[PSUBS-MAILIST] LED Light test

[Stephen Fordyce via Personal_Submersibles]

Hi Alan,
I'm glad your lights are going well!  There are a couple of things I may be
able to contribute after several iterations of designing the circuit for
my TFM caving/diving helmet lights.

*1. Linear vs switching LED drivers.  *
I looked at the datasheet for your LED driver chip and it appears to be a
linear regulator - this in general terms means it creates a variable
resistance to get the output current/voltage right, and as such can create
a lot of heat which may be wasteful.  Ie. if you have a 12V supply and your
LED needs 4V, 67% of the power will be lost in the driver!  But if you have
a 12V supply and your LED chain needs 11.5V, then it's quite efficient.
They are simple and easy, and small as you point out, with no external
components.

A switching driver uses very fast (MHz) PWM along with an external
capacitor/inductor to drop and smooth out the voltage, and is ~90+%
efficient over a big range of voltage drops.  This means it creates much
less heat and saves power.

I changed to switching drivers for my LEDS (input 7-8V, output 3-4V) and
noticed a huge difference in heat and efficiency.  Just something to be
aware of if you run into heat or runtime problems.

*2. Acrylic windows*
I have used lasercut acrylic (6mm) in my caving lights (which I've had up
to 80degC according to the internal temp sensor.  Lasercutting allows me to
get an oblong rectangular shape with holts for screws.  The lights have a
full high temperature burn test out of the water and then multiple dives to
100m in my pressure pot, with no acrylic failures to date.

Cheers,
Steve Fordyce

On Thu, Mar 9, 2017 at 6:12 PM, Alan via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Tested my 80W LED light in a housing, to see how hot it got in & out
> of the water.
> The good news was it didn't get warm at all after running at 70W for
> 25 minutes in the kitchen sink. Out of the water it hit 120F (49C) in 7
> minutes. The LED has a maximum temperature rating of 60C so was keeping
> back a bit from that.
> I dropped the current down & ran it out of the water at 33W & 25W but it
> climbed
> to 125F in 20 minutes for 33W & 15 minutes for the 25W.
> I am using a cast acrylic 8mm thick lens, & this didn't get hot either in
> air
> or water. Using acrylic instead of glass is saving me $90-.
> Am making a few minor housing design adjustments for the final iteration.
> Have also ordered a dozen of these 50 V 350 mA constant current regulator &
> LED drivers.
>
> http://www.onsemi.com/PowerSolutions/product.do?id=NSI50350AD
> They are TINY; about 1/4" square & you run them in series to get the
> desired
> amperage. They have a wide input voltage & would be great for a 36V system.
> Alan
>
>
> Sent from my iPad
>
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