# How to wire LED's?



## machinist (Jul 4, 2012)

I haven't kept up with technology. I'd like to learn how to use LED's as discrete devices, that is, how to know what I have in terms of req'd. voltage, current, mistakes to avoid, etc.. 

I am sure it is possible to, say use a cheap string of Chirstmas lights in some manner to convert for use with 12 volts DC. Polarity seems straightforward enough, since it is a diode, but i don't want to smoke a bunch of 'em learning the ins and outs....

Experts out there? 

I understand Ohm's Law, can wire a house for AC to code, have built a bunch of simple electrical stuff, battery charger, doing some solar work, etc. I can use a VOM to figure out polarity, and I suppose I could keep trying DC voltages from low to higher levels to figure out what it takes to light 'em up, but there must be a better way to finesse the problem.

I'm looking for ways to utilize cheap LED's with a 12 volt solar system.


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## Marcus (May 13, 2012)

http://en.wikipedia.org/wiki/Light-emitting_diode

From the link:
"There are three main categories of miniature single die LEDs:
Low-current - typically rated for 2 mA at around 2 V (approximately 4 mW consumption).
Standard - 20 mA LEDs at around 2 V (approximately 40 mW) for red, orange, yellow, and green, and 20 mA at 4-5 V (approximately 100 mW) for blue, violet, and white.
Ultra-high-output - 20 mA at approximately 2 V or 4-5 V, designed for viewing in direct sunlight.

Five- and twelve-volt LEDs are ordinary miniature LEDs that incorporate a suitable series resistor for direct connection to a 5 V or 12 V supply."


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## machinist (Jul 4, 2012)

COOL! Thanks for looking where I didn't think to look...

Yeah, I feel dumb for not doing my own digging like you did. 

Okay, I think I can take it from there. If if won't run on a couple AA's, and wants 3 of them (4.5V.) to fire, then it is a 4 V. Check current draw with a Milliammeter, and then figure the resistor. 1/4 watt resistor would be plenty. 

Thanks again. 

V = IR, so....

Lessee, if I find I have a high output LED that draws 20 MA = .02A, then R of the LED = 200 ohms.
And, if I change the voltage to 12 volts and want to maintain the same current, I get:
12 volts/.02 A = 600 ohms needed, total in the circuit. 
The LED has 200 ohms resistance in this example, so 600 - 200 = 400 ohm resistor req'd., in series with the LED. 

Did I do it right?


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## LincTex (Apr 1, 2011)

I did a fair bit of reading on this a while back.... I do remember that for just one LED only, you can do the resistance math, but if you use an "array" it wasn't as easy and you need to use a switchable power supply to make sure you don't over-current.

I seem to remember there were other drawbacks to using resistors.... due to the nature of LED's to draw excessive current when not regulated, there was a lot of heat energy (and successive energy waste) lost. The switching power supply only lets through the amount of electricity needed and no more.


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## LincTex (Apr 1, 2011)

All do this came about since I wanted to learn to convert these to 12 volt if needed:

http://www.harborfreight.com/27-led-portable-worklight-flashlight-67227.html

However, dedicated 12 volt MR11 bulbs are still *A LOT* cheaper... I just wanted to do it for info purposes.


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## Marcus (May 13, 2012)

http://www.ngineering.com/led_circuits.htm
http://led.linear1.org/led.wiz

Here's a couple of helpful links in designing your circuit.


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## LincTex (Apr 1, 2011)

I built a "pie pan light" as a prototype for my chicken run... It works pretty well,, I need to take some pics.

I start with one of these MR11 12 volt bulbs:
http://www.ebay.com/itm/MR11-G4-Warm-White-10-SMD-LED-Spot-Light-Bulb-Lamp-12V-/261056895861

(less than $3 each) and I aim them into an inverted pie pan for area lighting.

I am experimenting on solar power with my chicken coop, which is not near the house (about 100 meters/yards away). I want to light up the area so I can more easily see the raccoons at night when hunting.


