constant current or dimable? - The Planted Tank Forum
Old 01-04-2012, 12:17 AM Thread Starter
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constant current or dimable?

looking at meanwell drivers whats the difference between constant current and dimable do you use a potinciometer with a dimable driver or a constant current--I thought i read in specs that the constant current can be programed
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Old 01-04-2012, 03:01 AM
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Quote:
Originally Posted by they call me bruce View Post
looking at meanwell drivers whats the difference between constant current and dimable do you use a potinciometer with a dimable driver or a constant current--I thought i read in specs that the constant current can be programed
"Constant current"--- the term--- doesn't have anything to do with whether they are dimmable or not. Even the dimmable ones are called "constant current"--- although I understand why that looks odd.

The term "constant current" means basically that the driver will adjust it's voltage output so that the device being driven accepts whatever current level you intend it to get. That is the exact opposite of what a "constant voltage" device does (like an electric drill, or a standard light bulb). On those constant-voltage devices, the voltage is set at 120VAC (your wall outlet) and the device will just consume whatever amount of current is necessary.

LEDs work a bit differently--- you can't hit them with any random voltage number--- they have extraordinarily finicky voltage tolerances. Meaning, if you increase the voltage on them literally by 0.1 volts, they may try to suck in another 200-500mA of current if you put them on a "constant voltage" power supply (ie like a cell phone charger).

However, if you hook an LED to a 700mA constant-current device, the driver will ONLY put out the voltage needed by the LED to maintain a 700mA current level. When you dim them, the LED's need less voltage, so the driver drops the voltage and the current at the same time----- it's just a balancing act, that's all.

Now, how to dim a Meanwell. First, make sure you are buying specifically a Meanwell dimmable driver. Some are non-dimmable like you mentioned. Meanwell adds a letter tag to the end of the model numbers to indicate if it's dimmable, and if you are looking at the common ELN-60-48D model, that "D" on the end is what you are looking for.

Second, you need to give the Meanwell's dimmer a voltage source (a DIFFERENT voltage source than the wall plug 120VAC..... meaning your Meanwell will need two plug outlets, one for the dimmer, and one for the 120V power-in).

You only need anything that puts out 5-10 volts (any random voltage from 5-10 will work, BUT DO NOT EXCEED 10V or you'll blow the dimmer mechanism). You will splice in this voltage supply (like a 5 volt cell phone charger) with a 10K Potentiometer. The potentiometer just raises/drops the voltage going into the dimmer, which is how you are communicating with the driver on how bright you want the LEDs.

The Meanwell won't light up to a very high current with only 5 volts in it, as it comes from the factory, but there is a small plastic screw inside the Meanwell labled "SRV2" that you can gently, carefully turn up a little, to fine-tune the Meanwell to give you whatever current level you want with a 5.0v input (up to about 1,000mA). This is very easy to do and it's what it's made for.
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Old 01-04-2012, 03:15 AM
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Just note--- by the way--- that most Meanwells have a minimum voltage output of either 24 or 32 volts, I can't remember off hand---- which means they require 6-10 LEDs minimum.

A way, way, way easier driver to work with is this one from Inventronics, it is a bit more expensive than the Meanwells but it also comes with it's own built-in dimmer voltage and there is NO fiddling around with any internal screws like I mentioned above.

It will run around 5-15 LEDs (min/max) depending on the specific LEDs you want to use.

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Old 01-04-2012, 07:54 PM Thread Starter
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Thanks redfish for takeing the time to help Ive been studying this of and on for several months I think im almost ready to put the order in for the build.
Ill put together my plan to see if its right and post it here.
Any constructive critisisem greatly accepted!

My tank build is a 150 72"x20x 28 I think
I was going to get a 8" wide heat sink and run in XM-L's t5 one row cool white 24 leds
and a second row of warm white XM-L's t5 24 leds
the reason for the 8 inches was so i could run blues for moon and/or color adjustment.
maybe 6 inches is enough Ill have to lay it out
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Old 01-04-2012, 07:57 PM Thread Starter
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so with each group of lights I can add a potentiomiter?
Looks like Ill need 4 - 12 leds on each and a seperate one for the moon lights
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Old 01-04-2012, 08:58 PM
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this is why people like pwm's..

u can dim them on the driver and not use a pot.

and im not sure if u can use different pots on a series...

