LED sign help

cathouse9September 26, 2010

I bought a channel letter sign which was wired with led lights and am hoping to get it working. There are 14 modules in a chain.





What type of transformer or power source do I need? What else is necessary? Thank you in advance!!

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    Bookmark   September 26, 2010 at 3:08PM
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Hi carenlynn...

If you can answer these two questions I will be able to help...

- How many other letters in addition to the "R" above are you connecting ?

- Does each letter also use 14 circuit boards ?



    Bookmark   September 26, 2010 at 6:47PM
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Not quite sure if you are installing an entire store front sign or just trying to light up a single letter at home.

If this is a store front, the easiest thing would be to use a sign company that does neon/LED signs. They have power supplies designed just for this that would meet your needs based on all the lettering and LED module specs. They would also be able to provide info on any UL requirements.

If you are just trying to light up this one letter, it appears based on the the 2 red LEDs and 200 ohm resistor (and assuming all the 14 LED modules are in parallel) it would require approximately 9 volts DC at 280 mA, so a plug in wall transformer rated a 9 volts DC/350 mA would be able to supply the necessary power. You would need to identify the +/- leads from the transformer to match the LED string. Although 12 volts is usually used for these signs, the circuit board and components indicate 9 volts as more appropriate.

    Bookmark   September 26, 2010 at 6:58PM
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Marco - it's just the "R". I bought it at a flea market for a nephew's room and if I can get this one lit cheaply enough, I'll buy some of the others next time (to be lit separately also). It has an acrylic cover and is cool without the lights, but would be cooler lit up!

Bill - if by parallel you mean they are connected in one long chain, then yes. Where could I purchase the 9 volt plug in wall transformer? Thanks!!

    Bookmark   September 26, 2010 at 9:06PM
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Any store that sells electronic stuff.

A "wall transformer" is frequently called a "wall wart" and usually labeled as an "AC Adapter". We're talking about one of those little black things that power cordless phone bases.

Aim for 9VDC and AT LEAST 350mA. I usually find tons of them rated 500mA, which will work fine.

    Bookmark   September 26, 2010 at 10:19PM
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Locally, some place like Radio Shack. On the web I might use Digikey. And the more Amps the better (to a point).

    Bookmark   September 27, 2010 at 1:29PM
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Hi carenlynn,

Looking at your pictures again it appears that there are several bare wires you'll need to sort out. If you look at the picture of the component side of the circuit board (LEDs pointing up) you'll see the gray wires go to VCC, which indicates positive, and the bottom as GND, which indicates ground or the negative connection. Be sure that they all daisy-chain from one to the next keeping the polarity correct.

Then, you may end up with 2 wires coming out at each end of the daisy-chain - you can connect your power supply to either end but the other end must have the individual wires capped off separately using a couple wire nuts.

Before finding a wall transformer, you could test the circuit using a 9 volt battery. Just hold the gray wire on the + terminal of the battery and the white to the - terminal (it usually indicates it on the side of the battery case). Don't worry you aren't going to get shocked touching the terminals. The battery won't be able to power it for more than a few minutes without dying but at least you'll know it works.

As far as the transformer, I recommended 350 mA since you typically want to derate it to 80% capacity - it appears the LEDs would draw 280 mA, 350 mA x 80% = 280 mA. While 500 mA (1/2 amp) should be OK I would not use anything rated higher. The reason is, is that these are simple unregulated power supplies and the output voltage is at it's stated level when under it's specified load. If the supply is regulated, the maximum current above your needs isn't much of a concern.

As far as finding one, you might even have one in your closet from something you don't even own anymore! Radio Shack and department store's electronic areas (where the sell cables and stuff) are all good places to look.

    Bookmark   September 27, 2010 at 9:12PM
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Thanks so much for your responses! The loose wires showing were probably from one unit I took out to open up for pictures. But yes, there were originally 4 coming out the back (2 white and 2 gray). So I have capped 2 of them separately.

Anyway, I did hold a 9 volt battery to the wires and it lit up. So exciting! I then searched my misc AC adapters and found one that's close (9.5V / 300mA) hoping it wouldn't hurt anything, and it does light it up :)

So is this one safe to use? Or should I purchase one like suggested (9V/350mA). I bought this for a nephew's room and the last thing I want is a fire hazard!! Again, I appreciate your help on this.

    Bookmark   September 28, 2010 at 8:04PM
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Run it for a couple hours and see if the ac adapter is too hot. If not, go with it.

    Bookmark   September 28, 2010 at 8:53PM
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I agree with what pharkus suggested.

If all is OK, you should install a rubber grommet where the wire from the transformer passes through the sheet metal on the back - looks like a little rubber doughnut with a slit around the outside edge to fit into the hole (you can find them in the electrical section of hardware stores). Then pass the wire through the center to prevent the sheet metal from cutting through the wires.

Even though this is all pretty safe stuff, and the transformer should have an internal/thermal overload fuse, I wouldn't leave it plugged in 24/7. Just let him know to use it when he wants and not to leave it plugged in all the time.

Let us know how it works!

    Bookmark   September 28, 2010 at 9:33PM
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you should be fine leaving it plugged in all of the time if the transformer is not enclosed by bedding or other things that would restrict ventilation. behind a dressor is fine.just dont use one of those cheap extension cords or power strips-the contacts are too cheap and wear out and that will be a fire hazard. stick to the jobsite cords instead.

    Bookmark   October 13, 2010 at 11:01PM
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We're talking about something like a 20W load, that's about 1/6 of an amp at 120V. Cheap cord or not, you're not going to create a fire hazard with that.

We're MUCH more worried about the heat from the transformer itself, and even that is easily manageable.

The warnings/instructions for what the OP are doing should be no different than those for a cordless telephone base - and what do people do with those?

I submit for consideration that most of them are given the "plug it in and forget it's there" treatment. I'm not saying this is a GOOD thing, merely that it's typically done and I don't ever hear of houses burning down by mistreated phones.

If the adapter is running too hot, the transformer will eventually "burn out". This happens at a temperature below what is typically going to torch the house. Nothing's impossible, but we can strive for a very low level of likelihood, and we've already achieved that.

    Bookmark   October 15, 2010 at 1:46PM
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