To satisfy my curiousity, I purchased 100 off 3mm led's from China (roughly 10 cents each including post). No doubt half will not work, but what concerns me is the brightness. These lights are 15000mcd at 30 degree viewing angle, which I presume are very bright. Now running at 20 volts, with 20ma current rating and 3.3 volt forward current, I will need a minimum 1 watt 1000 ohm resistor. However, if too bright what are my options (more resistance maybe) ? If not possible then I will just go to the local electrical store and purchase a few frosted led's of less intensity.
LED info
- Thread starter Tim Brien
- Start date
I dont know about the resistor, but expect them to take longer than planned to get here, i have never had any regects on my china specials
I assume that you've calculated the resistor you require using voltage supply minus the forward voltage of the led divided by the forward current of the led? If they are too bright, you will need to experiment with higher values of resistor.
Do you have a multimeter? If so you should be able to test the led to establish whether they are all right.
Best of luck!
Do you have a multimeter? If so you should be able to test the led to establish whether they are all right.
Best of luck!
I have bought hundreds of LEDs via eBay and China. I must say the delay in post seems to be the only problem. For what 1 item costs here retail I can get 10 from China... No complaints apart from postal delays..... if you look you will find LEDs that come with resistors for the voltage you are going to run them off.
Resistors can be used to change the intensity of the light output.
Resistors can be used to change the intensity of the light output.
I use this site to calculate resistor values. The site also helps with resistor colour coding plus running series/parallel led multiples. 1000 ohms is correct for the 20 volts that I will be using. The 'free' resistors supplied are 470 ohm and these are only suited for 12 volt operation.
http://led.linear1.org/1led.wiz
Postal delay is subjective, so I am prepared to await a few weeks. The Chinese suppliers seem to have relatively good feedback.
In so far as cost per unit, a local supplier has led's starting at $2.40 up to around $3.50 each for a single 3mm light. The ready made led's seem to be only for 12 volts.
http://led.linear1.org/1led.wiz
Postal delay is subjective, so I am prepared to await a few weeks. The Chinese suppliers seem to have relatively good feedback.
In so far as cost per unit, a local supplier has led's starting at $2.40 up to around $3.50 each for a single 3mm light. The ready made led's seem to be only for 12 volts.
Why not use a voltage regulator and make up constant lighting boards??? I made up some using LM7805's and they work very well.They dont have to be as fancy as these but the do the job. I run 8 warm white with leds in parallel with one resistor... Works well and can be either directional or not...
I too have had excellent results with the LEDs from China. They come with resistors already soldered into the circuit, and eight inch +/- leads. I have also purchased them with resistors supplied separately. Sometimes these are easier to use when fitting them into loco headlights. No calculations needed for this dummy.
I most assuredly can post some diagramms.... In the end I actually ended up using LM317's as they are infinitly adjustable using 2 resistors; calculator here - http://www.electronics-lab.com/articles/LM317/ and a circuit diagram.
But LM78XX can be used too with a dropping resistor.
Ok so there is a schematic. you need to either put a single diode in series across the + supply for directional lighting or a brdge rectifier across the supply for non directional. Replace C1 with a humungous Electro cap I used 2200uF 16v this is to stop flicker, the diode stops it discharging back into the circuit. C2 well I didn't bother with it. If you wish to run a string of leds in parallel then use this to work out the current limiting resistor but with this LBT ( little black thing) you can set the voltage to what you need.
Some discussion here; http://www.gscalecentral.net/tm?m=168234&high=constant+lighting with my schematic sketched out, it will be noted that I'm heavily in to imperical design....
As can be seen I wanted to run 8 leds and this is a more efficient way of doing it than with a resistor for each led in my opinion.....
To finish an amusing anecdote, I wandered into Jaycar after a single red/green 5mm led so I says to the PFT ( pimply faced Tosser) can I have one led that needs a shrink... stunned look, you know one that is bipolar a schitso led?
still did't get it so I had to give him the catteldog number.....
But LM78XX can be used too with a dropping resistor.
Ok so there is a schematic. you need to either put a single diode in series across the + supply for directional lighting or a brdge rectifier across the supply for non directional. Replace C1 with a humungous Electro cap I used 2200uF 16v this is to stop flicker, the diode stops it discharging back into the circuit. C2 well I didn't bother with it. If you wish to run a string of leds in parallel then use this to work out the current limiting resistor but with this LBT ( little black thing) you can set the voltage to what you need.
Some discussion here; http://www.gscalecentral.net/tm?m=168234&high=constant+lighting with my schematic sketched out, it will be noted that I'm heavily in to imperical design....
As can be seen I wanted to run 8 leds and this is a more efficient way of doing it than with a resistor for each led in my opinion.....