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## NaeKid (Oct 17, 2008)

I purchased a set of "driving lights" for about $40 from the local PrincessAuto (Canadian version of Harbor Freight), in essence, they run on 12-volt DC-power, but, in reality they can run on a 3-volt coin-battery (CR2032) and do run on it in the package so that potential-buyers can see how bright these driving-lights really are.

In the wiring-harness there are voltage-regulators to drop the voltage from a working alternator (or similar automotive charging system) down to 3-volt (regulator shown below). As LincTex posted, use a reflector to expand on the LED's capabilities and use the voltage-regulators to make sure that you don't over-power the LED's.

You can also purchase on eBay (and similar sites) LED lighting-kits that will easily convert from auto-use to home-use ...


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## NaeKid (Oct 17, 2008)

I don't know if it matters, but, here is a "testing" picture of my motorbike while I was trying to figure out a good place to mount the LED driving lights on it and figure out how I would attempt to wire it. I am only using a spare UPS-battery to run the lights.

I am just waiting for a set of micro LED driving-lights (search for "Eagle Eye LED driving lights) to ship-in before I take everything apart and wire it all up on my bike ...


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## stayingthegame (Mar 22, 2011)

to use LED's for 12 VDC, use a 1200 ohm resister - that will give you 10ma of current. if 5 vdc, use a 470 ohm. if you want to run multiple lights, wire in parallel with each led using a 1/8 - 1/4 watt resistor. what are you using this led for? if it is a bike, they make an LED array that already has the necessary resistor included to connect directly to 12 VDC. Just make sure the polarity is correct!


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## machinist (Jul 4, 2012)

stayingthegame,

Just trying to figure out if it is sensible to rewire some Christmas lights to work on a 12 volt solar system. 

Thanks for all the info folks! Hope this continues so I will learn even more!


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## NaeKid (Oct 17, 2008)

I just received my EagleEye LED lighting and I gotta say that they are significantly bright and it looks like they have a very low power-draw as well - huge bonus there!

It looks like they embedded two ultra-bright LED modules into an aluminum housing and then capped them with a magnifying glass. Even in full daylight you feel like you are being blinded by the single unit (and I got four of them).

Depending on how you setup your system, they might be all that you need!


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## LincTex (Apr 1, 2011)

machinist said:


> Just trying to figure out if it is sensible to rewire some Christmas lights to work on a 12 volt solar system.


Easy answer = No. 
You do not get as much light as other LED's give for the amount of power used.

I have narrowed it down to two main LED types for 12 volt lighting:
1) "168 or 194 bulbs" - like the kind used for parking lamps, license plate lights, and such in automotive applications. These work great for spot lights (while reading) and also work nicely to light up a large area that needs "some" light - they light up the entire hallway in a house at night very nicely with VERY little power draw (one pointed at the white ceiling).

A string of Christmas tree lights would give off the same amount of light for a lot more power draw. 
Check these out: http://www.ebay.com/itm/380244360574

2) MR11 or MR16 12 volt bulbs - these have advanced to where you can get an AMAZING amount of light from just 1 or 3 watts. (like my "pie pan light")


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## LincTex (Apr 1, 2011)

Ooooooo..... these use one SMD "5050" bulb for only .23 cents each!

http://www.ebay.com/itm/Super-100pc...-Wedge-Light-Bulbs-168-194-1512-/330755646633

I am gonna have to play with these.... I can light up my whole yard!


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## NaeKid (Oct 17, 2008)

Just to show you the LED lights at full-sun, this is just one of them, just imagine what multiples of these LED's will do in a room at night ...


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## machinist (Jul 4, 2012)

Now that I've learned some things, I should ask different questions. I want to light the interior of an RV trailer at minimum draw. I'd prefer to find something reasonably priced (the RV places are astronomically priced) and more or less ready to install for 12 volt service.

Here's one I found, but no data on lumens or current: http://www.delcity.net/store/Rectangular-LED-License-Plate-Lamp/p_798176
This one would be easy to install without fabricating a bunch of stuff, but is probably not ideal for area lighting. It should work to mount on the wall beside the laptop, over the bed , or in a corner for a reading light.

