You wouldn’t know it from looking at today’s youth, but it’s actually possible to live without electronic devices. I’m pretty sure that if you ask the average non-prepping teen what their most important survival need is, they’d either tell you their smartphone or their favorite social media platform. Even so, while they might suffer without being permanently plugged into their friends via Facebook and Snapchat, their hearts would keep on pumping blood (although at an elevated rate) and their lungs would continue to take in oxygen.
But while it might be possible to survive without modern electronics, that doesn’t mean that doing so is desirable. While much of the electronics we use fulfill more of an entertainment role than anything else, there are also a wide variety of electronic devices which make life much easier to live. Some things, such as refrigeration and medical devices, can be considered almost critical to survival.
Yet the power grid is the most delicate part of our expansive infrastructure, readily damaged by anything from high winds to much more serious events. While losing power for a few hours due to a severe storm isn’t all that big a deal, losing it for weeks, months or even years is. For this reason, many preppers work on going “off grid” at least to some extent.
Why You Need A Power Bank
All means of off-grid power share one common flaw; they are unreliable. That’s not to say that they won’t produce at least some electricity pretty much every day, but how much electricity they can produce varies. There’s also the problem that they don’t produce any electricity at all when the right conditions aren’t being met.
Solar power only works during the daytime. Even then, rain and snow can seriously reduce your electric power production. Wind power only works when the wind is blowing at least 10mph. Hydroelectric is actually more reliable, but few of us have a river running alongside or through our property that allows us to produce electric power by hydroelectric means.
The solution to this problem of irregularity is to have some means of storing the electric power that is being produced. Then the solar or wind power system can charge that storage bank, allowing the power to stored for when it’s needed later. Hence, we have the need for a power bank.
Basics Of Power Bank Design
Most off-grid power systems are designed to work in conjunction with a 12-volt battery bank. In practical terms, this means they need to generate more than 12 volts of DC power, so that they can charge the batteries. Once the power provided drops below the nominal voltage of the batteries, they no longer charge. Solar panels, for example, typically produce a nominal 18 volts, helping to ensure that they are providing more than 12 volts to charge the batteries.
Twelve volts is a convenient voltage, because the most common, least expensive, high capacity, rechargeable battery systems are 12-volt lead-acid batteries, such as those used in cars. While there are other, more efficient, higher capacity batteries around, such as Lithium-Ion, they are also considerably more expensive.
What this means for you and I is that we can use used car batteries as the basis for building a battery bank. Any car batteries will work, regardless of size, and mixed sizes of car, boat and motorcycle batteries can be used together in the same system. As long as they’re 12-volt, they’ll get along just fine.
Related:The Battery That Can Power Your Home Completely Off The Grid
Battery Connection Theory
All batteries are direct-current (DC) devices, which means that they have a positive and a negative pole or connection. Electricity flows out from the battery at the negative pole and back into the battery at the positive pole.
Connecting two batteries together in series, with the positive pole of one battery connected to the negative pole of the other, allows the voltage of the batteries to be added. So two 12 volt car batteries connected together in series will produce 24 volts. Connecting three together will provide 36 volts, and each successive battery will add another 12 volts.
The other way we can connect these batteries together is in parallel, connecting all the positive terminals together and all the negative terminals together. In this case the voltage will stay the same, but the amount of current the batteries can provide is added together. So, if one car battery is able to provide 200 amps of power, then two identical ones in parallel would be able to provide 400 amps.
There is a limiting factor on the amount of power batteries can provide, besides the batteries themselves; that’s the size of the wire used. For example, to carry 100 amps of power you need 4-gauge wire. If you don’t have wire that big, and try to pass that much current through it, the wire will heat up and eventually act as a fuse, burning out. How quickly it does that will depend on how big the wire is.
However, there are very few needs for which you should have that sort of problem. While a battery might provide 200 amps of power storage, you will usually only be drawing off a few amps of power at any one time. The one place where you might have need of big wire is between the wire and the voltage inverter, but I’m getting ahead of myself.
Hooking Up The Survival Battery Bank
You can use whatever new or used car batteries you can find for a battery bank. Since we are going to connect them together in parallel it will be possible to connect additional batteries later, adding to the system. The only thing you want to do is to make sure that the batteries are still good, as a bad battery can short out the system, causing wires to burn.
