Specing a Buck Converter for a 400 LED Jacket - Page 1
Forum section: electronics / beginners

author: Mauronic
author_rank: Newbie
timestamp: August 17, 2015, 02:45:43 am
content: Hey Guys -I was wondering if you could help me pick the right buck converter for my project.I am making an animated LED jacket using a string of AS102 LEDs and a Hero Robotics Pixel Pusher. It is being powered by a 5000 mAh 2S LiPo.The manufacturer told me at each string of 50 LEDs (5v) would draw 3 Amps totally 24 Amps for my design. Before learning this, I hooked up a 3A buck for a 200 LED test and lets just say the buck rose to a temp of 150F when displaying "pure white". It ran much cooler when doing animations - 115F.Anyhow, the "biggest" buck converter I can find on eBay is this one:http://www.ebay.com/itm/161467615110which is rated for 12A and 300 Watts. It appears to fall short on the Amp rating but if I just looked at watts it appears to be fine. I am obviously a noob here so I am ultimately looking for some advice on how to best deal with my power requirements.Is this buck way too underrated? If I use an underrated buck will it even matter since it only heats up when showing a pure white? (This jacket will be animating in colors most of the time). Do I need to split my LED strings in 2 and use 2 bucks?Happy to post pics.thanks!pete

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 17, 2015, 09:45:39 am
content: yes post pics, vids in factYou can get away with small in two ways, one is to use patterns that never go over the total power that the power supply can handle. The other is a few big capacitors to let you do flashes here and there in the patterns. Unless you want it all to go crazy at the same time, small is ok.You might work out a second circuit too, where all the led strings have a diode running into them from a second supply, which is just a bunch of batteries with the exact voltage needed to run everything. So it would have like a go-crazy button that skips most of the cct.Oh, and Ni-cads will handle the pain in flashes no problem, they have really good current surges and are so cheap.

author: DavidMenting
author_rank: Contributor
timestamp: August 17, 2015, 01:25:14 pm
content: Try using multiple buck controllers close to the point of load (the leds in this case). That way, you're not only able to use small and cheap buck controllers, but you're also distributing the temperature rise.Also, your cable losses due to restistance of the supply wires will be smaller. Because you will be distributing 7.4V as opposed to 5V the current running through the cable will be about a third lower meaning you have a smaller voltage drop in the cables or you can switch to a smaller cable diameter.To reduce consumption even more you could lower the voltage of the LED strips. They are stated to work at 5V but in my experience they work just as well at under 4V without loss of brightness.

author: Starlord
author_rank: Frequent Contributor
timestamp: August 17, 2015, 02:27:56 pm
content: You could reduce the current draw by not running the LEDs at maximum brightness. You'd be hard pressed to notice the difference between an LED driven by 10mA and one driven by 20mA, and even 5mA can be more than enough for a super bright blue or white LED to make it appear bright. Plus your battery pack would last longer.Half the current does not equal half the brightness; the way your eyes work means it's more of an exponential curve. When I animate LEDs I set the brightness with a floating point value between 0 and 1, and I square that value before multiplying by 255 or 1023 or whatever is needed for the LED controller bit depth. So if I want it half as bright I pass 0.5, which becomes 0.25, so half brightness for a 20mA LED is actually 5mA not 10mA.

author: Mauronic
author_rank: Newbie
timestamp: August 20, 2015, 04:36:13 am
content: Hey Guys -Sorry about the delayed response, I had to travel on business for a couple of days.Multiple buck controllers could be a good idea.So the manufacturer said a strip of 50 LEDs at full brightness would draw 3A at 5V.Now here are some pictures of my powering 200 LEDs. Notice the color changes - perhaps a voltage issue.I also measured the load with a power meter inbewtween the 7.6V battery and the Buck input. It was 3.3A. That doesn't make sense, could it be that the buck is limiting the amp draw? I read everything I could about bucks but the information was either overly simplistic or overly technical so I am having some problems understanding the behavior.

author: Mauronic
author_rank: Newbie
timestamp: August 20, 2015, 04:37:37 am
content: And the other 2...(That last picture are me and my buddy's "V1" jackets from 2013 - single color, no animations)

author: eilize
author_rank: Contributor
timestamp: August 20, 2015, 11:08:10 am
content: Quotethe buck is a stepdown voltage but a step up current