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Author Topic: LEDs without Resistors  (Read 5273 times)

CERES

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LEDs without Resistors
« on: August 13, 2011, 11:42:37 AM »

Hi,
My Tug "Lady T" runs on a 12v battery system. The riding & Nav lights  are all Leds and would ithe this power pack be fitted with resistors and using a P44 Twin Switch.

Consiidering that the lights would be used probably twice a year during night sailings I am wondering if a smaller battery pack could be used for lighting only and at the same time eliminating the resistors or is a case that all leds use resistors no matter what the voltage is.

I shall use the P44 in my next Tug build "Fairmount Alpine".
Regards to you all.

Ceres.
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Re: LEDs without Resistors
« Reply #1 on: August 13, 2011, 02:22:06 PM »

You will require a resistor on the leds,regardles ..the resistor limit current .. in therory if a battery can deliver 1amp ..an unchecked led will draw 1amp,,destroying itself..
Generally on a 12v supply a 330 Ohm resistor will do ..now If you can find a 2watt or even two,330 Ohm resistor's..you can run your leds on one/two resistor. Even better if you can regulate your battery supply to Led with a LM7805 or LM317T ..

I have red,green,white,amber, running on a 330 ohm resistor's,different colored Leds require different voltage and current requirements. It would be wise to find out what your lowest required voltage is on your leds..start there with a resistor.


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Colin Bishop

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Re: LEDs without Resistors
« Reply #2 on: August 13, 2011, 04:14:35 PM »

You can of course buy 12v and 5v LEDs which have the resistors built in so you don't need to fiddle about with external ones. See here: http://www.maplin.co.uk/search?criteria=led&page=3 Squires also sell them. The 12v ones give a good light down to 6v if used as navigation lights.

Colin
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Subculture

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Re: LEDs without Resistors
« Reply #3 on: August 13, 2011, 04:55:44 PM »

You will require a resistor on the leds,regardles ..the resistor limit current .. in therory if a battery can deliver 1amp ..an unchecked led will draw 1amp,,destroying itself..

If you supply an LED with the correct forward voltage (e.g. regulated) you don't need a dropping resistor.

malcolmfrary

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Re: LEDs without Resistors
« Reply #4 on: August 13, 2011, 07:08:28 PM »

If you supply an LED with the correct forward voltage (e.g. regulated) you don't need a dropping resistor.
That is being very hopeful.  If the supply regulates just a few millivolts high, the LED dies rapidly.  If marginally low, its a bit fainter, any lower, it just doesn't glow.  The only safe way is to use appropriate resistors to limit the current.  If all the LEDs are identical, they can be wired in parallel and use a common resistor.
A few months ago I cobbled up a fish tank light using some Christmas LED lights (white, cheap, from Glynn Webb) and a battery eliminator just about capable of delivering enough current to light 4 of the LEDs at its lowest voltage setting.  The first attempt, they lasted a fortnight.  Second try, the addition of a resistor (15Ω, 3 watt) seems to be longer lasting, at least so far, with the same light output several weeks on and the resistor not noticably getting warm, supply still set for 3 volts.
Properly wired, LEDs are everlasting.  Otherwise, otherwise, and they can be a right pain to change.
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triumphjon

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Re: LEDs without Resistors
« Reply #5 on: August 13, 2011, 08:14:57 PM »

ive just encountered a problem fitting a mobile marine models kit into my tug , the kit as supplied consists of 7 leds and 3 resistors , the small instruction sheet recommends two leds per resistor , however this would leave an led un protected ! i have therefore wired three leds onto one resistor , upon powering the system up i have a problem , two leds are failing to illuminate althoough ive checked the power at the leds that arent working , one is showing 1.85 volts while the other is reading .5 volts ! jon
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cos918

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Re: LEDs without Resistors
« Reply #6 on: August 13, 2011, 09:34:40 PM »

ive just encountered a problem fitting a mobile marine models kit into my tug , the kit as supplied consists of 7 leds and 3 resistors , the small instruction sheet recommends two leds per resistor , however this would leave an led un protected ! i have therefore wired three leds onto one resistor , upon powering the system up i have a problem , two leds are failing to illuminate althoough ive checked the power at the leds that arent working , one is showing 1.85 volts while the other is reading .5 volts ! jon

