Do I need a voltage regulator in my LED circuit?

[bheilig]

I'm building an LED grow light, it will have about 30 parallel LED circuits. It is going to be powered by an off-grid 12VDC PV array.

The two key components are the Xantrex C35 Charge Controller and the Powersonic PS-1270 battery. The CC has two charge settings (Bulk and Float), with slightly different voltages (I can set them anywhere from 12.5 to 15.0 - the ideal for my battery is something like 13.4 and 12.5)

Since the loads and the CC are connected in parallel on the battery terminals, my concern is this: depending on the State of Charge on the battery, it seems like my LED circuit voltage could vary by up to 1V, which totally changes the size of the series resistor. To be safe, I could go on the high-resistance side, but I'm worried my lights won't light up under certain conditions.

I know there are products like this
http://www.ledsupply.com/04006-025.php

that would solve the problem, but they're expensive. Would this be overkill? Or does my application require something like the DynaOhm?

Thanks very much for any help,


Bret

 

[daddles]

You don't say what current each LED draws (and that's the important parameter). There are a couple of things to think about -- and resolve by some experimentation. First, when LEDs are run near or at their rated current, changes in the current make only small changes in the optical output. That 1 volt change won't all be seen by the LED because of the series resistor, so it may make little difference in real output (you can get a cheap phototransistor and use it as a light sensor by measuring its voltage with your DMM and make comparative measurements if you control the geometry in a repeatable fashion). It helps to have a DC power supply, although you can make a simple one with an LM317, a wall wart, and a pot.

Second, instead of using those fancy parts, you might consider using a cheap op amp and transistor as a constant current source. Transistors are cheap and you can get quad op amp packages for small change, so it's a technique to consider. This can ensure you drive each of the LEDs with a constant current in spite of voltage variations. It's a method that works very well; the only downside is you'll need a bit of PC board space.

 

[BobK]

I'm building an LED grow light, it will have about 30 parallel LED circuits. It is going to be powered by an off-grid 12VDC PV array.

I can sell you a 100% efficient solar powered grow light at a good price

Bob

 

[(*steve*)]

You know, if this were a common question we might have a sticky thread explaining lots of stuff about LEDs.

 

[bheilig]

@daddles, thank you, I will look into that!

@BobK appreciate it, but the key to the thing is going to be the form factor - it will be 2" wide, 3/4" deep and 4' long, so that it sits perfectly over my mantle, mounted inside a slightly larger steel C-Channel. If you're interested in building to spec, shoot me a note at [email protected].

@Steve, :*P Very sorry! I did a search and somehow managed not to find that. But thank you, it's a great resource.

 

[BobK]

@BobK appreciate it, but the key to the thing is going to be the form factor - it will be 2" wide, 3/4" deep and 4' long, so that it sits perfectly over my mantle, mounted inside a slightly larger steel C-Channel. If you're interested in building to spec, shoot me a note at [email protected].

I was referring to the fact that the sun is a pretty good grow light all by itself.

Bob

 

[bheilig]

Ha haaaa *sigh* I gotta read more carefully