Operating a relay

T

trickyrick

Guest
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
 
On Jan 14, 11:07 am, trickyrick <ri...@sympatico.ca> 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
Click to expand...
There are a few 24VAC relays on Ebay. Would they work on 85 volts
(add resistor to bring that down) 25 cycles
 
On Wed, 14 Jan 2009 09:17:10 -0800 (PST), trickyrick
<rickj@sympatico.ca> wrote:

On Jan 14, 11:07 am, trickyrick <ri...@sympatico.ca> wrote:
Is there any way to operate a small 12 volt relay with the ringing
voltage on a phone line.
Click to expand...
---
Yes.
---

I have tried to use a bridge rectifier with
a capacitor but the relay chaters. Any ideas
Click to expand...
---
Yes.

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

There are a few 24VAC relays on Ebay. Would they work on 85 volts
(add resistor to bring that down) 25 cycles
Click to expand...
---
Probably not.

Where'd the 85 volts come from?

JF
 
"John Fields" <jfields@austininstruments.com> wrote in message
news:76msm4ttg24uvnacuv3dtfcqb099p6fion@4ax.com...
On Wed, 14 Jan 2009 09:17:10 -0800 (PST), trickyrick
rickj@sympatico.ca> wrote:

On Jan 14, 11:07 am, trickyrick <ri...@sympatico.ca> wrote:
Is there any way to operate a small 12 volt relay with the ringing
voltage on a phone line.

---
Yes.
---

I have tried to use a bridge rectifier with
a capacitor but the relay chaters. Any ideas

---
Yes.

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

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

---
Probably not.

Where'd the 85 volts come from?
Click to expand...
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
 
On 2009-01-14, trickyrick <rickj@sympatico.ca> 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
Click to expand...
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?
 
On Wed, 14 Jan 2009 20:40:55 -0500, "Paul E. Schoen" <pstech@smart.net>
wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:76msm4ttg24uvnacuv3dtfcqb099p6fion@4ax.com...
On Wed, 14 Jan 2009 09:17:10 -0800 (PST), trickyrick
rickj@sympatico.ca> wrote:

On Jan 14, 11:07 am, trickyrick <ri...@sympatico.ca> wrote:
Is there any way to operate a small 12 volt relay with the ringing
voltage on a phone line.

---
Yes.
---

I have tried to use a bridge rectifier with
a capacitor but the relay chaters. Any ideas

---
Yes.

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

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

---
Probably not.

Where'd the 85 volts come from?

I suppose the ring signal can be about 85 volts, but is normally about
90-100.
Click to expand...
---
From what I've been able to determine, ringing voltage can vary from
40VRMS with a 4 REN load to 53VRMS with a 1 REN load.
---

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.
Click to expand...
---
A 1 REN load looks like this: (View in Courier)

T/R>---+
|
[8ľF]
|
[6930R]
|
R/T>---+


The capacitive reactance of 8ľF at 20Hz (the ring frequency) will be:


1 1
Xc = --------- = ----------------------- ~ 1000 ohms
2pi f C 6.28 * 20Hz * 8.0e-6F


and the impedance of the circuit:


Z = sqrt (R˛ + Xc˛) = sqrt (6930˛ + 1000˛) ~ 7000 ohms


So the current from the line (at 40VRMS) into the circuit will be:


E 40V
I = --- = ------- = 5.7mA
Z 7000R


A 24VDC relay with a 200mW coil will need about:


P 0.2W
I = --- = ------ = 8.3mA
E 24V


to energize, so something looking like this should work:

+-----+
T/R>--[4ľf]--[1000R]---|~ +|---+------+------+
| | |+ |K |
| | [4ľF] [Z24V] [2900R]
| | | | |
R/T>-------------------|~ -|---+------+------+
+-----+

and it seems to:

