LED's or bulbs?

[Eddy Matthews]

I'm fast approaching the point where I need to think about fitting the lighting to my towboat - I know it's not a paddler, but the question applies to any model...

In the past I've always used GOW (Grain of wheat) or GOR (Grain of rice) bulbs - Easy to work with and more to the point for my simple brain, I can easily work out the brightness by simply adding one more bulb to the circuit if they're too bright, or removing one if they aren't bright enough!

But now it seems more and more people are using LED's because they last a great deal longer than bulbs, but are they as easy to work with? I've read all sorts of stuff about having to use resistors and having to calculate values etc etc. What about the scenario above, where the lights are too bright or too dim - With bulbs I'd just add or subtract one from the circuit, but what about LED's?

Does someone fancy talking me through this and explaining the basics for LED's? Any help would be greatly appreciated.

[towboatjoe]

I have always used LED's for guard lights and navigation lights. I've never used resistors. All I do is wire them series parallel on 3 volts. They have a polarity + & - and have to be wired that way. If they're wired backwards they won't work.

I've got 30 LED's running off two "C" size batteries no problem. I'm getting ready to experiment with the ultra bright LED's for spot lights. I used to make spot lights from krypton bulbs and guts from mini mag lights.

Just run a positive and a negative wire to each LED. You can chain them together. You can't connect them in series like regular bulbs. They just won't work that way.

LED's come in two configurations, regural and (if you need them a little brighter) point source.
They are many different sizes. Four of the most common are
jumbos which are 8mm
T-1 3/4 which are 5mm
minature (T-1) which are 3mm
and sub-mini

You can check out different LED's here
http://www.allelectronics.com/cgi-bin/category/340/LEDs.html

I use the minature T-1 MLED-9 for guard lights

[mjt60a]

I set mine up in the Freshwater model using a resistor for each LED, the correct resistors were supplied with them for use on 12 volts (probably for model railway use) and as I'm using 12v batteries, I just used them. The resistors for 5mm dia LEDs are different to the ones for 3mm even though both are supposed to have a maximum voltage of 3.4v. I expect that is because the current used by each type is different.
They (the white ones) light up quite brightly enough on 3 volts.
I've found that four LEDs can be connected in series on 12 volts and they work OK - providing they are all the same type (they get 3 volts each the same as four 3v bulbs would) I can also wire two in series to run on a 6 volt battery. Presumably, three could be used with 9 volts....
I found out the hard way that they have to be the same type to use them in series, if three 5mm and one 3mm are used, the 3mm gets hot! I'm guessing this is because the larger LEDs are pulling too much current through it.
I also found that the red LEDs generally run on a lower voltage (at least, the ones I bought do, 2.6v max) and need a different value of resistor.
I would think it's better to wire in series where possible as the voltage is 'used up' by lighting LEDS, whereas with resistors it's converted to heat (they get warm) so is wasted from the point of view of our models...
Just have to remember, the long wire on the LED goes toward positive. Used in series, the long wire of the first LED goes to +ve and the short wire goes to the long wire of the next LED - and so on...

[Eddy Matthews]

Thanks Mick and Joe,

That explains the basics, but lets assume I wire 4 3v LED's in series from a 12v supply and find they are a bit too bright - Can I add a fifth LED to reduce the intensity, and will they still work on the reduced voltage?

[towboatjoe]

That I couldn't help you with for I never wire them in series. Main reason is because if one LED goes bad you lose all of them.

I also try to avoid running anything from the same battery that powers the motors. I like to be able to run all weekend without recharging.

I don't think you'll find the LED's too bright. If you can locate the point source they would be better for guard lights. LED's concentrate the light to the tip so the light is not as bright from the side.

Here's a photo of the regular T-1's (on the upper two decks) and the point source T-1's (on the main deck).I like the point source better.

[mjt60a]

They will work on a reduced voltage but to a point, they don't dim at all, beyond that they do but soon cut off. Adding a fifth LED might not make enough difference - or may switch them all off.
You could run them from an adjustable voltage regulator, someone mentioned using one, on the model boats forum when the same question came up there, I think maplins do them and como drills...
Or what I'd try is putting a wirewound speed control in series with them (or maybe a variable resistor, the type used for a volume control in radios) and adjust it to give the desired effect. then take it out and measure the resistance, replace it with a resistor of that value.
Or if it's a good enough one to handle the current for long periods, leave it in the boat as a dimmer switch!
I haven't tried that but I think it should work OK.
*Ive got some of those around somewhere, I'll give it a try....

[Eddy Matthews]

They will work on a reduced voltage but to a point, they don't dim at all, beyond that they do but soon cut off.

Thanks again Joe and Mick....

I guess I'll give LED's a miss for now - I like to play around with the light output, and from what's been said it sounds like I really need to stick with bulbs to do that easily....

I see all LED's are given a brightness rating using Cd's or Mcd's - That's fine if you can picture what it will look like in real life, but just meaningless mumbo-jumbo if you can't (like me!).

[mjt60a]

They will work on a reduced voltage but to a point, they don't dim at all, beyond that they do but soon cut off. ....

Well, I was wrong about that!
I'd noticed that by wiring LEDs temporarily to a battery by twisting wires together they worked 'erratically' and assumed it was because of high resistance in the unsoldered connections and therefore any drop in voltage would extinguish the light, but that doesn't seem to be the case....
I connected two AA cells in series with a wire from each end (3 volts total) and connected a white 'high brightness' LED to them. It lit up brightly.
I then added a 10 ohm wirewound potentiometer in series (as a dimmer) - it made no difference.
Replaced the 10 ohm with a 100 ohm and it could be turned from full brightness to slightly dimmer..... but didn't make all that much difference.
Replaced it with a 470K carbon track type... it now only gets to about half full brightness (the component seems to have an internal resistance even when turned up to the stop) but can now be controled 'all the way to off'
The 470K would be perfect if it had no resistance when turned all the way and this could be because I'm using old defective radio parts cannibalised from used equipment.... but more to the point, LEDs apparently DO dim right down like GOW bulbs.
The only slight drawbacks might be that the white ones actually look bluish - like mercury vapour lights (would make effective floodlights!) but that could probably be overcome by painting them with clear laquer/varnish tinted slightly brown with woodstain. Just how much to tint them could be determined by painting 'spots' of the mixture on some clear acetate type material (such as the packaging from tescos apple turnovers) and holding it in front of an LED to see which proportions of varnish/stain look best, then coating the LEDs with it.
The other thing is their 'directionality', the light emitting part seems to have a cup-shape inside like a headlamp reflector, sanding/reshaping the outside might help a bit (as it acts like a lens) but there's still no light from around the sides like a real lightbulb.

[mjt60a]

[quote="Eddy Matthews....I see all LED's are given a brightness rating using Cd's or Mcd's - That's fine if you can picture what it will look like in real life, but just meaningless mumbo-jumbo if you can't (like me!)... [/quote]
I couldn't picture how they'll look by knowing the 'Mcds' rating (milli-candles?), those are given in the maplin catalog (and probably other electronics suppliers too such as RS components...) but I just go by the general description - standard LED or high-brightness LED.
Standard ones are like those used on electronic equipment (hifi, video recorder, your computers hard-drive and power lights maybe...) High brightness ones are used in some types of outdoor garden spotlights, miniature pocket torch/flashlights and certain tiny cameras. Best way to see how they look is go to Maplins 'electronic components' area, my local one has a board with all the types of LED on it, lit so you can see what they look like.
That said, I don't buy them there, a bit pricey if you ask me....