I'm sure there are better ideas out there, but I haven't found them yet. I've been browsing eBay, but get 36,000 led strip lights for cars, etc.


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## LincTex (Apr 1, 2011)

machinist said:


> I want to light the interior of an RV trailer for 12 volt service.


What is the number of the bulbs you will be replacing? 1156? 194?


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## machinist (Jul 4, 2012)

Not just replacing bulbs. The old fixtures are shot, so I'm rewiring and starting over, pulling new wire from the fuse box out to the new lighting and 12 volt outlets. This was a freebie 28 foot trailer, and needed a LOT of work, but it's coming along. Replaced the whole LP system for cooking, all new roof vents and coating, new window operators and some glass, 4 good used tires, one screen door, modifying the floor plan a little, etc. Only going to move this thing ONCE, to our lot in the boonies, then do permanent solar install. Put a pole shed over it to preserve the roof and call it budget BOL. Shed roof sends water to a cistern. Totally off grid. 

So, I need light fixtures of some sort. I've made a couple decorative ones from old 120V. home fixtures, scrounged at Goodwill, and will use 12 volt CFL's in those. Ceiling is low and I'm tall, so most lights will go on the walls. I was looking for low-draw ways to have enough light to just get around in there at night, or small area lighting such as over the computer, kitchen sink, and table. Maybe something outside for a porch light kind of thing. 

I'm trying to keep my power use down, and thus be able to run on solar entirely. Got 720 watts of panels, but I want to run a fridge on it, mostly. A Summit brand 8.4 cu. ft. that uses about 800 watt hours a day on inverter AC. (Did that to get off propane use for the fridge.) So, with a 12v., 7 watt TV on an antenna, some tiny radios, a laptop that uses about 24 watts (satellite service), and a few lights I hope to get by. It ain't much, but it beats a backpack and a tent.

LED's are the most efficient it seems, but I have some trouble with the blue-white glare, so this is only for limited uses.

I appreciate the help, since LED's and RV's are all new to me. Learning the hard way can be expensive, too.

FWIW: I don't like the idea of bugging out, but wife and I are old, and the kids are next door to the BOL.


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## NaeKid (Oct 17, 2008)

You could probably do a search on "flush-mount" LED on eBay for some options, or search on "licence plate" LED as well.

A couple that came up that might do the trick for you ..

*$12* - http://www.ebay.ca/itm/2x-Bolt-12-L...r_Truck_Parts_Accessories&hash=item20cad0140a

*$26* - http://www.ebay.ca/itm/LED-Backup-L...r_Truck_Parts_Accessories&hash=item3376c76c54

I like the idea of the second one because you can do a "two-position-switch" to control off, dim or super-bright ...


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## machinist (Jul 4, 2012)

Thanks Neakid, 

That sort of thing looks pretty good. There are several places I could use them. I'll do some more digging.


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## LincTex (Apr 1, 2011)

machinist said:


> The old fixtures are shot, so I'm rewiring and starting over.


I would probably use these in that case: http://www.ebay.com/itm/10X-Warm-Wh...amp-Cabinet-Spot-Light-Car-Bulb-/130622606068

http://www.ebay.com/itm/G4-SMD-24LE...mp-Warm-White-12V-Free-Shipping-/261092644729

They are about as big as a 50 cent piece and nearly flat. I would solder the wires directly to the lamp as glue it where you want it.

When searching, use the "bulb number" for the type you want, and also include "Warm White" in the search.

I use:
194/168
MR11
MR16 
G4


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## machinist (Jul 4, 2012)

LincTex, 

Thanks, I'll work on it.  Off to a pig roast tonight....


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## LincTex (Apr 1, 2011)

These ones came from searching "warm interior LED":

http://www.ebay.com/itm/New-Warm-Wh...-Light-Panel-With-BA15S-Adapter-/110938565883

http://www.ebay.com/itm/9-SMD-5050-...arm-White-T10-BA9S-Dome-Adapter-/150886950097


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## machinist (Jul 4, 2012)

LincTex,

I need to buy at least one of those to see what they amount to for light, and see if I can figure out a fixture for them. 

