LEDs

Had another quick look at my problem here, I'm going to have to visit my local electronic shop and buy the resistors, the ones I have are nowhere near the correct value. I'll probably buy a selection as they're not expensive. Thanks for all your help so far, I'm sure I'll be back, keep your eye SW Gizzy!
 
Paul M said:
Had another quick look at my problem here, I'm going to have to visit my local electronic shop and buy the resistors, the ones I have are nowhere near the correct value. I'll probably buy a selection as they're not expensive. Thanks for all your help so far, I'm sure I'll be back, keep your eye SW Gizzy!
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Lucky you have such a place, if they cannot help you can get kits of selected resisters from Amazon at 8-10 quid. They have a listing inside the plastic storage box telling the values etc.
 
dunnyrail said:
Lucky you have such a place, if they cannot help you can get kits of selected resisters from Amazon at 8-10 quid. They have a listing inside the plastic storage box telling the values etc.
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I was half thinking of Radio Spares or Rapid Electronics in Colchester next time I was passing. As you suggested, like all useful shops, they are few and far between now.
Greg Elmassian said:
Note you can use higher wattage resistors with no problems...
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Yes the original one is so small, it's almost impossible to see the rating bands.
Did you get my PM?
 
I bought off of Amazon what was supposed to be an assortment of led colours. Which included clear. They sent me just blue and checked all 50 of them. The company contacted me via e mail to see us I was satisfied with what I got and if I even got it. I replied back and told them nope and why They replied back saying tough bananas ask amazon for a refund. I can't be bothered and won't order from that company again. I might get a couple of for sure clear bulbs for my snow plow head lights next time I am at a model railway store.
 

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I have now managed to get this sorted out, just need to fix the coach. I've learnt a lot with this, including that buying 1000 assorted resistors from Amazon, is as cheap as buying a few of what you actually need. Thanks everyone for your input it's very much appreciated.
(Greg, I've PMed you)
 
These calculations are valid provided you want the led running at full brightness. My experience is that 70% is usually enough, and reduces the risk of the led blowing due to overheating.

I generally use a 680 Ohm resistor for 3-6 leds of the same type on a 12v supply. This reduces the current significantly and I don't think I've ever noticed uneven brightness.
 
I always calculate... when you give someone a pat answer (and not pointing at you 3 minutes), what happens is someone then uses a 24v supply for what you recommended for 12v... years of experience (and burned out LEDs and resistors) force me to never give a "standard" to people who do not understand... the calculator is so easy and free...

The point about brightness is well taken, modern LEDs rarely need the 20 milliamps that "experts" often recommend...
 
3 minutes of fame said:
These calculations are valid provided you want the led running at full brightness. My experience is that 70% is usually enough, and reduces the risk of the led blowing due to overheating.

I generally use a 680 Ohm resistor for 3-6 leds of the same type on a 12v supply. This reduces the current significantly and I don't think I've ever noticed uneven brightness.
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I've used a 330 Ohm resistor with 4 in parallel, it seems to be fine. Out of interest, and as ive got plenty of bits to play with, whilst I'm repairing the damage, I'll have another play, and see what 680 will do. I'm assuming that the worse that could happen with a higher the necessary resistor is the lights won't work
 
You may be quite surprised how wide a range of resistors you can use..

You have greater problems, if you are trying to drive LEDs of different colours from the same source.
Then you can run into problems trying to get both colours to perform as you want.

If you use a bi-colour LED, then this limits you further.

PhilP
 
Paul M said:
I've used a 330 Ohm resistor with 4 in parallel, it seems to be fine. Out of interest, and as ive got plenty of bits to play with, whilst I'm repairing the damage, I'll have another play, and see what 680 will do. I'm assuming that the worse that could happen with a higher the necessary resistor is the lights won't work
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You have to reduce the current pretty substantially to stop the led lighting at all. The larger resistance will cause the leds to dim, which is not always a bad thing in terms of giving a more incandescent look.
 
So what you're saying is that as long as you don't go below the resistance you've worked out, and don't go too high, any value will work
 
Paul M said:
So what you're saying is that as long as you don't go below the resistance you've worked out, and don't go too high, any value will work
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Certainly never go below the calculated value for the maximum current flow. I tend to go for a higher value so that the led is less intense. To my eyes it just looks more realistic.
 
Paul M said:
So what you're saying is that as long as you don't go below the resistance you've worked out, and don't go too high, any value will work
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So the calcs for a white LED at 12 volts works out at 470 ohms, though I would use a 1K ohms, dimmer, but just as realistic.
 
Just a quick update. I've now got my coach lights operational, thanks for everyone's advice. I ended up using a 680ohm resistor as it gave a better glow, which confirmed to me that I don't know anything about LEDs as I thought that they were either on or off and nothing in between unless you used clever electronic wizardry.
PS as a bonus no magic smoke was produced apart from when I inadvertently put the soldering iron onto the wooden solder board I use to save the work surface
 
Paul M said:
PS as a bonus no magic smoke was produced apart from when I inadvertently put the soldering iron onto the wooden solder board I use to save the work surface
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Ah, I saw smoke but no flash to my SW.... :wasntme:
 
So LEDs are sort of on/off, in actuality they are either conducting or not, they are diodes, one way "valves".

You CAN vary the brightness a bit, but it a very narrow range of CURRENT that can produce the results, unlike incandescent lights which are VERY sensitive to variations in voltage (we have all seen house lights dim when a high current appliance starts)

This is why PWM (Pulse Width Modulation) works so well on LED dimming, you turn it on and off rapidly, so the AVERAGE intensity you see varies. Your eye is not "fast" and can only see "flickering" on/off at 60 Hz or less (that is why the US and many countries use 60 cycle per second AC, and why TVs in the UK seem to flicker for us US people (because you use 50 Hz)

Just some extra information on understanding LEDs vs incandescent bulbs.

Greg
 
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