# Using telephone line as power source?

1. ## telephone line as power

hi, I'm really new in electronics! Our Telephone line has 48V (DC). I turned on one LED ; but I can't turn on a small bulb lamp!!! WHY??

P.S. the small bulb lamp is about 1watt and can be turned on using my 3V DC adaptor.

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2. ## Re: telephone line as power

Hi..
I guess you have to use a DC lamp..Also I am not sure if it can drive this load as the current will be small..
BR
Vabzter

3. ## Re: telephone line as power

hii dana .... first the Telephone line has -48V (DC) not +48V try to exchang the polarity of led i.e the legs

4. ## Re: telephone line as power

Originally Posted by solidsnike
hii dana .... first the Telephone line has -48V (DC) not +48V try to exchang the polarity of led i.e the legs
I said that I can turn on LED but I can't turn on small bulb lamp(1 watt)!

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5. ## Re: telephone line as power

Hi,
Your telephone line gives 48V DC in open loop condition, i.e., when you do not draw any current from it. Normal telephone lines are rated to provide only 20mA of typical current while the telephone is in offhook state with a typical terminal voltage of around 12V for the telephone. This means the internal resistance of the telephone line is around 1.8K Ohms (48-12)/20*10-³.
Your filament lamp when it works at 1W at 3V will need 330 mA of current, which means it will have only a hot resistance of about 9 Ohms and its cold resistance will be almost zero. When you connect such a low resistance to your telephone line, you will get only milliVolts across the lamp ( 20mV if the lamp has one Ohm) and it will not be sufficient to light up the lamp. Please observe the line voltage when you connect the lamp across it, using a multimeter.
Regards,
Laktronics.

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6. ## Re: telephone line as power

thanks laktronics!
voltage is 0. I arranged another test:
With only one 10 ohm resistor, the current was:(I=59 mA). I think this is the maximum current that we can take from tel line.
I need at least 120 mA to turn on the lamp. Can I amplify the current? how?

7. ## Re: telephone line as power

Take also into account that most telephony provider remove power from the line if they do not detect a dial signaling within a certain timeout.

8. ## Re: telephone line as power

Hi,
Why do you want to amplify the current just to drive a lamp? Why do n't you use a high bright LED which will glow bright at 10 mA current. Also what is the purpose of your project? If you connect such small loads in parallel to telephone line, it will be seen by exchange as always in offhook state and your telephone line will not work. If it is for indication puposes, an LED with a parallel reverse protection diode, connected in series with the telephone instrument may be used.
Regards,
Laktronics.

9. ## Re: telephone line as power

Originally Posted by laktronics
Hi,
Why do you want to amplify the current just to drive a lamp?
Suppose we live somewhere that there is no electricity and we have only telephone!
now we want to light on a room.

10. ## Re: telephone line as power

You need to look into the local laws and regulations about items connected to the telephone wires. If you connect something that is forbidden you could have your service stopped, possibly for years.

11. ## Re: telephone line as power

Originally Posted by flatulent
You need to look into the local laws and regulations about items connected to the telephone wires. If you connect something that is forbidden you could have your service stopped, possibly for years.
Thanks! my discussion is scientific and I suppose there is no limit!
My problem is not Law; My problem is :How to turn on the lamp with 50mA current?

12. ## telephone line as power

If we live somewhere with no electricity, and...

One solution is to use a series/parallel connection of lets say 10 ultra bright LEDs. it gives a pretty good light just with a few mA. Note that the effeciency of filemant lamps is lower than LEDs.

13. ## Re: telephone line as power

Hi,
Please note that you can not get typical power more than 12V* 20mA =240mW from a standard telephone line even though you may find little more power in specific cases where you are located close to an exchange. But in any case if you use this power to light up a lamp, your telephone will not work.
Better you use a solar lantern for your application.
Regards,
Laktronics.

14. ## Re: telephone line as power

Thanks to all dear friends!
Regards,
Dana74

15. ## Re: telephone line as power

I sugest you to run a dinamo with a bike!!! You could use it to amplify the current to get more power... If you can watch TV that way, you can drive the lamp...
Or you can make a wind generator, then just open the window and a door and you got wind. It is not good as bike, but it works, and you dont get sweaty...

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16. ## Re: telephone line as power

Hi Dear dana74!

You know the telephone center is usually a smart one! I mean if the current drawn from the line is more than a defined current the line is cut and you can't draw any current from the line. So you can turn on a LED easily becuase it needs a small current but can't turn on a lamp cause it needs more current.

Thanks!

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