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Mark Peterson View Drop Down
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    Posted: November 12 2015 at 12:29pm
[Again I need help from the electronic wizards here. Please skip to page two and my latest post for the continuing story. Smile]

I have a question for those of you who know LED's and/or have made your own LED lights. 

Question Can a commercially produced light be dimmed with a DIY or commercially produced dimmer?

I was looking around and from previous discussions at meetings and here on the forum, I thought I remember that dimming is more complicated than simply reducing the voltage. In fact I believe I remember that reducing Amperage is more effective than reducing voltage. Am I right?

Here's the situation. A two year old Hamilton Technology 1W LED light strip has lost so much intensity that it no longer supports coral in my Dentists tank(pics below). I already had to replace the power supply when it degraded and then failed. I looked around but could not find anything skinny(2" wide) and bright enough than Hamilton's 3W LED light strip. After hearing my story, they offered a $100 discount for the 36" unit, so I bought it for just $150 plus shipping. 
It will arrive next week and I'd like to make/find a dimmer. It contains 18 x 3W LED's for a total of 54W. If more info regarding the power supply is needed, I'm sure I could get that.

Thanks for any assistance you can give.
Aloha,
Mark  Hug

Dimensions are 36"x4"x20"





Edited by Mark Peterson - December 13 2016 at 2:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: November 12 2015 at 12:45pm
Trying to dim LEDs by changing voltage will cause them to fail. There are two ways to dim LEDs that work. Current control and PWM (pulse width modulation). Current control would probably work the easiest in your case. It really depends on the driver that is used to run the LEDs.

If the driver has no control input on it then you must find a dimmer that can handle all the voltage and current that is being provided and allow you to control it inline with the power. Do you know the specs on the driver? How many volts and how much current? Then we could probably figure out something that would work.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatman Quote  Post ReplyReply Direct Link To This Post Posted: November 12 2015 at 1:32pm
I assume it's a 4 foot tank? Not a lot of watts over that size tank. About the easiest and most cost effective way is to just change out the driver to an adjustable and run it on a timer. You can set up pots (like the old radio volume knobs)to do the primary adjustment and then let the timer run with it. Looks like you'll need something that can deal with about 65 volts to drive it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: November 12 2015 at 3:44pm
Thanks for the info. That's what I remember, that to work properly for their full lifetime, LED's need the proper voltage across them. If the new Kona Sun fixture is like it's lower wattage cousin, for a driver it comes with an ordinary AC-DC switching power adapter just like that used for a laptop computer. In this case it appears to me that a PWM dimmer will not work. I'll report the exact specs when it arrives. 

The exact dimensions of that tank are 42" wide x 4.5" deep x 21" tall. Coral are losing their zooxanthellae, turning pale and shrinking for lack of light. I will definitely need to acclimate the tank to the greater intensity of these 3W LED's.

Of course, the simplest solution would be to physically tape/block out some of the LED's to start off with and each time I do maintenance just uncover a fewSmile

Aloha,
Mark  Hug


Edited by Mark Peterson - November 12 2015 at 3:47pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote phys Quote  Post ReplyReply Direct Link To This Post Posted: November 13 2015 at 11:45pm
I have these on my mean well drivers and work fantastically. http://www.ebay.com/itm/DC-Motor-Speed-Control-PWM-HHO-RC-Controller-10-50V-40A-2000W-MAX-/141607466889?hash=item20f8767789:g:9wYAAOSwqu9VB6bp
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baghtal Quote  Post ReplyReply Direct Link To This Post Posted: November 13 2015 at 11:45pm
Hi Mark (and company),

Why would a PWM dimmer not work? Granted I'm brand new to aquarium lighting, but PWM dimmers are cheap and easy to plug in.

http://smile.amazon.com/dp/B00IYXGEEQ

http://www.lutron.com/TechnicalDocumentLibrary/048360a_PWM_vs_CCR_LED_App_Note.pdf
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Post Options Post Options   Thanks (0) Thanks(0)   Quote phys Quote  Post ReplyReply Direct Link To This Post Posted: November 13 2015 at 11:48pm
They can be used with a constant amperage system and provide pwm control of installed after the power supply and before the lighting source.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: November 13 2015 at 11:53pm
Most PWM controllers cannot handle driving high amperage loads like LEDs directly. They are meant to be the low voltage control signal for a driver that can handle driving the voltage and current needed for LED lighting.

There are many options for how to dim LEDs but until we know what voltage and current we are dealing with in these specific lights it is hard to recommend any that will work for sure. It's all a guessing game without that information.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote phys Quote  Post ReplyReply Direct Link To This Post Posted: November 13 2015 at 11:55pm
The builds I found on ebay are good for 20+amps.... Plenty for running leds.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 8:55am
Originally posted by phys phys wrote:

They can be used with a constant amperage system and provide pwm control [when] installed after the power supply and before the lighting source.
When I saw this schematic of a PWM unit, I figured that connecting the output from the power supply into a PWM unit is not the correct way to do it and would probably shorten the life of the LED's. Am I right?



