Hello,

The ledsign you have drawn is NOT safe.
There is NO isolation betwen the sign and the mains.
When you continue to use unisolated circuits, the staff is allowed to close the thread.
See section 7 of the UA:

I would go for a low voltage power supply to power the ledsign.
There are enough powersupplies that will provide 24 Volts, so you can put a number of leds in series.

Bertus

 

Use a 12 or 24v power pack. Arrange red LEDs in series groups of 5 for 12VDC or 10 for 24v supply. Let us know which LEDs you select and we can help you pick the resistor for each series grouping.

For white or blue LEDs, with a "typical" 3v forward-voltage, arrange 3 per series for 12VDC and 6 or 7 LEDs in series groupings for 24v power pack. Again, let us know which LEDs you select and we can help you with the resistor values.

 

kindly elaborate instead of being vague

Well, if this for a business and is installed in a building, in the U.S. it must meet the national electrical code. Which includes certification by UL or another nationally recognized testing lab.

Bob

 

OK, I highly appreciate your feedback guys. I'll send the diagram tomorrow, but for clarification, I emulated some people who made it seem easy, that is, making LED signs in series. An example of what I'm doing, for elaboration
For example, lets say I have 100 red leds for my sign. I was thinking, use the rectifier to turn 240v AC into 240v DC. I should now find the value of the resistor to use. My guide (he makes these signs, but located a little far away from me) said regardless of LEDs color, they calculate with an average voltage of 2v per 5mm LED. So, with this, the resistor value is 1.6k or higher. With the 100 red LED bulbs, "in my head", this sign is complete.

For this project, i have to do the sign with a couple hundred LEDs.

So, that's my setup/rundown. What could go wrong?

After seeing the gravity of my project! I've drawn the schematic asap.

http://imgur.com/a/P47Lbd9

You probably can't see it from where you are, but your guide is leading you to danger and you're following in the footsteps of idiots. I have no doubt that's exactly how your your guide as well as some random people on the internet make LED signs, and I have no doubt that they work. But that is the electrical equivalent of strapping a propane tank to your bumper to power your car. And then selling the car to a family with 5 kids and two parents who don't know any better than to drive around with a gas bomb right in the place where it's most likely to get crushed and kill all of them. I'm sure you don't want to be responsible for the burning down of any of your clients homes and/or businesses, so please abandon this idea as literally every person on this is recommending or would recommend, and use a proper LED power supply.

So again, how many LEDs, what kind?

 

Hello,

The ledsign you have drawn is NOT safe.
There is NO isolation betwen the sign and the mains.
When you continue to use unisolated circuits, the staff is allowed to close the thread.
See section 7 of the UA:
View attachment 237169
I would go for a low voltage power supply to power the ledsign.
There are enough powersupplies that will provide 24 Volts, so you can put a number of leds in series.

Bertus

At one point, one of the restricted topics in that list actually was "LEDs connected to mains." Where did that go?

 

Putting safety issues aside for a minute, those LEDs are going to flicker like crazy @ 50/69 Hz.

Also, putting 100 LEDs in series is just nuts!

Solve the safety issues, then you will get some meaningful feedback.

 

At one point, one of the restricted topics in that list actually was "LEDs connected to mains." Where did that go?

To the list of efforts to propiciate another American business success story?

 

Hello,

Also, putting 100 LEDs in series is just nuts!

ElectricSpidey is right.
With 100 leds in series and one fails, the whole string will be off and it will be a tough job to find the faulty one.

Bertus

 

240VAC rectified and filtered is not 240VDC. It's 1.414*240 The DC current is about 60% of the AC current ratings.
You need an isolation transformer. But you really need something more than that.
There are IC's that would help you design such an animal.
There are Chinese companies that make this stuff.
What happens when the LEDs start shorting?

What about brightness vs ambient light?
What about uniformity?
It's likely the LEDs need to be binned by Vf and the strings adjusted.

 

Putting safety issues aside for a minute, those LEDs are going to flicker like crazy @ 50/69 Hz.

Also, putting 100 LEDs in series is just nuts!

Solve the safety issues, then you will get some meaningful feedback.