Offhand, I'm thinking to use some storm door glazing acrylic, hit if with the sandblaster, or coarse sandpaper to fog it for a lens, and then figure out how to make a frame for it. 

Maybe I could heat the acrylic in the oven and let it sag over a form, like vacuum forming, and make a one piece cover for the light. With LED's, I don't have to worry about the bulb overheating the acrylic in use. That heat from the old filament bulbs is what ruined the original fixtures in the RV. If I made a dozen at once, it would pay pretty well, compared to buying complete fixtures. 

That means I could have really tough light covers, 1/8" thick, and use a good toggle switch for durability. So, I get a fixture that will last 10 years instead of one or two.


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## LincTex (Apr 1, 2011)

machinist said:


> Offhand, I'm thinking to use some storm door glazing acrylic, hit if with the sandblaster, or coarse sandpaper to fog it for a lens,


You can just buy adhesive window privacy film, does the same thing with less work.



machinist said:


> and then figure out how to make a frame for it.


I make them with the table saw.


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## machinist (Jul 4, 2012)

Yup! That'll work!


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## LincTex (Apr 1, 2011)

I did some testing last night of various 12 volt LED lamps that I own, for brightness, color, dispersion, etc. The results were surprising! 

I will be starting a new thread with photos shortly.


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## machinist (Jul 4, 2012)

Got way to measure current on them? That would be a big help for planning.

This solar thing for me is a big project. Got a Summit brand fridge ordered for the RV, and just ordered an inverter http://www.solar-electric.com/sa10wa12vosi.html to run it. I've been very happy with that supplier--very competitive and helpful, good service.

Since the fridge will gobble a lot of power, I am really hoping for good results with LED's for lighting.


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## LincTex (Apr 1, 2011)

machinist said:


> Got way to measure current on them?


Yes, my digital multimeter can handle up to 20 amps.


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## hwmonkey (Oct 8, 2012)

LincTex said:


> I did some testing last night of various 12 volt LED lamps that I own, for brightness, color, dispersion, etc. The results were surprising!
> 
> I will be starting a new thread with photos shortly.


Where did you start this thread? I cannot find it and I am very interested.

Thanks.
HWM


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## LincTex (Apr 1, 2011)

hwmonkey said:


> Where did you start this thread? I cannot find it and I am very interested.


Never started it.... Been too busy!!!!

Where can I get a cheap luminosity meter? it would be better data than "this one is much brighter than this one".

I will be doing pictures, and that will provide some usable data.


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## machinist (Jul 4, 2012)

LincTex, 

Maybe try a solar cell from one of those cheap yard lights, and hook it to a milliammeter? Use a standard distance, etc. Thought it might be something you'd have laying around to try. Dunno if that would work or not. Have to put it in a shoebox or something to get rid of ambient light variations.


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## LincTex (Apr 1, 2011)

machinist said:


> LincTex,
> 
> Maybe try a solar cell from one of those cheap yard lights, and hook it to a milliammeter? Use a standard distance, etc. Thought it might be something you'd have laying around to try. Dunno if that would work or not. Have to put it in a shoebox or something to get rid of ambient light variations.


That is NOT a bad idea!!!


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## machinist (Jul 4, 2012)

LincTex,

Well, Dad said that even blind hog finds an acorn now and then... 

Hope it works for you!


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## pawpaw (Dec 21, 2011)

An episode of 'MythBusters' once showed a movie scene where a series of mirrors lit up an entire underground chamber using the sun.
They showed why it wouldn't work -"BUSTED!" , but then showed that beam reflecting off Adam's large white coat. The result was about 3 times the luminosity, I think.
I can't find the episode, but I remember vowing to study the concept for prepping purposes, and found it's true. Simply shining an LED at a semi-gloss white wall as the reflector has led me to experiment with all sorts of reflector-all white, and all shiny. I'm still waiting on some reflective safety tape-the same stuff they put on road worker vests & big rig trucks. It comes in a roll, 12" wide. Now I'm stewing on how to effectively multiply some LED light with it. Any ideas?


