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Author Topic: LED's for lighting  (Read 16887 times)

meechingman

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Re: LED's for lighting
« Reply #25 on: September 25, 2006, 08:55:16 PM »

Here's the diagram for the power supply system for my tug. 9V comes from a PP3, though I could have used the 7.2V from the battery pack, if I'd felt like drilling through the watertight deck hatch! The 5V from the regulator then goes through 4 pots, all set to give different levels of brightness.



Andy G

You can see the diagram a bit better at http://i30.photobucket.com/albums/c334/andygilbert/ledpowersystem.jpg
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cbr900

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Re: LED's for lighting
« Reply #26 on: September 26, 2006, 03:26:36 AM »

Maybe a light shade is the wrong choice of words, what about reflector for a standard lamp. that type of thing, are these available or do you have to make your own..



Roy
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Martin [Admin]

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Re: LED's for lighting
« Reply #27 on: September 26, 2006, 04:33:17 AM »

Speaking of LED's anyone got an idea how to defuse led so they give off a more incandescent glow?
I want to put an led in 2 mast head oil lamps on Jan's Puffer but want them to give off a glow....

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cbr900

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Re: LED's for lighting
« Reply #28 on: September 26, 2006, 09:12:55 AM »

MARTIN,

If you want them to be duller, paint the globe with the same colour paint then you will only get a glow not a bright light....




Roy
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meechingman

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Re: LED's for lighting
« Reply #29 on: September 26, 2006, 09:57:20 AM »

Use a fine file on the led, so that the surface is no longer smooth. File off the top and paint the sides that won't show, as detailed in my earlier post. Then adjust the power going to them with a resistor or pot [see diagram]. My nav lights glow but the others are brighter.
Andy G
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Subculture

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Re: LED's for lighting
« Reply #30 on: September 26, 2006, 01:11:17 PM »

Speaking of LED's anyone got an idea how to defuse led so they give off a more incandescent glow?
I want to put an led in 2 mast head oil lamps on Jan's Puffer but want them to give off a glow....



LED's tend to give off a rather cold blue or greenish white light, compared with a tungsten filament lamp.

However there are now 'Warm white' LED's available, which mimic conventional lamps. They are more expensive, but will look more authentic in your case. The other alternative is to paint the LED with a thin coat of translucent yellow paint.

http://www.theledlight.com/5mmwhleds.html

Guy Bagley

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Re: LED's for lighting
« Reply #31 on: September 27, 2006, 02:20:44 PM »

i have used suppliers listed on www.ledlight.co.uk, some great stuff on there..... the great thing is white LED's when potted in clear resin work so well underwater on my submersible.....
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tigertiger

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Re: LED's for lighting
« Reply #32 on: October 14, 2006, 01:19:36 PM »

Anybody

Before commit myself to a pile of smoke ::),
Could someone check my circuit for me (see below), as I don't know what I am doing.

I want to try and do things with circuits in series as it simplifies the wiring and would make it neater as I will have wiring going up one mast, along the triasic stay and down the other mast. It will also allow me to hide a single strand of wire below the rail.

I have used the calculator given in a previous link to work out the resistance needed, but I am worried that the currents may be too low.
Would I be better of with a small variable resistor, if such a beast exists ???

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Subculture

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Re: LED's for lighting
« Reply #33 on: October 14, 2006, 02:13:59 PM »

That won't work.

You musn't feed different voltage LED's in series. Group the voltages together and feed them in parallel legs.

Andy

tigertiger

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Re: LED's for lighting
« Reply #34 on: October 14, 2006, 02:33:01 PM »

That won't work.

You musn't feed different voltage LED's in series. Group the voltages together and feed them in parallel legs.

Andy

Why is this? I am trying to understand and learn. ::)
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Subculture

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Doc

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Re: LED's for lighting
« Reply #36 on: October 14, 2006, 02:55:52 PM »

The primary reason not to feed different voltage devices in series is that there is the chance of the max voltage of one device being exceded.  That doesn't mean that you can't, just that you should take care in doing so.  It also means that the higher voltage device won't give full output, but that's your reason for doing it, right?  The 'other' problem with series fed devices is that if one goes out (burns up) all the others go out too (series fed Christmas lights? Finding the 'bad' device is such fun!)  Still doesn't mean that you can't do it.  I favor parallel feeds when at all possible... cuz I'm lazy.
 - 'Doc
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Re: LED's for lighting
« Reply #37 on: October 14, 2006, 06:14:38 PM »

tigertiger, your circuit will work since all the "voltages are per LED" are below their maximum accepted voltage however you will find that those rated at 3v will be dimmer than those at 2v. ::)

I agree with "Subculture" in that you should group the LED's together, I have attached the circuit below if you are going to use that method, this should light the LED's up at their full capacity.

