LED gurus....

[Kmot]

My Bristol Bay has a bunch of LED lights. They run on a battery pack of 2 AA's for a 3V rating.

The LED's are not super bright, even with fresh batteries.

I just installed another 2 LED's in parallel. When I powered it up, all the red LED's looked good, but all the green and white LED's barely were lit. This was on older batteries. After I installed brand new batteries, the green and white LED's were also visible but not very bright in comparison with the red LED's.

Question:

Do you suppose the LED's could be powered by a slight increase in voltage and not blow them out? Say three NiMh batteries at 3.6V? Or would three alkalines at 4.5V be safe?

I spent an enormous time today completely re-wiring the LED lights in the wheelhouse of my Bristol Bay because when I did the smoke stack mod a year or so ago I drilled through the wire harness and they have been out of order since. The two LED's I added are rated as 3V and they are red and they shine brightly. I would like to get the other colors to shine a little more brightly as well.

[boat_builder]

Kmot.

I've noticed the same thing with the LEDs on my Atlantic Harbor boat. My best guess is that they are really cheap LEDs and they fade pretty fast. IMHO I think they would get even worse if you applied even slightly more voltage. I guess it's worth a shot but I do know that LEDs do not have much tolerence for being over volted. An incadecent bulb will take the abuse much better, but an LED is basically like most other electrical components that are rated for a specific value, too much voltage and they will burn good and bright for a few seconds and then it's lights out for good. LEDs are a type of Diode (L.ight E.mitting D.iode) and like some other electronic components must be operated within their voltage rated value. :( I never replaced mine yet but I'm afraid that thats what it's gonna take if I want them to burn bright again. Somone else may have another opinion or advice but from what I've learn the hard way too much voltage even slightly can cause them to blow pretty quick. :( You may get away with 3.6volts but any higher like 4.5volts will be an undoubted death almost instantly. :(

It seems like red and clear LED's always burn brighter than others even when rated at the same "mcd" rating. To me it's a mystery, or may just be my eyes and the way my brain processes the light.?.?. :o If you want them all to be the same intensity you would almost have to use either the red and white (clear) ones of a lower "mcd" value or get the green and others at a higher "mcd" value than the red and white (clear). :)

[Kmot]

Thanks for the reply. That helps a lot.

Anyway, there is definitely something going haywire. I think one of the LED's I just installed may have been bad.

When I connected the wheelhouse to the harness, the mast LED's went dim as well as the wheelhouse LED's were dim. When I disconnect the wheelhouse from the harness, the mast LED's burn bright.

Next, the green and white LED's in the wheelhouse started to flicker, and got brighter. But one of the new red LED's is now not lit. As well as another red led (starboard light).

I am tempted to rip the whole thing apart and start from scratch, with all new LED's and an entire new harness from my construction.

[patmat2350]

Also... you know that LEDs NEED a resistor in series to control the max current. But what, you say there are no resistors in your BB? Ah, but there are! The wires themselves are the skinniest imaginable, and their own resistance is enough in this case. Can't say if higher voltage will just be that much more power lost in the copper, or if the current realized might exceed the LEDs' limit ("poof"!).

[Kmot]

I don't understand that Pat. A resistor in series would drop the voltage.

But yes, I did add about 6" of 24ga wire to the system.

[Kmot]

Okay, just found this:

http://www.allelectronics.com/mas_assets/spec/LED_Hook_Up_Guide.pdf

[patmat2350]

Exactly!
Here's the deal:
An LED (or any diode), will always drop a fixed voltage (like 0.7v for a standard diode, a bit more for LEDs), NO MATTER what the applied voltage is. But they have like NO internal resistance (hey, it's a semiconductor thing...), so by themselves, they won't limit current. Want proof? Try putting 6v across most any LED with test leads, and tell me how long the light lasts!

