Electronic noob wants to make underwater LED lights

[crazybry79]

My familiarity with electronics is minimal, so please excuse my ignorance.

Not sure if this is the right place for this either, so I offer my preapologies.

I own a large boat, and watch to install underwater lights.

I found these,
http://www.oceanled.com/underwater/amphibian-xtreme/a4-xtreme-series.html
and of course this is what I want...but I'm not paying that price!

So here's my plan. I would like to purchase some BRIGHT LEDs, and assemble my own.

I plan on building this project and sealing it in epoxy, thus making it waterproof. My finished light can be up to 2.5" tall x 10" long. My source power is 12V.

Not sure where to start with LED selection. I found these
https://www.sparkfun.com/products/8860
but after converting the MCD to lumens, I was let down. (Not sure if I should be...) I had originally planned on putting 10 of these in a fixture, but after doing the lumen math, I'm afraid of being let down.

Any thoughts on sourcing a brighter LED?

Once I find WHAT led to use, I will need some help on how to build the circuit.

Thanks for your help!

 

[crazybry79]

Actually, I found these
http://www.topbright88.com/5-pcs-10mm-40°-1w-watt-blue-led-300ma-250000mcd-p-531.html

I think if I put 15 of these LEDs in an epoxy enclosure, I should get the output I'm looking for.

How complex would the circuit be for this?

 

[Jouellet]

Check on ebay: you can purchase 10w LED, that connect directly on 12v - no need for an extra resistor !

Also, you may want to check this site: www.smoothon.com . They sell resin, urethane & epoxy. One of their product is crystal clear & UV resistant.

 

[crazybry79]

Thanks fir the tip! I'll check on it.

One question. I see these are rated for 10-12V. Since boats use an automotive style charging system, they reach 14.5v while running. Will this harm the LEDs?

 

[Gryd3]

Thanks fir the tip! I'll check on it.

One question. I see these are rated for 10-12V. Since boats use an automotive style charging system, they reach 14.5v while running. Will this harm the LEDs?

Depends on the LEDs you use...
You can find "12V" LEDs that are meant for automotive use which will be fine. Otherwise you will need to build or buy a driver for the LED to protect it and run it properly.
If in doubt, share it and we can take a look.

 

[Jouellet]

Check these :

http://m.ebay.com/itm/390876125031?nav=SEARCH

http://m.ebay.com/itm/151130881880?nav=SEARCH

http://m.ebay.com/itm/261756785754?nav=SEARCH

The last link includes a 12-24 driver, which would solve your issue. Otherwise you may need a hi wattage resistor in serial with your LEDs

Check on google for a LED-resistor calculator

 

[crazybry79]

These were one of the first ones I found.
http://pages.ebay.com/link/?nav=item.view&id=111175065601&alt=web
The ad says it would require a resistor.

Would I be able to put 3 of these in a "light"?

 

[crazybry79]

I just missed your reply. Sorry.

I forgot to mention, I am looking for blue leds.... sorry

 

[Gryd3]

These were one of the first ones I found.
http://pages.ebay.com/link/?nav=item.view&id=111175065601&alt=web
The ad says it would require a resistor.

Would I be able to put 3 of these in a "light"?

If it does not tell you specifically that it's for automotive use, or give you an decent input voltage range, then you will most likely require a driver (or at least a resistor).

You can connect as many LED's as you want to make a 'light'... but they need to be wired correctly.
The simplest wiring method is simply a resistor and an LED connected in series. If you want additional LEDs then you need to read their specs and determine the 'forward voltage drop' of the LED. If the forward voltage drop is 4V for example, you can safely chain 1 resistor and 2 LEDs together to make one light. (If you used 3 LEDs, the sum of the forward voltage drop would be too close to the supply voltage on the boat. This will cause the resistor to either make the LEDs dim when the motor is not running, or too small to properly limit the current through the LEDs.) If you want to add more LEDs but you cannot 'string' more together in series, you can add more in parallel. This would simply be making two of the smaller 'lights' and hooking them up in parallel in the same enclosure.

 

[Jouellet]

They will need a resistor.

If each LED has its own resistor then the wattage of the resistor will be smaller than if the 3 LEDs are in parallel with only 1 resistor.

Write down the specs of the LED and Google a LED calculator

 

[Gryd3]

Check these :

http://m.ebay.com/itm/390876125031?nav=SEARCH

http://m.ebay.com/itm/151130881880?nav=SEARCH

http://m.ebay.com/itm/261756785754?nav=SEARCH

The last link includes a 12-24 driver, which would solve your issue. Otherwise you may need a hi wattage resistor in serial with your LEDs

Check on google for a LED-resistor calculator

The first link here would require at least a resistor, but would benefit more from an 'LED driver'.
The second link appears to have a built-in resistor, but I am unsure how it will handle 14.4V (It's meant for automotive... but that does not mean it was engineered properly)
The third link has a driver and would be idea.

As far as color... you can find the driver by itself, but you can also put a colored lense in front of it to make any color you want. (It just wont be as vibrant as if it were an actual blue LED)

 

[Jouellet]

Sorry Gryd3 for comments redundancy: I was typing mine while you published yours...

