DIY LED driver for reef lighting

If you can power down.

Interrupt the line out of one of the regulators and replace it with your meter leads. Set your meter up for DCmA . Perhaps cut a wire somewhere you can just add a bit of solder to repair once you're done.

Tell me the milliamps running thru that line,(which is the load on the regulators), and I'll tell you how to help your regulators.
 
Good idea kcress, that's pretty easy to do in the setup, I still have everything breadboarded and open. Goin to sleep tonight, but I'll check on that tomorrow on lunch. I can interrupt the line in and the line out for giggles
 
Just the out-of-the-regulator please. And be careful you don't open that line while the system is running. Often that can blow a lot of things up.
 
Looks like I'm doing 38.5mA out of the regulator which at 19v drop is .7315 watts. A decent amount for sure. Splitting the difference with a heat-sunk 7815 might be the easiest way to do this, especially since I have them laying about...
 
Using an interposing regulator is a kludge. Using semiconductors to dump heat is a less than optimal solution.

Best would be 24V - 5V -2V = 17V
That includes 2 volts for the regulator to use to keep in regulation.

17V / 38mA = 447 ohms.
The closest standard values are 450 and 442. You could use anything between 450 and, say, 390 ohms.

P = 450 ohms x 38mA^2
P = 650mW

So pick or find one of the above values and use a 2 watt resistor.

Place it just ahead of any capacitor that's in front of the regulator.

Adding a resistor will shave off all that head voltage using something lacking a delicately tuned semiconductor junction.

You can also make up that resistor with whatever you have laying about. Like two 220ohm 1watts. Or four 1/2W 100 ohm. Etc., etc., etc.
 
I can see that if I have resistor lying around, butt also only works at a set current. i see this as a kludge also. When I looked at power resistor before (1 ohm) they ran closer to $0.50-1.00 the 7815 is only $0.25. Can you give me a better reason? I really thought you would be arguing the other way around if someone had suggested a resistor - so know I am real curios.
 
Yes. Every regulator is a potential source of instability. They generally need more capacitors which tend to have shorter lives also.

The resistor does not work at just one set current. It works at the maximum and below. As the current drops to some lower point the resistor does less. Except the lower current also means less is needed so it tends to work out nicely.

I see a resistor for 20 cents:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=430W-2-ND

What did the (4) 100 ohm 1/2W cost?
 
This is probably a question for kcress, but anyone the know feel free to answer. The general recommendation has been to run a power supply at 80%. So for a 24 volt 6.5 amp supply the recommendation is to only draw 5.2 amps. But what if I turn it down to 19.2 volts (80% of the voltage) then is is safe to draw 6.5 amps since you are still at 80% of the rated power? I believe it is the power we want 805 of, but would just like some confirmation.

Thanks
 
TheFishMan65 said:
This is probably a question for kcress, but anyone the know feel free to answer. The general recommendation has been to run a power supply at 80%. So for a 24 volt 6.5 amp supply the recommendation is to only draw 5.2 amps. But what if I turn it down to 19.2 volts (80% of the voltage) then is is safe to draw 6.5 amps since you are still at 80% of the rated power? I believe it is the power we want 805 of, but would just like some confirmation.

Thanks
Click to expand...

Hi Fish.

Just to be clear. You CAN run a power supply at 100%. It's just going to fail sooner. It's sort of like LEDs. The difference being that LEDs will grow dimmer faster whereas a supply just fails sooner. And if you don't supply excellent cooling to a supply and you draw 100% from it it might fail a lot sooner.

As for your question:
With a linear regulator it's the 'power', (V x I), the regulator has to deal with. So turning down a linear supply's output will likely stress it even more.

But with a switcher, since a switcher doesn't 'shave off voltage' with its own body like a linear it's more about the current. The losses in a switcher are caused mostly by the current. So turning down the voltage doesn't help the switcher a lot. It helps, but not a lot. Turning down a switcher's output voltage doesn't allow you to increase the current by the power difference. :mad:
 
shikhyung said:
HI, Does anyone know what is the output Freq at the PWM from the arduino? Thx.
Click to expand...



Base frequencies:
* o The base frequency for pins 3, 9, 10, and 11 is 31250 Hz.
* o The base frequency for pins 5 and 6 is 62500 Hz.

* PWM frequencies are tied together in pairs of pins. If one in a
</pre>
* pair is changed, the other is also changed to match:
* - Pins 5 and 6 are paired.
* - Pins 9 and 10 are paired.
* - Pins 3 and 11 are paired.
*

All you info on the Arduino can be found HERE.
</pre>
 
I believe that I remember reading in this thread that it was possible to get more than 1 amp through a string of LEDs. Was it just a matter of running two drivers to the same string? For example, have each driver outputting 750mA and connect them to one string for a total of 1.5A running through the string of LEDs. Am I way off on this?

Scratch that, found the answer.
 
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