LED Grow Light Questions

[karhas]

Sorry, here. View attachment 63231

 

[audioguru]

LEDs have a range of voltage. Your white lEDs might be 3.3V, 3.5V or 3.7V each. Then they will quickly burn out or be dim.

If all your white and blue LEDs are exactly 3.5V then their current is 3.6A and they will instantly burn out since the 1.8 ohm resistor value is way too low.

If all your red LEDs are exactly 2.1V each then their current is 760mA.

Why do you have a switch connecting between two blue LEDs?

Your power supply does not have its polarity shown.

EDIT:
Oh, you said that the power supply is only 18V, not 24V as shown on the schematic.
Then instead of having 4V across the resistors you have only 0.5V which might burn out some LEDs or make them very dim.

 

[karhas]

How do I determine their individual voltages?
How can I string together anything like this with LEDs if they vary so much?
The switch is intended to be an on/off switch for the whole thing.
I haven't gotten all the parts yet, will the polarity of the power supply matter as long as it is facing the right direction?

When I said I was new to all this, I wasn't joking. That is literally my first attempt at circuit building, so please, rip it to shreds. Help me figure this crap out.
Thanks!

 

[audioguru]

How do I determine their individual voltages?
How can I string together anything like this with LEDs if they vary so much?

Half-decent American LEDs are already measured and grouped into BINs with very tight voltage tolerences.
The different voltages of the LEDs doesn't matter if there are a few volts across the current-limiting resistor.

The switch is intended to be an on/off switch for the whole thing.

It is shown connected completely wrong.

Will the polarity of the power supply matter as long as it is facing the right direction?

If the power supply is connected backwards then all the LEDs might be destroyed.
If one LED is connected backwards then it might be destroyed and its string of LEDs will not light.

 

[Diver300]

How can I string together anything like this with LEDs if they vary so much?

Keep the voltage across the resistor a larger fraction of the power supply.

If you have 3.5 V LEDs, that might be as low as 3.2 V, and a 18 V supply, only put 4 in series. Then the voltage across them could be anywhere between 12.8 V and 14 V. That leaves 4 - 5.2 V across the resistor. If you have LEDs rated at 300 mA, use an 18 Ω resistor. That will give you between 289 mA and 222 mA.

If you use a string of 5 LEDs there will be less voltage across the resistor, so the changes will be a much larger proportion of that voltage and the LED current will be less well defined.

Conversely, if you have fewer LEDs the current will be better defined. Of course, the fewer LEDs you have, the more power is dissipated in the resistor.

 

[audioguru]

I think the LEDs will be extremely hot when operating at their absolute maximum current without seeing how the manufacturer recommends how to cool them (a high velocity fan blowing across liquid nitrogen?). We don't even know if the absolute maximum current is for only short duration pulses or continuous.

 

[karhas]

Would something like this https://www.instructables.com/id/Super-simple-high-power-LED-driver/ added to the circuit help to avoid overheating?

So fewer LEDs per string with bigger resistors, and more strings will help?

I thought the switch could be added pretty much anywhere. Where does it need to go?

I'll work up another draft with all this great info and be back.

Thanks again!

EDIT: I can change the voltage of my power supply, could I just kick it up to 19, 20, 22, or 24?

 

[audioguru]

Would something like this https://www.instructables.com/id/Super-simple-high-power-LED-driver/ added to the circuit help to avoid overheating?

Here we go again.
Many instructables are written by little kids who know NOTHING about electronics. One Instructable that causes many problems was written by a kid who is only 10 years old.

This instructable was written by a student (a big little kid) who missed an important capacitor that stops the regulator IC from oscillating. It gets very hot when it oscillates.

I thought the switch could be added pretty much anywhere. Where does it need to go?

If a switch is connected in the wrong spot then it can cause a fire!
Since you know nothing about electricity or electronics then you should ask a friend who knows about them to make it for you.

EDIT: I can change the voltage of my power supply, could I just kick it up to 19, 20, 22, or 24?

Most power supplies have a fixed voltage. Kicking it usually it does not change its voltage but the voltage might drop to NUTTIN).

 

[KJ6EAD]

The LM317 as a current regulator is what I often recommend but you'll still need some heat sinking for the LEDs, possibly just some large copper areas on a PCB.

AG, the power supply is one of those universal replacement types and is switch selectable to those voltages. I'd probably run it at it's highest voltage; it would be more efficient.

 

[karhas]

OK, so not that Instructable, but is that kind of thing what I'm looking for?

The point of doing this is to increase my own knowledge, not to have someone else do it. I don't have any E.E. friends, so here I am, on the internet, looking for answers. I was trying to do something like this:View attachment 63261 but with more, stronger LEDs and a constant power source. What is different between that diagram and mine? On one side of the power source, a switch goes in before the current goes on to the LEDs.

So keep the source at 24, but keep the strings around 20? Or even lower?

I'm still trying to learn ExpressPCB... because most of the components are surface mount, can I cover most of the back in copper as a heatsink?

 

[ronsimpson]

because most of the components are surface mount, can I cover most of the back in copper as a heatsink?

1 watt LEDs need all the heat sink you can give them.

 

[karhas]

Will something like this work to be able to control the entire system? Or is this guy missing parts too?

Thanks again for helping me folks!

 

[KJ6EAD]

So keep the source at 24, but keep the strings around 20?

Yes.

Can I cover most of the back in copper as a heatsink?

Whichever side the leads are soldered to.

 

[Dr_Doggy]

hello, i just seen this, but you can get on ebay:

https://www.ebay.ca/itm/168-Red-Blu...683?pt=LH_DefaultDomain_0&hash=item2ebd0bb8f3

they run on ac; and provide spectrums & ratios;
i got mine similar somewhere else for like 15$ but i cant find anymore

 

[karhas]

Do those work well enough? I have a cheap panel of LEDs, but it's not as powerful as I want, hence my explorations into electronics. I don't think it corresponds exactly, but that's a 14 watt bulb, and this (if I get it working) will be closer to 30.

At this point in the project, I feel a need to finish it, so I will press ahead. If this bulb does the trick, I may order a couple and feel less urgency about this project.

Thanks!

 

[Sceadwian]

You should ignore wattage and try to find out the lumen equivalent as that's what important as far as light output goes.