RCHYFLYER

My Feedback: (1)

I want to change my landing lights on my Cessna to led super or ultra bright LED's. Right now the are incandescents that run of 4.8v receiver battery. What I was wondering is there and where can I get LED bulbs that I can just cut the old out and solder the new bulbs into the 4.8volt system? Also I'm hearing you can reverse LED bulbs to be brighter or dimmer any help would be appreciated!

FHHuber

You can not simply clip the old bulbs and insert LED's. You can find LED's that should fit the location though...

An LED has nearly no resistance. If you use it as a replacement for an incandescent, you must put a resistor n line to limit current. LED's are rated on what amount of current will light them up to the rated brightness.

E=IR is the formula to determine the resistor required. Given a known voltage (E) and the rated current of the LED (I)... solve for R. Add the resistor in-line (series) with the LED.

Radio Shack and about any passable electronics supply store witll have what you need.

Deadstik

My Feedback: (8)

Hi,

I wanted to expand a bit on FH's response. As far as where to get the LEDs, I have them in almost every color...ultra bright white/red/blue/green..water clear 5 mm LEDs ..... FH is correct that current is the main animal where LEDs are concerned.. They are fired and regulated by current. Most LEDs run on 20 mA (milliamps) and will do so for 100,000 hours plus. You can drive them harder and I have found by experiment that you can go up to 20% over rated with little or no degradation of life. You will also find that LEDs have a point where they simply will not increase in brightness no matter how much current you apply. If you look at LED stoplights, they are super bright.. but each LED is only drawing 20 mA... and that is why you see them everywhere.. the savings are HUGE.. For models, that is just what you want to as you don't need a seperate battery pack. How you figure what the current limiting resisitor is... is to first find out what voltage the LED uses (Voltage measured across the LED) when being driven at 20 mA. I do this with a regulated power supply, an ammeter, and a voltmeter. Let's say the LED uses 3 volts at 20 mA. You have a 4.8 volt (nominal) receiver pack. That means you must limit the voltage across the LED to only 3 volts and the resistor you put in series with the LED must have 1.8 volts dropped across it. To figure the resistance you use the equation R=E/I or resistance equals voltage divided by current. The voltage here is 1.8 and the current equals .020 AMPs. This gives you an answer of 90 ohms Resistance. Keep in mind your basic resistors are going to run +/- 20 % tolerance so a 100 ohm resistor in series with the LED will work out just fine. YOU CANNOT REVERSE THE POLARITY ON AN LED TO MAKE IT DIMMER. IF you reverse polarity it simply will not work and if you apply too much reverse voltage it will simply burn up. (Not Pretty) If I can be of help.. just let me know.


Deadstik

PS.. Radio Shack is a terrible place to buy components... may I suggest Digi Key or any of the other electronic supply houses..

3dd

My Feedback: (6)

to jump in here,i took a 6 volt 20 mil led and wired it onto the end of a servo ext and pluged it into my open channel on my reciver to give me a radio on warnning light but did not use any resisters.is this not a good idea or did i do it right.don't want to drain the batteries but it looks cool flashing in the dash

FHHuber

[X(]AAAACK!!![X(]

DON'T FLY THAT!!!!

You have essentially put a DEAD SHORT across your battery back. I'm suprised you have not melted your switch harness. Get a resistor in that circuit!

Stick Jammer

Any LED that is rated for 6 volts must surely have a resister already built in.

Deadstik

My Feedback: (8)

Yep... Stick would be right about that....


Deadstik...

ifixairplanes

My Feedback: (9)

i would not power any lights on my plane with my RX battery. Well actually, the LEDs on my voltwatch, but thats it!!! I wounted my voltwatch inside my fuse (funtana s) and i cut a long rectangle hole in the bottom of the cockpit that is only about 1/8" x 3" for the voltwatch LEDs to shine through. Basically i can see all the voltwatch lights through the canopy but you cant see the voltwatch itself. very clean looking and i see the lights when my switches are on.

sean

RCHYFLYER

My Feedback: (1)

I test my receiver battery before and after every flight with a volt meter. As far as my Cessna the landing lights are y-ed into my flaps servo so they only come on with flaps down,and that is why I want to change them from incandescents to led for the min amount of draw LED's require!

