Cheap DIY light for 75 gallon - The Planted Tank Forum
 
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post #1 of 11 (permalink) Old 02-11-2017, 04:36 AM Thread Starter
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Cheap DIY light for 75 gallon

I know I have a big thread going on m 120 project that's kinda in limbo while me and many others wait to see what O2 comes up with on his new project

I want to get my 75 light changed over and just diy something for fun on the cheap. my current rough plan but need a few few details confirmed if it will work.

thinking of basically doing 10 Watt 9-11 watt cheap ebay multi chips. 8 Cool Whites 4 Warm Whites I really want to do this cheap so i'm thinking maybe I could wire them up Driverless with a TC420 controller and use resisters to drop the voltage to the proper levels.

I'm thinking of running the chips in groups of 4 in parallel, from my research if I'm powering the whole mess with 12 volts off an old PC power supply I would need a 2 ohm 2 watt resistor for each white LED to drop voltage to 10 (specs are 9-11 1amp).

Heatsink wise I'm thinking of just getting a 4ft peace of Aluminum U Channel, is this to little?

Is this stupid? I know its a bit old school and crude but by my calcs I should be able to build it for under 75 and have a pretty bright light with some nice ramping ability
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post #2 of 11 (permalink) Old 02-11-2017, 06:46 AM
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Mornin'
Not stupid at all.
That is exactly what I did. A mix of 10 watt, 1 Amp, multi chip cool white, warm white, a couple of reds and three blues for dusk/moonlight over my 50 gallon. Used a TC420 and a redundant PC tower PSU. Wired up to 4 LED's parallel to each output channel. Didn't use any resistors, 12V in 12V out. Cemented LED's to an aluminium heatsink which is hanging on wires. Program TC420 to ramp up/down and also able to dim to required setting. Running at 30% on my low tech required no forced cooling. These boys are very bright but do get hot at 100% so would probably need a cooling fan. Been running since July '16 glitch free so far. Not sure how much I saved but I enjoyed the experience. HTH

Last edited by Parablennius; 02-11-2017 at 07:00 AM. Reason: spelling
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post #3 of 11 (permalink) Old 02-11-2017, 07:19 AM Thread Starter
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Quote:
Originally Posted by Parablennius View Post
Mornin'
Not stupid at all.
That is exactly what I did. A mix of 10 watt, 1 Amp, multi chip cool white, warm white, a couple of reds and three blues for dusk/moonlight over my 50 gallon. Used a TC420 and a redundant PC tower PSU. Wired up to 4 LED's parallel to each output channel. Didn't use any resistors, 12V in 12V out. Cemented LED's to an aluminium heatsink which is hanging on wires. Program TC420 to ramp up/down and also able to dim to required setting. Running at 30% on my low tech required no forced cooling. These boys are very bright but do get hot at 100% so would probably need a cooling fan. Been running since July '16 glitch free so far. Not sure how much I saved but I enjoyed the experience. HTH
kinda what i'm looking for, just to enjoy the experience and make something for myself, and get my feet wet in diy projects again before I spend real money on my 120 fancy setup.

you have any pics or did you do a build log on your setup?
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post #4 of 11 (permalink) Old 02-11-2017, 01:59 PM
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Why not 5 groups of 2?

Anyways a resistor from 1 Ohm to 2.3 2W is cheap insurance...

From a theory standpoint.. adding a LM317 (about $1) and a resistor (same as above)
2Ohm produces about a 635mA output.
Just picture power supply on the left not the volt. regulator.


https://www.reddit.com/r/HandsOnComp...building_your/

This will create a constant current circuit to the LED. Not sure how it will respond pulsed from the tc-420..

LM317 / LM338 / LM350 Current Regulator Calculator and Circuits

As parablennis pointed out it is possible to run the chips straight..but as thermal conditions on the chip changes mA draw gets wonky..

Well the regulators are $1-ish for 10...
Resistors are 10/$4
https://www.newegg.com/Product/Produ...A&gclsrc=aw.ds
so basically pennies per diode..well 50 cents.

"A man with a watch knows what time it is. A man with two watches is never sure."
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post #5 of 11 (permalink) Old 02-11-2017, 07:04 PM Thread Starter
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The groups of 4 were based on the 4amps each channel on the tc420 can power. Giving me 2 channels open for or possibly adding a deep red channel and a blue/cyan channel later.

I'll look into that simple circuit for a driver. Doesn't seem to hard. But if it's not dimmable kinda defeats the purpose of what I'm trying on doing.
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post #6 of 11 (permalink) Old 02-12-2017, 12:00 AM
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You "need" the resistors anyways..
Only $10 to be my guinea pig..

It should be fine btw..
I am a bit curious why it isn't done commonly...

"A man with a watch knows what time it is. A man with two watches is never sure."

