Model Boat Mayhem
Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Chaos32 on December 18, 2015, 07:11:21 pm
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Hello all
I have a tug with LED lighting fitted,3 nav lights on the mast,one each in galley and wheelhouse and one stern light.
These have never been connected just the wires loose in the superstructure, i cannot seen any signs of any resistors either!
The model runs on 12v any of you bright sparks be able to tell me how i can go about connecting them up?
The mast ones wires are buried in a wooden mast so would be difficult to change!
Many thanks in advance for any helpful advise i don't want to put any power through them incase i blow them!
My electrical knowledge is fairly limited
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Your problem is not knowing if they have a resistor inline or not. Assuming q white led get a largish resistor and solder it to one of the wires then connect the wires across a battery. A 470 ohm resistor would be the standard for one led and 12 volts. Double it (put two inline) that should dim the output markedly. Then half it, if the led gets a lot brighter you know you need to put a resistor in. If on connecting one 470 and it is dim already, its most likely already has a resistor inline.
Below is led calc which will work it out for you. Also an instructable article that Martin added to the forum.
http://ledcalc.com/
http://www.modelboatmayhem.co.uk/forum/index.php/topic,52197.0.html
sadly as everything is all sealed in, there is no easy way to find out.
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Thanks for that Brian i will get some resistors the weekend and give it a try on the stern light as this one is wired by its self
the others are two and three in series! I will let you know how i get on :-)) :-)) :-))
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I would start from the other end of the voltage range and then there is no chance of blowing your LEDs.
Apply 3volt to each LED pair of wires; if they light up, then 3v is correct irrespective of the resistors fitted.
If very dim, or not lighting up at all, then try applying 3*AA batteries (4.5volt), then 6volt and so on up to your main 12 volt supply.
Test each circuit separately.
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Thanks Kinmel that makes sense i will give it a go over the weekend :-)) :-))
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Kinmell yo should be aware that red and green led's are usually rated for 2 or 2.2volts. adding a 3 volt battery to those would damage them immediately! Also it is my understanding that irrespective of voltage applied, led's do need a current limiting resistor in series with them. Ie a 3 volt led and a 3 volt battery the led would still need a resistor, even if it was only 1 ohm, the resistor 'smooths' the flow of voltage through the led.
I stand to be corrected by the electronic experts, but that is my understanding from reading articles on the interweb.
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http://www.lutonmodelboat.co.uk/frame_hints.html
dave in the link above are a couple of articles on LEDS have a read and see if they are useful! If i can follow them then you can!!! new technology!!!
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Kinmell yo should be aware that red and green led's are usually rated for 2 or 2.2volts. adding a 3 volt battery to those would damage them immediately! Also it is my understanding that irrespective of voltage applied, led's do need a current limiting resistor in series with them. Ie a 3 volt led and a 3 volt battery the led would still need a resistor, even if it was only 1 ohm, the resistor 'smooths' the flow of voltage through the led.
I stand to be corrected by the electronic experts, but that is my understanding from reading articles on the interweb.
Brian - I have also read that about resistors even if the voltage is 'correct', and I would like to understand why. I have a number of sets of LED Christmas lights (red, blue and white) which work either from 2 x AA batteries or from a 3 volt power pack, and NO RESISTORS in sight. These have given good service now for a number of years - why haven't they failed?
Barrie
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http://www.lutonmodelboat.co.uk/frame_hints.html
dave in the link above are a couple of articles on LEDS have a read and see if they are useful! If i can follow them then you can!!! new technology!!!
Klunk,
Good link :-)) :-)) :-))
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Brian - I have also read that about resistors even if the voltage is 'correct', and I would like to understand why. I have a number of sets of LED Christmas lights (red, blue and white) which work either from 2 x AA batteries or from a 3 volt power pack, and NO RESISTORS in sight. These have given good service now for a number of years - why haven't they failed?
Barrie
LEDs are not resistors, and do not behave like them. They are voltage sensitive diodes. Below their sensitive voltage, they do act a bit like resistors, at and above that voltage they suddenly lose their resistance and will pass as much current as they can until something melts. Some have a limiting circuit built in to prevent this, some rely on the loom wiring to provide the resistance, some rely on having a power supply that can only give just enough current. The 2 AA cells mentioned probably have enough internal resistance to prevent any damage by limiting current to a safe value. With a couple of D cells or a more capable 3v supply, it would probably be a different story. On model boat setups, where the power supply usually has very low internal resistance, it really is vital to make sure that the current that LEDs can pull is limited to a value that they can survive.
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In the absence of accurate info, I work on an operating current of 18 ma. I know it varies a little according to colour, but this caters for most. After that, use Ohms law, voltage divided by current will give the approximate resistor value. I am not trying to teach my Grandad how to suck eggs, just trying to help. Pete
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Good, good!
VERY informative thread - one of the better ones certainly!
Just when I was wondering, where you get the amps, I came to the last post by Petermun.
...good...
I will go with "pre-resisted" 12 V leds. By far the most practical, as I am at an early stage and can choose.
Thank you all