So a resistor in series serves as the current limiter. Assume you have 7.2v in your BB. The LED drops its "forward voltage", say 1.2v. And the LED wants no more than say, 20 mA (0.020 A). Any resistor will drop the remaining 6v, but we pick one that will draw .020 A on 6v drop, using the old V = IR formula (or R = V/I = 6v/0.020 A = 300 ohm). And of course this assumes negligible resistance in your wires.

For a calculator which picks the nearest safe available resistor, see
http://led.linear1.org/1led.wiz

[Rex R]

from my playing around with radioshack leds, I've found that the white rs units don't pull their rated current(something to watch out for) the 5mm white high
intensity were only pulling a smidge over 0.01 amps (package said 0.02a). had I not been conservative I'd have blown the led. red leds might only be rated to 3v while the white may be rated to 4v.

[Tugboat Andy]

I found this thread from about the same time last year. After watching Toesup run Scoot with lights, I decided that at least one of my boats will have running lights.

This is an interesting topic and I'm glad it was brought up again.

Thanks for the paitience on learning us this stuff, Pat! ;)

http://www.rcgroups.com/forums/showthread.php?t=603835&highlight=led

[patmat2350]

Rex- per the above, the LED doesn't "pull" the current... you SET the current with your resistor. And the value given is the max you should set for that LED.
If only 10 mA were flowing, there must have been some resistance in the circuit somewhere...

[rmdesignworks]

Another reason for the differences is shown in the attached wavelength spectrum graph..red is the highest while green etc is in the middle and violet at the lesser of the spectrum

[MILLERTIME]

Tom,

LED calculator - Very good site, bookmark it.
http://led.linear1.org/1led.wiz

Don M.

[Kmot]

Thanks guys!

Now that it is dark, I turned them all on again and they are not so bad. Except the burned out ones of course, and the remaining red LED I just installed has gotten dim.

Pat, they are all running in parallel on a 3V battery so if they are 3V LED's they do not need resistors, is what I was thinking. I have to go read all this tech stuff.

[LtDoc]

An LED can be supplied by any voltage as long as the current going through it is limited to whatever it's designed for. An LED's typical current limit is about 20 mA or 0.02A. Ohm's law says that E(voltage) = I(current) x R(resistance). If you know what the voltage is(E), and you know that the current(I) is .02A then the R(resistance) needed is easy to find, just plug in the numbers. That works just fine for parallel circuits since the voltage applied to all the thingys in parallel is the same. For series circuits, you have to allow for the voltage used/dropped by the preceeding thingy(LED), subtract that amount from the total and you have the voltage applied to the next thingy. And so on, and so on. For example; 9 volt supply, 20 mA (.02A) current for the LED. E = I x R, or R = E/I, so R = 9/.02, or 450 ohms of resistance for that LED. Since most LED manufacturers are sort of 'conservative' in their ratings, a resistor somewhere between about +/- 20% will make them light up. Want a little brighter LED? Reduce the resistance a bit. Dimmer? Raise the resistance a bit. And since all LEDs are NOT the same, you need to know their specs to do any of this figuring. These are all 'ball-park' figures so are not going to be 'right' for all applications, and only for DC, not AC.
- 'Doc

[Kmot]

Thanks Doc. Unfortunately for me, All Electronics does not give any info about what the LED's are rated for. I bought them in the store, and they have them in the counter only listed as 3V LED's and they also had 12V and 24V LED's. Nothing else, no current ratings, etc.

This is what I bought:

http://www.allelectronics.com/make-a-store/item/MLED-1/MINI-RED-LED/-/1.html

[rmdesignworks]

u can use resistors to match your led's too,,brighter ones can be given higher resistance while dimmer ones lesser resistance to even them out like with nav lights or different mast lights

[Kmot]

I just found this webpage. "LED's For Dummies". That's me, a dummy!

http://www.theledlight.com/ledcircuits.html

http://ledcalc.com/#calc

[John Pilot]