They'll flicker at 100Hz, not 50Hz; which is a lot less noticeable. Plenty of those LEDs signs you see that say "open" or "closed" or "cold beer" (though we don't like cold beer over here) are all in series off straight off the mains. They are in a plastic box, behind an arcylic panel, so are perfectly safe.
True, if one LED fails, they all go off, but it's possible to find the faulty one quite quickly with a "binary search" technique; but LEDs don't tend to fail within the guarantee period of the sign.

 

Do you have good professional indemnity and product safety insurance?

They'll flicker at 100Hz, not 50Hz; which is a lot less noticeable. Plenty of those LEDs signs you see that say "open" or "closed" or "cold beer" (though we don't like cold beer over here) are all in series off straight off the mains. They are in a plastic box, behind an arcylic panel, so are perfectly safe.
True, if one LED fails, they all go off, but it's possible to find the faulty one quite quickly with a "binary search" technique; but LEDs don't tend to fail within the guarantee period of the sign.

And because there is no regulated power supply, the builder saves $15 to $30 per sign. Some signs don't even have bridge rectifiers - they use antiparallel strands of series connected LEDs (like some fluorescent replacement tubes). The LEDs are close enough and flashing alternate AC cycles that you don't notice any flicker.

 

And because there is no regulated power supply, the builder saves $15 to $30 per sign. Some signs don't even have bridge rectifiers - they use antiparallel strands of series connected LEDs (like some fluorescent replacement tubes). The LEDs are close enough and flashing alternate AC cycles that you don't notice any flicker.

And if they are all in series in ONE string, (or two antiparallel strings) no need to bin for Vf. And I doubt very much if anyone cares about a bit of brightness variation on a sign that says "open" and "closed".

 

Hello,

As an example, this ledsign uses a 12 Volts DC power supply:
https://www.glowspecialist.nl/en/eurolite-eurolite-led-sign-open-large-with-remote.html

Bertus

 

I don't think that would be legal in most parts of the world.

It would certainly be legal in Europe, provided that it is built in such a way that no-one could touch anything live, and had a suitable fuse.
It would have to pass a safety test that if any single LED were shorted out or went open circuit that it would fail safe. Two simultaneous failures are excluded from the test.
And it must not overheat at 253V AC input.

 

Harmonic current regulations are strict on lighting above 25W, so most will have a PFC front-end which boosts the mains to 400VDC, then the LEDs will be driven in a string directly off 400V, probably with a buck regulator which sets the current.

 

I emulated some people who made it seem easy, that is, making LED signs in series.

For example, lets say I have 100 red leds for my sign. I was thinking, use the rectifier to turn 240v AC into 240v DC. I should now find the value of the resistor to use. My guide (he makes these signs, but located a little far away from me) said regardless of LEDs color, they calculate with an average voltage of 2v per 5mm LED. So, with this, the resistor value is 1.6k or higher. With the 100 red LED bulbs, "in my head", this sign is complete. What could go wrong?

Several things. Among other things, the output of your bridge rectifier will be 340 Volts peak. For another, the difference between the forward voltage drop (Vf) of a red LED compared to a white LED is only ***100%***.

But your biggest problem is that you are equating a flashlight with a Las Vegas light show. The hundreds of LEDs in the video you posted are *individually addressable*. They are *not* 100 LEDs in s single series circuit with one current limiting resistor. You are correct that that can work - if all you want is one big light. But the video shows hundreds of LEDs, each with its own individual driver and current limiting circuit, being turned on and off under computer control. All sign boards are variations of the same theme.

In your circuit with 100 LEDs in series with one bridge and one resistor, how would you turn on only the even numbered ones? Or only every 10th one? 105 LEDs is enough for three 5x7 dot character blocks. With only one string through everything, how would you get that string to display "abc"?

ak

 

I have read somewhere a Wheatstone bridge is the thing you need.

No, you didn't.

ak

 

I stand corrected, they will flicker @ 100 Hz not 50, But that is still pretty annoying, especially if you scan across with your eyes.

 

Use one of these for a higher quality option

https://www.mouser.com/datasheet/2/302/nxp_phgls25707-1-1740464.pdf

And a video of a T8 tube LED using the SSL2109

 

I stand corrected, they will flicker @ 100 Hz not 50, But that is still pretty annoying, especially if you scan across with your eyes.

A small capacitor will solve that.