Version 4
SHEET 1 880 680
WIRE -240 0 -368 0
WIRE -80 0 -160 0
WIRE -32 0 -80 0
WIRE 48 0 32 0
WIRE 160 0 128 0
WIRE 256 0 160 0
WIRE -80 32 -80 0
WIRE 160 32 160 0
WIRE 256 32 256 0
WIRE 256 112 256 96
WIRE 336 112 256 112
WIRE 464 112 336 112
WIRE 656 112 464 112
WIRE 464 144 464 112
WIRE 336 192 336 112
WIRE 656 192 656 112
WIRE -368 224 -368 0
WIRE 464 240 464 208
WIRE 160 352 160 96
WIRE 336 352 336 256
WIRE 336 352 160 352
WIRE 464 352 464 304
WIRE 464 352 336 352
WIRE 656 352 656 272
WIRE 656 352 464 352
WIRE -224 368 -224 48
WIRE 160 368 160 352
WIRE 256 368 256 112
WIRE 656 416 656 352
WIRE -368 480 -368 304
WIRE -224 480 -224 448
WIRE -224 480 -368 480
WIRE -176 480 -176 48
WIRE -176 480 -224 480
WIRE -80 480 -80 448
WIRE -80 480 -176 480
WIRE 160 480 160 432
WIRE 160 480 -80 480
WIRE 256 480 256 432
WIRE 256 480 160 480
FLAG 656 416 0
FLAG -80 32 TIP/RING
FLAG -80 448 RING/TIP
SYMBOL diode 176 96 R180
WINDOW 0 43 31 Left 0
WINDOW 3 25 -4 Left 0
SYMATTR InstName D4
SYMATTR Value MURS120
SYMBOL voltage -368 208 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(0 57 20)
SYMATTR InstName V1
SYMBOL cap 32 -16 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 4E-6
SYMBOL voltage -224 352 R0
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(0 1 0 1E-6 1E-6 2 6)
SYMBOL sw -144 0 M270
WINDOW 0 32 15 Left 0
WINDOW 3 32 44 Left 0
SYMATTR InstName S1
SYMBOL cap 320 192 R0
WINDOW 0 42 34 Left 0
SYMATTR InstName C1
SYMATTR Value 4e-6
SYMBOL diode 272 432 R180
WINDOW 0 -35 34 Left 0
WINDOW 3 -102 -1 Left 0
SYMATTR InstName D1
SYMATTR Value MURS120
SYMBOL diode 240 32 R0
WINDOW 0 40 33 Left 0
WINDOW 3 23 -1 Left 0
SYMATTR InstName D2
SYMATTR Value MURS120
SYMBOL diode 144 368 R0
WINDOW 0 -36 33 Left 0
WINDOW 3 -97 75 Left 0
SYMATTR InstName D3
SYMATTR Value MURS120
SYMBOL res 32 16 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 0 56 VBottom 0
SYMATTR InstName R2
SYMATTR Value 1000
SYMBOL res 640 176 R0
WINDOW 0 -47 35 Left 0
WINDOW 3 -58 65 Left 0
SYMATTR InstName R1
SYMATTR Value 2900
SYMBOL zener 480 208 R180
WINDOW 0 -37 59 Left 0
WINDOW 3 -137 31 Left 0
SYMATTR InstName D5
SYMATTR Value BZX84C12L
SYMBOL zener 480 304 R180
WINDOW 0 -34 34 Left 0
WINDOW 3 -128 4 Left 0
SYMATTR InstName D6
SYMATTR Value BZX84C12L
TEXT -344 536 Left 0 !.tran 20
TEXT -352 504 Left 0 !.model SW SW(Ron=1 Roff=10Meg Vt=0.5Vh=0)
TEXT 712 200 Left 0 ;24V
TEXT 688 232 Left 0 ;200mW
TEXT 704 264 Left 0 ;COIL

Since a relay's dropout voltage is typically 25% of its rated voltage,
that 50% ripple ought to be OK.

If not, C1 can be increased substantially without getting too much
higher than a 2 REN load.

JF
 
On Jan 15, 10:22 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
John Fields wrote:
Where'd the 85 volts come from?

A typical ringing voltage.

Graham
Click to expand...
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
 
"John Fields" <jfields@austininstruments.com> wrote in message
news:kl8um4pk2pcfbd84agelfk1umm1nvf6eb7@4ax.com...
On Wed, 14 Jan 2009 20:40:55 -0500, "Paul E. Schoen" <pstech@smart.net
wrote:


"John Fields" <jfields@austininstruments.com> wrote in message
news:76msm4ttg24uvnacuv3dtfcqb099p6fion@4ax.com...
On Wed, 14 Jan 2009 09:17:10 -0800 (PST), trickyrick
rickj@sympatico.ca> wrote:

On Jan 14, 11:07 am, trickyrick <ri...@sympatico.ca> wrote:
Is there any way to operate a small 12 volt relay with the ringing
voltage on a phone line.

---
Yes.
---

I have tried to use a bridge rectifier with
a capacitor but the relay chaters. Any ideas

---
Yes.

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

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

---
Probably not.

Where'd the 85 volts come from?

I suppose the ring signal can be about 85 volts, but is normally about
90-100.

---
From what I've been able to determine, ringing voltage can vary from
40VRMS with a 4 REN load to 53VRMS with a 1 REN load.
---
Click to expand...
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
 
On Wed, 14 Jan 2009 08:07:12 -0800 (PST), trickyrick <rickj@sympatico.ca> 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.
 
On Thu, 15 Jan 2009 23:43:10 GMT, Ross Herbert <rherber1@bigpond.net.au> wrote:

:On Wed, 14 Jan 2009 08:07:12 -0800 (PST), trickyrick <rickj@sympatico.ca>
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.
 
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