going up again, in the timer mode of the switch. This did not happen, however, in the constant light mode. Putting the blame on the switch, I bought and installed a new one, of the same type but from a different manufacturer. To my extreme surprise, the phenomenon appeared again!
Then I went to measure the voltage on the input (L) and output (4) terminals of the switch relative to N. With the light switched off, the input was, as expected, the mains voltage of 223 v. With the bulbs lit and the switch in the permanent light mode, the voltage on both terminals was 208 v (voltage drop of 15 v probably due to internal resistance in the mains) and stable. However, in the timer mode the voltage fluctuated between 210 and 216 v. Thus we observe instability in voltage drop, which is due to instability in current, which in turn is due to instability in effective load resistance. Now the load consists of the same 9 bulbs plus the wires leading to them, so it must be constant. So where do the fluctuations come from?!
Another question: the observed voltage changes are small compared to the mains voltage, whereas the light changes are fairly strong. It is known that a LED works on DC voltage, which is obtained by rectifying the input AC voltage. Does this mean that there is some threshold voltage in the LED circuitry that cuts the input voltage at some some level close to 200 v, so that the above voltage fluctuations are felt very strongly?
Any reasonable explanation and advice should be appreciated.

 

[Pete999]

I live in a condominium with a staircase lit by 9 LED bulbs of 10-11 w each. The bulbs are controlled by a time lag switch produced by Hager Electro, with 3-wire connection. Several months ago the lights started flickering, or even fading for several seconds and then going up again, in the timer mode of the switch. This did not happen, however, in the constant light mode. Putting the blame on the switch, I bought and installed a new one, of the same type but from a different manufacturer. To my extreme surprise, the phenomenon appeared again!
Then I went to measure the voltage on the input (L) and output (4) terminals of the switch relative to N. With the light switched off, the input was, as expected, the mains voltage of 223 v. With the bulbs lit and the switch in the permanent light mode, the voltage on both terminals was 208 v (voltage drop of 15 v probably due to internal resistance in the mains) and stable. However, in the timer mode the voltage fluctuated between 210 and 216 v. Thus we observe instability in voltage drop, which is due to instability in current, which in turn is due to instability in effective load resistance. Now the load consists of the same 9 bulbs plus the wires leading to them, so it must be constant. So where do the fluctuations come from?!
Another question: the observed voltage changes are small compared to the mains voltage, whereas the light changes are fairly strong. It is known that a LED works on DC voltage, which is obtained by rectifying the input AC voltage. Does this mean that there is some threshold voltage in the LED circuitry that cuts the input voltage at some some level close to 200 v, so that the above voltage fluctuations are felt very strongly?
Any reasonable explanation and advice should be appreciated.

I live in a condominium with a staircase lit by 9 LED bulbs of 10-11 w each. The bulbs are controlled by a time lag switch produced by Hager Electro, with 3-wire connection. Several months ago the lights started flickering, or even fading for several seconds and then going up again, in the timer mode of the switch. This did not happen, however, in the constant light mode. Putting the blame on the switch, I bought and installed a new one, of the same type but from a different manufacturer. To my extreme surprise, the phenomenon appeared again!
Then I went to measure the voltage on the input (L) and output (4) terminals of the switch relative to N. With the light switched off, the input was, as expected, the mains voltage of 223 v. With the bulbs lit and the switch in the permanent light mode, the voltage on both terminals was 208 v (voltage drop of 15 v probably due to internal resistance in the mains) and stable. However, in the timer mode the voltage fluctuated between 210 and 216 v. Thus we observe instability in voltage drop, which is due to instability in current, which in turn is due to instability in effective load resistance. Now the load consists of the same 9 bulbs plus the wires leading to them, so it must be constant. So where do the fluctuations come from?!
Another question: the observed voltage changes are small compared to the mains voltage, whereas the light changes are fairly strong. It is known that a LED works on DC voltage, which is obtained by rectifying the input AC voltage. Does this mean that there is some threshold voltage in the LED circuitry that cuts the input voltage at some some level close to 200 v, so that the above voltage fluctuations are felt very strongly?
Any reasonable explanation and advice should be appreciated.

could be the driver is either faulty or the wrong sort.

 

[ariemich]

could be the driver is either faulty or the wrong sort.

You mean the internal driver of one of the bulbs?

 

[picturevalve]

Perhaps your led lamps are not meeting the minimum load for proper operation? Have you checked the manufacturer literature?
I've just turned up this web page which suggests a solution, the customer has the same problem as you. Certain time delay switches are not suitable for led/low loads:

LED Bulbs installed on a circuit with a timer are flickering - Well Lit

Customer Question Hi, I have bought some 9W e27 led bulbs from you for indoor and indoor use. Indoors they are fine, as well as some outdoor fixtures (ip rated). However, when applied to some of the fixtures outdoors, they flicker continuously when not turned on. Do you know how I can solve...

well-lit.co.uk

 

[dmxtothemax]

Try adding another load to the circuit,
try an incandesant lamp 100 to 150w.
See if it behaves better.

 

[ariemich]

Try adding another load to the circuit,
try an incandesant lamp 100 to 150w.
See if it behaves better.

We had no problem of flickering or flashing with incandescent lamps. We replaced them with LEDs to save energy while gaining luminosity. I am almost sure that if we had an old-fashioned bi-metal time lag switch instead of electronic one, there would be no flickering. But they are not on sale any more.