KMOT,

Typically the red, green and yellow LED's have a forward voltage of about 2.00 to 2.50 Volts. The bright white ones are around 3.30 to 3.80 V forward voltage.
This is what I do to figure out the forward voltage in case I'm not sure. This does require the use of a benchtop adjustable power supply with Amp and Voltage readout, or, if you have a seperate ampmeter and voltmeter, you can rig something up as well:
1. Turn the output of the benchtop supply to zero volts
2. Attach the LED, ampmeter (in series with the LED) and voltmeter (parallel to the LED) to complete the circuit
3. SLOWLY increase the voltage. Once you get to about 2 Volts you'll see the LED start to light up (or about 3 volts in case of the white ones).
4. Keep on increasing the voltage until the Ampmeter shows about 25 - 40 mA (depending on how bright you want it - typically you don't want to go past 40 mA, however, there are some high-brightness LED's that can handle much higher currents).
5. The voltage that gives you the 25-40 mA reading can be considered the forward voltage of the LED.
6. Once you have the forward voltage, you can determine the series resistance needed as described earlier in the thread.

By the way, there are some fairly simple electronic circuits that will put out a constant current to an LED over a wide variety of input voltages, that way, as the voltage of your batteries changes, the brightness of the LED's will stay the same. Here's an example: http://www.onsemi.com/pub_link/Collateral/AND8109-D.PDF

(This dicussion is actually very timely because I just managed to burn up a high intensity white LED that I originally had hooked up to a 6V power supply, with a 68 Ohm resistor. I switched to a 12 V battery, forgot to change the resistor and turned the LED into an incandescent - for about 30 seconds - after that,... funny smell, puff of magic smoke & lights out! :D )

[retoabcr]

Wrong post,sorry!

[Umi_Ryuzuki]

In my SDM, I created a voltage regulator that puts out about 3.2 volts.
That keeps the green and white LED at their brightest.
I add a resistor at each of the red and yellow LED to limit the voltage/current.

Using the LED Calculator that Millertime linked, it is possible to run your LED
off of any voltage using the recommended resistors placed into the wiring or
at each LED.

Also, LED brightness can be rated anywhere from a dim 800 mcd, to a
bright 10,000 mcd and then the high heat 1-3watt Luxeon LED.
All of these are single "bulb" led ratings, sort of like light bulb wattage.
So it's good to pay attention to the the specs when purchasing and
setting up the voltage and wiring.

:)

[nick_75au]

The Link Kmot found is perfect, I had a problem with the BEPS trying to run 3 white leds on 6 volts in series, wont work.
Each colour has a different forward voltage rating. the red,green and 1 white in series did work. you need a resistor in all cases with leds.
I kind of suck it and see, I brought a bag of multiple value resistors , start with a high value and drop values until I get the required brightness :)
Nick

[mfr02]

In the original post I got the idea that the LEDs were being run off dry cells. These tend to have their own internal resistance, which puts a top limit on available current. This is often in the comfort zone for one or two strings of LEDs, but connect any more and none of them get the current needed because the battery just won't supply it. The most reliable way is to start with a higher voltage, and have each string of LEDs have its own resistor.
Different colour LEDs do have different efficiencies, and therefore need different current for the same brightness.

[Rob_P]

Just my two cents.
I went to RS Electronics and bought some individual "Ultra brite" LEDs, that way you get the full specs for each one (colour). These are used as nav lights on one of my planes and close up they are so bright you can't look directly at them. I power the LEDs from a single spare channel on my Rx and I wired them such that each LED has its own resistor matched to the LEDs specs.

Rob

[tghsmith]

check hosfelt electronics for leds and lots of other stuff, target has battery powered 18 minni led strings in thier christmas stuff now 5.99 , off course I bought a bunch thats getting applied to halloween stuff......

[time4420]

Just my two cents.
I went to RS Electronics and bought some individual "Ultra brite" LEDs, that way you get the full specs for each one (colour). These are used as nav lights on one of my planes and close up they are so bright you can't look directly at them. I power the LEDs from a single spare channel on my Rx and I wired them such that each LED has its own resistor matched to the LEDs specs.