The pot would limit the voltage going to the branch of the series after where the pot was.

To do what your asking... have different lights dim at different levels, you would need more then 1 driver, where the driver itself would have a pot.
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Old 01-04-2012, 09:12 PM
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Quote:
Originally Posted by Naekuh View Post
this is why people like pwm's..

u can dim them on the driver and not use a pot.

and im not sure if u can use different pots on a series...

The pot would limit the voltage going to the branch of the series after where the pot was.

To do what your asking... have different lights dim at different levels, you would need more then 1 driver, where the driver itself would have a pot.
The dimming pots don't limit the voltage available downstream of the driver. The just reduce the constant current output of the driver.

Hoppy
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Old 01-05-2012, 02:07 AM Thread Starter
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looks like i could get invetronics driverd if i can get 1 to run 24 leds Ill get 2 drivers on for 24 cool whites and 1 for 24 warm whites or nuetrols and a small one for the moonlights down the middle
I like the idea of the pot for the ease of adjusting it set up in a nice control box.

hoppy so the pot is much like a dimmer in your house the voltage is constant just the current is limited
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Old 01-05-2012, 02:13 AM Thread Starter
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if I use this driver its max is 700ma wouldnt i be limiting myself if i use XM-Ls that have a max drive of 3000ma and fowared voltage of 2.9 @ 700ma
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Old 01-05-2012, 02:26 AM
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Quote:
Originally Posted by they call me bruce View Post
looks like i could get invetronics driverd if i can get 1 to run 24 leds Ill get 2 drivers on for 24 cool whites and 1 for 24 warm whites or nuetrols and a small one for the moonlights down the middle
I like the idea of the pot for the ease of adjusting it set up in a nice control box.

hoppy so the pot is much like a dimmer in your house the voltage is constant just the current is limited
It isn't like a household dimmer at all. That dimmer works by chopping the alternating current so only part of each cycle of current makes it through to the light. A constant current driver provides a constant 700 mAmps, for example for total LED forward voltage drops of 10 to 36 volts, for example. The dimmer circuit pot adjusts that 700 mAmps down to perhaps as low as 150 mAmps, but still DC current, at 10-36 volts. In addition, with Meanwell drivers, you can also adjust the max voltage up about 5-10%, and the constant current to a slightly higher value or much lower value, using little adjustment screws inside the housing.

I like the external control box idea very well too. Using two white colors you can adjust the mix to get the color temperature appearance to what looks best to you, and you can also adjust the moonlights if you want that capability too. All from one control box out of sight under the tank.

Quote:
Originally Posted by they call me bruce View Post
if I use this driver its max is 700ma wouldnt i be limiting myself if i use XM-Ls that have a max drive of 3000ma and fowared voltage of 2.9 @ 700ma
You will want to limit yourself anyway, so you aren't forced to use a big, expensive, fan cooled heatsink to keep the LEDs from overheating too much. Just use the charts in Cree's pdf showing the specs for the LEDs to decide how much current you need for the PAR you want to get. (That isn't easy to do, so you end up relying on the dimming ability of the driver to do the final adjustments.)

Hoppy
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Old 01-05-2012, 03:21 AM Thread Starter
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I know the par at the substrate isnt easy to figure with leds --Ive read dozens of your posts
ill look at the specs for cree leds and try to nail this down i would like the ability to be able to adjust higher if need be so if i go to a 1000ma or 1500ma driver i stillcould run it lower say 800ma that way im not running wide open
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Old 01-06-2012, 01:26 AM Thread Starter
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I hit a dead end I dont want to drive XM-Ls with only 700ma max i want that to be my low end cause u never know what your going to need
any ideas?
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Old 01-06-2012, 01:36 AM
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Quote:
Originally Posted by they call me bruce View Post
My tank build is a 150 72"x20x 28 I think
I was going to get a 8" wide heat sink and run in XM-L's t5 one row cool white 24 leds
and a second row of warm white XM-L's t5 24 leds
the reason for the 8 inches was so i could run blues for moon and/or color adjustment.
maybe 6 inches is enough Ill have to lay it out

If your tank has cross braces, you might want to consider using heatsinks that are "modular" (ie, giving light in a way similar to halide pendants)--- use 3 heatsinks that are roughly 8X20.

