Welcome back to the Digilent Blog!
As you all have probably noticed, there are two mainstream ways that electronic devices are powered– by plugging its cord into a wall or through the use of batteries. But as our world becomes more mobile (in multiple senses of the word), it makes a lot of sense that a variety of devices are now using batteries as their source of “wireless” power. However, there are still quite a few things out there that need to be plugged into a wall. While this makes sense for large devices like a welding machine, you’ll still find most table top fans need to be plugged into the wall socket. What is preventing this change from happening?
In principle, there really isn’t anything preventing us from physically rewiring the electronic component so that it runs on batteries rather than the (more or less) constant wall power. But that also brings us to the first problem with the battery powered option–it inherently cannot supply a constant source of power. If you’re hoping to use a fan all day because it’s hot or if you need to have constant internet access through your router, the portability with batteries is great…until they die. Certainly, there are rechargeable batteries that can save you money in the long run, but they too end up running out of power eventually.
The other major issue is the energy requirement of whatever device you’re hoping to make more portable. For example, there have been multiple occasions where I have wished that I didn’t need to plug in my desktop monitor so that I can use it. Looking at the power brick adapter for the monitor though, it says that it supplies 14V and up to 2.14A to the monitor. Granted, the maximum current rating is likely higher than what the monitor actually requires to incorporate a safety buffer, but we’ll work with these numbers for the sake of example. If we ran the monitor for one hour, this will end up requiring approximately 108,000 Joules of energy, which sounds like some random number, but bear with me. If we use a set of batteries that add up to 14V and are each rated for 2200 mAh (this means it can supply roughly 2,200 mA or 2.2 A for an hour; it’s not exact, but works for our example) they would add up to about 111,000 Joules of energy, meaning that the set of batteries would theoretically be able to run the monitor for just over one hour before they die and you have to replace them.
If you’re like me though, you’ll find yourself in need of more than an hour of monitor time though. But even if you used a set of Li-Po batteries with a rating of 5000 mAh, this only gets you a bit over 2 hours of using your monitor. Simply put, it’s a lot easier to just plug the monitor into a wall outlet. Not everything needs to draw that much energy though; a wireless router might only require 12V and 1A. A set of AA batteries with a 2200 mAh rating would power it for about 2 hours, and a higher powered battery at 5000 mAh would correspondingly only run it for about 5 hours. This might suit you needs if you are running a wireless demo at a trade show for an afternoon, but you’ll definitely be running against the clock.
Finally, there is a third issue of the fact that batteries have no inherent way of limiting the current draw from the battery itself, much like an open barrel of water has no way of preventing you from siphoning a large amount of water from the open top. To get an understanding of why this is a potential problem (for those of you that don’t know), imagine that the energy stored within a battery is potential energy and once the battery is hooked up to a circuit (a load), electricity starts to flow as kinetic energy. Ideally, this kinetic energy is used up on the attached load which could be a light bulb, a heater, a motor, or anything that needs electricity to run.
However, if there is no load attached to use the kinetic energy, that energy instead has to be released as heat through the internal resistance of the battery or the wire connecting the two ends of the battery. Consequently, if you are drawing a lot of current all at once, there will be a lot of heat released simultaneously within the wire and battery, potentially causing them to melt or (in an extreme situation) explode.
To be fair, I certainly do hope that we get some more battery powered objects that can be easily used out in the wild (that is, not next to a wall outlet) such as a battery powered coffee maker (which exists!) that I could easily use on camping trips to avoid suffering through insta-coffee, even if I do have to recharge it from time to time.