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Picture of How to Get Emergency Power from a Phone Line
What do you do if the power is out and you need to charge your cell phone to make an emergency phone call? Don’t worry. There are plenty of potential power sources all around you. One of them is the phone line. In this instructable, I am going to show you how you can use the phone line to power your small electronic such as your phone or other USB devices in an emergency.

Note: This project is intended for emergency situations only. Please be aware of applicable local laws regarding phone lines in your area. 

 
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Step 1: Background Information: Power in the Phone Lines?

Picture of Background Information: Power in the Phone Lines?
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You may have noticed that corded phones don't need to be plugged into an electrical outlet. That is because they get all the power that they need to operate directly from the phone line itself. The phone company sends this power directly to your house through a pair of dedicated wires that connect to your phone jack. When the phone is not in use, this is a constant DC signal (about 50-60 volts). When the phone rings, the signal is a 20 hertz AC signal (about 90 volts). When in use it is a modulated DC signal (between 6 and 12 volts). 

The phones lines even have power during a blackout in most cases. This is because the phone company maintains their own backup power system. Your phone lines may be powered even if you don’t have a land line service set up.


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JosephP1216 days ago

what is voltage for telephone wire ?

As stated above "When the phone is not in use, this is a constant DC signal (open circuit voltage of about 50-60 volts). When the phone rings, the signal is a 20 hertz AC signal (about 90 volts). When in use it is a modulated DC signal (between 6 and 12 volts)"

Just so I get this straight, since you are not using into any of the signal wires on the phone line will the voltage always stay at 50V? Or will it modulate when other phones are in use? For instance if I have my phone plugged in and charging then all of a sudden someone calls my home phone will it send 90V AC into the voltage regulator and fry it?

The issue here is the difference between "open circuit" voltage and "operating" voltage. "Open circuit" voltage is what you would measure if you hooked up a multimeter to the output terminals without any load. "Operating voltage is what you would measure when a load is connected.

Due to the limitations of a power supply, the more current you try to pull out of it, the more the voltage will drop. So the output voltage is highest when the output current is 0. This is "open circuit voltage." But as soon as you connect the power supply to a circuit, the voltage will drop. You can see this if you measure the output of a DC power supply with and without the circuit connected.

So in this case the open circuit voltages are 50V when idle, and 90V when ringing. But when the phone is in use (powering the phone) the voltage drops way down to about 6V. So don't worry about the voltage drying the parts. But if you are in a situation where the phone might ring, you may want to add a diode to turn the AC signal into a DC signal.

ardreeceo1 month ago
Why not just use the phone that is plugged into the socket? Then Its not stealing.

Brilliant!

SheikhM15 days ago

Oh 7805 is for 5V. Then let me know the number of voltage regulator for 12V.

(input will be 50V)

DIY Hacks and How Tos (author)  SheikhM15 days ago
With this series of voltage regulators, 78 indicates the series number and the last two numbers are the voltage. So a 12V regulator in this series would be 7812
TomJ51 month ago

If, in fact, the ring voltage is anywhere from 90 to 150 VAC and, if the current is around 45 to 75 ma, then it will not kill you, but would cause lots of pain.
As a former US Marine Electronics Technician (2841 Ground Radio Repair, Basic Electronics, etc.), the first thing you learn is that DC voltage alone is typically non-lethal; thus stun-guns with 90,000 to 2,000,000 volts will knock you back and unconscious, but won't generally kill you - unless you already have a heart problem or other such issue - pacemaker, etc. BUT, if it is "AC" (Alternating Current), then 200 ma = "extreme pain" and 300 ma = "instant death." That's what we are taught. I've never cared to test either of those theories. So, if you see an AC circuit that is 20 Amps; and you were to test across that circuit with your body, you're dead, because that is WAY more than 300 milliamps; so way more than enough for "instant death."
But, if it truly is only 45 to 75 milliamps, it would be very strong pain, and that's about it.

mykb773 months ago
Why not just get a usb adaptor for your car and use your car battery to charge your phone in an emergency? If the power is out for long enough for this method to become a problem you wiĺl have more pressing issues.
DJS43 months ago

what kind of diode would I need planing to power roter at 12vDC 2A in uk

DIY Hacks and How Tos (author)  DJS43 months ago
You won't be able to get that much power out of the phone line. Check the graphs on step 2. At 12V you will only get about 63mA.