Thr led cant get enough power .IE to many LED on that resistor. on small resistor you should run 2 led max


John
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triumphjon

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Re: LEDs without Resistors
« Reply #7 on: August 13, 2011, 09:53:27 PM »

thank you , i will remove one led from the circiut and get another resistor at maplins in the morning , i take it the colour banding will tell those more knowledgable than me what value it needs to be ? jon
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barriew

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Re: LEDs without Resistors
« Reply #8 on: August 14, 2011, 12:16:04 PM »

You may find this site useful

http://led.linear1.org/1led.wiz

This one calculates values for multiple LEDs

http://led.linear1.org/led.wiz

Barrie
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triumphjon

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Re: LEDs without Resistors
« Reply #9 on: August 14, 2011, 04:33:52 PM »

thank you for the link barrie , however i now have a further problem , the diagram show from mobile marine show the resistors on the positive side of the leds , yet the diagrams on the link page has the resistors on the negative side of the leds , does it make any difference providing they are all wired the same please ?
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malcolmfrary

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Re: LEDs without Resistors
« Reply #10 on: August 14, 2011, 05:31:39 PM »

thank you for the link barrie , however i now have a further problem , the diagram show from mobile marine show the resistors on the positive side of the leds , yet the diagrams on the link page has the resistors on the negative side of the leds , does it make any difference providing they are all wired the same please ?
No.

The LEDs don't care where they are in the circuit, they do care intensely which way round they are connected in that offering a higher reverse voltage than they are rated for will kill them.  In some installations it is more convenient to site them connected to negative, in others its more convenient to hang them off positive.
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triumphjon

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Re: LEDs without Resistors
« Reply #11 on: August 14, 2011, 07:27:02 PM »

due to the switching unit working from a neg feed im switching through the -ve side of the leds , with all 7 of the leds wired to the same +ve feed i seem to be getting a voltage drop on my coloured leds ?
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CERES

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Re: LEDs without Resistors
« Reply #12 on: August 14, 2011, 09:03:19 PM »

Triumphjon's reply quoting 7 lights with his kit. My Lady 'T' is also from MM and was also supplied with 7 Lights & resistors. if you contact MM they will confirm that this is correct in fact I connected a resistor to the f'wd mast lights one for the Nav lights and one for stern lights .In connecting to the 12v Bat as a test they all Lit-up nicely.
Ceres.
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triumphjon

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Re: LEDs without Resistors
« Reply #13 on: August 14, 2011, 09:29:33 PM »

the kit ive bought has 7 leds but only 3 resistors , with a wiring diagram that states one resistor per two leds !
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CERES

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Re: LEDs without Resistors
« Reply #14 on: August 16, 2011, 07:07:37 PM »

Triumphlon.
That is correct. I fitted my 3 resistors as follows. 3 fwd lights -1 resistor, Nav lights(2)- 1 resistor and 2 stern mast lights -1 resistor. These were brought alltogether into the Action switch assembly and functioned correctly.

Now when I get round to building my Alpine Tug I am going to use Leds with built in resistors.
Ceres.
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triumphjon

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Re: LEDs without Resistors
« Reply #15 on: August 16, 2011, 08:15:37 PM »

after several consultations with mmm we think we have found the initial problem , my switcher ( a graupner sxm ) switches from a neg feed , so unfortunatly  my leds have all been fed on 12 volts instead of the resisted supply ! another set of leds & resistors are being sent to be wired with the resistors on the neg side of the leds
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Paul S

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Re: LEDs without Resistors
« Reply #16 on: August 17, 2011, 01:39:51 PM »

Hi guys.

