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Author Topic: LED resistors  (Read 4935 times)

hama

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LED resistors
« on: December 28, 2020, 02:56:13 pm »

Hello!
I'm hoping someone can help me out.
I've connected a number of LEDs in parallel, with a resistor to each of the LEDs. Its working fine but the resistors are getting really hot. I've not had this before in other builds but then I've had higher voltage. Do I need to change resistors or is there something else I've done wrong?
White LEDs 3,0-3,6v
Resistors 470ohm 0,25w
Battery 9,6v.


It's the first time that I've made a sort of "array" of the resistors to have them in one spot, otherwise I've put them on location sort of.


Hope some of the electric wizards can help me out!
Hama
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HMS Invisible

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Re: LED resistors
« Reply #1 on: December 28, 2020, 05:24:05 pm »

I wish the usual strong advocates of one resistor per led would use a bit more imagination sometimes!

At 9.6v you would get about 12mA current per branch and 0.1 Watt per resistor but if you have 8 NiMH cells your voltage will be much higher.
The temperature rise is because the resistors have a small surface area.It may melt hot glue but the resistors are metal film and can deal with it ok.
You could get the same led current with two leds in series to make 6.6 volt and get 12mA by wiring a pair of resistors in parallel.

If your supply was beyond 10 volt you could have run three white leds in series from an older 10-16v ac-dc led lamp driver at near 100% efficiency.
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Stan

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Re: LED resistors
« Reply #2 on: December 28, 2020, 05:45:07 pm »

I have used this method many times using different voltages  I've used the formula found in the component shop hand book and fitted the correct resistors and never had any problems . I have said many time keep it simple to much techno  stuff just baffles people. The link below show how i have fitted resistors in my latest model all are wired in parallel


Stan.


https://www.modelboatmayhem.co.uk/forum/index.php?board=91.0
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HMS Invisible

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Re: LED resistors
« Reply #3 on: December 28, 2020, 05:55:57 pm »

...I have said many time keep it simple to much techno  stuff just baffles people. The link below show how i have fitted resistors in my latest model all are wired in parallel...
No, every time, Stan.
A constant power driver pulled from a 3 watt led MR11 downlight would drive all these leds if the supply was 3s Lipo or 12v Pb battery. There would have been four solder joints.
 
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Stan

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Re: LED resistors
« Reply #4 on: December 28, 2020, 06:14:40 pm »

I have no wish to doubt what you are saying is correct but that means nothing to me and I am sure others also. I have used a very simple formula on all my models and never had any problems. The L E D fitted in my models all work never had any getting hot. I am no electronics expert Just a model builder that uses this simple formula with out getting involved in to much technical info. But I respect your comments on this matter.


Stan
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HMS Invisible

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Re: LED resistors
« Reply #5 on: December 28, 2020, 06:28:11 pm »

I have no wish to doubt what you are saying is correct but that means nothing to me and I am sure others also. I have used a very simple formula on all my models and never had any problems. The L E D fitted in my models all work never had any getting hot. I am no electronics expert Just a model builder that uses this simple formula with out getting involved in to much technical info. But I respect your comments on this matter.


Stan
It is good if you put a link or link to whatever info you can. I don't have a problem with that sentiment.
I see the opportunity for some to learn clever and very useful alternative ways is discouraged when it doesn't get beyond that method.

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HMS Invisible

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Re: LED resistors
« Reply #6 on: December 28, 2020, 06:51:46 pm »

This is what I mean by a constant power 12v ac-dc led lamp.
Youtube video 

The output current (for brightness control) to array of leds can be changed by a change to one resistor on the circuit board.
The ac to dc rectifier diodes give reverse polarity protection. If removed, led driver in the video would work probably function until the supply voltage was well below 7 volts.
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john44

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Re: LED resistors
« Reply #7 on: December 28, 2020, 06:59:59 pm »

Without getting too technical with resistor values and voltages, why don’t you have a look at component shops
voltage reducers. They do a standard version input up to 30v and output down to 1.2v max current 1amp.
Because all your led,s are white wired in parallel you can set the output to 3.3v no resistors needed.
Just an alternative suggestion.