To finish an amusing anecdote, I wandered into Jaycar after a single red/green 5mm led so I says to the PFT ( pimply faced Tosser) can I have one led that needs a shrink... stunned look, you know one that is bipolar a schitso led?
still did't get it so I had to give him the catteldog number.....
Trev,
you are right in that Jaycar seems to be in a race to the bottom as regards shop assistants who know nothing but mobile phones and computer sales. I dread every visit as it seems an insult to the staff to ask them where something may be located.
Even asking the assistant to cut some wire for me caused me a disasteful grimmace from the cash register bound assistant.
As regards shipping time, the eBay dealer has emailed that the items have been posted. Up to China post now.
you are right in that Jaycar seems to be in a race to the bottom as regards shop assistants who know nothing but mobile phones and computer sales. I dread every visit as it seems an insult to the staff to ask them where something may be located.
Even asking the assistant to cut some wire for me caused me a disasteful grimmace from the cash register bound assistant.
As regards shipping time, the eBay dealer has emailed that the items have been posted. Up to China post now.
Question... with 3 pin bi colour leds do I need a resistor on each anode or will a sigle resistor on the centre cathode be ok?
Good question.tramcar trev said:
If only ever using one colour at a time I'd tend to use only one resistor on the common connection. If there's a chance of using both colours simultaneously, sometimes done to create a third colour, I'd put a separate resistor on each of the other two leads.
I too have purchased a batches of 100 leds from the ebay supplier...and they've all arrived within a week. I've used them for coach lighting, I connect 3 in series, and use the supplied resistor running on 10 volts, this gives a current of some 3 mA. Three sets of these 3 lights run off a large capacitor for quite some time, the cap. is fed by a bridge/smoother/regulator circuit.
The leds are quite directional, and for an experiment in the future, I'll be cutting the LED domed end off with side cutters, to see if leads to a more diffused lighting effect. ( gives rise to internal reflections withing the led, and more light emerges from the body of the led...that's the theory )
Malcolm
The leds are quite directional, and for an experiment in the future, I'll be cutting the LED domed end off with side cutters, to see if leads to a more diffused lighting effect. ( gives rise to internal reflections withing the led, and more light emerges from the body of the led...that's the theory )
Malcolm
I found cutting the ends of square just gave a pinpoint of light ( looks very realistic for a headlight). The solution if you have a lathe is to chuck each led and drill a depression into the tips, I used a centre drill as they seem to stay on centre then you get a nice spherical light outputBrixham said:
.... Dont ask me why Im not into optics but I noticed this was the case with LED Xmas Lights and tried it out with 3mm warm white leds for interior lighting
Paul,
this is the link to the items that I purchased. He has plenty of LED's.
http://www.ebay.com.au/itm/310296281834?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
this is the link to the items that I purchased. He has plenty of LED's.
http://www.ebay.com.au/itm/310296281834?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
try this supplier they sell all sorts and are sensibly priced as you can see.....SGR said:Does anyone have a link to this LED supplier please?
http://www.ebay.com.au/itm/10value-...ltDomain_0&hash=item2c5fec00f7#ht_3385wt_1330
yes I know you dont want 500.... but have a look around
500 will do nicely. I ordered a box. If I see them before February (Chinese New Year) that will be great. I had to log onto ebay.au with my ebay.co.uk details. That took a while to work out!tramcar trev said:
I also ordered some various leds from ebay.co.uk with very much smaller pack sizes and slightly higher individual cost.
A long time ago I was taught the theory of diodes. We never got to prove that in the lab. When my DC power supply arrives (also made in China, been waiting months and months for CE (European) approval - US manufacturer) I will do some testing. That's not what most people on this forum mean: not playing! Testing = actual work ! ! !
If I can find a suitable affordable device I will try to include photometric data, but after a lifetime in professional lighting applications, I doubt if that will be completely scientific ([style="color: #ff00ff;"]or useful). Candelas and lumens to me are as obvious as horse power and torque to a professional mechanical engineer: not something that you explain to the general public. So if you find that hard to understand your lux out (technical / extreme geeky) joke. And let's not mention kVA and kW !
I'm offering a Rule #9!
[style="color: #ff00ff;"]If lighting looks OK, then its OK.
This obviously applies only where there are no rivets involved, so lighting qualifies. Beware of the difference between sunny, light, dusk and dark conditions before deciding, though.
So many thanks for the link.
Incidentally I read your blog with a great deal of jealousy. Rule #8 is great, but 45mm gauge for 4'8 1/2" (1435mm) is more like 1:32. An old trick (which I believe is Rule #8.1) is to put the larger items in the foreground. Works for me!
Don
Dont know about the UK but 5-6 days to me is around average from this guy....
Oh I thought that was rule 8.1V2.3.3.3.3
Oh I thought that was rule 8.1V2.3.3.3.3