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LED Plexiglas Table, newb needs assistance please!

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sparky73

New Member
I am building a 3'x8' table that will incorporate 3 pieces of plexiglas. Two of the pieces are white with white lights, and one is green with green lights. I am to the point where I need to wire everything together, and really don't know where to start.

There are a total of 88 LEDS, and I would like it to plug into a standard wall outlet AND have the option of having it portable, so running off a battery pack or something.

This is my first time attempting something like this, although I have done a lot of automotive wiring.

Could someone please give me some links on power supplys and everything I need, as well as the best way to wire everything together on a single 'on/off' switch.
 

sparky73

New Member
Here are the stats on the LEDS:

Size (mm) : 3mm
Lens Color : Water Clear
Reverse Current (uA) : <=30
Life Rating : 100,000 Hours
Viewing Angle : 180 Degrees
Absolute Maximum Ratings (Ta=25°C)
Max Power Dissipation : 80mw
Max Continuous Forward Current : 24mA
Max Peak Forward Current : 75mA
Reverse Voltage : 5~6V
Lead Soldering Temperature : 240°C (<5Sec)
Operating Temperature Range : -25°C ~ +85°C
Preservative Temperature Range : -30°C ~ +100°C
MCD : Either 6000 or 8000, not sure.
Voltage : 3.0 - 3.4V
 

sparky73

New Member
As of right now, I have nothing for power. I need to purchase a battery pack with charger or something. I'd like some opinions on what to buy, and it'd be nice if the battery would power the LEDS for 4-5 hours at least.
 

Hayato

Member
Well, you could use a 24V battery.

Then you'd need to make about 15 rows of 6 leds each in series, each row with a 180 ~ 220 Ohms current limiting resistor in series.
 

sparky73

New Member
Could you please give me an example? So if I have a 24v source, 6 LEDS in each series, wouldn't that be 4v per LED? The info on the LEDS says they are 3.0-3.4v. Where is a good online store to buy a power supply and resistors and such?
 

Hayato

Member
Well, to light your leds bright, you'll need about 20 mA running through them.

If you parallel 6 led, each led has a 3.4V drop. So it will be 3.4*6 = 20.4 V total drop.

Your battery is 24V and your resistor is 180 Ohms:
24-20.4 = 3.6V
3.6/220 =~ 16mA, so you'll have about 16mA running through the 6 leds.
 

sparky73

New Member
Ok guys, I've been trying to figure this all out by reading lots. Please let me know if this will work or what I need to change.

I am planning on using a UPS. There are thousands out there, and I really don't know how large to get. I know something really small should probably power them for a long time, but HOW small?

Here is a link to the multiple ones I am looking at:
Amazon.com, UPS

With using one of these, and having the multiple plugs, I could just use any standard 110v plug that converts it down to the correct voltage. I have a ton of these laying around from old electronics I've had, but which should I use?

I have the most 12VDC, so wouldn't I just wire 4 together in a series, and wire them sets in parallel? If not, I could get a 9VDC and do 3's or even 6VDC and do 2's.

Let me know if I am understanding the little bit I am correctly lol.
 

Hayato

Member
UPS? You are trying to kill an ant with a bazooka.

Just use a common supply to do that.

If you wire four 3.4 V LEDs in series, then you would have a total voltage drop of 13.4V.
13.4 V > 12 V. Your leds would light very faint or won't light at all.
 

Sceadwian

Banned
It's a little bit more complicated than that sparky, but not by much. Most wall warts like you're talking about are unregulated, the voltage they put out is not exact and at no/low load they're much higher than what's listed on the pack. You would have to test each one at it's loaded current.

Assuming you can get 3 LED's in series on a 12 volt supply, that's 88LED's / 3 (approximately 30 strings of 3 each) Your nominal current is 20ma's (best to shoot a little low) So you'll need a 12 volt supply that's only 600ma's for the entire set. You should be able to find a 12 volt supply capable of about 1 amp that'd work.

To test a loaded power supply you'd need a dummy load, like a power resistor to draw the amperage you expect your your LED's and then adjust your current limiting resistors to match. Your full load current is almost 1 amp though so the problem is testing it all under load without the real led/resistors to determine what resistors you need to match to your LED's to get the real current.
 
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Hayato

Member
Well they are very efficient, too much for your project.

You won't need anything thats supply more than 15W for your project. Anything above that is a waste of money.
 

sparky73

New Member
Oh, haha. Is there such a thing as a power supply like I was looking at, but something that isn't extreme overkill? :D
 

Sceadwian

Banned
If you're lucky forever considering it plugs into the wall.
If you run your LED's in 3 series which would be best for 12 volts, you'll need 90 LED's or 30 strings of 3 with a limit resistor for each string. Use the worse case scenario of 3.4 volts per LED and figure 20ma's of current per string which is a good safe current for those LED's you'll need a dropping resistor of
3.4 * 3 = 10.2 volts dropped in the LED's
12 volt supply, that leave 1.8 volts left to drop, at 20ma's that's a 90ohm resistor. I don't think you can find 90 ohm resistors although if you can use them, I'd be safe and go with the next highest which is 100ohms.

Worse case that uses 600ma's at 12 volts. Or about 8 watts. Any UPS you pick will have a watt rating and should have a chart which shows you how long it will run at a certain percentage of it's maximum rating. The problem with using a battery directly is that you have to regulate it somehow. A car battery will go from around 14 volts fully charged to around 10 volts close to flat, which is not exactly good for average brightness over the full discharge range, so your idea of using a UPS is not that bad idea, the main problem being they almost always beep really loud when power is lost =)
 
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Sceadwian

Banned
As far as stupid simple goes. 90 white LED's 30 100 ohm resistors, 1 12 v 1amp regulated supply and a UPS that will run that for your desired run time will work out of the box. Minus the hours you'll spend soldering that many LED's.
 
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