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28vdc
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28vdc

by zburhop on Fri Aug 11, 2017 8:18 pm

I have a segment of 12 vdc RGB STRIP. I need to have this run off of 28 VDC. Whats the easiest way to do this?
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Re: 28vdc

by adafruit_support_mike on Sat Aug 12, 2017 1:37 am

Use a 12v voltage regulator.

LED strips tend to use a lot of current, so you'll get the best results from a switching regulator. Linear regulators like the LM7812 burn off extra voltage as heat, so from 28v an LM7812 would generate more heat than the entire LED strip. Switching regulators use PWM, which generates a lot less heat.

We don't carry anything that works for those voltages, but check over at Pololu:

https://www.pololu.com/category/131/ste ... regulators

They focus on robotics, and have boards for a wider range of power levels and voltages than we do.

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Re: 28vdc

by zburhop on Sat Aug 12, 2017 3:50 am

Hi,
Thanks for the reply. My use is very space scarce. I'm running only 1 segment consisting of 3 leds. Is there another option for such small load other then bulky boards?

Thanks again for your help,
Zach
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Re: 28vdc

by zener on Sat Aug 12, 2017 7:54 pm

How much current do you need?

This one does an amp and is about the size of a nickel:

https://www.pololu.com/product/2834

I don't know what would be any smaller than that.

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Re: 28vdc

by zburhop on Sat Aug 12, 2017 9:03 pm

Your right! I dident see that guy! I think I have just enough room for it. My problem was that everything im running is 28vdc but I just wanted some cool lighting so that's the only thing I'm powering with it.
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Re: 28vdc

by zburhop on Sat Aug 12, 2017 9:05 pm

One more question. Anyone know how much heat I can expect. It's housed entirely in a 3D printed housing with no ventilation.
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Re: 28vdc

by pdh on Sat Aug 12, 2017 10:14 pm

Quoth the Pololu page: "During normal operation, this product can get hot enough to burn you." Although they also say its efficiency is 80% or better, so it may be that with low loads the heat wouldn't be quite so bad.

Do you know how much power you'll be drawing? If you assume the worst (80% efficiency) that would imply 1 watt of power dissipated as heat for every 4 watts that your load draws.
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Re: 28vdc

by zburhop on Sat Aug 12, 2017 10:53 pm

Their wording sucks lol. Hot enough to burn you is relative. I'm drawing in the neighborhood of 60ma at worst 180ma. I ordered one. We will see.
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Re: 28vdc

by pdh on Sun Aug 13, 2017 9:54 am

Well, they do say it "can" burn you, not that it "will" burn you :-)
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Re: 28vdc

by adafruit_support_bill on Sun Aug 13, 2017 10:09 am

They don't specify whether they mean 1st, 2nd or 3rd degree burns. But it is no unusual for surface temperatures on high-current switching ICs to reach 100C or more. The Sizzle Test* is one common method of checking whether a chip is approaching maximum operating temperature.

*Lick a finger and quickly touch the surface of the chip. If it doesn't sizzle as the moisture on the tip of your finger boils away, you are not close to overheating.

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Re: 28vdc

by zener on Sun Aug 13, 2017 12:56 pm

If you are using less than 20% of the regulator capacity then I would not expect it to get too hot.

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Re: 28vdc

by zburhop on Tue Aug 22, 2017 6:47 am

FYI its produces almost no heat. Pretty great design.
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