John
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Stan

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Re: LED resistors
« Reply #8 on: December 28, 2020, 08:13:55 pm »

Thank you for the U tube video but once again this means nothing to me or others who have very limited knowledge of electronics. Most model builders want a simple solution on how to get round problems. I have no wish to sound harsh with my replies but simple is best
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roycv

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Re: LED resistors
« Reply #9 on: December 28, 2020, 10:47:55 pm »

Hi I bought a voltage reducer to run a small motor they work extremely well.  You have a potentiometer with a screw driver adjustment and a digital meter to check the voltage.  It could not be any simpler.  They are not very big and weigh very little.

Roy
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Stan

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Re: LED resistors
« Reply #10 on: December 28, 2020, 11:44:51 pm »

Hi Hama a P/M sent to you with some Information. Have to agree if the LED are all the same a simple voltage regulator from component shop will do the job no resistors. If you need to fit resistors the formula in the Component Shop catalogue is ideal simple but it works.


Stan
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HMS Invisible

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Re: LED resistors
« Reply #11 on: December 29, 2020, 03:17:37 am »

Thank you for the U tube video but once again this means nothing to me or others who have very limited knowledge of electronics. Most model builders want a simple solution on how to get round problems. I have no wish to sound harsh with my replies but simple is best
Stan, the youtube link went into a separate post as if to say it is for hama or anyone else. Please disregard any notion that I am conveying a harsh tone to you. However I strongly believe that alternative solutions should be offered to those who ask and explained/clarified can be given if needed.

In this case, and the I emphasise the message is in a take it or leave it basis for anyone.
A feature of white and blue leds is they stop conducting before a single lithium cell is over discharged. If you wish to power many white leds, they can be connected in parallel and run from a pair of alkaline cells, a Lithium cell & one resistor, a hacked poundland powerbank & one resistor.

If there are simpler ways then I'd like to read them.

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hama

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Re: LED resistors
« Reply #12 on: December 29, 2020, 08:15:30 am »

Hello!
Thanks for all your input, I really appreciate it!
First I must admit that I checked one of my other boats and found that the resistors on that one also run hot and has been doing so for several hours without a problem. I just hadn't noticed as they are all situated one by one around the boat.
As for my choice of resistors, I bought these a few years ago and figured that a slightly higher value would only be safer in regards of protecting the LED.
When I tried to find best way of fitting resistors to parallel LED I read that if you use one resistor in series with your parallel LEDs you may have one or two LEDs that  don't light up, hence the one resistor per LED. Maybe I misunderstood this?
I have some options here I guess;
1. Use a voltage regulator.
2.Change to a lower value resistor.
3. Modify to have one or two resistors in series.
4. Just leave it be, the boat won't catch fire from the heated resistors.


Again, thanks for all your help and commitment!
Hama
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HMS Invisible

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Re: LED resistors
« Reply #13 on: December 29, 2020, 08:39:40 am »

Hello!
Thanks for all your input, I really appreciate it!
First I must admit that I checked one of my other boats and found that the resistors on that one also run hot and has been doing so for several hours without a problem. I just hadn't noticed as they are all situated one by one around the boat.
As for my choice of resistors, I bought these a few years ago and figured that a slightly higher value would only be safer in regards of protecting the LED.
When I tried to find best way of fitting resistors to parallel LED I read that if you use one resistor in series with your parallel LEDs you may have one or two LEDs that  don't light up, hence the one resistor per LED. Maybe I misunderstood this?
I have some options here I guess;
1. Use a voltage regulator.
2.Change to a lower value resistor.
3. Modify to have one or two resistors in series.
4. Just leave it be, the boat won't catch fire from the heated resistors.