Rob


Do you have the candela rating on that "super bright" LED??
I'm converting my nav lights on my sailboat. Has to be at least 2 NM range.
What do you guys think of the Radio Shack LED's?

[Rob_P]

I had no luck at Radio Shack, they just had bags of assorted LEDs but without giving specific performance details of each.

Fortunately we have a local -

http://www.rselectronics.com

and I was able to go and pick from their stock.

I'm not sure what the mcds were but I could take a look tonight. I would suspect that 2NM is a tall order for something approx 5mm dia.
You also need to take into account the viewing angle as there is a huge diff' in apparant brightness as the angle changes on the object as it passes by.

[DanL]

Use a small potentiometer to find the voltage.
Using the actual batteries in the model, fully charged, hook up a potentiometer on the + lead before the LED (I use a small 1000ohm pot), and turn the pot down slowly from max resistance until the LED is at desired max brightness. Then measure the R of the pot and you have the approx value of resistor needed for that LED. Each color LED may need a different value resistor in front of it to get similar brightnesses.
No calcs needed. I use 6-7V as typical supply voltages, and usually end up using resistors in the 100 to 330 ohm range, depending on LED color, size and wiring particulars.

[pkboo]

Thanx for the idea Dan of the potentiometer, might be a solution to some other idea I have concerning spotlights dimming. I do usually run lights, using a resistor or two, from the main battery which range from 6V to 11,1V on my latest project. Boo

[ragss]

try http://superbrightleds.com/led_prods.htm . This sight gives full specs on each led

[Kmot]

I went to an electronics store today. New to me, it had a funny old Asian guy and he was a real curmudgeon! :p

Anyway, I ended up with some resistors and today I peeled out all the harness and LED's I had installed recently as well as one of the factory original LED's that had burned out as a result of my installing two more LED's without resistors.

I tested a new LED with one resistor and it lit well, I tested with a second resistor in series and it dimmed it too much. I am using 100 ohm 1/4W resistors which is what the old curmudgeon insisted I buy. So I installed three new LED's into the system.

Anyway, it is all working again on the bench, really well. The new LED's as well as the factory originals all light brightly and equally.

Thanks to all for the help and suggestions. :)

[LtDoc]

All kind of 'tricks' you can play with resistors. Two of the same value in parallel means half the resistance and twice the current. Three in parallel means 1/3 the resistance and 3 times the current, etc, etc. Series means just the opposite two of the same and you get twice the resistance and half the current, etc, etc. If you combine series/parallel resistances, there's even more possibilities. When those combinations get to looking like, and the size of a bee hive, quit, you've gone too far :).
- 'Doc

[Kmot]

Here is my Bristol Bay with the repaired nav lights and spotlight working again, and the addition of two red interior lights for the wheelhouse. The port nav light is also a replacement, and it is the same red led as used on the interior along with a resistor.

The lighting looks all stock, except for the glow from the wheelhouse. But the good news for me is that all the LED's are bright again. :)

[avidjeepr]

That looks good. :cool:

[Kmot]

Thanks! :)

[gpzy]

I like it, should look good running at night!!!!

[Kmot]

I hope so! :)

[Kmot]

Another question for the gurus:

Can LED's safely be placed under water while powered by a voltage source? Or will they short out by the leads getting wet?

I know a regular DC bulb would be okay, but I know very little about LED's yet.

[LtDoc]

A typical LED can be used under water if you don't expose the leads to that water, water proof them. If the water were pure it wouldn't matter if the leads were exposed or not, or an incandescent bulb for that matter. Pure (distilled) water is an insulator. The more impurities that get in it, the more conductive it gets. Don't know about where you live, but around here, you'd better water proof those leads :).
- 'Doc

[Kmot]

Well, as for 12V DC lightbulbs they will work for days or even weeks with the lighting element half submerged in disgusting, foul, recycled wash water.

The buses I used to work on go through a bus washer every day, (just like a car wash only super sized) and lots of times headlights and side marker lights get cracks in them and they start to fill with water. Or in the rainy season, driving through flooded streets will power force dirty street water even into "sealed" headlamps and you can see the water sloshing around inside them and the lights will still work.

