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post #8 of (permalink) Old 07-05-2012, 05:42 AM Thread Starter
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Join Date: Aug 2009
Location: Vancouver, WA, USA
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8. Drivers

How do I choose one?
You need a driver. It converts the power from the AC outlet (US) to a DC current, and lowers and regulates the current to a useable level for our emitters. Your options are vast in this department, and so are the prices.

Good with electronics and feeling brave? DIY one! For someone familiar with building circuits, this is a fairly simple build. O2Surplus has generously provided some links here that can get you started. More info on DIY drivers and such:

DIY PCB's for DIY LED Systems

And another...
SmartyCat: O2Surplus' ultimate all-in-one driver/controller (now complete!)

For a newbie, you may be better off with an off-the-shelf variety such as a MeanWell or Inventronics dimmable driver.

Either way you choose to go, there are two important specs you need to know about your driver: current, and DC output voltage.
The idea is to get a driver (or drivers for larger builds) that can adequately power the emitters you wish to use. This is where things get technical. Check the max current of your emitters. Itís measured in amps or milliamps (mA). Some can handle up to 1700mA or more, others are more limited. The life expectancy of, and the amount of light emitted from an LED are both largely dependent upon the current at which they are operated. Lower the current, and you lower the operating temperature and the light emitted. Increase the current, and you increase the operating temperature and light emitted. Higher operating temperatures decrease the life expectancy of an emitter (for more info on temperature see: heat sink).
The most efficient way to increase the life span of an LED is to purchase an emitter that is rated with a higher current (ex: 1200 mA) and run it with a driver that provides less current (ex: 650mA). This will allow you to have good light with lower running temps, and your LEDs will last longer. You can also purchase a better heat sink for passive cooling, or add active cooling such as a fan, etc. Some drivers (such as the popular MeanWell drivers) have an adjustment knob that you can (and should) use to lower or raise the current.
Forward voltage is the amount of voltage dropped after passing through an LED. After dropping all of the provided voltage, a dimmer can power no more emitters. The driverís voltage rating determines how many LEDs you can power using that particular driver. How to figure this out? Add up the forward voltage of your emitters. If it is more than the DC output voltage provided by the driver, then either subtract emitters until you have a value under the driverís voltage rating and get another driver to power the rest, or find a driver with a higher DC output voltage rating.
IMPORTANT: because the forward voltage on each emitter can vary quite a bit, allow yourself 2-3 volts for margin of error. This will help avoid problems after wiring your circuit.
To dim? Or, not to dim?
Depends on how fancy you want to get. The benefits of adding a dimming function are the ability to adjust and fine-tune light output to attain a specific PAR value, and the ability to program your fixture to do fancy tricks.

There are commonly two different ways to dim LEDís. One is Pulse Width Modulation, or PWM. This method uses an electronic controller to pulse the emitters very rapidly to achieve different perceived levels of intensity. Another is through controlling the current manually within a specific margin.
What can PWM dimmers do?
To achieve fancy controlled effects using programmable controllers, one can use a dimmable driver compatible with PWM dimming. Using a controller you could program your lights to fade in at dawn, and fade out at dusk. You could program a noon burst to give your plants an extra midday push. You could get really fancy if you have some coding experience and program an Arduino to create a ďstormĒ sequence with changing light to simulate clouds and even flashes of lightning, and control of misters or a drip irrigator to produce a rainstorm. Add a sound system with recorded thunder, and it would be like living in the Amazon. Or the produce section at Safeway. Talk about production value!

Here is a thread by sink and O2Surplus, who paired up and went crazy with a DIY driver and an Arduino, and created a phenomenal code that produces great dimming simulations.
What is the alternative to PWM?
You could keep it simple by purchasing a 1-10v dimming driver and just wire in some potentiometers to adjust it manually. There are also available analog controlers that will function much the same as the digital controllers mentioned before. Either would allow one to dial in a specific PAR value (using a PAR meter for reference) allowing flexibility in hanging height and more accurate light control.

Last edited by theblondskeleton; 10-03-2012 at 04:07 AM.
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