When it comes to powering your Ultimate Tesla Electrical Thingorama, you’ve really only got one choice, since you don’t want to be tied to an electrical outlet:
Batteries.
Batteries are DC (Direct Current) versus AC (Alternating Current) — AC is what the power company delivers to your house. A dirty little secret is almost everything that isn’t a motor actually runs on DC, and has a small “rectifier” that converts that AC to DC…those are all those “wall warts” that things plug into…and it’s really pretty inefficient. But let’s leave off the rant for now.
Electrical power consists of two power parts: voltage and current. This article explains it pretty well: “Electricity flowing through a wire is like water flowing through a garden hose. The amount of water that can fit through the hose depends on the diameter of the hose (amps). The pressure of the water depends on how far open the faucet is (volts).”
A sidenote…The original Arduino is designed to run off 5v of power or greater. This is conveniently what you get from your computer’s USB port or a set of 4 conventional AA/AAA batteries, or even a 9v battery (but see below for my opinion on 9v batteries.) Newer Arduino versions, like those I covered last time in”But the Arduino is too big!” often come in 2 versions: a 5v version and a 3v (really 3.3v, but you can ignore that) version. When in doubt, go for the 3v version but make sure everything you do is 3v compatible…this is mostly a problem if you’re running motors or servos, which often need more current.
So. Batteries. You really have 2 types to choose from: disposable or rechargeable.
Disposable batteries are often called alkaline batteries because of their chemistry, but you can have other types as well. They’re the normal AA and 9v batteries you’re used to. Use them until they’re empty and toss them. The plus sides are they’re available everywhere, cheap, and come in standard sizes and currents. The A series (mostly commonly seen as AA and AAA) provide 1.5v of current each, and contain 1800-2600 MaH (milliamp hours) of power. But the sizes are the downside: if you can’t fit the batteries in your project you’ll be SOL, and for most of the cool projects we’re looking at you’ll need at least a pair (2×1.5v = 3v, close enough to our needs of 3.3v.) Personally, if you have the room, this is the place to start, and it’s what I’ve been using. My Tesla Cane runs on 3 AAA disposable batteries. A side note, the extremely common CR2032 “coin cell” battery is a disposable 3v battery, and they’re pretty small. They work well for 1-2 LEDs, but you can’t really run an Arduino from them…not enough amperage.
Here’s that note about 9v batteries: I hate them. Really, I know some makers like them, but they really suck. 9v is quite often far more power than you really need, and the 9v battery has horrible amperage…565 mAh versus the 2000+ of a AA. If you can fit a 9v battery in, you can probably fit in a pair of AAs instead. You’ll have 3v instead of 9v, but around 4 times the lifespan!
Rechargeable batteries, often called NiCad (Nickel Cadmium), NiMH (Nickel Metal Hydride), or various forms of Lithium such as LiPo (Lithium Polymer) and Li-Ion (Lithium Ion). They happen to come in the same standard physical sizes are the disposables, so we’re quite likely to find the AA and AAA sizes. Due to the nature of the more traditional nickel rechargeables, they are really 1.2v each instead of 1.5v, so you’ll likely need 3 AAs (1.2vx3=3.6v) to run your project with rechargeables instead of 2 disposables. But…they’re better for the environment and cheaper in the long run, as you only buy them once and recharge them using a charger from regular AC power. The NiCad variety contain notoriously less amperage than their alkaline cousins (possibly half!) but the newer NiMH ones are much better, and can actually contain slightly more amps. You also have the same downside as disposables…the standard shape and size, and also now have to carry a charger. There is also an issue of the rechargeables losing power if they just sit around. I use rechargeables around the house, but not in props.
The newest battery technology to hit the maker community is the availability of low-priced LiPo (Lithium Polymer) rechargeable batteries. LiPo batteries run at 3.7v, which makes them ideal for our needs of 3.3v or higher. Remember that the newer specialty Arduinos I’ve mentioned from Adafruit and Sparkfun have a 3.3v version? You’ll need a pair of disposable AAs (1.5vx2=3v) or three rechargeable AAs (1.2vx3=3.6v) to power those…but only one LiPo battery! They also come in much smaller sizes, so they are a great choice all around! The LiIon versions tend come in round(ish) shapes and the LiIon versions tend to come in flat shapes. My suggestion is to figure out how much power you need for how long, add a bit, and try one out! They do have some downsides that you need to be aware of! Lithium is nasty stuff, and if treated poorly these batteries tend to catch on fire or even explode. No, I’m not kidding. Do your homework about these first!
Start with Adafruit’s excellent tutorial on LiPo batteries here — in short, only buy batteries from known sources (Adafruit) and use only known chargers (again, from Adafruit). The good news is that the tiny USB charger Adafruit sells (it’s adorable!) is $6, so you can leave them in devices and just plug in a USB extender cable (from a computer or cell phone charger) to charge your device!
Go to Adafruit and search for LiPo batteries…they carry a lot, and they aren’t bad in price ($8-$30 depending on amperage). I’m going to be moving to Lithium batteries for most of my stuff.
I hope these are helpful, and keep making!