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Electronic noob wants to make underwater LED lights

crazybry79

Mar 10, 2014
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http://pages.ebay.com/link/?nav=item.view&id=251463352085&alt=web

The are the ones I think I'm going to use. I think.... Their lumen ratin is....meh.... but I'm 99% sure these Chinese ratings are bogus anyways. (Gotta impress the fishes!)

Anyway,
9-11 forward V
1000ma

I was using this calculator

http://ledcalc.com/#

If I put in 14.5v input (max input)
and 9v forward (min forward)
and 1000ma power,

It gives me
5.6Ω resistor
And it gives me 5400 mW power disipated.
I was assuming that means I need a 5.4W resistor (I might be wrong)
 

Jouellet

Feb 2, 2015
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That sounds about right....

Of your 14.5 v, 9v volts will be "consumed" by your LED

The remaining, 5.5v needs to ho thru a resistor.

Current will be the same, that is 1000mA (1 amp)

Power = Amp2 * volt
Power = (1*1) * 5.5 = 5.5 watt

Try to build array of 1 watt LED, maybe....
 

crazybry79

Mar 10, 2014
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Ok, you lost me on the last sentence...Following ya on everything else.

Build a 1W array?
 

Jouellet

Feb 2, 2015
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1watt LED, blue, have a forward voltage of about 3.5 v

3 LED in series, will "consume" about 10.5 volts (better than the 9 volts of the 10 watt LED). Only 4 volts "left"

Current (by memory) is about 350 mA (.35 Amp)

P = I2 x V
P = (.35 x .35) x 4
P = 0.49 watt

Now, of course you have only 3 watt compared to 10 watts but you can arrange many string like that in parallel

Advantage: if 1 LED burns, only that string is dead. Also uses smaller resistors
 

crazybry79

Mar 10, 2014
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Gotcha gotcha. Thanks for clarifying.

The ultimate question....will It be as bright. Or brighter...

These are the lights I'm attempting to replicate
 

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Arouse1973

Adam
Dec 18, 2013
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Hello

I guess you realise this will be 10A of current combined can the electrics handle this? At this sort of current you will be wasting quite a bit of combined power in the resistors. You would be better off using a dedicated LED driver so the brightness is maintained even when the engine is idling. Worst thing I can think off is LEDs that keep changing their brightness dependant on engine revs.

Adam
 

crazybry79

Mar 10, 2014
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this is where my mind floods, and frustration sets in.

The brightness fluctuations don't bother me so much. The complexity scares me a bit. ...

Don't mean to sound trivial, but the MAIN scope is bright. Bright. BRIGHT! :D

which way to turn...
 

Jouellet

Feb 2, 2015
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At 14.5v they will be brighter than at 12v, no doubt !

LED driver will "stabilize" the brightness, but it is more expensive than a simple resistor....

It all comes down to how much are you willing to pay, to get the result you want !?!
 

Gryd3

Jun 25, 2014
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If you are attempting to put out a lot of brightness like the example.. I would urge you to build or buy an LED driver.
Remember the calculation you did above with the 5 Watt resistor?
That is 5Watts wasted as heat, and nothing more... And each string you put in parallel will add to this...
An LED driver will be much much more efficient, and will allow you to run more LEDs with less current.
 

crazybry79

Mar 10, 2014
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Ok. You said the magic word....more!

Let's start over...

My complete project will involve 2 "lights", one on each side, both being identical.

Do I want 2 drivers? Or 1 for both?
 

Gryd3

Jun 25, 2014
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Ok. You said the magic word....more!

Let's start over...

My complete project will involve 2 "lights", one on each side, both being identical.

Do I want 2 drivers? Or 1 for both?
Depends on availability.
Personally, I would do one driver for each side. If I could not find a single driver to power the LEDs I plan to cram in a single 'light' I would use a couple smaller ones.
 

crazybry79

Mar 10, 2014
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Everything I search for "led driver" cones up with AC/DC converter. ...
 

Gryd3

Jun 25, 2014
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this is where my mind floods, and frustration sets in.

The brightness fluctuations don't bother me so much. The complexity scares me a bit. ...

Don't mean to sound trivial, but the MAIN scope is bright. Bright. BRIGHT! :D

which way to turn...
I have a couple 10Watt White LEDs at home with a driver that work on 12V. They are bright.. like a single 10Watt LED outshines a 60 soft white incandescent.
The picture you provided is kind of hard to tell how bright they are in reality... the exposure settings and the brightness outside could both affect the reality of the LEDs
 

crazybry79

Mar 10, 2014
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Ok, that link you just sent. Input V and output V look good, but it only provides 900ma. So I'm assuming they wouldn't power The 9-11V 1000ma LEDs I was looking at. Right?

If it would, I'm assuming I would need 1 driver per 10w led?? If my single, one side "light" has (5) 10W LEDs, each light would need 5 drivers?
 

Gryd3

Jun 25, 2014
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Ok, that link you just sent. Input V and output V look good, but it only provides 900ma. So I'm assuming they wouldn't power The 9-11V 1000ma LEDs I was looking at. Right?

If it would, I'm assuming I would need 1 driver per 10w led?? If my single, one side "light" has (5) 10W LEDs, each light would need 5 drivers?
900mA to 1000mA is not a huge difference. The driver I linked is for a Cree 10W LED.
You are right in your assumption of needing 5 drivers for 5 LEDs.
The only way around that is to get creative...
A boost converter will bump the voltage from 12V to say... 60 ;)
From there, you would need a 'constant current' regulator. (Buck, or linear type)
You will need to manually set it to 900-1000mA, but you can then use that to run 5 of those LEDs in series.

The other alternative is to get lucky and find a constant current boost converter that you can manually adjust for 900-1000mA. This can be purchased or built.
The other keywords here for you to search is 'constant current', 'boost converter', 'adjustable'.

I don't have an example product unfortunately for you. I have been lazily looking for one myself that can run 80 - 100W of LEDs. . . I may end up just trying to build one myself
 
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