I'm thinking that using a power supply that delivers less current without changing voltage is the best way to do this, right?

Aloha,
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatman Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 10:24am
Originally posted by Krazie4Acans Krazie4Acans wrote:

Most PWM controllers cannot handle driving high amperage loads like LEDs directly. They are meant to be the low voltage control signal for a driver that can handle driving the voltage and current needed for LED lighting.


Think of the PWN controller as the brain, the connecting wires as the nerve and the driver as the muscle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatman Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 10:34am
Mark, that driver is woefully under sized for what you need. The LEDs shown there are would need to be the small 20mA ones like those used in a computer as indicator lights. The NPN won't hold up to the load of a bigger set of lights. You have your current being divided into three at the top LED junction where the input power goes parallel. So if you feed it 300ma each string of lights will get 100. As Krazy said we need more information.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baghtal Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 11:04am
I agree, we need the data on the driver. But just for the academic fun of it let's make some assumptions (You know what happens when we do that!). With all of our heads together I'm sure one of us will come up with something fun to mess around with. Or if not someone can tell us (me) how far off base we (I) am with my electrical engineering skills.



Let's say Kona Sun uses CREE LED's (seems plausible, and even if not whatever they do use will probably be similar). DataSheet is here, http://www.cree.com/~/media/files/cree/led%20components%20and%20modules/xlamp/data%20and%20binning/xlamp7090xre.pdf 

We already know that the wattage is 54 Watts from Mark's link. Using the Datasheet, we find that the lowest voltage they will work at (judging from the graph because the numbers aren't printed) is around 2.3, lets say 2.2 to be safe.

2.2 Volts @ 54 Watts works out 24 Amps. add 15% to be safe = 28 Amps. So on the EXTREME high end we need a 30 amp PWM dimmer. It seems FAR more likely that the LED's have resistors on them, and if they are driven by constant Voltage (regular laptop power supply), They are probably driven at 5v (11A/ 13A to be safe), 12v (5A / 6 to be safe) or 24v (2.25 / 3 for margin).

I think the 12v transformer would be the best bet which means that the 8A or 20A PWM solutions would work.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote phys Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 11:28am
Not sure why you're quoting such a high amperage. Youd only need that if you were to run the leds in parallel circuits. Running them in series strings would keep the amperage low but increase the voltage. Decreasing the voltage or amperage does not ruin the leds. Pwm works by cutting some of the voltage but for extremely short amounts of time, like 10000Hz. Lowering either voltage or amperage simply decreases light output but there is a minimum voltage and amperage required to light them. Running leds in parallel isnt smart if you're using a constant amperage supply since, if one string fails, it increases the voltage to the rest of the leds and will cause them to burn up. Baghtal's calculations wouldn't be accurate.
Mark, looking at your led strips, I'm assuming you're using the 48inch strip. Its a 72 watt strip rated around 2.2v max (as baghtal suggested). It says it used 24 leds so to get the voltage required to power them at 100%, you would need to multiply the 2.2v by 24 to give you about 52 volts. Im assuming theyre running a constant amperage supply where most leds would use less than 1amp. If theyre using a constant voltage supply, it's going to be required to have at least a 48volt output and anywhere from 0.5 to 5 amps. The second option allows to string multiple strips in parallel without causing a burning sensation in the leds if one strip fails. Either way, you'll need at least a 48 volt, 5amp PWM control which would to dim your lights.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 7:07pm
Just so we don't get down the wrong road here. PWM does not reduce voltage or current. It simply turns the LEDs off and on AT&T a high speed. The longer they are off the more dim they appear.

Lowering voltage or current on LEDs causes the light produced to be different than the rated spectrum. This is why all of the current commercial fixtures use PWM and not current reducing dimming methods.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote phys Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 8:03pm
It does change the output but only a shift of a few nanometers in spectrum and does it for both unless pwm is quite high in hz. Having a full spectrum LED setup would allow you to do either with very little problem. PWM does have a higher waste in energy since it dumps the power for each off/on cycle as heat. Compared to dimming the led via a current dimming device is more efficient since its not wasting power, but suppressing it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 8:34pm
Not sure where some of that information is coming from but I disagree on a few of those points. I'm not going to derail the thread debating it add we are still working with speculative numbers. I think I'll wait to write a novel until we have some actual numbers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote phys Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 8:55pm
my bad, I confused the downfalls of it with a rheostat. PWM doesn't dump off the excess to heat.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatman Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 8:56pm
Ok, so now I'm confused and I thought I understood LEDs. I'm seeing 28-30 amps kicked around to run a string and my understanding is 350-1100 mA for a standard 3 watt. We need some real numbers, like max volts per LED, forward voltage, max current rating. Bring them by Mark and I'll desolder one and we'll destroy it to see what it really is rated at.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: November 14 2015 at 9:00pm
Hang in there. You're not losing your mind quite yet. There is fact in your numbers. Lol

I like the tear it apart and hook it to a scope idea. :)


Edited by Krazie4Acans - November 14 2015 at 9:00pm
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