Thanks Doc, you have answered my question. ;)

[mfr02]

Getting the glass bit of a filament bulb wet would only be a problem if the glass broke, same with a LED except the resin is much less likely to fail.
Like Doc says, the problems start when the leads/contacts get wet. A bit of spray like happens in a vehicle wash should be no problem - its when permanent full immersion happens, and the problem is not so much shorting out as the onset of corrosion.

[Massey]

A little to add about LEDs. While voltage to them is inportant the LED is actually driven by current not voltage like a standard light. Even if the voltage levels are low but the current is too high (like from dropping AC into DC using a transformer and rectifier) you can still blow the LED. Since current is common series and voltage is additive you should be fine wiring them in series. In parallel current is additive, so unless you use the same rated resistor in each branch you will not get even lighting.

And for running underwater, Just like any electric device you can use them under water untill the current is great enough to conduct through the water. It takes less current to travel in salt water than in fresh and distilled water is an insulator. I would waterproof the leads of anything electric going under water just for the sake of corrosion. I hope this helps

Massey

[Shaun Hendricks]

Water is anathema to higher voltage systems. Generally the risk at 24v and above increases greatly. 12v DC systems are usually not a problem, even in saltwater. The resistance of ocean water to low voltage sources is normally greater than most low ohm resistors, however, having said that, if you have higher resistance values (greater than the water it is immersed in) the energy will travel through the water to your led and give you interesting results, even blowing the LED's depending on circuit design. However, it will likely go 'inert' at that point, delivering the same voltage to each lead and you get a dead-shorted LED that does nothing. Dry it out, and it will likely work again.

So, waterproof your leads, but if you don't expect water intrusion but get it, it'll probably be okay. I've had servos and esc's survive immersion in some pretty nasty stuff. They stop working but dry them out and all is forgiven.... sometimes... ^_^

[mfr02]

LED specs quote two voltages - forward and reverse. Forward is the voltage that is dropped by the LED when conducting and therefore glowing, and is fairly constant. Reverse is the maximum it will stand up to without dying when accidentally connected in reverse (bi-colour LEDs are really two in the same pack, connected back to back so that each also protects the other)
When you have produced Doc's beehive, measure it and buy the nearest value to that.

[stduck54]

The trick is not only in the rating and voltage. a key factor is the clarity of the LED "head" plastic material . Many are opaque and look very dull when lit. Many of the high intensity ones are bright only when you look straight into them. From the side they again are very dim. The difference in the materials are quite significant. Radio Shack just does not have the spread. I spent an hour in a small "hole in the wall" electronic component shop in Singapore and hunted out 3MM red , white and green leds (for running lights) that have a very clear heads. At 3V they look good from every angle, almost like incandescent bulbs. It took quite some time and perseverance but the end result is very worth while.

[LtDoc]

Just to keep things in perspective...

There is a technical term very seldom made known to the general public, a sort of secret electrical thingy. That term is "Yeahbut". All electrical devices have 'yeahbuts', the 'trick' is in finding them and then compensating for them. 'Yeahbuts' are constantly being generated, there are always new ones. So the electronics field is a constant learning process. Electronics people (like me) really hate to reveal secret stuff like this, so I'm taking a chance of being ostracized, you better appreciate that!
- 'Doc

(Hint: print out this post. Hang it over your yard. Lush, beautiful, TALL stuff will grow in your yard.)

[rmdesignworks]

speaking of water proofing leads one thing that works well and is readily available in most "big box stores" or home centers is a product called "Plasti-dip" which is a rubber/plastic material in liquid/gel form kinda like honey in a small can which is intended to water proof or shock proof or skid proof tool and other surfaces, you can dip or brush on the stuff to almost anything, and it becomes electrically isolated and waterproof,,just follow the directions on the can,,at least two coats will due in most cases for just about any electrical connection or whatever,,,and this stuff sticks to a lot of different surfaces and materials