Again, thanks for all your help and commitment!
Hama
4. is perfectly ok. You wouldn't notice the heat on a circuit board.If they are all the same, two in series & lower the resistance with two 470s in parallel to make  235 ohm  0.5 watt resistors.You at least save half the current.
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malcolmfrary

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Re: LED resistors
« Reply #14 on: December 29, 2020, 10:23:53 am »

The wattage rating of resistors is based on how much power they can dissipate before they damage themselves, and always assumes an ambient temperature of 25C, but the specs rarely tell you what the actual temperature is.  Small, high wattage resistors are made of material that lets them get VERY hot.
A bunch of resistors, all dissipating power in a shared space will warm each other, and their surroundings, up, and reduce the overall rating, but in practical terms, if the ones used are not going an unhealthy colour, they are OK.  And their surroundings.  I have seen higher powered resistors cook the plastic insulation on nearby wiring.
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hama

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Re: LED resistors
« Reply #15 on: December 29, 2020, 11:11:21 am »

Thanks Malcolm,  that's good to hear as they have not changed colours yet :}
I realise that I've built a radiator of my resistors, and I actually bent them upwards away from the surface to let them cool off a bit.
You live and learn every day,  and thanks for your input :-))
Hama
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Plastic - RIP

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Re: LED resistors
« Reply #16 on: December 29, 2020, 04:11:42 pm »

I've never really understood why people are happy to waste valuable battery power dropping voltages for a bunch of leds.     Surely it's always going to be more efficient to use some kind of dc-dc converter to do all the voltage dropping / changing for you - whether it be a lamp driver or even a variable psu giving you the exact voltage you need for the leds.    Simpler wiring, no waste heat, longer battery life - can't think of a downside.
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Tug Fanatic

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Re: LED resistors
« Reply #17 on: December 29, 2020, 04:42:26 pm »

I've never really understood why people are happy to waste valuable battery power dropping voltages for a bunch of leds.     Surely it's always going to be more efficient to use some kind of dc-dc converter to do all the voltage dropping / changing for you - whether it be a lamp driver or even a variable psu giving you the exact voltage you need for the leds.    Simpler wiring, no waste heat, longer battery life - can't think of a downside.

I guess that it depends on how many led's we are talking about and how many different colours/ sizes all of which can change the voltage / resistance required.

If you have 3 colours (say white, red and green) you might require 3 different voltages / resistors / dc converters.
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Plastic - RIP

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Re: LED resistors
« Reply #18 on: December 29, 2020, 04:46:07 pm »

I guess that it depends on how many led's we are talking about and how many different colours/ sizes all of which can change the voltage / resistance required.

If you have 3 colours (say white, red and green) you might require 3 different voltages / resistors / dc converters.
Then just fit more DC converters - I last bought some on ebay - 5 for 99p - adjustable output with led voltage readout - they've literally done all the work for you.
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Stan

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Re: LED resistors
« Reply #19 on: December 29, 2020, 06:47:29 pm »

We could go round in circles flogging this to death do it this way do it that way does it really matter in the end. If you wish to fit lots of regulators  to control you L E D  lighting that's fine. Me personally I fit resistors in groups or sections these in turn are turned on electronically. All the L E D in my models are supplied from the main drive battery with no detrimental loss of running time and certainly no heat problems. Yes I would use a voltage regulator supplied from the drive battery if i was using all the same colour L E D.
Stan.Keep it simple :-)) :-)) :-)) :-)) :-))

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HMS Invisible

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Re: LED resistors
« Reply #20 on: December 29, 2020, 06:51:07 pm »

I have fifty of these dc converters but wouldn't even use one in this particular case unless flicker was unacceptable.

 A ninth matching white led for a 3 x 3 series-parallel array would already have sufficient internal resistance to mean external regulating resistors were so low in value to be redundant where the charged 9.6 pack tops out at 10.8 volt when allowed time to cool.

Free speech rules!
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Stan

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Re: LED resistors
« Reply #21 on: December 29, 2020, 06:56:05 pm »

Totally agree free speech rules so does keeping things simple.

Stan
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Bunkerbarge

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Re: LED resistors
« Reply #22 on: December 30, 2020, 09:51:18 pm »

Don't worry Stan, there will always be someone looking for an opportunity to make themselves look clever.


Let's face it though do you really want your electronics to look like this?





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john44

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Re: LED resistors
« Reply #23 on: December 31, 2020, 09:39:19 am »

I like that bunkerbarge  {-) {-) {-)


John
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swiftdoc

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Re: LED resistors
« Reply #24 on: December 31, 2020, 11:55:11 am »

Great idea! ...Stairway to Heaven.... :-)) :-)) :-))
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