If you go with "Doc"s method of wiring them in parallel I am more than happy to come up with a circuit for that too. ;)

Hope this helps! ;D

OMK

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Re: LED's for lighting
« Reply #38 on: October 14, 2006, 06:37:33 PM »

T-tiger,

Going on that the assumption that you've heeded Doc and Subculture's advice, then it's a safe bet thet you're pretty up on LED theory by now.
For what it's worth, here's a tried and trusted method of resistor calculation...

1) Assume Red and Green LEDs to have a forward voltage drop of 2-volts. In simple terms, this means a red or green LED would need at least 2-volts in order for it to glow.
2) Assume White and Blue LEDs to have a forward voltage drop of 3.5-volts to 4-volts.
3) All LEDs will glow with a current (not voltage) of between 10mA and 50mA.
4) Do not connect the LED without its current-limiting resistor (it's bound to blow, else).
5) Do not shove more that 50mA up there.
6) As you might know by now, never mix differing-voltage LEDs in series.

While re-drawing your original circuit I noticed that you're running from an 18-volt supply. So in case you're wondering how I arrived at the resistance values shown, or if you find yourself needing to run from a supply other than 18-volts, here's how...

First of all, ascertain the LED forward voltage, then deduct this number from your supply voltage. i.e: let's assume you're using a white LED. This means you have to deduct 4-volts from 18-volts to arrive at 14-volts.
Next, decide on the needed current. 10mA would yield a less-bright LED than if you were pumping, say, 50mA through it. But bear in mind that the higher brightness will mean more drain on your battery supply. A good trade-off is a current of around 20mA.
So now you've decided on the LED, and the the amount of current flowing thru it, you need to ascertain the resistance value.
Simply divide 14 volts (your battery voltage minus the LED forward voltage drop), by 0.02Amps (20mA). The answer is 700 ohms. But since 700-ohms is a non-standard value, round the number off to the next nearest value... in this, it's 680 ohms.

It's easier to do the math than it is to explain.
Hope it's of some help.
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tigertiger

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Re: LED's for lighting
« Reply #39 on: October 15, 2006, 03:03:13 AM »

...The 'other' problem with series fed devices is that if one goes out (burns up) all the others go out too....
 - 'Doc


I was lead to belive that LEDs (unless over driven) have extremely long lives, and it is unlikely they will burn out.
Is this incorrect?
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tigertiger

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Re: LED's for lighting
« Reply #40 on: October 15, 2006, 03:55:46 AM »

Read and digest-

http://www.lsdiodes.com/shop/index.php?main_page=page_4&zenid=4104721b49f9174cf66281956e152be4

Thanks for the link subculture.
Looking at it, I think I can mix voltages.
If wired in parralel I need to use resitors to balance the voltage.


If wired in series it may not be a problem, as I will get lower light emmision from the higher voltage LEDs (as suggested by Fireboat).

But there does seem to be a difference of opinions on the use of differrent voltages in Series.
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tigertiger

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Re: LED's for lighting
« Reply #41 on: October 15, 2006, 04:20:40 AM »

Firstly thanks for all the advice so far guys. ;D

Secondly,
Sorry for three posts in succession, but I thnk one subject, one post, helps clarity.
And there is more than one discussion. 8)

Third,
Slight change of direction here
I am unclear :-[, from diagrams I have seen, how to close the circuit (physically)

In the attached diagram, which circuit is correct. Circuit one or circuit two? ???


I always work on the premise that the only stupid questions are those that are not asked.
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Doc

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Re: LED's for lighting
« Reply #42 on: October 15, 2006, 06:01:55 AM »

tigertiger,
Use circuit #2!  Circuit #1 will short circuit the battery, no lights lit, battery gets very hot, not a good idea - lol.  The circuit is 'closed' ~through~ the LEDs.  Or, place a switch in the line going to or from the LEDs from/to the battery (I think that sentence confused me!).
And you're right, the higher voltage LEDs on lower voltages will not be as bright.
 - 'Doc
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Malc Reade

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Re: LED's for lighting
« Reply #43 on: October 15, 2006, 07:27:45 AM »

Doc is absolutely correct.  All circuit #1 would do is fry your battery in very short order!

Some mention of fusing for these circuits might not go amiss at this point?  ALL wiring circuits in a model should be afforded overload and short circuit protection. The easiest way to achieve this is by inserting an auto fuse (or similar) of the correct rating in the initial (positive) leg of the circuit needing protection.  Use a fuse value that is closest to, but above, the normal operating current (in Amps) of the circuit.

Modellers think of DC supplies in model boats as being pretty benign - it's difficult to get any meaningful electric shock at the normally used voltages, BUT BEWARE, short circuits that are unprotected can very quickly turn into serious fires.  A short circiut might be defined as one where there is a continuous current path across the supply terminals of the power source, i.e. no device with inherent resistance in circuit.

The differences between DC (Direct Current) and AC (Alternating Current) are also worthy of mention, if only for general interest, with regard to short circuits and protection:

In a DC circuit, a short will cause an exponential and continual increase in current until someting gives, either a fuse blowing if one is fitted, or if one isn't fitted, the wiring or some other component burning until the circuit breaks itself.  At higher voltages, DC circuitry is highly dangerous and has to be very carefully designed.

