AC LED string lights flickering.

Thread Starter

Biocellguy

Joined Jul 14, 2021
4
I am converting white LED string lights into over head outdoor lighting. The box says I can connect up to 45 strings. I will only need about 10.

Since they flicker, I made a functional rectifier using 4 x 1N4007 (2 x 2 series and 2 x 2 parallel). During the test, I used a capacitor rated 4.7uF and 400 V. [All 5 components I desoldered from old phone chargers.] All of the lights turn on and stopped flickering.

When I finish, all will be encased in weatherproof housing.

Each full wire (70 LEDS) is 4.8 W and 0.04 A, and each LED is 3.4 V and 0.068 W.

One full string is actually a manufactured two strings of 35. At the end of the full 70 (2 x 35), is a two prong female outlet designed for daisy chain. [With the rectifier, I have to make note of the rectified polarity.]

My home is standard US 120 V.

I know directly rectified DC is more dangerous than the corresponding AC.

Once I create this bridge, how much should I decrease the DC to allow for 10 strings (700 LEDs) and be safe?

Is there a better off the shelf device I could buy?

Can I possibly use an old cell phone charger? Maybe remove some post rectified components to increase the DC to the needed output for 700 LEDs (10 strings x 70 LEDs).

Thank you for your feedback.
 

DickCappels

Joined Aug 21, 2008
7,707
AC is more likely to stop your heart than is DC.

You wrote: "The box says I can connect up to 45 strings. I will only need about 10." I am curious because it might be important: What box? The box the lights came in?

How are the LEDs interconnected? Are all 70 of them series connected 4.3V x 70 =238V) or are they set up as two stings of 35 (119V)? Remember 120VAC has a peak voltage of √2 x 120V =170V Peak.

I think you lessen these concerns but still reduce the flicker by using a full wave bridge rectifier to double the flicker frequency to 120 Hz and omit the capacitors people are not very sensitive to 120 Hz flicker (My own threshold with even bright LEDs when in a normally lit room is well below 100 Hz) unless I move the LED rapidly.

Your idea of adapting a phone charger is an interesting one. There are some chargers that can put out that kind of power, but you would have to follow it with a power supply to boost the voltage to that required to drive the string. Maybe somebody will suggest an inexpensive boost supply that can fill you need.
 

Thread Starter

Biocellguy

Joined Jul 14, 2021
4
The diagram is like on this site: https://lastminuteengineers.com/wp-...Bridge-Rectifier-with-Smoothing-Capacitor.png .

In that, D1 to D4 are 1N4007 and RL is the LED string.

The LEDs on strings directly connect to the main. There are no other components on the wire or plug (except for 2 fuses).

The LEDs are 70 split into 2 (parallel) x 35 series (119V each).

The box refers to the original packaging the lights came in.

I found someone selling the exact "Christmas Lights" I have:
https://www.ebay.com/itm/133778898620 .
 

Dodgydave

Joined Jun 22, 2012
10,050
Don't forget the leds will only work on one half cycle of the mains, so the batch will be wired back to back in series, so one half will work on the positive cycle and the other half on the negative cycle, so they will have a 30Hz flicker .
 

Thread Starter

Biocellguy

Joined Jul 14, 2021
4
Isn't the output from a full rectifier DC? My fear is if somehow some one touches it, being high DC would lock an individual.
 

DickCappels

Joined Aug 21, 2008
7,707
Don't forget the leds will only work on one half cycle of the mains, so the batch will be wired back to back in series, so one half will work on the positive cycle and the other half on the negative cycle, so they will have a 60Hz flicker .
Edit:
I have night lights in my house wired That way. The power is 50 Hz here. The 50 Hz flicker is not apparent until I get very close to the LEDs because at a distance my visual system cannot distinguish between the individual LEDs which are placed adjacent to one-another.
 
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Thread Starter

Biocellguy

Joined Jul 14, 2021
4
I was thinking about what you wrote. With the full bridge rectifier and without the capacitor, it is like an AC-DC hybrid. The AC is converted to "pulsing" DC. So it is basically safer than true DC.
 

DickCappels

Joined Aug 21, 2008
7,707
I was thinking about what you wrote. With the full bridge rectifier and without the capacitor, it is like an AC-DC hybrid. The AC is converted to "pulsing" DC. So it is basically safer than true DC.
You are right, it should be safer than AC. As a benefit the flicker rate is doubled from 60 Hz to 120 Hz which is more difficult to see.
 
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