I’d like to note here that deep cycle batteries, sometimes called marine/RV batteries, are usually used for these sorts of systems. The reason for this is that they are not as easily damaged by what is known as “deep cycling.” This is where the battery is discharged more than 50 percent. However, normal car batteries can also be used. The only potential problem is that they might not last as long. However, this gives you the opportunity to make it out of used car batteries, saving a considerable amount of money.
Please note that your car batteries will not be damaged if you avoid deep cycling; they will only be damaged if you discharge them beyond the 50% threshold.
There are two other components you need to go with your batteries and the wire; they are a charger and a voltage inverter.
The Charger
You will need some sort of battery charger to top off your car batteries. What kind you use will depend on the power source that you want. If you are using the survival battery bank alone, without any sort of off-grid power, you can use a normal automotive battery charger, which gets its power from your home’s electrical outlets.
The other option is to tie your survival battery bank in with solar panels or a wind turbine. This gives you the capability of producing and storing power during an emergency. In this case, you’ll need a power charger that accepts a 12 – 24-volt DC input, rather than the 120-volt AC input a regular car battery charger uses. This is called a “solar charge controller.”
The Voltage Inverter
The output of your survival battery bank is going to be 12 volts DC. You could connect any automotive charger to this, for charging cell phones and other small electronics. But if you want to use to power small home appliances, your refrigerator or electric power tools, you’ll need to boost the voltage to 120 volts AC. This is done through a voltage inverter.
The voltage inverter will come with cables to attach it to the batteries. These are large, because the way that the voltage inverter boosts the voltage to ten times what it originally is, is to use ten times the amount of current. In other words, if you are connecting something that draws 5 amps, like a refrigerator, the voltage inverter will need to draw 50 amps from the batteries. Therefore, it would be a good idea to use the same size wire for the jumpers between the batteries.
One important note about voltage inverters: They are rated for both continuous output and peak output. Some manufacturers will advertise the peak output, rather than the continuous. Be sure to buy one where the continuous output is more than you need, as it can only operate a few minutes at a time at peak without causing damage.
The finished system will look something like this:
Connecting It All Together
The entire system is connected together in parallel. That means the positive output of the solar charge controller is connected to the positive terminals on the batteries and the positive lead entering into the voltage inverter. Likewise, all the negative leads are connected together.
To make this easier, I manufactured two terminal strips out of ½” square copper bar stock. All this required was drilling and tapping ¼”-20 holes every ½ inch through the length of the bar stock (6” long) and then mounting it to a plastic base for insulation (the base is white). I have two strips, as shown in the picture above; one marked in red for positive connections and the other marked in black for negative connections.
System Capacity
An important thing to consider is how much power you will actually use in an emergency. The only way to determine that is by looking at how much power your “critical” electronics draw. Don’t think you can power your whole house from this sort of system, unless you’re going to build a huge one. Rather, only plan on providing power for the electronics you will need the most, such as your refrigerator, some lighting and any medical devices your family needs.
There are two parts of the system’s capacity that you need to consider; the battery capacity and the charging capacity. In both cases we can generally say, “the more the better.” Your battery capacity will determine how much power you can use before your batteries go dead.
Related:How To Set Up Your BlackOut Kit
Battery Capacity
Automotive batteries are rated in “reserve current.” This number refers to how much power they store. Multiply the reserve current by .4167 to find out the Amp-hours, which is the specification used for other types of batteries. One amp-hour is one amp of power for one hour. So, if we go back to our refrigerator example, which drew 5 amps, running it for one hour equals 5 amp hours of power.
Keep in mind that to provide one amp-hour of power, the voltage inverter must draw 50 amp-hours of power from the batteries. So, a single 200 amp-hour battery will only run that refrigerator for two hours, before hitting the 50% charge level.
Charging Capacity
The charging capacity of the system is the capacity of the solar panels, wind turbine or other power source you are using, as well as the maximum capacity of the charger. If you are using a typical automotive battery charger that plugs into house current, this would likely be six amps. So to get that 50 amp-hours of power into the battery would require 8.33 hours.
By comparison, most solar panels are in the 80 to 100 watt range. But how do we convert that to amps, so that we can make a real comparison? To convert from watts to amps, divide by volts, which in this case, is 12 volts. So an 80 watt solar panel produces 6.67 amps of power, just a bit more than that automotive battery charger.
What this means is that in order to run anything major, such as your refrigerator, you’ll need more than just one solar panel; you’ll need several. If all you’re going to do is charge phones and other small devices, one panel will probably do. But the more you want to do, the more panels you’ll need to have, in order to keep your batteries charged.
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