Model Boat Mayhem
Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: hama on December 28, 2020, 02:56:13 pm
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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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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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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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...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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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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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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This is what I mean by a constant power 12v ac-dc led lamp.
Youtube video
(https://www.youtube.com/watch?v=i-Roc5TLdnw&t=4m)
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Totally agree free speech rules so does keeping things simple.
Stan
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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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I like that bunkerbarge {-) {-) {-)
John
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Great idea! ...Stairway to Heaven.... :-)) :-)) :-))
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{-) L.E.D ZEPPELIN!
Back to the subject, surely a converter will draw power and generate heat as well?
I haven't done any changes yet, but I have a adjustable DC/DC converter and new resistors of 330ohms so I have all the options.
Hama
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HI Hama if this was me I would fit the resistors. But because they are all the same you could use a voltage regulator instead. L E D use very little power so I cannot imagine the voltage regulator getting hot
Stan. :-)) :-)) :-)) :-)) :-))
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How does a DC/DC voltage convertor control the current flow?
C-3PO
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How does a DC/DC voltage convertor control the current flow?
C-3PO
Does it need to do so?
Surely it controls the voltage and then the thing on the end (in this case LED's) take as much current as they want just as they would do with a low resistance battery. If it is more than the converter can handle then the magic smoke appears. This is very unlikely unless you have an awful lot of LED's.
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HI Hama if this was me I would fit the resistors. But because they are all the same you could use a voltage regulator instead. L E D use very little power so I cannot imagine the voltage regulator getting hot
Stan. :-)) :-)) :-)) :-)) :-))
A voltage converter works like an ESC - it chops up the dc at a high frequency and puts it back together at a different voltage - the only heat generated is produced during the minute rise-time (the time it takes to go from off to on) of the on/off pulses it's chopped into and as most transistors work well into the MHz, that rise time is negligible - so no heat generated.
A regulator dumps its excess power though heat - it's permanently hovering in a half on, half off mode - just like a big resistor.
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These are the DC voltage regulators fitted in my lobster boat supplied from Component Shop one for the pump the other for the lights. They take power straight from the drive battery the output voltage is set with the small brass screw. With the small amount of current used by the light and pump you would not expect the to get warm. The first question was why do my resistors get warm the correct value should have been 330 ohms not 470 ohms. Some of the answers to the initial question were just to hitec and once again I will reiterate keep it simple.
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These are the DC voltage regulators fitted in my lobster boat supplied from Component Shop one for the pump the other for the lights. They take power straight from the drive battery the output voltage is set with the small brass screw. With the small amount of current used by the light and pump you would not expect the to get warm. The first question was why do my resistors get warm the correct value should have been 330 ohms not 470 ohms. Some of the answers to the initial question were just to hitec and once again I will reiterate keep it simple.
No the the initial answer was correct, Stan. He would need to stack two leds in series.
If hama changes to 330 ohm his perceived problem is worse. - More power loss.
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HI Plastic I have to say I have used V/ R mainly my lighting and never had any problems with them. Once again to much technical info that very few understand. {:-{ {:-{ {:-{ {:-{ {:-{ {:-{ {:-{ {:-{ {:-{
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Well all can say is this poor guy will be even more confused. All my models work fine using resistors wired I parallel. With that in mind I will leave all you techno guys to confuse him even more. {:-{ {:-{ {:-{ {:-{ {:-{
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HI Plastic I have to say I have used V/ R mainly my lighting and never had any problems with them. Once again to much technical info that very few understand. {:-{ {:-{ {:-{ {:-{ {:-{ {:-{ {:-{ {:-{ {:-{
Stan, do you understand that a voltage regulator is basically a self-adjusting resistor? It dissipates exactly the same amount of heat as the equivalent resistors would - just it's spread over a physically larger thing so the heat escapes easier so it 'feels' cooler.
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Thank you for that explanation in simple terms.
Stan. :-)) :-)) :-)) :-))
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Hello everybody!
Thanks again for all your input, now it's up to me to handle all the information given.
I'll see how I'll proceed, but it will take some time as I'm off to work for two weeks now.
All the best!
Hama
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Yeah, you're spot on about the converter. I used one for a LED project in my garage. It did heat up a bit, but as long as you keep it in a spot with good air flow, it should be fine.
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You're right about the converter. I used a DC/DC converter for a LED project I did a while back. It did draw some extra power and got a bit warm, but nothing too crazy. The key is to make sure it's well ventilated. I made sure mine had enough space around it to avoid any overheating issues.
And those 330ohm resistors sound like a good choice. It's all about balancing the resistance with the LED's requirements. I had to read some reviews on leds.to (https://leds.to/) and play around with a few different resistors before I found the right match for my setup.
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The Germans know how to do model instructions, LED section of wiring they even give all the resistor values for all the colours.
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Wow, that's typical of the type of diagram FLJ would have produced. RIP Dave.
Regards Ian.