Of the many things that we use every day, electrical power has become one of the most important. Just about everything we do relies on electric power in one way or other; sometimes in ways we don’t even realize.
Yet our electric power grid is the most fragile part of our infrastructure. All it takes is a good storm to knock out our power. Sometimes they get it fixed in a couple of hours, other times it can take them days. The question then becomes – what do we do for power in the meantime?
The standard answer to that question in the prepping community is to turn to solar power. That’s great, if you can do it. Solar is cheap and abundant, if you don’t live somewhere like Seattle, Washington, where it rains something like 156 days per year. Of course, the idea of it being cheap doesn’t include the cost of the solar panels themselves, which can be quite costly.
Gasoline generators are a good alternative for the short-term; but cost a lot to operate if you’re going to need them running for days or weeks. Besides that, you’ll likely run out of gasoline if the power stays out for more than a day or two.
This isn’t to say that we shouldn’t use solar panels or gasoline generators. With all our needs for electricity, it makes sense to use every means for producing electricity we can find.
One such source that’s right in our homes is our telephone connection.
Before cell phones and wireless home phones, the older rotary dial and pushbutton phones didn’t need any electrical power connection. That’s because the power to operate those phones came in over the phone lines.
Phone companies have the capability of producing their own electrical power from generators, although they might use power from the electric company for normal operations, saving their generators for emergency use. They are required by regulation to have those generators in place, along with several days of reserve fuel for the generators.
So, even if the power is out in the entire region, home phones will work from the power supplied by the phone company. More importantly, for our purposes, that power is available for other uses, like charging our cell phones, if we know how to tap into it.
I’m not talking about a lot of power here. You’re not going to be able to run your refrigerator off the electricity that’s coming through your phone lines. The wires aren’t big enough to carry that much current and the voltage isn’t right for running a refrigerator anyway.
Just How Much Power Is Available?
Before talking about how to access the power available in our phone lines, we need to understand just how much power we’re talking about.
The phone company keeps electricity flowing through the phone lines, even when they’re not in use. This current is rated at 48 volts DC, but is not tightly regulated, so can run as high as 60 volts DC.
This voltage is the “carrier voltage,” intended to provide power to telephones connected to the line.
It will drop to somewhere between 6 and 12 volts when in use.
When the phone rings, the voltage can jump to over 100 volts.
Under the wrong circumstances, this is enough that it can be lethal. Therefore, take care not to touch both bare wires at the same time.
For those who are unfamiliar with the term DC, it refers to “direct current,” where electricity flows in only one direction. It’s the type of electric current found in most portable devices, especially anything that runs off of batteries, whether they are rechargeable batteries or alkaline ones.
The other type of voltage is AC, which stands for alternating current. This is what’s in your home’s electrical outlets and is different than DC in that the current flows back and forth, rather than in just one direction.
The importance of that, for our discussion, is that devices which are designed to run on DC current won’t work on AC current and those which are designed to run on AC current won’t work on DC current. So, we can only use the current coming through the phone lines for devices that require DC current.
Phone wire is either 22 or 24 gauge. For most newer homes and systems, 24 gauge is used. That size wire can only carry a maximum of 0.577 amps of electricity.
That’s not enough to run appliances, even small ones, but it is enough to charge handheld electronics. You should be able to pull 75mA (milliamps, or thousandths of an amp) at 5 VDC (volts, direct current), which is enough to charge a smartphone.
Before going any further, you’ll want to check and ensure that your phone lines are live and actually have power running through them.
This will require the use of a multimeter. Remove the wall plate to access the wires and strip off a bit of the insulation from both the red and green wires.
It is best to do this in staggard locations, so that the two bare spots can’t touch one another accidentally.
Connect the two leads of the multimeter to the two bare wires, measuring the actual voltage running through your lines. Anything from 48 VDC to 60 VDC is acceptable.
Hooking Up a Voltage Regulator
Today’s portable electronics all charge off of 5 volts DC. That’s the voltage available at a USB port and the chargers are pretty much all designed to plug into a USB port, whether that be installed in a computer or in a charger.
So, we need to reduce the voltage from the phone wires to 5 volts DC, regulating it so that we will get a consistent output voltage. This is actually very easy to do, using a one chip regulator, the 7805. I’m not sure if you can still get these from Radio Shack, but I found them available on Amazon.com.
The 7805 makes for a one-piece voltage-regulator circuit.
It is intended for a much lower input voltage than what we are going to receive from the phone line.
However, it can handle the voltage that the phone line will provide, especially at the current we will be drawing.
The three terminals on the 7805 are numbered, as shown in the diagram.
Besides the 7805, you’ll need input and output connectors. For the input, a standard modular phone line will work. You probably have one sitting in a box of cords that came with your computers and other electronics. Cut off one plug to expose the red and green wires. These will be connected to the appropriate terminals as shown in the schematic diagram below.
For the output side of the circuit, a USB panel mount socket will be needed. Those are a little harder to come by, as they are typically mounted to circuit boards. If you have an old computer board with a USB socket mounted to it and a soldering iron, one can be scavenged. Those sockets can be purchased, but are a little hard to find. Even so, I managed to find a package of them on Amazon.com.
Notice in the diagram above that the wire leaving pin 2 of the 7805 connects in a “T” to wires that lead both to the input and output. The easier way to do this is to connect both input and output wires directly to pin 2 of the 7805. Be sure to solder all connections securely, so that they have good electrical and mechanical connection.
Plug the modular phone plug into a phone outlet in your home and connect the charger cord for your phone to the USB connector at the other end of the circuit. Verify to see that your phone is charging.
An Alternate Connection
As I was writing the above, it occurred to me that there are panel mount USB connectors, designed to mount into the dashboard of a vehicle. While designed to run off of 12 volts DC, they are essentially the same thing as what we’ve done with the 7805, albeit a bit more expensive.
The big advantage with them is that they have the USB socket already connected. All that would be required would be to cut the plug off of a phone extension line and connect the wires: red to red and green to black. When plugged into a telephone jack, a USB cable connected from the panel mount USB to your phone should charge your phone.
For Other Voltages
While most things that we might need to power off of our phone jack will be 5-volt, there’s a possibility that you might need to power some other voltage. The same series of voltage regulators that the 7805 comes from, also includes regulators for a variety of other voltages, specifically:
- LM7805 regulator – 5 volts DC
- LM7806 regulator – 6 volts DC
- LM7808 regulator – 8 volts DC
- LM7809 regulator – 9 volts DC
- LM7810 regulator – 10 volts DC
- LM7812 regulator – 12 volts DC
- LM7815 regulator – 15 volts DC
- LM7818 regulator – 18 volts DC
- LM7824 regulator – 24 volts DC
These would need to be hooked up the same way as the 7805, with the exception that the output jack would need to be something appropriate to the piece of equipment that the adapter is going to be used for. Avoid using USB connectors for this, as it might cause confusion. The best power adapter to use is whatever input power connector is on the device that the charging adapter will be used with.
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