3dd

My Feedback: (6)

so stick you seem to know something about electronics so am i safe with just a 6 volt 20 mil led or am i just screwing up without a resistor in the line,if i need a resistor do i need to just put it in line on the positive side or jump across pos to neg sure would like to be right so i don't just drain my battery pack oh the pack is a 6 volt 2700 mil pack

ifixairplanes

My Feedback: (9)

you would put the resistor inline, not jump it from poitvie to negative. It also dosnt matter whether it goes on the positive side or the negative side, as long as you put it in series with the light. I still strongly disagree with running a light off of the Rx other then a batt checker that is designed to be a low current drain.

sean

kingair41

My Feedback: (13)

If you have an LED that is rated at 6 volts and 20 mils and you use a 6 volt battery pack whether it's a recvr battery or a separate pack you do not need to use a dropping resistor. Only when using a higher battery voltage than the rating of that device would you start considering using a resistor to limit the current. For example: if you were using that same LED and wanted to power it with a 9 volt battery you would want to limit the current to 20 mils. 9 volts minus 6 volts = 3 volts to limit. Divide 3 volts by your current of 20 mils ( .020 amps ). The resistor would be a 150 ohm. It's that easy. Do get in the habit of using separate batteries for all extra devices on board. Have fun.

ifixairplanes

My Feedback: (9)

kingair, i would have disagree. A LED has almost no internal resistance, if you have a battery that is 1100ma, when you connect the led to it, you will be running nearly the batterys full power through it. I dont think a standard LED will last long with 1.1 amps running through it. You need a resistor inline to limit the CURRENT. the resistor is causing a voltage drop and because current and voltage are directly proportionate, your are limiting the current. Some LED's have a resistor built in though, so you dint need one. The manu. gives you the max current rating so you dont burn it out.
fact of the matter: if the LED does not have a resistor built into it, you NEED to put one there, otherwise you are essentially putting a dead short across the power source.
Sean

FHHuber

I've never seen an LED with a built-in resistor... Sounds like a good idea if they are made... I just haven't seen one.

You can hook up a micro-switch to actuate the landing lights running them off a second battery pack. I have done this for my on-board glow ignitor systems. (I don't buy them I make them.)

Cut a large round servo wheel to a cam, and mount the microswitch to the servo. There is a size microswitch that is ideal... fits the same holes as a Futaba S-3003's mounting screws at one end. Requires a 1/3 inch spacer between the grommets and the microswitch to put it in line with the cam. Microswitches prduce VERY little RF when they make or break contact. Ground tests might see a tiny blip when the swithc clicks... but it won't be noticeablen the aircraft's performance. (thats why I use the microswitch.)

Then you drill the cam-servo wheel for the control link to the surface being moved. (I use a ball link here... to get the pushrod well clear of the microswitch)

Simple and effective switching of the lights or glow ignitor... and its cheap to set up. (the microswitch is about $2.50) AND you can easilly separate a load from the RX. (I also advise against running lights fromt he RX pack.)

Another oprion... you could Y in one of the GP "Electrafly" electronic motor switches. Clip the positive lead on the Y between the electronic switch and you isolate it from trying to supply power to the RX with its BEC section. (It will still get the signal from the RX and the battery for the electronic switch will drive the lighting system.) This is about $12 or $15

kingair41

My Feedback: (13)

Sean do the math. Your way suggest that you put a resistor inline with 6 volt led and a 6 volt battery. To figure the resistor, subtract 6volts ( led rating ) from 6 volts ( voltage supply ) what do you get? 0. Now divide that by the current you want supplied to the led. What do you get? 0. Thats the resistor you want inline. With semiconductors Sean the question is not resistance. Rather the voltage required to conduct or forward bias that device to function or conduct. When you put your brakes on in your car your brake lights come on. You have a 12 volt system that drives the electrical devices such as your brake lights. When your bulbs burn out do you replace them with one of a different voltage such as a 6 volt one like some European designs or a 12 volt one? The resistance of that bulb when cold may only be 1 -2 ohms. Don't try to put a 1-2 ohm resistor across your car battery or risk burns or a fire. The bulb pulls what it needs from that voltage supply to light up across the filament. Now there is differing wattages but that's another story. A 110v bulb in your house functions the same way. With bulbs which have resistance rely on heat to change it's resistance. Once lit a bulb will change it's resistance to a level required to stay lit without burning out. So an led operates on a function of conduction and biasing. Not resistance. Try lighting an led on a voltage under the required rating for that led and the intensity will drop. Sure you can run a 6 volt led on voltage under 6 volts but it becomes dimmer as the voltage drops to a point where it doesn't emit light. A dropping resistor is required any time you exceed the voltage of that device. The higher the voltage the higher the current can be driven through that device. Hence something to reduce that current.

kingair41

My Feedback: (13)

