Connecting 200 LEDs to AC (120V)?

I think I'd forgo rectifier and the resistor. Limit the current with an inductor instead, like a fluorescent lamp. Hmm, a LED ballast. Better efficiency with no resistor losses. Wire the LEDS back to back in strings of 20 back-to-back pairs in series.

But can it be done in Canada? I don't know.

Regards, Bob

Explain the hazard in an open circuit transformer.

I think you're forgetting that 120 Volts RMS means a 170 Volt amplitude (the maximum voltage in the sine wave's cycle). The above circuit will result in a too-high peak forward current of 66 mA (assuming 3.6 V per LED), and a too-high peak reverse voltage of 6.8 V

The most efficient way would use a rectifier and capacitor to supply a (roughly) DC voltage to work with. But if you were to do this using AC with just current-limiting resistors and the LED's, you might try using THREE of the following:

A string of 34 series LED's In parallel with that, another 34 series LED's with polarity opposite to the first string. And, in series with those two parallel strings, a current limiting resistor of 2.4k (or whatever the closest standard resistor is), 1 Watt or greater.

Wiring the LED's with opposite polarity would mean that some LED's are on during each half-cycle of the mains supply, and also that the peak reverse voltage would be under 5V.

Three of these circuits would use a total of 204 LED's.

Again, if you want more efficient lighting, it would be much better to use a rectifier to convert to DC.

Mark

There's a product on the market. I used to work for an electronics company that manufactures an LED light stick that is a direct replacement for an incandescent bulb in exit signs 110 or 220 Vac

50/60 Hz. It has 16 LED's and was the size of an average cigar. I have several at home that I use for night lights. They have a 30 year life span, the company guarantees them for 25.

I think you are right. Just buy the LED bulbs

LinkWaves Corp

29980 Technology Drive, Suite 6 Murrieta, CA 92563 909-725-9143 We buy sell all Cisco, Discount up to 80% off on New Used Cisco.

snipped-for-privacy@netzero.com wrote:

Explain the hazard in an open circuit LED.

120 VAC across a device designed for 2 or 3 volts DC. You don't see a hazard there? You might want to check with a fire marshal or electrical inspector.

WOW, someone needs to learn what "open circuit" means.

I lost track of where this started.

But, it sure has gone over the edge !!

What do you think it means?

That'd work, but you'd need 8 of them...

a bridge rectifier is more efficient.

Bye. Jasen

"redbelly" schreef in bericht news: snipped-for-privacy@e63g2000cwd.googlegroups.com...

Mark,

I did not pay much attention to the peak current but it has to be taken into account. Most LEDs that are designed for 20mA continuous DC current can handle peak currents of a multiple of that 20mA. Whether 66mA is too high or not should be concluded from the datasheet. When in doubt you can always raise the series resistor to 1k5, 1k8 or beyond.

No reverse voltage accross the LEDs while using a bridge rectifier. (Both the OP and I mentioned it.)

The bridge rectifier and series resistor method is the most simple approach that I can imagine. That's to say without becoming hopelessly inefficient. When using a smoothing capacitor and currentregulators you can do - let's say - 5 strings of 40 LEDs. Each with it's own current regulator. If you want to be energy aware you can even use switching regulators. But that's not simple anymore.

petrus bitbyter

Really? How? It adds more loss to the circuit, lowering efficiency.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Thanks all for your comments. I will try your solutions. Also I got some idea from following links (by putting 170 Volt and 200 LEDs into the first link)

Homer wrote:

I really don't like hooking up to the AC without transformer isolation.

The transformer will add a substantial safety factor to the lamp assembly. Without it there may be insurance liability problems. A reduced secondary voltage is also highly desirable.

You really haven't paid any attention at all, have you? Only an idiot would waste time and effort to build something so unsafe when you can just buy the finished product.

They're called LED Christmas lights. I bought three sets on clearance at Target in Jan/Feb for a really cheap price (one set is blue, one is white, and the last is multi-colored). From what I can tell, the LED's are just wired in series from one side of the 120 volts AC to the other. They're their own half wave rectifier. I believe the plug has the "standard" Christmas light fuse for safety.

I actually bought them because, on clearance, they're the cheapest source for fairly high intensity LED's I've seen. They're as easy to remove from their plastic sockets as the little, low voltage, incandescent Christmas lights. ;-)

Jeff

--
    "They that can give up essential liberty to obtain a
     little temporary safety deserve neither liberty nor
     safety"
- B. Franklin, Bartlett\'s Familiar Quotations (1919)

As purchased, they presumably have a UL label, which means they are fit for use as is. Alter the design and that no longer applies.

Hello Petrus,

Yes, the 20 mA can be exceeded for pulsed operation. Not all datasheets address this. One sheet I looked at spec'ed a pulse current for 10 us pulses, which would not apply here since the pulses are several ms long.

Okay, I missed that.

Efficiency should only be a minor concern. The LED's themselves will consume about 14W at most. Even with a 50% efficient drive circuit, you're still using under 30W. Agree that going to switchers is more trouble than it's worth for wall-outlet power. If it were to be a battery driven configuration, you'd likely want to do anything possible to extend battery life.

Mark