Way back when, I was a field wireman in the US ARMY. Part of our training involved hooking up to civilian wire, carrying the same voltage as todays phones. When we were in the process, the instructors always watched to see if we happen to touch the wrong wires, and if we did, we were rewarded by ringing voltage. It stung, made you jump, and if you were up a pole, you nearly fell off, however it never killed any of us, and I can assure you todays' phone lines will not kill you either. It will be far less painfull then a taser (ya being a cop, I had to get tazed myself before being allowed to carry one.) I am building one of these, a bit more formally then the photo, using a board instead of just soldering together. I have an excess of boards. I am also putting it in a project box with input sockets, and a power output socket. We don't have outages often but when they happen they can last for a week or two at a time up here in the Dakota's, this will be added to the solar chagers I have picked up here and there so I can use my cell phone, PDAs and laptops during the long hours of cold while the power company rebuilds the damaged lines and poles.

JonW14 months ago

Ok. So I am currently, no pun, a central office tech. This would work. We have what is called LIJ's they are left in jumpers, or wires connected to customers lines that have disconnected their service. It has a constant 52.80 volts. You can call 911, or the phone company to order service. It is stealing, albeit minimum power, if you construct a way to harness it. In my office, I started cutting them to reduce power output of my office. However, they don't seem to appreciate my efforts, so if you have a jack in your house with DC output, it will work. The common sense thing to do is, keep a battery source charging, like what I take on my boat to jump it in an emergency, always plugged in. This will charge everything such as cell phones, laptops for days. They are about 50 bucks and most have lights built in.

JonW1 JonW14 months ago

Also, I might add, you can probably light a dozen LED night lights with that disconnected jack, unless the local CO Tech has removed it. Pre deregulation we were required to give you EDT(express dial tone) for an emergency, but not now!

JonW1 JonW14 months ago

Also, I might add, you can probably light a dozen LED night lights with that disconnected jack, unless the local CO Tech has removed it. Pre deregulation we were required to give you EDT(express dial tone) for an emergency, but not now!

JohnD410 months ago

I see one issue here, if power goes out so do cell towers.

nitrobusa JohnD45 months ago
The big LTE cell towers have a array of large batteries to supply the system for 3 to 4 days. In case the main grid gets disconnected.

Wired phones have -48~vdc on the line at approx 40-60mA, called "battery" because they
come from the central office, inside those central offices they have
HUGE batteries and massive generators, with thousands of gallons of diesel...they are required to have them,
they will be running MUCH longer after the power goes out in an
emergency (cell phone towers have generators as well but nowhere near as much fuel as the central offices). The battery voltage is there to prevent corrosion on the lines by having a constant but very miniscule current flowing thru the copper wires and all it's connections.

It really won't be enough to charge anything...you would be better off with a small solar panel and portable Li Ion power unit

mk48411 months ago

Having worked for a phone company years ago their mains concerns with unregistered equipment were:

1) Is it safe for their linesmen and exchange (central office) staff to work on (while your new age gizmo is doing its thing across THEIR phone lines?)

2) Will it cause interruptions/power loss/damage to that part of the network?

Even if the answer to these questions is "NO", they still take a dim view of people plugging in any old thing, at any old time to their phone lines.

However, people who are stuck in an emergency situation usually don't have time to break out the rule book and read it, so if they have the knowledge, tools, parts and the skills, they probably would try it.

As far as the line voltages and currents go, -48 volts DC (it's a +ve earth/ground system over here,) is the usual line voltage in Oz, and the current flowing in that line with a phone 'off hook' is normally just enough to trip the detection circuitry back at the exchange/central office, to let the sub processor know that your phone is off hook and ready to make a call. I doubt whether it would be enough to charge a cellphone for any length of time, but may be OK for a top up.

As for the regulator input voltage being exceeded, the moment it was connected across the Telco line, the 50 volts DC could probably drop way below 30 volts on average, so maybe the +35 volts maximum input volts for the regulator IC would not be a risk factor?

Also, whenever a telco line is 'looped' (active with a resistive device/load across it) the line is itself, is place on "line lock out" for all incoming calls - a dangerous ring voltage may not materialise, because the computer back at the exchange/central office won't tell the sub processor to send a ring voltage, seeing the line has already been flagged as "busy".