In simplistic terms, in an AC circuit the current reverses direction (a sinusoidal wave form) at the designed frequency, typically 50 cycles per second (Hertz) on the UK national grid.  This does vary from country to country around the world.  Fast operating fuses, or more commonly these days, circuit breakers, for AC circuits are mostly designed to blow or trip often within half of one cycle i.e. within 100th of 1 second.  The current draw on the circuit does increase, but for such a short duration that the consequential damage is minimal.  ELCB's (Earth Leakage Circuit Breakers detect current in the Earth path of the device and trip the breaker in the shortest practicable time. These have largely been replaced by RCD's in modern installations (see later post).

Given the choice, from a personal safety perspective, I would rather work on AC circuitry all the time, particularly at anything above 24 Volts.

Another word of warning, electric shocks from voltages as low as 24V have been known to kill people with certain heart conditions.  And on that happy note....

My best regards,

Malcolm


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Colin Bishop

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Re: LED's for lighting
« Reply #44 on: October 15, 2006, 10:54:42 AM »

Quote
electric shocks from voltages as low as 24V have been known to kill people with certain heart conditions

Ah! So now I can achieve my longstanding ambition to fit my boat with a death ray!  :D

Seriously Malc, that's very good advice. Modern batteries of almost all types now have the ability to deliver very high currents and many people are unaware of the high potential fire risk. Just look at the recent laptop battery recall for example. ALWAYS protect the circuit with a fuse or similar. It not only makes things safer but can save you a great deal of grief and money too.
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tigertiger

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Re: LED's for lighting
« Reply #45 on: October 15, 2006, 02:47:47 PM »

Would I be right in guessing a 1 amp auto fuse would do in most cases?
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Re: LED's for lighting
« Reply #46 on: October 15, 2006, 03:35:57 PM »

For circuits using LEDs, yes.  It is possible to get lower values intended for instrument use, but a 1A fuse will do the job. Somewhere else on the forum I mentioned using a thin enamel insulated wire - a 1A fuse will not protect this stuff, rather the other way round.  Remember that the fuse is supposed to be the weakest link, so that it blows to protect the rest, and can be easily replaced when the problem is solved.
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Re: LED's for lighting
« Reply #47 on: October 15, 2006, 07:32:52 PM »

tigertiger:-
Quote
In the attached diagram, which circuit is correct. Circuit one or circuit two? Huh

Go for circuit one, I presume your having indoor heating as well as lighting? --> Just let me know when you try it on the water and I'll get the Fireboat ready! ;D

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Re: LED's for lighting
« Reply #48 on: October 15, 2006, 10:02:34 PM »

May I add some clarification to reply 43.

1. In a D.C. circuit under fault conditions the current will increase only to a level that is allowed by the circuit voltage (ie the battery voltage) and the ohmic value of the resistance of the fault. With a true short circuit (a very low value of resistance between the poles of the supply) this can be a high value. On a 12v supply you could be looking at around 120 to 1200A, a high enough value to completely destroy your boat wiring system quite easily. A photograph was once published of the results of someone getting their metal watch strap connected across a 12v battery. The results were not very pretty. Fusing is the only way to go to offer protection to your installation.

2. Residual Current Devices: These do not detect current in the earth path, they operate by sensing the diffference in current between the phase and neutral conductors supply a load. On a healthy circuit or installation the current in both conductors will be equal but under earth fault conditions the current in the phase conductor will be larger due to the current leaking to earth.

3. Safety (A.C. compared to D.C.) D.C. is more difficult to control in "real" situations, double pole switching and fusing is the norm and, because there is a constant current waveform (a straight line as compared with an A.C. sine wave) it is more difficult to break a D.C. circuit. This results in D.C. equipment being much larger than the equivalent A.C.
It has one "benefit" however, if you come into contact with a high voltage (mains value), normally it will throw you off.
A.C. acts on the human body very diffferently. It will cause your muscles to attempt to operate at the frequency of the supply. This often means that your muscles will seize up - and as your heart is a big muscle......... It is often a consequence of shock that the person is left hung up in contact with the live conductor (can you open and close your hand 100 times per second?) with a grip that makes Superman look like a wimp!

I hope these opinions are taken in the spirit that they are offered in. To me safety, particularly electrical safety, is essential.
Sorry to deviate from the original L.E.D. thread.

Regards



   
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Malc Reade

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Re: LED's for lighting
« Reply #49 on: October 15, 2006, 11:13:05 PM »



Quote
2. Residual Current Devices: These do not detect current in the earth path, they operate by sensing the diffference in current between the phase and neutral conductors supply a load. On a healthy circuit or installation the current in both conductors will be equal but under earth fault conditions the current in the phase conductor will be larger due to the current leaking to earth.

Sorry, classic error on my part - confusing RCD's with ELCB's (it's an age thing).  ;D ;D ;D

Malc



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