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Old 07-28-2019, 05:42 AM   #1
maxslo
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Question lighting circuit modification

Hello, it's been a long time since my last post and i'm here again seeking advice from more experienced guys

I have a night light that had it's incandescent 10W bulb die recently, and i've bought a 2.3W LED to replace it, but i've immediately noticed that when it should turn on, instead it's flickering. There was only ~130ish Volt AC across the leads for the bulb so i've thought that this must be some sort of dimming mechanism for the incandescent bulb. I've since taken it apart and drawn a schematics to the best of my ability.

No here is the question. What would be the easiest thing to change in the circuit, to maintain the night/light sensing and be able to run the LED off it properly?

Here's the schematic:


Thanks in advance for any input
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Old 07-28-2019, 02:23 PM   #2
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Default Re: lighting circuit modification

you need a resistor in parallel with the led lamp.
i dont know what value, but that circuit uses the lamp as a source of power to the light sensor.
led lights are not resistive, they are inductive.
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Old 07-28-2019, 02:32 PM   #3
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Default Re: lighting circuit modification

Quote:
Originally Posted by stj View Post
you need a resistor in parallel with the led lamp.
i dont know what value, but that circuit uses the lamp as a source of power to the light sensor.
led lights are not resistive, they are inductive.
Ok thanks, i can measure the resistance across LED's circuit, would that help in determining the required resistance?
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Old 07-28-2019, 02:46 PM   #4
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Default Re: lighting circuit modification

MCR100 is an SCR, so when it is turned on it outputs only 1/2 wave pulsing DC to the light bulb.
Your LED lamp probably does not like this and may not work if it uses a capacitive dropper- then it really wants AC, not pulsing DC coming in.
If you post a pic of the LED lamp's circuit, you can figure it out if it will work.
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Old 07-28-2019, 02:55 PM   #5
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Default Re: lighting circuit modification

Ok i'll check if i can take it apart without breaking it.
Just a thought would it be possibile to change the MCR100 out for another element (if it exists), that would output entire sine wave to the lamp.

Edit: I have been able to remove the plastic cover over the LED's, but the circuitry is inside the bulb's base and is not accessible unless i destroy the base :/

Last edited by maxslo; 07-28-2019 at 03:13 PM..
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Old 07-28-2019, 03:35 PM   #6
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Default Re: lighting circuit modification

I did find the same night light circuit but using a CR02AM-8A triac which should give full-wave to the lamp. It is hard to find very sensitive gate (100uA) thyristors.
Attached Images
File Type: jpg automatic-light-dimmer-circuit_triac.jpg (31.4 KB, 20 views)
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Old 07-28-2019, 06:27 PM   #7
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Default Re: lighting circuit modification

Duplicate the circuit in reverse ...
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Old 07-29-2019, 12:38 AM   #8
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Default Re: lighting circuit modification

Thanks, this might be just what i was looking for, i'm just a bit confused about the information i read from the spec sheeet.

namely this:
Capture.PNG

why does it say half sine wave?
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Old 07-29-2019, 04:26 PM   #9
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Default Re: lighting circuit modification

The I2t (amp squared seconds) value is based on the time for a fuse blowing 10-16msec, or 1/2 cycle.
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Old 07-29-2019, 06:59 PM   #10
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Default Re: lighting circuit modification

i might add a capacitor if led flickers too much
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Old 07-30-2019, 12:15 PM   #11
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Default Re: lighting circuit modification

Ok thanks, i've ordered the relay. I'll update the thread once i install it
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Old 07-30-2019, 03:47 PM   #12
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Default Re: lighting circuit modification

Relay? The schematic on your post 1 using the SCR which means the 10W lamp is only be using 5W of power due to half wave action of the SCR, so when you use your meter the Voltage you test is the pulsing DC so it will not show 230VAC.
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Old 07-30-2019, 08:15 PM   #13
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Default Re: lighting circuit modification

Half wave recitification.
https://www.physics-and-radio-electr...rectifier.html
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Old 08-01-2019, 10:54 PM   #14
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Default Re: lighting circuit modification

Your project remind me a electronic project I have tried before about Electric Car Lamp, it's here: https://3celectrons.com/2019/07/25/d...-power-supply/
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Old 08-02-2019, 12:29 AM   #15
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Default Re: lighting circuit modification

This is a night light- how does it remind you of a bicycle light? Nothing in common unless you are trying to sell something.
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Old 09-16-2019, 12:57 AM   #16
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Default Re: lighting circuit modification

Quote:
Originally Posted by maxslo View Post
Ok thanks, i've ordered the relay. I'll update the thread once i install it
Sorry my bad, I meant the triac.. I've just seen that it was rejected to ship out of china due to security issue??? never had that happen before, so i've just ordered one from UK to avoid extra 1-2 months of wait time
I'll post back with results when i receive and intall it.
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Old 10-05-2019, 12:53 PM   #17
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Default Re: lighting circuit modification

The triac arrived an i've installed it. The light now doesn't flicker anymore, however the light also doesn't turn off when it's daytime xD.. i'll give it another go tomorrow
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