I agree with the sentiments about 'testing the telco line with a meter and your fingers involved' - that could be risky, if not dangerous. Convert a set of probe leads into leads with insulated crocodile clips on each end - that might make any such tests a lot safer..

I won't add any comments to the legal and poor (unsafe) electronic design issues, but I'd like to warn that what is shown at step 2 picture (checking voltage by holding the probes and the landline together with your hands) is really dangerous: If you receive an incoming call while doing that, you'll have 90-150 ac volts across your arms, with the current path passing through your heart (the worst scenery). I'm not exaggerating, it happened to me a long time ago while trying to repair an old style dialing wheel telephone.

It won't kill you, the area of contact is too small and it lasts for 1 sec max, but it does hurt and it definitely makes you jump. It teaches you not to do it again.

wow! it must be hard to feel it :-)
1) If the phone line is powered, you can make the emergency call on it.
     ( As several other people have said.)

2) This is dangerous. Fifty volts is where volts have already started getting dangerous.

3) I am an electronic technician, and I would never do this.

4) You can keep a spare charged phone battery to use when the first is flat. (As I do.)

5) You can have a second phone charger in my car. (As I do.)

6) You can have a USB cable to charge your phone from your laptop. (As I do.)

7) What happens if your phone hack prevents some of your neighbours from making emergency calls on their landlines ?    Do you want to be responsible for someone's death, just because you are too mean and selfish to take reasonable sensible LEGAL precautions for power cuts like everyone else does ?

8) DO NOT encourage people to do dangerous illegal things.   If they do, and they suffer for it, you share the responsibility.   (But I'm sure you will deny everything.)

2) No, 48V telephone battery is not dangerous. Up to 60VDC is rated as Safety Extra Low Voltage (SELV) and is safe to touch. See UL60950 for definition.

3) Your choice.

7) This is no different to going Off Hook with a regular phone. So you won't block anyone else's calls. If you don't make a call after 5 mins or so the phone company cuts off the power anyway.

8) It's not dangerous but it is illegal to use telephone company power for any purpose other than making a call. See Code of Federal Regulations CFR Title 47 Part 68.

i too am a electronic tech...... and as my rule of thumb, 30 volts or above is dangerous

It is not dangerous. There is 48-52 volts, but very little amps.
donclark1 year ago

Very curious! Is anyone selling these as a complete kit, or something similar? I would like to use an old phone jack to power 2 usb ports or more, led night light - or ac outlet and keep the phone jack too. Or could someone point me to someone that would create it for me (for money)?

You should keep in mind that the output of a phone line is very limited (75 mA at 5V). USB ports are designed to output up to 500mA per port. So don't expect to be able to power a bunch of high current USB devices with the phone line.

Thx for the info. Still curious if there is a way... What are your thoughts on this? http://www.maximintegrated.com/app-notes/index.mvp/id/1923

It seems like overkill. And all those components are going to eat power and lower your output capacity.

thecensor1 year ago

This is porbably illigal normally but can be done in an emegency when the main power is out for a long time.

Im amazed nobody has stated the obvious. go to the store, spend $5 on a regular corded phone, keep it around for emergencies. in most cases if your phone line is connected you can call 911. if not the odds that this is a better solution than finding someone else with a cell phone is still pretty slim

can any one tell me plzzz.. That if the telephone set is on call then there will be out put voltages or not???

If the phone line is connected, then there is always a voltage. But if a phone active on that line, then this can effectively reduce that voltage.
ntense992 years ago
HAHAHA I am just trying to be funny, but someone should ALSO use this phone line voltage and pipe it into one of those cheap chinese Grid Tie Inverters to take the Phone DC voltage send it to the Grid Tie Inverter and send that back into your electrical panel to help slow down your power meter, HAHAHA

That would be a great idea! BUT...wouldn't the power be out during an emergency so the meter would not be spinning anyway? :) unless you are thinking everyday use...you could be onto something (JK)

Good luck with that, the amount of power you can pull from the phone lines is minute, to wind your meter back you'd be better off turning off power to your house and hoping the power company makes a mistake reading your meter.
My 7805 voltage regulator's datasheet says its absolute max input voltage is 35V. So your 7805 might not last very long in this setup, though it should work for a while in an emergency. It might be better to use a higher-voltage regulator first, and then give its output to a 7805.

Or, if you have a car, charging from a car charger is another option in an emergency.
voltage regulator not working properly...
voltmeter...
showing 3.7 volts
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