DIY Moonlights

[BigJPDC]

OK, today was DIY Moonlight day. I followed a basic design - 4 LED's in a piece of 36" 3/4" PVC, and they don't look that bright at all to me. I was hoping for some critique. I expected these things to really pop after seeing some pictures on eBay. This is the first time I've done anything like this.

LED's - Radio Shack Blue. 3.7volt, 20mA, 2600mcd, 468wave.
Resistors - Radio Shack. 1kohm, 1/4watt, 5% resistance
Power Supply - Radio Shack. 300mA 12v.

I wired the LED's each with their own resistor following some stuff on some websites - be nice.

Let me know how you've wired your own LED's and how I could have made these brighter - at least I found out the soldering skills I learned in 7th grade didn't disappear.

jp

 

[Sm0kin]

not positive but is that to much resistance?

 

[Fish'InMN]

I put 4 blue LEDs over a 15 gallon High, using this basic circuit. Instead of the DC supply, I used a 9V battery, and included a switch inline. Works very well, not too dark and not too bright.

 

[badpacket]

OK,

OK,

Sounds like you wired these in parallel, with each led getting 12v dropped across the led and individual resistor.

Doing that, you should be using a 470 ohm resistor for each led.
Google led calculator, and use the very first link that comes up.

Actually, they have a nice series/parallel wizard as well,
http://led.linear1.org/led.wiz
Here is another basic electronics calculator.
http://home.cogeco.ca/~rpaisley4/LEDcalc.html

With the 1k Ohm resistor, you are probably getting ~9 ma. Since LEDs are very senstive to current, and the light they produce is proportionally or greater to the supplied current, you are drastically underpowering it. Although, those leds are very poor light producers anyways. You should be looking for 5-9k mcd, try ebay.
On the plus side, you might get 150,000 hours out of them instead of 100,000

 

[BigJPDC]

Awesome feedback - this board rocks!

I used Ohm's law to come up with needing 415ohms for resistance, but wasn't sure if that was one resistor total or one per LED.

RS didn't have the 470ohm resisters, but I was really psyched to do this today so I bought the 1Kohms.

I just looked again, and now I think I have a good amount of light. I put something in the tank and raised the bar a few inches off the top and it's pretty well flooded with nice blue light. I bet it looks even better with water in there. =) It is painful to look directly into the LED, so I think they are good.

I'll keep my eyes open for the smaller resistors and the higher mcd lights, and I have got to try this with a 9v battery like Fish'n did.

jp

 

[kgolem]

Re: DIY Moonlights

<a href=showthread.php?s=&postid=6826856#post6826856 target=_blank>Originally posted</a> by BigJPDC

Let me know how you've wired your own LED's and how I could have made these brighter - at least I found out the soldering skills I learned in 7th grade didn't disappear.

jp

This is my first post here at RC, I hope I can help you out.

The secret to designing with LED is controlling the current through the device. Your LED's are rated at 20 mA with a forward voltage drop of 3.7 volts.

This means that the maximum amount of current through the device without damaging the LED (guaranteed by the manufacturer) is 20 mA. And the voltage drop across the LED when it is on is 3.7 volts.

I assume that you wired the LED in series with the resistor. If the LED drops 3.7 volts across it then the remaining voltage (12 - 3.7 = 8.3) will be across the resistor. If the resistor is 1000 ohms then the current through the LED/Resistor circuit will be (8.3 / 1000 = 0.0083 Amps) or 8.3 mA.

Since the LED is rated at 20 mA then you can adjust the size of the resistor to allow 20 mA of current through the circuit.

(8.3 / X = .02)

Solve for X yields a value of 415 ohms for the resistor.

Practically; here are a few things to do to ensure the brightest and longest lasting LED's

Measure your power supply voltage under load and use the measured value for calculating your resistor value. Wall adapters are sometimes 10 - 20 % higher voltage than the rated value.

You can probably over drive the LEDs by up to 20 percent without serious damage. Try one with 24 - 25 mA , if it lasts a day, it will probably last 10 years.

 

[kgolem]

BigJPDC

You posted as I was composing my response. Looks like we came up with the same value.

Good Luck.

 

[BigJPDC]

I think I am pretty close to understanding this - getting stuck on the mA part.

The power supply I'm using is 12v 300mA - am I overdriving the LED's?

The first website badpacket gave me tells me to use (2) 270ohm resisters for the four LED's - would I see significant brightness if I took what I did apart and redid it?

thanks again,
jp

 

[BigJPDC]

<a href=showthread.php?s=&postid=6827624#post6827624 target=_blank>Originally posted</a> by kgolem
BigJPDC

You posted as I was composing my response. Looks like we came up with the same value.

Good Luck.

Cool - thanks kgolem, this was very helpful!
jp

 

[kgolem]

<a href=showthread.php?s=&postid=6827657#post6827657 target=_blank>Originally posted</a> by BigJPDC
I think I am pretty close to understanding this - getting stuck on the mA part.

The power supply I'm using is 12v 300mA - am I overdriving the LED's?

The first website badpacket gave me tells me to use (2) 270ohm resisters for the four LED's - would I see significant brightness if I took what I did apart and redid it?

thanks again,
jp

The power supply is rated at 300 mA, this is amount of current that it can supply to a load without burning up. The amount of current is controlled by the resistance of the load or circuit.

You should use a separate current limiting resistor for each LED, that way if something fails, then it won't cause damage to other LED's.

To calculate the power rating, multiply the current through the device by the voltage across it, in this case;

8.3 V * .02 A = .166 Watts ; use 1/4 watt resistors.

Kev.

 

[BigJPDC]

Very cool. I think I am getting the hang of this, thank you again for all your help.

