How to Get Emergency Power from a Phone Line

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?
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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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.
donclark2 months 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)?

DIY Hacks and How Tos (author)  donclark2 months ago
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?

DIY Hacks and How Tos (author)  donclark2 months ago

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

thecensor2 months 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

FAIZKHAN1083 months ago

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.
ntense991 year 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 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...
showing 3.7 volts
Battlespeed6 months ago
This idea should work. However:

1. Unfortunately, in most of the sorts of emergencies/disasters that might excuse you (legally) for using this kind of hack, charging your cell phone will be a useless exercise because experience shows that cell towers/channels are totally jammed and/or nonfunctional. (However, it is worth noting for your general stash of "emergency information" that when voice channels are jammed/unavailable but towers remain functional, text messaging may still be possible.)

2. My main objection is that the time and effort involved in preparing to implement this solution would be better spent on acquiring any of a number of other emergency charging solutions that are far better, more reliable, and far less problematic.
swatson168 months ago
come on people! The author of the post/ instructables CLEARLY states not to go if for any ole reason (as in only if SHTF and you have NO other choice). Use common sense.
Actually all the nay-sayers do have a point....

But IF the current being drawn, was the same as the phone being off the hook... like what comes through the hand piece - which one would imagine, would be a regulated current and voltage - and not the ringer circuit, then this I "THINK" (at face value) that this is a good idea.

But I also think that with all the rooting around, that it would be easier to just keep a 5 or 10W solar panel on standby with a car battery (with the relevant charge controller???), for some LED night lighting etc... and as a standby power supply.

Not a HUGE fan of the phone company... I think leeching SOME power is fine.. if it is safely done, but the amount is SO small, and the fines so huge, that probably better off investing in the said solar panel and car battery.

actually a car battery its designed to be drained like that, u'd kill it in months. where as a deep cycle or universal battery of golf cart batterys would be even better tho. wioth a basic charge controller an inverter.
With regards to use in the United States:
  • FCC Part 68 regulations do indeed require that devices connected to the wired network have a minimum load resistance of 5Mohm across tip and ring when not actively communicating. These regulations are primarily intended to be applicable to manufactures of line connected equipment rather than the Tel-Co customer.
  • Wired phone systems have been highly reliable for over 100 years because the system is robustly designed. This includes effective protection against faults such as dead shorts, surges, and even lightning strikes. While it is possible that connecting unapproved, or experimental equipment to a home phone line could cause damage, it is highly unlikely that damage would extend beyond that individual customers line.
  • You can't draw any more power from an individual line than the system was designed to provide. Hypothetical scenarios suggesting that X number of customers in an area using a device like this could crash the system is very improbable.
  • Up to approximately 750mW of power can be drawn from an individual home phone line without triggering an open-line (off hook) condition. This means that the line is still fully functional for communication.
and only if the power transmission line were designed an maintained like the phone lines are then we'd never have a black out in the first place. but we live in the real world an politic and back room deals take over.
Dr_Stupid1 year ago
Too bad doing this in the US is illegal.

Better make damn sure its a bonefied emergency otherwise you'll be charged with theft and interference with communications is a felony.
only if u transmitt over the said phones lines
LP2 Dr_Stupid1 year ago
How is paying a monthly fee for service theft?
*bona fide*
shortw1 year ago
It is illegal here in the US. Period....

This instructable should state that it is illegal to use in most countries and that there may be lawful consequences to use such a device.
It also should state that it may fry your cellphone with such circuit or that there could be property damage such as fires if unattended.
please stop with the negitive remarks unless u state that u work 4 directly with / for a phone company
paddys01111 months ago
the maximum voltage rating for the LM7805 is 35Vin - this must be getting seriously hot. What sort of current are you getting when charging the phone? Surely the resistance caused by the heating is seriously limiting this?
DIY Hacks and How Tos (author)  paddys01111 months ago
As illustrated in the last graph of step 2, the phone line can output a maximum of 75 mA at 5V. Then you lose some efficiency with the regulator.
ahh yeh - see that now. Have you tried any alternative circuits for improving the efficiency?
DIY Hacks and How Tos (author)  paddys01111 months ago
I was really trying to focus on simplicity rather than efficiency
yeh - guess that makes more sense for the context you are proposing this idea in. Its a great tutorial anyway - I look forward to giving it a go!
Great Instructable!
LaserDave1 year ago
It's sad to read all of these negative comments, some of them are so far off the mark it's funny. Some are spouting off technical jargon and safety concerns where they clearly have no idea what they're talking about. NO, the phone line is not a fire hazard no matter how you use it.

I'm not going to argue about the legality of it, but MOST Telcos allow a current draw for peripheral electronics PROVIDED you remain within their limits. They already have current limiters on the line that prevent ALL interference with other subscribers' lines, and it WON'T cause a system failure and prevent others from calling. Come on people, some common sense please.

It seems people have forgotten that there are many, many telephones and gimmicks that use the phone line power for operation. Drawing power off the line is allowed and is even expected with the range of available gadgetry.

The circuit *may* work, but the input voltages, polarity / AC issues, and the quiescent current requirements of the regulator make it a poor choice for this idea. Since you get roughly 20mA at 6v from most lines after filtering and regulating without putting the phone in the off-hook condition, every milliamp counts so you don't want to waste it with a hungry regulator. The LM317L is a better choice, it's a TO-92 package and uses less power.

IN AN EMERGENCY - that circuit may be okay for bashing together in the dark, but if you decide that you want to prepare such a device ahead of time a better approach should be used. Then again, if you are thinking that far ahead, a small $10 battery backup device would be better - Black and Decker makes a pocket power-pack that has USB output AND 110v AC inverter that could also be used to charge a phone. It's about 3/4" thick by 6" long by 4" wide, and I picked it up for $10.

For a working circuit though, you should "isolate" the circuit from the line, so a bridge rectifier will take care of that, plus the AC and polarity issues right from the start. Add two capacitors like 100uF with a 35v rating in series across the output. Using a low-current switching circuit to provide your 5v would maximise the efficiency and waste very little power. iPhone devices need a voltage divider to put 2.5v across the two middle pins on the USB connector (data lines), which will tell the device to charge using a minimum current draw - either one divider for each line, or connect the two lines and use one divider.

This Telco power topic was debated a couple of years ago when an emergency LED light was proposed, and the same "nervous nellies" were there too with the same fears. I posted a drawing of a circuit that I tested and verified, and I will include it here in case anyone is interested. For what it's worth, I'm an electronics engineer - 25 years.

PM if you have questions, I'd be happy to help.

Phone Line-powered LEDs.jpg
tyson421 year ago
I love how so many people here comment on this being illegal. It is clearly stated above that the legality of this is questionable and should only be used for emergency purposes. If used during an event for which this type of thing is intended, I seriously doubt the phone company would be rushing to your door to fine you. They will most likely have much bigger issues to deal with and families of their own to worry about. You're not supposed to burn tires either, but in an emergency situation, that fact would be overlooked.

Another comment I saw a lot of is why not just use the land line. That would be great if you have your whole contact list memorized or printed on paper. But most people these days store all this info electronically and never even look at the number after it gets programmed into the phone.

One thing to add to that circuit would be a voltage divider to feed 2 volts to the clock and data lines. I don't know if this is needed for all iPhone models, but every one I've tried so far needs this to tell the phone to charge.
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