Last edited by jeffkrol; 02-12-2017 at 12:19 AM. Reason: edit
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post #7 of 11 (permalink) Old 02-12-2017, 04:46 AM Thread Starter
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Quote:
Originally Posted by jeffkrol View Post
..
Only $10 to be my guinea pig..
hahahahah I see how it is, but I see what your saying if no go its a small price to pay i'm trying to convert most of my lights over to ramp timers. after I did my first I really liked how it let me have viewable light for more than 8 hrs without having an algae farm.

now it says the LM317 is rated at 1.5amps does that mean if i don't wire the resistor to the middle pin it will limit at 1.5amps? if I wanted to make it simpler couldn't I just wire up 2 10 watt chips in parallel to it running them at 750ma? random thought.

second thought I had. since the groups of 4 will be wired in parallel could I just 1 bigger resister for the voltage drop? calculator I found recomended a 1ohm 8 watt for 4amps. so don't see any of that exact size but see 1 ohm 10 watt resisters, would this work to simplify the wiring if I just went with the resistor method?
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post #8 of 11 (permalink) Old 02-12-2017, 06:38 AM
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Quote:
Originally Posted by Kampo View Post
kinda what i'm looking for, just to enjoy the experience and make something for myself, and get my feet wet in diy projects again before I spend real money on my 120 fancy setup.

you have any pics or did you do a build log on your setup?
Sorry, no. I just followed my nose as I went along really. Very amateurish! I used CH1 for a pair of reds wired in series as they're only 6V each. Ch2/3/4 for the twelve whites and CH5 for the blues. You'll get much better guidance from Jeffkrol than I can give, probably safer, too!

Last edited by Parablennius; 02-12-2017 at 06:44 AM. Reason: added text
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post #9 of 11 (permalink) Old 02-12-2017, 02:53 PM
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Quote:
Originally Posted by Kampo View Post
hahahahah I see how it is, but I see what your saying if no go its a small price to pay i'm trying to convert most of my lights over to ramp timers. after I did my first I really liked how it let me have viewable light for more than 8 hrs without having an algae farm.

now it says the LM317 is rated at 1.5amps does that mean if i don't wire the resistor to the middle pin it will limit at 1.5amps? if I wanted to make it simpler couldn't I just wire up 2 10 watt chips in parallel to it running them at 750ma? random thought.

second thought I had. since the groups of 4 will be wired in parallel could I just 1 bigger resister for the voltage drop? calculator I found recomended a 1ohm 8 watt for 4amps. so don't see any of that exact size but see 1 ohm 10 watt resisters, would this work to simplify the wiring if I just went with the resistor method?
Running parallel is problematic from 2 standpoints 1)variation in chips means variable output (amp dist. is "uneven") Some add current balancing circuit (basic transistors) but see no cost difference between that and a current regulator.

According to a calc if resistor is Zero Amp output is infinity.. or I assume power output of the ps.
It acts like it is not there..
1 Ohm = 1.25A out..
No, one needs a resistor.

Building 10 units is cheap and easy
Removing them just as easy.



Current balancing:

http://www.ledlighting-eetimes.com/c...rings/page/0/2
you know it is kind of funny since the chips are already parallel/series arrays..
I don't think 1 large r Watt resistor on 2 parallel branches would be problematic and may work fine but you now get into resistence in parallel circuits..Prefer to just go to simple..
One "string", one resistor..just not complicated enough to do any other way..


simple I can do.............

Quote:
As in standard diodes, the forward drop of LEDs decreases with increasing temperature. If one string gets significantly hotter than the other, its forward drop decreases and it begins to draw more current. This added dissipation heats it further, increasing its current and possibly leading to LED failure due to this thermal runaway. This situation requires that the voltage driving the strings is current regulated and is constant.

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Last edited by jeffkrol; 02-12-2017 at 03:10 PM. Reason: edit
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post #10 of 11 (permalink) Old 02-14-2017, 02:43 AM Thread Starter
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found someone that sells warm and cool versions of these led chips in 30 and 50 watt versions in 12volt. I think thats the ticket for what I want. I'm thinking 2 50 watts would be ideal but thats 4.3amps which is a bit over the specs for the TC420, curious if there is a bit of headroom on it to do it.
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post #11 of 11 (permalink) Old 02-14-2017, 01:38 PM
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Quote:
Originally Posted by Kampo View Post
found someone that sells warm and cool versions of these led chips in 30 and 50 watt versions in 12volt. I think thats the ticket for what I want. I'm thinking 2 50 watts would be ideal but thats 4.3amps which is a bit over the specs for the TC420, curious if there is a bit of headroom on it to do it.
Just need to pick a resistor that keeps your current below 4A.

You are the one that decides the amp draw..by limiting the voltage to the chip via resistor...

Going resistor-less and wanting to adj. current just get a power supply that can we tweaked.. Say drop output voltage to say 11.5V


Headroom is unknown though at one point I looked up the MOSFET specs in my unit and it was close... at constant DC.

"A man with a watch knows what time it is. A man with two watches is never sure."
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