LED Drivers

[jbdreefs]

Another DIY LED project is upon me. While I BS'ed my way through the last one, I'm knowledgeable enough this time to ask questions that may have an impact on the performance of my fixture.

I'm trying to understand how the drivers power LED's. When looking at drivers, many of them are rated with a range for volts and amperage. For example the Mean Well ELN-60-27D is rated as such:

0 ~ 2.3A current range
13.5-27V DC Voltage

Which of these values is adjusted when we dim our LEDs. I realized that the drivers are "constant current". Is it a change in voltage that dims the LEDs?

If so, I would suspect that a driver with a wider range in voltage output would give me more control over the brightness of the fixture.

Can anyone help me understand this process?

 

[johniii]

JBDreefs;802624 wrote: Another DIY LED project is upon me. While I BS'ed my way through the last one, I'm knowledgeable enough this time to ask questions that may have an impact on the performance of my fixture.

I'm trying to understand how the drivers power LED's. When looking at drivers, many of them are rated with a range for volts and amperage. For example the Mean Well ELN-60-27D is rated as such:

0 ~ 2.3A current range
13.5-27V DC Voltage

Which of these values is adjusted when we dim our LEDs. I realized that the drivers are "constant current". Is it a change in voltage that dims the LEDs?

If so, I would suspect that a driver with a wider range in voltage output would give me more control over the brightness of the fixture.

Can anyone help me understand this process?

Dimming will drop the voltage. The amperage will drop because voltage is dropped.

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[johniii]

And most meanwells have a pot internally that controls the voltage output. This allows you to be able to run different chip configurations.

The dimming circuit will still dim your setting down to 10% or so. Some drivers can output 1% of the set voltage.

In a series circuit the voltage is dropped. So if you know the resistance you can figure out the actual output voltage.


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[jbdreefs]

JohnIII;802655 wrote: Dimming will drop the voltage. The amperage will drop because voltage is dropped.

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So what does it mean when they say "constant current". This is very conusing to learn that the current fluctuates also.

 

[rdnelson]

JohnIII;802655 wrote: Dimming will drop the voltage. The amperage will drop because voltage is dropped.

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Not according to Ohm's Law. E(volts) times I (amps) = Watts. Therefore, since the wattage of the LED does not change, if volts are decreased amps will increase.

 

[johniii]

http://en.m.wikipedia.org/wiki/Constant_current">http://en.m.wikipedia.org/wiki/Constant_current</a>

Easier this way.


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[johniii]

rdnelson99;802664 wrote: Not according to Ohm's Law. E(volts) times I (amps) = Watts. Therefore, since the wattage of the LED does not change, if volts are decreased amps will increase.

My bad got it backwards.

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[rdnelson]

Easy to do. I can run the calculations without thinking when I am designing a project but this is the second time someone has posted simalarly and both times I had to pull out my "Ugll's" book that has Ohm's law on the cover. Just to be sure. LOL

 

[johniii]

But the wattage does change with the voltage. Resistance on the other hand does not. So if I=E/R then if the voltage drops but resistance stays the same then current will drop.
That's why people say 3watt LEDs ran at 2watts for longevity.

But I will agree if you have the same watts the amps go down while voltage increase. Ie a 1hp motor on 208 will pull more amps than a 1 hp motor on 460.

But that is not the case here. Wattage of a led chip is just a calculation of volts to milliamps.

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[jbdreefs]

So regardless of how high or low a 3w led is dimmed, it will still consume 3 watts?

I'm still missing the understanding of how we use constant current drivers but the current fluctuates. Is it better to think of it as constant wattage?

Edit:

JohnIII;802680 wrote: But the wattage does change with the voltage. Resistance on the other hand does not. So if I=E/R then if the voltage drops but resistance stays the same then current will drop.
That's why people say 3watt LEDs ran at 2watts for longevity.

But I will agree if you have the same watts the amps go down while voltage increase. Ie a 1hp motor on 208 will pull more amps than a 1 hp motor on 460.

But that is not the case here. Wattage of a led chip is just a calculation of volts to milliamps.

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I think this helps and makes sense to me. Thanks!

 

[rdnelson]

I believe this will answer your questions. I did not read every word but skimmed it.

 

[johniii]

rdnelson99;802705 wrote: I believe this will answer your questions. I did not read every word but skimmed it.

http://www.digikey.com/us/en/techzone/lighting/resources/articles/how-to-dim-an-led.html">http://www.digikey.com/us/en/techzone/lighting/resources/articles/how-to-dim-an-led.html</a>[/QUOTE]

All this led stuff giv

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[johniii]

All this led stuff makes my head hurt.
Which us why I bought kessils

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[rdnelson]

JohnIII;802710 wrote: All this led stuff makes my head hurt.
Which us why I bought kessils

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LOL Lately, it has made my backside hurt. LOL

 

[coolsurf]

If your going to be in the market for drivers, Steve's LED's are some of the best I have found and are very small. He sells singles all the way up to quads and they are dimmable.

 

[jbdreefs]

coolsurf;802833 wrote: If your going to be in the market for drivers, Steve's LED's are some of the best I have found and are very small. He sells singles all the way up to quads and they are dimmable.

Thanks for the tip. I'll check it out.

 

[bruce 1]

What kind of drivers are you looking for? I might have a place to get them from.

 

[jbdreefs]

Not entirely sure which direction I'm going with the Leds so it's hard to specify a driver at this point. I know that they will need to be controlled by a 0-10v source. I'm toying with using the 50w chips but i'm scared the spot lighting will be too much for my liking. Trying to find examples in use to to see.

I was talking to a guy in Canton but I accidentally deleted his pm with contact info. If you see this, please reach out to me again.