LED on Microwave stays lit when switch is off

[techwannabe]

Hi! I'm not an EE or anything. . just a home fix-it guy with an Over The Range Microwave with the external light that shines down on the stove which I replaced with an LED bulb. . .love the color temp over the original incandescent. . .did the same thing with my last microwave without problems. . .this new one however is an issue. Works great but when I hit the switch to turn it off, it still stays lit! Not at standard brightness but enough that at night it lights up the kitchen. I've read that there's a tiny amount of electricity still running through the bulb. . not enough to light an incandescent bulb but the LED's require so little that this is apparently a common problem (Google "Microwave LED Light won't turn off"). Can I somehow either cut the current going to the bulb or put a resistor or something in line to get the "phantom current" from keeping the light on? Either that or find a nice, bright high-color-temperature incandescent to replace it with? Thanks in advance!!

 

[Externet]

It is a common behavior from capacitive leak in 120VAC conductor lines to yield a faint illumination. I have it too on a night table lamp.
Actually myself, I would be happy to have that faint illumination all night in my kitchen from a near zero power consumption.
A resistive or capacitive tiny load added in parallel to the lamp should fix it. Or a relay if you want it elaborated.

 

[techwannabe]

Hey Externet! Thanks for the reply. I agree and faint illumination at night is helpful. . .saves bumps and bruises! That being said, I'd still like the option. . it's really not all that dim! (Maybe I'll try to get a picture at night. . it's basically a night light) To reiterate, I'm not at all familiar with electronics components. . .can you please be specific as to what you'd suggest re what resistor I should be looking at? I'm guessing it's still 120 Volts. . .and "in parallel". . In Googling it, I saw a guy who had the same problem with LED's in his car and he basically just popped out the bulb that has a connector at each end. .and clipped each end of the resistor in with each end of the bulb when he popped it back in. . I'm guessing with this bulb I'd need to place the resistor spliced in one of the power supply lines? Again, much appreciated if you can suggest an actual resistor designation as I have next to no idea ~ thanks again!

 

[Les Jones]

The problem is caused by capacity coupling between the live feed and the switched wire to the lamp. A resistor in parallel with the lamp would solve the problem but would consume power when the light was switched on. I have used a capacitor in parallel with the lamp. This has current passing through it when the lamp is on but it is 90 degrees out of phase with the voltage so it does not consume any power so it does not get hot. I use a contact suppressor (which is a capacitor with a low value series resistor.) rather than just a capacitor. The reason I use these is that they are available with flexible lead connections so I can just connect it to the lamp holder connections. This is the sort of thing I am talking about.

Les.

 

[techwannabe]

Hi Les! Thanks for the thoughtful reply. Again, I know very little about electronics. . resistors, capacitors, values, etc. or even what to order but I'm attempting to educate myself a bit. I like the sound of "a resistor in parallel" as it seems to be the simplest to install and as the LED emits light even with very little current flowing, I'd have to guess that whatever power the resistor consumes when it's on wouldn't even be noticeable, am I right? If so, what spec resistor would I purchase and how/where would I install it? I found a video that kind of explains this phenomenon but, again, it's a bit over my head. .

. How exactly would I connect that Contact Suppressor and is that the exact one that I'd need that you linked to? The light I'm using is a 4W LED 120 volts. Here: https://www.amazon.com/dp/B074RGCPK1 . Thank you again

 

[Les Jones]

It is not practical to calculate the minimum value of capacitor that will solve the problem . To do that you would need to measure the capacitance between the live feed and the switched wire and also the voltage at which the lamp does not light at all. I think the 0.22 uF suppressor will probably work. It will depend on how long the power feed and switch wire run close to each other. The suppressor is connected directly in parallel with the lamp. The one I linked to was just the first one I found on CPCs website. (CPC is part of the Farnell group.) The main thing to make sure of is that it has flexible termination wires so it is easy to fit without using soldered joints and heat shrink sleaving.

Les.

 

[KeepItSimpleStupid]

If a triac is used to control the incadesent bulb, it needs a minimum load to turn off.

Do you know the bulb # you took out?

DC or AC to the bulb?


When I replaced the interior lamps and trunk light with LED, all sorts of weird things happened. When the "max on time" expired, the lamps would turn off. if you opened one door, the trunk light would come on part bright. if you closed the trunk and the door and opened the trunk, the trunk would be full bright. A power resistor in parallel with the trunk LED only fixed it.

Bulbs #; find current; at 12V. Calculate resistor value and wattage for entire or part of the current.

Back when LEDs were fairly new, I replaced a stereo indicator with a LED and I had the partial lighting issue. i have the circuit somewhere that I used. I think I used a Zener diode and some resistors to fix the problem.

A UPB dimmer connected to a LED lamp had the no turn off problem. Added a small incadesent light in the fixture. The fixture was dual bub.

 

[picbits]

I'd agree with KISS above - it is probably a triac driven light and isn't turning off properly given the low load.