Sean another note here. If you put a 6 volt led across a 4.8 volt pack at 2200 mah what would it do? It may light but will be very dim. Your suggestion is to put a dropping resistor across any device whether it's a bulb, motor, Led, or anything where the current rating of the supply voltage exceeds the current rating of that device. The voltage is the first thing to look at when figuring whether it needs a dropping resistor or not. The amperage of a battery is an indicator of how much power we can store to run the various system components that we put in the circuit. A servo operates on a nominal voltage of 4.8 volts. The batteries we use in a standard set-up is 4.8. At full deflection against a resisting force will still only have 4.8 volts maximum. But the power increases to over come that resistance and how long can we sustain that resistance is determined by the battery capacity and of course the windings of the motor, wire size, heat dissipation, etc, etc... Then some one came along and figured that why not run 6 volts through our servos to get more power. Higher the voltage the higher current or power we can run. Most servos have 2 torque ratings. One for 4.8 and 6 volts. But most people didn't realize that they ran out of power sooner til it was to late. A 1.5 volt D size battery can pump out 2-3 amps of power but for a very short time. But we can run a 1.5 volt bulb at 10 mils easily across it. Flash lites run bulbs rated for the voltage of the batteries used. By voltage not current. Voltage will tell us if we need a resistor. Then current will give us some indication as to how long that device will run at that pull rate. Cover the unknown value with your finger and the rest is the equation needed to find the missing value.
Kingair

E
____
IXR

ifixairplanes

My Feedback: (9)

i only said an LED. the LED's have an internal resistance of almost 0 ohms. would you put a 0 ohm connection (a jumper) across your battery?? Let's say just for *****s and giggles the resistance of the LED is 1 ohm, very minimal, that with 6 volts gives you 6 amps. do you want a 6 amp draw on your battery? Even if the internal resistance is 5 ohms you still have a current draw 1.2 amps which is still too high to but across an RX batt.
Again, an LED has almost NO INTERNAL RESISTANCE! I did not say anything about electric motors either, they produce a CEMF when they spin up, thus increasing their impedeance as they speed up (series wound magnet type motor) creating less of a current draw as they go faster. I dont need electronics preaching, i know my stuff. Putting an led directly to a power source is like putting a dead short there.

sean

ifixairplanes

My Feedback: (9)

kingair on another note here: would you take a regular diode and put it directly across a voltage source so it is forward biased? NO!!!! It would burn out from TOO HIGH A CURRENT DRAW. what is an LED, well its a light emitting DIODE. c'mon man, you sound like you enough about electronics to understand what i am saying!!

sean

Stick Jammer

Take a look at Radio Shack. They have them all the way up to 12volt ratings with internal resistors. Physically they look the same, you can't see the resistor. If you put too much voltage to a regular LED it will just instantly burn it out, it won't be a dead short.

kingair41

My Feedback: (13)

Sean, a regular diode for this discussion can't regulate the amount of current flowing through it with out external help when applying it directly across a voltage supply.It may exceed that components ratings. Thus you need a dropping resistor. An led can regulate it's current when operated across a voltage supply within it's voltage spec by the nature of it's design. Leds will regulate the current passing through them as long as the voltage is the same as the led it's operating. Leds can and are used as regulators in circuits all the time where a cetain current is needed to be regulated and at the same time light up to show that the circuit is active. Some what like a zener diode only it's limiting the current passing through it to the rest of the circuit. Any body reading this can prove this themselves. Get any led be it a 1.2, 3, 6, 9, 12volt and put it across the battery voltage equal to that leds voltage specs, for example, a 1.2 led will run nicely on a nicad battery of 1.2 without a dropping resistor. A 3volt led will run nicely on two 1.5 batteries in series, and so forth. and they will stay lit for some time depending on the battery and condition of that battery, without a dropping resistor. Now add a circuit that can flash that led at a rate settable by the user and now you have something. They do have available leds with built in resistors in one package for convenience. Iam refering to leds without those built in resistors. I still go back to my previous post Sean. If I have a 6 volt led at 20 mils, and apply 6 volts to it what would be the dropping resistor and how did you figure it out. I showed you and everyone reading this how it is done. That's ohms law. This law has worked from the begining when electrons were discovered, and a way to control them was needed. Don't take my word for it. Do the test. You'll find that leds are neat to use for a wide range of uses, and they last for ever and don't pull any thing as opposed to bulbs. If you want a copy of my schematic let me know. Even a light bulb can be used as a current limiter.
I have used them for battery chargers for trailers for years as a slow charger at about 1 amp average. I can tell how the charging is doing by the state of the bulb. Lit or out. And Sean, this is not an attack or any means an attempt to discredit you. I merely am trying to show with alittle help how easy it is to add something to any plane for as little as possible in monies laid out. I think I have informed anyone willing to try using leds to test this themselves. It's easy and fun.