If you're using aluminum C-channel (another decent option and way, way cheaper), get C-channel that's around 4-6mm thick (3/16" to 1/4" thick) and around 1.5 to 2" wide.

Mix your blues in with the whites, in between them. If you want blues to adjust color temp, over a tank your size, you will want at least 12 of them for it to be good even coverage, I recommend the XTE Royal Blue.

Quote:
Originally Posted by they call me bruce View Post
looks like i could get invetronics driverd if i can get 1 to run 24 leds Ill get 2 drivers on for 24 cool whites and 1 for 24 warm whites or nuetrols and a small one for the moonlights down the middle
I like the idea of the pot for the ease of adjusting it set up in a nice control box.
Exactly. BTW I do not know how low those Inventronics drivers will go, they may or may not be dim enough to use for moonlights.

Quote:
hoppy so the pot is much like a dimmer in your house the voltage is constant just the current is limited
Hoppy explained it better than I can in technical terms (esp since I understand LED driver dimming better than I understand a dimmer on house light lol).

But I'll add just a bit to it. The dimmer's potentiometer itself has nothing to do with the electricity that is powering your LEDs. Meaning, the voltage you are dropping with the potentiometer is just a communication device to the LED driver that "tells" it what current you want.

Basically, it works like this. You give it 1 volt, it runs them at 10% of the driver's max current setting. 2 volts, 20%. 8 volts, 80% (they aren't quite that linear, actually, but pretty close).

So the dimmer is literally just a data input device that uses analog DC voltage as the language. Both Meanwell analog dimmable models, and Inventronics are this way. Inventronics are easier to work with though.

Quote:
Originally Posted by they call me bruce View Post
if I use this driver its max is 700ma wouldnt i be limiting myself if i use XM-Ls that have a max drive of 3000ma and fowared voltage of 2.9 @ 700ma
Like Hoppy said, you are limiting yourself. You could do this whole thing with half the # of LEDs if you used a 2100mA driver but you'd be spacing them out farther apart and giving yourself larger shadows in the tank.

Note that the XML is still brighter than other 3-volt class Cree, Rebel, Bridgelux, Chinese, or other LED's at 700mA, and you're actually running them at a way more efficient drive current (ie, you're getting more light for your electricity usage).

But all that being said, I'd actually use Cree XPG over your tank, they are ***almost*** as efficient as the XML and they are HALF the price and look just as lovely.
redfishsc is offline
Old 01-06-2012, 01:40 AM
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Quote:
Originally Posted by they call me bruce View Post
I hit a dead end I dont want to drive XM-Ls with only 700ma max i want that to be my low end cause u never know what your going to need
any ideas?

Actually, if you put 700mA as your bottom end, and you're using 48 of them total over your tank, you may end up with nothing but algae hell. That would probably be a lot of light!!

XML's are extraordinarily bright at 700mA, and like I said above, they are brighter than any other 3-volt class LED at 700mA (or really any drive current to be honest).

Besides, if you ran the XML at 2100mA or 3000mA, you will need some SERIOUS heatsinking since they do get hot (I know, I've driven them that high before, it's nuts).

It's not so much an issue of you "under-driving" a Lamborghini. The XML is actually more like a Honda Accord that just happens to be so finely tuned that it can go 240mph. Better off drive it at normal speed and be happy at the advanced efficiency of this particular LED.

Again though, cost is what drives me back to suggesting the XPG.
redfishsc is offline
Old 01-06-2012, 03:01 AM
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Because there are now so many choices in LEDs, many of which are very good for lighting a planted tank, it can be a challenge to make all of the decisions about how to DIY a light. Back when I was working, one of my managers discovered the word "plethora" one day, and from then on, always tried to find a way to use it. So.....we have a plethora of LED choices now.

Hoppy
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