We are saying the same thing !

 

[Gryd3]

They will need a resistor.

If each LED has its own resistor then the wattage of the resistor will be smaller than if the 3 LEDs are in parallel with only 1 resistor.

Write down the specs of the LED and Google a LED calculator

LEDs should never be placed in parallel with only 1 resistor... There are small differences in LEDs that could allow one of the 3 to pull more current than the other two. This would cause it to fail prematurely, and then the remaining two would fail shortly thereafter because they will have 1.5x more current shoved into them.

 

[Gryd3]

Here is a resource on the forums that cover driving LEDs in great detail :
https://www.electronicspoint.com/resources/got-a-question-about-driving-leds.5/

This is one of the LED Calculator websites that will work out resistor values if you want the simpler method of driving LEDs. (Simple method uses more power, using a 'Driver' will be more efficient)
http://ledcalc.com/

 

[crazybry79]

Ok, I'm pretty sure that I'm following this pretty good.

Do I need a driver for each led? Or would 1 driver run several leds? (I'm looking at 3 - 4 of the 10W in a "light"). If yes, then would one driver power 2 "lights"?

 

[crazybry79]

Ok. I hate to go off on a tangent.... but somebody slap me if I'm wrong.

Found these.
http://pages.ebay.com/link/?nav=item.view&id=321165717694&alt=web
There's 10 of them. If I wire 1 of these to a 3.9 ohm resistor, and hook it up to my 12v system I'm good. (Assuming 14.5v)

If I'm right, I could put 10 of these led+resistors in parallel and be good.

Wired like this, if 1 led takes a dump, the other 9 will be fine and continue working. Right?

If my above assumptions are right, I have a question. This is a 12V system, and can reach 14.5v. But normally it will run 13.8v. My question is, using the calculator link, if I change input voltage from 14.5 to 13.8, my resistor drops to 3.3ohms.
Would I be OK with a 3.3ohms resistor, or do I need the extra resistance for the occasional 14.5v. I guess I'm wondering how forgiving LEDs are, and how creative I should be with my numbers.
would you notice an intensity difference in 3.3ohms to 3.9ohms?

 

[Gryd3]

Ok, I'm pretty sure that I'm following this pretty good.

Do I need a driver for each led? Or would 1 driver run several leds? (I'm looking at 3 - 4 of the 10W in a "light"). If yes, then would one driver power 2 "lights"?

You need one driver for each series of LEDs. (The driver is meant to actively regulate the output current.)
-Or-
You need one Resistor for each series of LEDs. (The resistor will passively limit the current based on the math used for the supply voltage, forward voltage drop of the LEDs and the resistor value)

Ok. I hate to go off on a tangent.... but somebody slap me if I'm wrong.

Found these.
http://pages.ebay.com/link/?nav=item.view&id=321165717694&alt=web
There's 10 of them. If I wire 1 of these to a 3.9 ohm resistor, and hook it up to my 12v system I'm good. (Assuming 14.5v)

If I'm right, I could put 10 of these led+resistors in parallel and be good.

Wired like this, if 1 led takes a dump, the other 9 will be fine and continue working. Right?

If my above assumptions are right, I have a question. This is a 12V system, and can reach 14.5v. But normally it will run 13.8v. My question is, using the calculator link, if I change input voltage from 14.5 to 13.8, my resistor drops to 3.3ohms.
Would I be OK with a 3.3ohms resistor, or do I need the extra resistance for the occasional 14.5v. I guess I'm wondering how forgiving LEDs are, and how creative I should be with my numbers.
would you notice an intensity difference in 3.3ohms to 3.9ohms?

*Slap!
Your not wrong, don't worry.
You've picked things up quite well.
As far as the 3.7Ω vs 3.3Ω debate is concerned. It's almost always best to be safer than sorry. The occasional 14.4V will cause the resistor to allow too much current through the LED. This in itself will not cause immediate failure, but it will diminish the longevity of the LED. When using the LED calculators, it's a good practice to use the 'lowest' forward voltage drop for an LED, and the 'highest' voltage source. This will result in a resistor sized too large for the average the LED will see, which means the LED will not run at it's brightest, but will live much longer

 

[crazybry79]

Gotcha, a million thanks.

'Nother noob question.... went shopping for resistors. Oh boy, he we go....

I see half watt, quarter watt Everywhere. WATT do I need? :-/

I see the calculator says the resistor disipates 3141mW. If my math is right that's 3.141 W.

So I need a 3.5W resistor? if so, can I make the resistor too big? Am I OK if I go to a 5W, or am I over killing this...

 

[crazybry79]

Holy chit.... I was using the highest forward V. I changed it to the lowest, and that brought it up to 5.6ohm and 5.4W.
am I doing this right? Sure don't want to have lights that even the fishes can't see!

 

[Jouellet]

Calculator tells you how much needs to be dissipated. If you go lower, resistor will destroy it self....

Watt is an amount of energy that needs to dissipate !

Let's say you need a 10 Ohms/3 watts resistor. You could put 3 x 3.3 Ohms/1watt in series.

Using many smaller resistors might be cheaper ....