Cautionary Tales of Power
Posted: November 27, 2015 Filed under: Coding, Creations, DIY, Explorations, Getting A Clue, How-to, Pearls of Folksy Wisdom, So that didn't work | Tags: arduino, blinky, DIY, fastled, fire, glow, glowy, LED, LEDs, light, power
When doing an LED electronics project, there seem to be three big “P”s that have to be tackled:
1. Pixels (which ones, how many, what configuration?),
2. Programming (what do I want, and how can I do that?), and
3. Power (how much, from where, and how do I distribute it?)
And people (by which I mean: perpetual newbies like me) tend to do them in that order: first wire up some pixels, then program them, then figure out how to power it all for real.
And of course, this often leads to a problem where you get stuck between steps 2 and 3, where you have your creation sort of up and running on the lab bench — but now there’s this little problem of how to power it, and you have to go back and rethink and rework other parts of the project to accommodate the power situation. So it’s worth planning for power from the start — which is easy to say, but hard to do!
What could possibly go wrong? (A list)
So what happens if you don’t plan for power? Well, here are some power problems that I have personally had. How many of these can you diagnose just from the description? (“Failure to plan” is a nice catch-all phrase here if you get stuck.)
- Hrm, now how do I get power all the way up there?
- Gee, that’s a long run of wire… but if I use fat wire, it’ll be expensive and heavy and cumbersome. Nah…
- I’ll use skinny wire, it’s much cheaper… Hey, why is it only reading 4v at the far end? And does anyone smell something burning?
- OK, I switched to thicker wire, and I’ll just re-use the power connectors from before. Holy cow now the connectors are getting hot!
- Fine, I’ll switch to these big thick nonpolarized connectors. Huh, that’s odd, it’s not working now. Does anyone smell something burning?
- For this other wearable project, I’ll use a simple battery holder and regular alkaline batteries… hey… why are the colors so ‘warm’.. no blue? And now no green, too…
- OK, switching power to one of those ’emergency phone chargers’ that takes AAs and puts out 5v from a USB socket. Hey! Why are the batteries dying so fast?
- OK, fine, I’ll switch to this lithium battery pack… hey, it said 5000mAh… so why did it stop powering my 5000ma project after only half an hour?
- How come my WS2811 project works fine from my computer, but then flickers like crazy when I power it from this cheap USB wall power adapter?
- For this big outdoor project, I’ll use this big, burly 12V lead-acid marine battery. Hey… how come it won’t hold a full charge after the first time I let the lights go all night?
- Everything was working fine yesterday, before last night’s rain!
- Everything was working fine yesterday in the cold and snow, so it should be working fine today now that it’s warming up, right?!
- I think I’m going to switch microcontrollers. The old one had a power regulator that could handle 12v input. Hey… do you smell something burning?
- Why is this power switch getting hot now? And why is it now totally stuck in the “on” position? And … do you smell something burning… again?
So: Plan For Power.
The lesson to learn here is that for basically any real project, calculate and plan the power first. Before you wire up any pixels. Before you write any code. Just stop for a minute and think about how much power you’re going to need, and where it has to come from, and where it has to go.
Use on-line calculators that will help you figure out how much power you’re going to need, and what gauge wire you’ll have to use given how long your cable runs are going to be. I also really like the “LEDstimator” app for iOS to help explore some “what-if” values for things like wire gauge. https://itunes.apple.com/us/app/ledstimator/id945794010?mt=8
And above all else… uh… wait… do you smell something burning?