rigging for LEDs ?

[hankaye]

Howdy All;

Thanks for the links and thoughts about LEDs.

Would still would like to know if "Light boards" ='s Light fixture?
The rate that our language is evolving if ya miss a step seems like
ya fall back a century or 2 ...

hank

[WoodSmith]

Electronics is just like any other industry, we all have specialty words that are confusing to "outsiders". Sometimes is seems like they are just made up to make life difficult, other times there is good reason for the odd language. I hope I can ease some the strangeness for you.

An LED is typically a very small component. I'm sure you have seem 5mm LED's in various places of your every day life.
They are available in many colors, but not plug and play for someone who is still smarting from that there damp thumb vs outlet incident.
Other LED's are available that are even more difficult to use because they don't have wires connected to them, they are called "surface mount" because they solder directly to little pads of metal on the surface of a Printed Circuit Board or PCB. These can range from tiny, to ridiculously small.
This kind of LED is often sold (for an additional LOW LOW price) pre-mounted to a PCB. This PCB may have either "Flying Leads" (shortish, usually red and black wires, which you connect to your power supply) or small holes or square pads to which you may solder your own wires. These often have additional circuitry on the board to make them easier to use. This is what I believe is being referred to as an LED board.
Some LED's are sold as direct replacements for existing incandescent bulbs, and are usually going to be shaped similarly to the bulb they are replacing (like the Automotive bulbs referenced earlier or the newish LED bulbs you can buy at Home Depot and Lowes to replace household light bulbs.

LED's, like all electronics, operate on magic smoke. The magic smoke is measured in 2 ways; Current, measured in Amps, is how 'fast' the magic smoke goes through the device. Voltage, measured in Volts, is how hard the smoke is being pushed into and through the device. If the current or the voltage is too high, the magic smoke comes out of the device and it no longer works. Electronics 101 uses water pipes as an analogy. Voltage is roughly equivalent to the pressure of the water (Pounds per Square Inch). Current is roughly equivalent to the flow rate in your pipe (Gallons Per Min).

Probably the best place for you to start with LED's is with the replacement versions. If you have a 12V incandescent light in your trailer (or perhaps the cabin light in your tow vehicle), look for a replacement for that type of bulb. If it is sold as a replacement for that bulb, chances are that it will be safe to use in the same light fixture. As you get more familiar, the next step would be to look for LED fixtures that are sold as requiring a 12V power supply. These too, should be safe connected to the 12V system of your trailer. The next step would be to go to either LED boards or strip lights that you can design your own mounting system for. Again, as long as they are marked as 12V you are good to go. I was window shopping with my 9 year old daughter and she spotted a window framed with LED strip lights. She called my attention to them, and as we looked at them closer we noticed every 3 or 4 inches were some pads marked + and - and 12VDC. These could be used in a trailer on the 12V system, there are even some that are weather proofed which could be used outside the trailer.

The next thing to think about is how many LED's you are going to put on the same battery. Just like plugging too many strings of lights on the Christmas tree into the same outlet can cause on overload, turning on too many LED's at the same time can also. In general, LED's are more efficient at generating light than incandescent bulbs, which generate light almost as a by-product of generating heat. This is why household LED bulbs are sold as, say a 60 watt EQUIVALENT - it produces as much light as an old fashioned 60 watt bulb, but only uses a fraction of the power. This is good if you want to use just enough light to get the job done and sip the power from your battery. However, it also opens up a can of worms for some of us - because, SHINEY "Hey, if I used to use a couple amps for this one bulb, I can now use the same couple amps and have a small SUN!"

Advanced topic:
LED's can also be dimmed, FUNCTIONALLY like the dial dimmer light switch in your house. In PRACTICE, they are typically dimmed using Pulse Width Modulation (PWM) which takes advantage of the fact that electronics are fast and the human eye is really kind of slow. A PWM circuit would be designed to turn the LED's on at full brightness for say, 10% of every time period T, and leave it off for the rest. As the control is increased, the amount of time that the LED is on (always at full brightness) increases, and your eye perceives that as a brighter light, rather than as a faster flash.

LED's are available with different colors, and certain kinds can be used to create thousands of different colors with the same LED. If you are just looking for White, there are even different colors of white available. And here is where the Artsy-Fartsy people start sticking THEIR strange language into electronics, Warm-white, Cool-white, Bright-white, Pure-white, Natural-white. WHAT? I just want something to read my data sheets with!

WoodSmith

[Gonefishin]

http://www.superbrightleds.com/moreinfo/led-vehicle-replacement-bulbs/36-led-1157-pcb-lamp/175/

This is what I was calling a board. Its actually a bulb, but looks like a board with a bunch of leds to me! See what kind of bulb fitting your fixture has, then choose the bulb type from this store. In my case, the fixtures had 1157 bulbs. They sell the entire fixture as well. Look at some of them and you'll see.

So, the fixture is the housing and wires for the light bulb, or light board, in my case.

[hankaye]

WoodSmith, Howdy;

I have seen the 'magic Smoke' depart many items in my life time...
Was always surprised that it could be hidden within some of the objects
I saw it escape from ... Great explanation of the theory. So, I'm guessing that the
tripping of a circuit breaker would be the equivalent of an electrical fart ???
I was under the impression and see many objects that hold the 'magic smoke'
also referred to has having watts and they completely ignore the volts and amps.
This is especially true with these LED things as volt and amp are rarely mentioned.
How do watts fit into the 'Magic Smoke' ?