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## LincTex (Apr 1, 2011)

pawpaw said:


> Simply shining an LED at a semi-gloss white wall as the reflector has led me to experiment


All of the LED's in my house are aimed at the white ceiling.

Most LED's have a pretty narrow angle of light... they are most typically "spot" lights more than "flood" lights. But, once aimed at a white ceiling and reflected down, even "spot" narrow LED's will light a pretty big area.



pawpaw said:


> reflective safety tape...12" wide. Now I'm stewing on how to effectively multiply some LED light with it. Any ideas?


Try a cheap bathroom mirror. The angle of light deflected outward will be the same angle that the light is projected.


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## The_Blob (Dec 24, 2008)

machinist said:


> COOL! Thanks for looking where I didn't think to look...
> 
> Yeah, I feel dumb for not doing my own digging like you did.
> 
> ...


OR two more LEDs in the same series circuit :dunno: :sssh:


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## LincTex (Apr 1, 2011)

The_Blob said:


> OR two more LEDs in the same series circuit


Yes and no... "LEDs are current-driven devices - a small increase in forward voltage usually results in a significant increase in forward current. That's why you can blow them up with just a slight increase in voltage."

depending on the installation, you still need to add a resistor to prevent excessive current draw. LED's (of any real brightness) tend to kill themselves by drawing more current than needed and overheating themselves.

There is also the issue of no two LED's being created equal, and the stronger one can kill the weaker one in series (in certain circumstances). LED's are not linear "resistors" (of which makes a circuit very easy to do the math on). So, there is no balance; there is no way to regulate or control what percentage of resistance/electricity each LED will share in that arrangement.

Really high powered LED's require a "driver" circuit to limit the current to spec. These are the ones people want because the light is bright enough to be "usable".

I have to add this quote:
"Well, actually, an LED is a diode, which means it has a fixed forward voltage (may vary slightly with current level, but generally, it's fixed, look at a datasheet for Vf).
With that respect, it depends on how you are driving the LED. If it's a passive circuit, which means, basically just a series resistor with the LED, the current will depend on what value of resistor you choose, and what the Vf of the LED is. Here is an example.

Vf of a particular LED is 4V. If you have a battery that had a nominal voltage of 6V, and you wanted to drive the LED at 1A (amp), then this is how you would select the resistor.

V=I * R (ohm's law, I = current in A, R = resistance in ohms, V = voltage in V)
R=V / I
R=(Vp - Vf) / I [Vp is the voltage provided by the batteries, since the voltage across the LED is fixed, you can assume at this point, that the voltage across the resistor is now fixed (as long as the battery stays constant)]

R=(6 - 4) / 1
R=2 ohms.

Notice the VERY low resistance value. Most high power LED's don't use this type of configuration, for one, the power lost in the resistor is wasted at heat, and secondly, using an active circuit can provide regulation of the light output of the LED, even when the battery voltage is declining.
Active circuits usually consist of either a PWM (pulse width modulation) circuit, which basically looks like a square-wave of pulses at a high frequency, which in the end, average out to be an average voltage, or a constant current source.
This is probably over the scope of this thread, but thought I'd point some things out.
So, based on the above example though, over driving an LED can be accomplished several ways, leaving everything else constant, you could do the following:
1. Decrease the resistance; more current flow, with the same voltage.
2. Increase the battery voltage; more current flow, with the same resistor."
http://www.candlepowerforums.com/vb...r-drive)-a-light-high-voltage-or-high-current

Here's a primer on how voltage and current are related in LEDs:
http://www.candlepowerforums.com/vb/showthread.php?77221

http://www.candlepowerforums.com/vb/showthread.php?72528

http://www.tigerhawkt3.com/welcomemat/ledfaqs.htm


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## LincTex (Apr 1, 2011)

As long as you are not playing with high-powered LED's this little calculator will get you in the ballpark:

http://led.linear1.org/led.wiz


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