kingair41

My Feedback: (13)

Sean, I just pulled a standard duty diode ( 1n4006 ) and checked the resistance in the forward position and read 2.2 megs. 0 in the reverse position. But both of us know it will self destruct when switched on in a circuit when placed directly across a supply of sufficient voltage and current. I pulled another diode, a 1n60 which has a voltage drop of .3 volts and measured 46k. Neither one would last long across a supply generally speaking. And I'm sure you have some that measure considerably lower than the ones I just happen to have on hand. So with the wide range of diodes measuring all over the place it hardly seems that that is a way to accurately indicate the functionality of that device in operation, unless for a quick check to see if it is shorted in both directions. A more accurate and acceptable way is to use the diode checker most DVOM's have to actually check the diode in operation. It applies a voltage across the diode and measures the drop to see that is working properly. Typically .6-.7 drop is normal. So to say a diode has very little resistance is misleading in the sense that measured while in the off state is high enough to do little in terms of a resistor but putting it in a circuit as described and switched on will go up in smoke. An led is like a diode but differs in it's abillity to govern it's self when applied as mentioned previously ( within operating specs ). This is not a lecher to you but a discussion on the basics of the operation and differences of diodes and leds. Cause there is some interest in using these devices on our planes and with the advent of high intensity leds these gems can be used and seen very easily even in bright day lite.

Deadstik

My Feedback: (8)

King Air,

You are very correct in your readings of resistance in a diode. They vary of course depending upon type/use. One thing I wanted to bring up on the LED topic. As I said in my earlier post, you first have to know the voltage drop at RATED current prior to doing the math and putting in your current limiting resistor. LEDs vary WIDELY in voltage necessary so it isn't a one resistor fits all. If you do the measurements on your components, it is easily possible to not even use a current limiting resistor. An example would be using 4 LEDs that each use 3 VDC at 20 mA. You could put this string across 12 VDC and it would happily run forever. This is not a good guess or a bad procedure as I have spent the last 8 years doing LED research. Yep, I've got some REALLY cool LEDs... and the funny part is, they are becoming something that is the opposite of what they were designed for. LEDs primary purpose in life is to provide a light source at a very low and efficient current level. The problem is...people want them as bright as incandescent light !!!.. So.. now, those LEDs are becoming available at really high prices.. but.. they give you the light.. but they also draw the current and they reduce the life span to do it. Just an observation but they really do have great uses for our planes. I have landing lights on my planes and even at a 5000 mcd rating.. you can see them over 100 yards out on a bright day. Maybe I'll make a commercial set.....


Deadstik [8D]

kingair41

My Feedback: (13)

My point exactly Deadstick. I was trying to keep it simple by using only one diode in the circuit not 2, or 3, or more. If we can't get through the first grade you don't teach the second grade. I've used the 10,000 mcd leds but with a reduced angle of emission. The 5,000 and 6,000 offer a wider angle and seem to be just as bright from these sets of eyes. You have more time than I do if you package them commercially. I wanted to let readers know that they can do it themselves relatively cheap as opposed to the store bought units and how to do it. And as modelers go we are an innovative bunch that would like to fiddle with projects or add ons or whatever the task at hand may be. Though Radio Shack may get a thumbs down on some of their products, I have found that led holders and magnets for latching hatches closed, and light lenses, and a general duty npn, or 555 timer, and so on is pretty handy in a pinch. Look at their led holder # 276-080. Looks just like a head light. For $2 you have two. A switch for another $2 or $3, an led ( H. I. L. ) at around $1.60, a 9 volt battery, connector, dropping resistor and some wire you got a nice looking landing lite set for well under $10. Who would'nt what one or two. I've made available to anyone who wants a flasher unit schematic to make bulbs or leds blink on and off. All the parts are available at Radio Shack. We are not talking Radio Shack electrical parts to fly my $5,000 bird. In one word---- NO WAY!![:'(]

Deadstik

My Feedback: (8)

KingAir,

If you don't mind, could you send me a copy of your blinker schematic? I'd like to see how you did it. I've seen and used several designs w/555 timers and am always interested in seeing what others have done. Many times I've found that the people who tinker with electronics can do a far better job than those who "engineer" electronics... they don't have a deadline or a budget or 50 people who know how to do it better than they do!!

thanks,

Deadstik [8D]


[email protected]

JPOFL

My Feedback: (36)

Hey guys check out dreamworksrc.com for Light sets of all kinds.
Can be seen in full daylight.
Paul[8D]