Thanks,

hank

[WoodSmith]

An electrical fart. I've never heard it described such, but I suppose you could describe it that way. The circuit breaker relieves the pressure in the circuit and trips before (hopefully) the smoke comes out and the component - ummmm -- poops the bed.

Lets tackle Resistance (measured in Ohms) first, its a fairly simple concept and our water pipe analogy works well with it.
Resistance is like the size of the pipes, larger pipes allow the water to flow through more easily, smaller pipes increase the resistance, making the water flow more slowly. You may have seen this with a hose on your spigot at home. If you have different diameter hoses, the larger diameter hose will deliver water to the end at a faster rate than the smaller one. Likewise if you have a longer hose, even once the water starts to flow, it will take longer to fill a given bucket than it will from a short hose.

So we have the golden triangle of voltage, current and resistance. Volts, amps and ohms, or in our water pipes, Pounds per Square Inch (PSI), Gallons Per Minute (GPM) and Pipe diameter measured in inches. Mathematically these all relate to each other as stated in Ohms Law: V=I*R -or- Volts = Current times Resistance. What this means is that you can control two of the three variables. If you pick a voltage and a resistance, the current will always be the same and can be calculated by dividing volts by the resistance. I=V/R. If you want to fill a five gallon bucket with water in five minutes, you have chosen your flow rate as 1 GPM, you have only one hose, so you can't change the resistance, but you can adjust the pressure of the spigot by opening it more or less. If you want a faster fill rate, increase the PSI. If you dunk your bucket into the lake and pick it up, your flow rate has approached infinity, and the pressure has approached zero. It's important to remember that these three things are inter-related

A standalone LED will have a data sheet that will tell you how bright the LED will get at a given current. Combined with some other stuff in the data sheet (the forward voltage of the LED, which is kind of like a user fee), you can choose a current limiting resistor (one of the things that may have come up in your reading) for a given power supply. A fairly standard LED will light quite brightly at around 20 milli-amps (0.020 amps) and has a forward voltage of around 1.5 volts. So with a 5 volt supply, we pay the user fee of 1.5 volts leaving us with 3.5 volts. We now can calculate the size of the current limiting resistor using Ohms Law. 3.5v/0.020 = 175 ohms. If we use this LED and this resistor with a 12 volt supply, we can calculate the current as (12v - 1.5v)/175 ohms = 0.060 amps or 60 milli-amps, quite possibly enough to show us that magic smoke.

Since watching smoke is not our goal, we should pick a different current limiting resistor, same formula as with our 5v supply.

(Supply voltage - forward voltage)
---------------------------------------- = current limiting resistor size
desired current (from data sheet)

(12v -1.5v)/0.02 = 525 ohms. This should keep our LED brightly lit and the smoke inside.

The boards and incandescent replacement devices often have other circuitry built in so you don't need to do the math, just plug and play.

Watts is a measurement of work or power. It is calculated as the product of Volts and Current: Watts = Volts X Amps. In electronics it usually winds up as heat. To be sure our LED in the above example is safe, we should check what wattage resistor we need for each different supply. Resistors are rated to be able to dissipate a certain amount of heat before they too release their smoke. So at 5v the 175 ohm resistor will be dissipating 3.5v * 0.020A = 0.07 Watts (We use 3.5 rather than 5 because the LED took its user fee.) 70 mw is nothing, if you put your finger on it, you will probably heat the resistor more with your finger. A typical 1/8 watt resistor would be fine. When we tried the 175 ohm resistor with the 12v supply, we went to (12v -1.5v) * 0.06a = 0.63 Watts or NINE times more power. This would require a much bigger wattage resistor to keep the resistor safe, assuming the LED didn't go POOF first. To be on the safe side for the resistor, we would probably need to go with a 1 watt.

When we re-sized the resistor with the 12v supply, we reduced the current to what the LED is rated for, so now (12v - 1.5v) * 0.020a = 0.21 watts. As you can see, this calculation is important, because if we assumed that a 1/8 watt resistor was good to go, the resistor would likely blow, and will certainly cause a very cute but painful branding on your fingertip when you poke at it. This resistor should be at LEAST a 1/4 watt, and to be safe, a 1/2 watt.

I hope this made sense, (heck, I hope my math is right) I'm up late for the second night in a row. Let me know if you have nay more questions. Or if I doidn't answer the ones you had.
Glen

[hankaye]

WoodSmith, Howdy;

Magic smoke rolling out both ears at present ... followed path of least resistance.
Deeply detailed explanation is good ... keeping it simple much better.
My problem with trying to figure out which items may 'work' best for me is trying
to figure out what wattage to get. Most of the items that are being sold are listed
using watts. I can use the formula W = V x A, substituting the V with 12 or 10.5
to be more accurate I suppose and either divide it by the wattage or the wattage
by the voltage (less user fee), to find my amperage draws ???
Going to be thinking this through today, driving to Phoenix to get some engine work
done, so I'll have 6 to 7 hours to mull this over.
Thanks for taking the time to to as thoroughly into this as you have.

hank

[WoodSmith]

If what you are looking at buying is giving you the watts, just use the recommended voltage to calculate the current. Point us at a couple of the items in particular that you are considering and I can use them in a calculation rather than example numbers.

The devices that you are considering may have all the circuitry built in to handle wider voltage ranges. Similar to household appliances that have whats called an autoranging power supply in them for USA and Europe and can use either 120Vac or 240Vac. At 120V it may draw 3 amps, but at 240V it would only draw 1.5 amps. Notice that either way it is still a 360 watt load.

Glen