Operating a relay

[trickyrick]

Is there any way to operate a small 12 volt relay with the ringing
voltage on a phone line. I have tried to use a bridge rectifier with
a capacitor but the relay chaters. Any ideas
Rick

 

[trickyrick]

Is there any way to operate a small 12 volt relay with the ringing
voltage on a phone line.  I have tried to use a bridge rectifier with
a capacitor but the relay chaters. Any ideas
Rick

There are a few 24VAC relays on Ebay. Would they work on 85 volts
(add resistor to bring that down) 25 cycles

 

[Paul E. Schoen]

---
Yes.

Post the resistance of the coil or the power needed to make the relay
contacts or, preferably, the manufacturer and part number.

I suppose the ring signal can be about 85 volts, but is normally about
90-100. Close enough. It would probably work best to rectify the voltage
directly with a FWB, add a 200 VDC capacitor (probably 100 uF or more), and
then drop the voltage to the relay. There is a limit to how much power can
be drawn from the phone line ring signal, so a sensitive relay might be
needed. Even better might be an optoisolator or opto-relay that will work
on 5 mA or so. In that case, a 20 uF capacitor might be OK.

If you want to use the phone line with the relay connected, you may need to
add a series capacitor so it will not draw DC current when you go off-hook.
Or you can sense the off-hook condition and disconnect the relay circuit
when the voltage drops or the line draws DC current.

Paul

 

[Jasen Betts]

Is there any way to operate a small 12 volt relay with the ringing
voltage on a phone line. I have tried to use a bridge rectifier with
a capacitor but the relay chaters. Any ideas

try a larger capacitor in parallel with the relay.

do you need the relay? could you use a NE2 (neon indicator) + photo-transistor
optopcoupler instead?

 

[Eeyore]

Where'd the 85 volts come from?

A typical ringing voltage.

Graham

 

[neon]

the ring and the tip

Well the voltage is there but no power to speak of . you need both to operate a relay. there is the tip and the ring voltage butr no power. You may use either voltage for detection but not to operate aq relay

 

[trickyrick]

A typical ringing voltage.

Graham

Thanks Guys for the input I got it
I used a very small relay connected to a bridge rectifier with a cap
in series on the AC side
Works good
Thanks

 

[Paul E. Schoen]

This article says 90 VAC at 20 Hz:
http://www.telecomaudio.com/article02.html

Here is more detailed information, that indicates 90 VAC into 5 REN:
http://www.sandman.com/ringvoltbul.html

It also says that it is 75 VAC in Europe.

Paul

 

[Ross Herbert]

:Is there any way to operate a small 12 volt relay with the ringing
:voltage on a phone line. I have tried to use a bridge rectifier with
:a capacitor but the relay chaters. Any ideas
:Rick

I have done this many times using a 48V DC relay, bridge rectifier and 100uF
electrolytic capacitor. The relay (I have a few hundred) is a Meisei M4-48H
which has a 7,800 ohm coil. It works perfectly.

 

[Ross Herbert]

:On Wed, 14 Jan 2009 08:07:12 -0800 (PST), trickyrick <[email protected]>
wrote:
:
::Is there any way to operate a small 12 volt relay with the ringing
::voltage on a phone line. I have tried to use a bridge rectifier with
::a capacitor but the relay chaters. Any ideas
::Rick
:
:I have done this many times using a 48V DC relay, bridge rectifier and 100uF
:electrolytic capacitor. The relay (I have a few hundred) is a Meisei M4-48H
:which has a 7,800 ohm coil. It works perfectly.


I forgot to say that the input to the bridge rectifier is DC isolated using a
2uF, 250Vdc capacitor.