LED lighting on a budget!

[knetz31]

Help Please

Help Please

I could not really figure out where to get some help and i saw this thread and it seems a lot of you guys know what you are doing. I recently purchase a rimless 24x24x12 and i cannot figure out a good led setup for good coverage and enough to grow sps. Please help, any info is really really appreciated. Thanks, Neil.

 

[der_wille_zur_macht]

Neil, this thread does have several "experts" in it, but it's primarily targeted at the approach kcress described of using resistors to control current instead of active drivers. With such a general question as yours, you might be better off starting a new thread to help keep this thread on topic.

 

[knetz31]

sounds good

sounds good

i might be back to add to the subject when i get my build going.

 

[TropTrea]

I could not really figure out where to get some help and i saw this thread and it seems a lot of you guys know what you are doing. I recently purchase a rimless 24x24x12 and i cannot figure out a good led setup for good coverage and enough to grow sps. Please help, any info is really really appreciated. Thanks, Neil.

Sounds like you have a very shallow 30 gallon tank here. I would put 20 to 24 3 Watt LEDs on it, without lens to get an even coverage throughout the tank. For LED's I'd take 6 Neutral Whites, 6 Blues and 12 Royal Blues. Set them up on three circuits.
Circuit A Pre Dawn to Post Dusk = 6 Royal Blues
Circuit B Dawn to Dusk 6 Blues and 6 Royal Blues
Circuit C Midday 6 Neutral Whites

Run this for about 2 weeks than make a personal observation to what you like or dislike about the system. You could add 6 additional LED's if you so desire to either make it either more blue or more white, if you so desire.

 

[Ronic]

After looking at this for the last hour i think my brain is mush.

I have a question about using wall warts to power the led's. At work they are getting thrown out because of new equipment that we are getting uses different power supplys.
Will a 12v 1.5a wall wart run 2 strings of 3 leds?
If I have read this right I can do 3-3.5v led's with 1.5v left over, to get rid of that 1.5v i will need a 2.14ohm resistor.
Digi-key has 2.15ohm 5w resistors in packs of 10 they can order, the fast blow fuse F2313-ND, and the terminal blocks.
Or do I have somthing wrong?

 

[kcress]

I can't recommend fixed resistors in your application. You should use the adjustable type as described above in this thread. It is not possible to predict the drop of the LEDs accurately enough to avoid using adjustable.

 

[Ronic]

Thank you for the reply Kcress,
I saw in the thread about having to change the resistor for the drop. But im stuck wondering why? Why do we have to worry about voltage drop on these drivers and not on the meanwells?

 

[TheFishMan65]

In theory it works, but is it 3 or 3.5 it makes a big difference in the resistor. I would recommend a real driver.

[EDIT]
Oops missed the last page

 

[kcress]

Why do we have to worry about voltage drop on these drivers and not on the meanwells?

Meanwells are current sources and wallwarts are voltage sources. Voltage sources driving LEDs need a power resistor to limit the current.

 

[Ronic]

ok i think i have it.
Using a variable resistor is a rheostat that will keep the current under control and make it so I can change for voltage changes in the led's. And if i want to dim the leds with a potentiometer, that will change the voltage but not the current. :headwallblue:

 

[kcress]

Almost.. :LOL

Changing the voltage most definitely changes the current too in voltage mode LED lights.

What you would do is put an ammeter in series with your string then move the resistor to the highest resistance point.

Power up.

Check the current.

Too low?

Being careful not to burn yourself adjust the resistor down in resistance. As you do the current will go up in the string.

Do this until you're at about 600mA.(given, say XPG and XTE LEDs)

Now that your rig is running nicely power down and install it in place.

Run it with everything the way you expect it to run air flow and temperature wise.

Power-up again and watch the current. You will see it slowly drift upward as the fixture heats up. This is the dread negative thermal coefficient that LEDs are notorious for. It's why current controllers are so popular. But I digress. You should see the current rise tapper off eventually at an equilibrium point.

Best would be around 700mA. I wouldn't push a resistor based build too far.

Once you've seen where your fixture tops out, expect it to go a bit higher on a hot day.

You can now power it down and switching your meter leads back to ohms and volts, set it to ohms and measure across the resistor.

Write that number on your fixture somewhere near the resistor.
Now whenever your fixture is on you can set you meter to Volts and measure across the resistor.

The current thru your string will be:
Voltage measured divided by this pre-measured resistor value.

This way you can measure the current without breaking into your LED string in the future just by measuring the voltage across the resistor.

A final note: We can mess with the resistor on a running string only when the string is fed with a voltage driver. Doing that with a current driver would likely destroy some LEDs.

 

[tazzy123123]

Need help ppl I have my LEDs working with a pc psu at 24v but to do that I have to use the -12v blue wire and a +12v wire all works but can anyone tell me how to get pwm from a arduino to work when I have a-12v ground and the arduino has a 0v ground

 

[perkint]

Are you using constant current drivers?

Tim

 

[tazzy123123]

Yes I am I've got them to dimmd but they only start to come on at 60% to 100%

 

[oreo57]

After looking at this for the last hour i think my brain is mush.

I have a question about using wall warts to power the led's. At work they are getting thrown out because of new equipment that we are getting uses different power supplys.
Will a 12v 1.5a wall wart run 2 strings of 3 leds?
If I have read this right I can do 3-3.5v led's with 1.5v left over, to get rid of that 1.5v i will need a 2.14ohm resistor.
Digi-key has 2.15ohm 5w resistors in packs of 10 they can order, the fast blow fuse F2313-ND, and the terminal blocks.
Or do I have something wrong?

Technically fine except no need for the fuse..
Without the exact specs of the LED's at various voltages it is only a shotgun approach.. but doable..
Just heat sink them good..

At 1.5A in the PS your choices are limited..
increasing the size of the resistor will decrease the current draw on the LED strings..


The resistor is used to 1)limit the voltage the LEd's "see" 2) Offer a much higher resistance than the LEd's themselves..(why, I'm honestly not sure.. but that i what "they" tell me )

 

[perkint]

Yes I am I've got them to dimmd but they only start to come on at 60% to 100%

What drivers?

Tim

 

[tazzy123123]

Diy ones

And put together