Color mixing with buck pucks

[Zephos]

Hey there everyone,

I'm working on my first build, and I'm using an Arduino.

I want to use a Cree RGB High Powered LED, but I have some questions.

First, is there a way to run the LEDs in series and still be able to mix the colors (dim them independently, using pwm)? I'm afraid that running them in parallel would drain the battery way to fast because it pretty much triples the amount of current being drawn. Or, is there a way to run them in parallel and still have a decent battery life? If I do parallel, I would use some buckpucks I found that let me use pwm logic to dim the leds, as well as a 5v output that I can use to power the arduino. Is there a better way?

Also, the leds are rated to run at 1000mAh max. Is it bad to puch them all the way to the max, or is that the only way to get them to their maximum brightness? I ask because if I ran them at a lower current I could save battery life.

Thanks.

[Silver Serpent]

If you wish to dim the LEDs independently, you must wire them parallel. In practice, you're only likely to double the current required, since powering all three R/G/B dice will just give you white. Most times you're only mixing two dice at a time.

The LEDs can be run at a lower current than 1000mA. I believe they'll light up as low as 350mA or so.

[Sevinzol]

depending on your design, I think you will be short of space. an arduino and 2-3 buck pucks will take up a lot of room

[Zephos]

That is one of my concerns. I'm wondering if there is a way to use only one buck puck for constant current, and then dim each led independently using mosfets instead, since they are a tad bit smaller. It's starting to look like color mixing comes with a significant price though, with the extra space and power requirements. Oh, and I'm using an arduino mini variant so its pretty condensed, and the sound board I'm using is really small too. Hopefully that will help.

[Forgetful Jedi Knight]

That is one of my concerns. I'm wondering if there is a way to use only one buck puck for constant current, and then dim each led independently using mosfets instead, since they are a tad bit smaller. It's starting to look like color mixing some with a significant price though, with the extra space and power requirements. Oh, and I'm using an arduino mini variant so its pretty condenses, and the sound board I'm using is really small too. Hopefully that will hlep.

Probably not, mostly because they blade will be exceptionally dim. This sounds like another case of "Use the right tools for the job" to me.

[Obi1]

Why buckpucks? If you have a PWM capable arduino board, all you need is a mosfet afterwards (preferably n-channel) and you can do the dim. Just make sure it has a Vgs threshold somewhere in the middle of the 5V range. As I'm also working on an arduino Project right now I can tell you for sure that it works perfectly.

As to powering an arduino, most of them come with a 5V regulator and an external supply Input which can be connected to a higher voltage source, like 7.4V (2x18650 used frequently for sabers, ut you can even go higher).

[Zephos]

I was told by someone that Mosfets put off a lot of heat and are inefficient compared to buckpucks, and that LEDs require a constant current to work well and not get damaged by voltage/ current variations. Mosfets can't limit the current that goes through them. Am I wrong?

[Obi1]

You are not wrong. That someone who told you so was wrong

It's the sole purpose of MOSFETs to control current via voltage to put it simple. LEDs will definitely not get destroyed by MOSFETs, if you know how to use them. To put it simply: if the MOSFET is fully open, it acts like a low resistance wire. Then your LED will see the full battery voltage. If that is dangerous in your application, use still resistances to limit the current. But MOSFETs are also good for that. By changing the gate voltage using PWM, you can control the current flowing through your LED (limit them if you like).
BTW, all the Plecter Lab products use MOSFETs for LED drive, incl. the power extenders. When Erv "talks" about drive settings in his Manuals (to be used with caution), he means exactly what I described above.