How much RGB LED strip can I switch with 3 MOSFETs?
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How much RGB LED strip can I switch with 3 MOSFETs?

by MRHunter on Thu Jan 17, 2013 10:38 pm

Good evening, Adafruit forums. Please have mercy on my first, likely to be very noobey, post.

The situation is this: I'm in charge of lighting up my girlfriend's Quorra (character from TRON Legacy) suit with a lot of LED strip sections. I've followed the Adafruit Learning System's tutorials on these strips (http://learn.adafruit.com/rgb-led-strips/overview) and I'm using the wiring diagrams and components listed there in my own system. I'm using this diagram specifically:

http://learn.adafruit.com/system/assets ... 1353964350

And I'm using the listed beefy 30A MOSFETs and 30 LED/m RGB strips. By my math, I have just over 3A worth of strip to power in total. I'll be powering the system with 8xAAs kept inside this case (http://adafruit.com/products/875).

I had intended to wire the drain of each LED colour's MOSFET and +12V to its own strip on some stripboard, and power the three sections of the suit (two arms and the torso/leg) in parallel through those strips.

My question is this: any idea if this particular setup will work? If it makes any difference, I'll be using the LED strips at 50% brightness via my Arduino Micro's PWM pins. Thanks in advance, and I'll post diagrams/doodles/whatever's needed as requested.
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Re: How much RGB LED strip can I switch with 3 MOSFETs?

by john444 on Fri Jan 18, 2013 1:28 am

Hi Mr Hunter,

MRHunter wrote:any idea if this particular setup will work?

It sounded ok until you got to this part:
MRHunter wrote:I'll be powering the system with 8xAAs

AA cells do not have much current capacity so they will not last long
supplying 3-A (or even 1.5-A at 50% pwm).

The FETs should be fine. Didn't check your math.
Also, stripboard should not be a problem if it simplifies your wiring.

Would love to see it as it comes along.
Good Luck, John
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Re: How much RGB LED strip can I switch with 3 MOSFETs?

by MRHunter on Fri Jan 18, 2013 10:23 am

Thanks for the quick reply. Yes, I realized that AAs wouldn't give us much running time, but it's the most affordable and portable option we have at the moment. We still have a month before the first convention, so I have time to experiment with other options. Therefore, if anybody has any ideas, I'd love to hear them.
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Re: How much RGB LED strip can I switch with 3 MOSFETs?

by adafruit_support_bill on Fri Jan 18, 2013 10:29 am

Experiment with the PWM levels. The visual perception of brightness is not linear, and you will probably get an acceptable brightness level and increased run-time at considerably less than 50%.
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Re: How much RGB LED strip can I switch with 3 MOSFETs?

by MRHunter on Thu Feb 07, 2013 4:27 pm

Thanks a lot for the help. I will surely post a few pictures of the results when time allows.
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