So if I can find the 1/4 watt, 470 Ohm resistors that they were out of at RS, I would be putting 17.65mA through each LED (8.3\470), which should be way brighter than the 8.3 I'm doing now. The package actually says max 30mA so I bet I could even go bigger.

And the 300mA power supply I scavenged could run up to 16 of them at once (300\17.65), but won't damage the four that I have wired right now.

jp

 

[BigJPDC]

Two quick follow-ups:

1. It sounds like the resistors are redundant once you get past the required resistance - is that correct? i.e. am I providing 1000ohms of resistance per bulb, or 4000 for the whole array? A calculator gave me a diagram using two 270 ohm resistors, but if one failed the other one wouldn't meet my requirements - do resistors ever fail?

Should my total resistance be what I am trying to get to 415 ohms, or for each bulb?

2. How am I driving (4) 3.7v bulbs with a 12v power supply? Many calculators I found on the web broke when I tried this equation, but all you have to do is go on eBay to see moonlight rigs that have a dozen LED's in them.

thanks!
jp

 

[chipmaker]

What voltage is your wall wart actually putting out since it is not regulated, I would check open circuit voltage and use that as the amount of volts output. I have a lot of wall warts, unregulated, and they all put out more open circuit voltage than the rated voltage. Typically a lot of my 12 VDC warts put out anywhere from 15 to 18 VDC. Only put out the 12 VDC plus or minus some volts at the rated MA load.
I come up with 3 leds in series with a 47 ohm res and one led with a 470 ohm resitor, or 2 leds with a 270 ohm res, x 2, figuriing 12 volts as the source. LEDS do not pull much current so even open c ircuit voltage being higher can have an affect on overall brightness and lifespan of LED's. I normally run em about 10 to 20% less than max rated volts and ma rating.

 

[DCFix]

Since you already bought 1kOhm resistors but actually need 470, just take 2 of them and twist them together in parallel. Since they are 5%, you'll get between 475 to 525 Ohms.

 

[kgolem]

<a href=showthread.php?s=&postid=6829705#post6829705 target=_blank>Originally posted</a> by BigJPDC

And the 300mA power supply I scavenged could run up to 16 of them at once (300\17.65), but won't damage the four that I have wired right now.

jp

You probably should not run the power supply at greater than 80 % of rated current for extended periods of time. This supply will get hot if you use for to supply more than 240 mA for hours at a time.

You will not damage the LEDs, but the power supply may fail.

 

[kgolem]

<a href=showthread.php?s=&postid=6829766#post6829766 target=_blank>Originally posted</a> by BigJPDC
Two quick follow-ups:

1. It sounds like the resistors are redundant once you get past the required resistance - is that correct? i.e. am I providing 1000ohms of resistance per bulb, or 4000 for the whole array? A calculator gave me a diagram using two 270 ohm resistors, but if one failed the other one wouldn't meet my requirements - do resistors ever fail?

Should my total resistance be what I am trying to get to 415 ohms, or for each bulb?

2. How am I driving (4) 3.7v bulbs with a 12v power supply? Many calculators I found on the web broke when I tried this equation, but all you have to do is go on eBay to see moonlight rigs that have a dozen LED's in them.

thanks!
jp

1. Each of the LED's and resistors are parallel circuits, so there is 1000 ohms per LED. Each parallel circuit will not affect the other.

Resistors will fail if you exceed their power handling rating.

2. Because each of the LED/Resistors circuits are in parrallel to each other, the 12 V appears across each leg of the overall circuit. The current from the supply is spread out among each LED/Resistor leg.

I alway thought of DC electronics similiar to plumbing. Where Voltage is the water pressure, and current is the rate of water flow. The resistors are like restrictions in the pipe and they only allow a reduced amount of water to flow at a given pressure.

I hope this helps.

 

[BigJPDC]

After researching this further, I can't believe I am getting any light at all. My wiring diagram looks like this:

V+ - resistor - diode - resistor - diode - resistor - diode - resistor - diode - V-.

Is that parallel or series? I have no idea.
This weekend I'm going to do another one like Fishin, but with 270ohm resistors. And it better be a lot brighter. =)

jp

 

[ChemE]

This is what I did. Works great...
http://www.dragonhome.org/~lucas/esr/lighting/

 

[Fish'InMN]

BigJPDC,
That's a series circuit, and quite an interesting one. Like you said, getting light at all is a lucky, but I believe its because you have an unregulated supply. In my VERY basic electronics mathematics understanding, each resistor and LED simply adds up the amount of current required. The unregulated voltage is very common, I had a 4.5V DC wall wart that allowed me to run 4 2V LEDs in series.

ChemE's page is a good one, and the "Wizard" that is mentioned therein is a VERY good place to mess around with circuits.

Good luck with future projects, may the power be with you. :hammer:


PS: Definetly look at purchasing LEDs, resistors and the such online. I bought 50 blue LEDs off eBay for less than $6, including shipping. Power supplies can be found anywhere, from old cellphones, digital cameras, etc. We used to have "The Box", where all miscellaneous cords and power adapters went. Just be safe and sane around live wires!

 

[BigJPDC]

FYI - here is what I went with in the end. Thanks for all the advice, I went from zero to a finished project with your help.

It is a ton brighter, and a lot cleaner too.

Fishin', I ordered some 5000mcd LED's on eBay - 10 for 4.98. I am going to build another bar, using six of them, and hopefully that will be the end solution.

I also ordered a T5 retro kit, 2x39 11k aquablue bulbs, and am wondering if these LED's will be sufficient actinic supplimentation, given just how bright they are. I'll keep you posted.

jp