Definitely stick with resistors either in series with one LED, or parallel the LED's with 2 or more although technically that is frowned upon! but it works fine.  The maths is dead easy, what you need is the Typical forward voltage (V) and Typical forward current (I).  Current is usually about 20mA and voltage 2v, this does vary with the colours.  As an example with a 12v battery, subtract from that the forward voltage say 2v leaves 10v.  Then divide that  by the forward current in Amps, which for 20mA is 0.020Amps.  Gives us 500 Ohms.  'Simples'

Cheers

Paul
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malcolmfrary

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Re: LEDs without Resistors
« Reply #17 on: August 17, 2011, 06:20:04 PM »

Well, fairly simples. 
The range of resistors commercially available has a limited set of values.  The nearest to 500 is 470, yellow, violet, brown.  It will dissipate about 200mW, so a quarter watt type will be OK, but several in a close space could start to get a bit hot. 
That leads to the other advantage of using one resistor for a string of LEDs.  Same current, less voltage to drop, less power to lose.  With the same notional LED, but two of them, the LEDs account for 2+2=4 volts, leaving 12-4=8 for the resistor.  20mA at 8 volts gives 400 ohms, nearest is 390, orange, orange, white, brown.  Wattage is down to 0.16 watts, the quarter watt rating will run much cooler, and there will be fewer of them.  Stringing three carries on the same way, and so on.  The limit is where the fluctuating voltage of the battery gives a big difference across the resistor, thus the current through it, thus the current through the LEDs, and a reduction in their brightness.
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Re: LEDs without Resistors
« Reply #18 on: August 17, 2011, 10:17:41 PM »

If your using a 12v volt system ..You could regulate the current with a LM317 ....only problem with that is 2volt will be lost to the regulator..roughly 10v left to drive the leds. The other option is to get a capacitor in the circuit ..like 10,000uF 35volt or better..May hold about 12 watts,after its been on for a minute or two..,enough to take the flutter out of the leds ..I think :embarrassed:
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Paul S

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Re: LEDs without Resistors
« Reply #19 on: August 18, 2011, 01:31:20 PM »

This is a useful resource, does it all for you and gives you the diagram: 

http://led.linear1.org/led.wiz


Cheers

Paul
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Re: LEDs without Resistors
« Reply #20 on: August 18, 2011, 02:16:01 PM »

The link I posted in the thread bellow, that application has that two..Also theres various other app's in there ..like if a guy just needs a 910 Ohm resistor, plug the value in and it spit out the band colors..
Using a 555 Timer I was able to make a rather simple circut all from throw away electronics that was going in the trash or recycler..The circut will ramp the led up to full on in about 1.5secs,on  for 4 sec's and then fade out in about 1.5sec, off for 2 sec's.. handy little beacon light.. I intend to use this one on a mast tip.
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CERES

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Re: LEDs without Resistors
« Reply #21 on: August 23, 2011, 07:38:26 PM »

It does seem that my Topic caused quite a lot if interest and from all the info I have learnt a lot.

However:- As some of our fellow boaters are aware I have confessed on previous topics and toatl  lack of grasping certain problems with wiring. If I am  presented with a proper circuit drawing I do not have any problems following it.

Now:- having set up all my lights of my tug and they all WORK, my delemma is whilst I need to connect to a battery I also need a switch to control when & where I light up. I cannot find anywhere a diagram that will show me which two connections I need to use on the switch since whichever one I use the "Off" side only acts just ther same as the "On" side. and no the switch is not an off-on-off.
The only thing I can think is that I am not connecting the "Live" side or "Neutral" side in a correct manner.

I would be extremely gratefull for some guidence on this and hopefully an emailed diagram.

Many thanks,
Ceres.
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barriew

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Re: LEDs without Resistors
« Reply #22 on: August 23, 2011, 08:43:05 PM »

Ceres,

I assume you mean the switch has three contacts underneath. Connect one lead to the centre connection and the other to either of the outer connectors. The switch will be ON when the toggle points AWAY from the contact you have just wired to.



Hope this helps

Barrie
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CERES

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Re: LEDs without Resistors
« Reply #23 on: August 23, 2011, 10:41:31 PM »

Barrie,
Thanks for that info. Do I take it that both connections off the switch are the positive side one to LED and one to battery and that the negative goes straight to the battery from the LED negative side.
Ceres.
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Re: LEDs without Resistors
« Reply #24 on: August 24, 2011, 02:04:30 AM »

the switch can go on the negative or positive ..but on your switch never both wire (positive and negative) to the switch..

the wire from the battery to the center terminal..the wire from the ciruit to either or both out side terminals..

Your switch is a center off switch ..you can wire your circut to both the outside terminals ,,this way no matter which way the switch geoes the circut is comes on ..center is off.
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