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What type of relay (or something else) for a 19" monitor???

S

SA Dev

Jan 1, 1970
0
Hi,

I've got a 19" monitor that I want to power on and off automatically.
Currently it has no power switch and is on when plugged in. Is there some
sort of 120V AC relay I could use? I have 12V and 5V signals I could tap to
tell the relay whether I want the monitor on or off. Any recommendations or
part numbers?

Thanks,

SA Dev
 
J

John Popelish

Jan 1, 1970
0
SA said:
Hi,

I've got a 19" monitor that I want to power on and off automatically.
Currently it has no power switch and is on when plugged in. Is there some
sort of 120V AC relay I could use? I have 12V and 5V signals I could tap to
tell the relay whether I want the monitor on or off. Any recommendations or
part numbers?

Thanks,

SA Dev

For long life and low noise, solid state relays are very good, though
you may have to parallel the monitor with a night light bulb, to
achieve the holding current necessary to keep them on, since the
monitor supply will draw pulses of current only at the peaks of the
cycle.

Something like:
http://dkc3.digikey.com/PDF/T041/1029.pdf
 
I

Ian Stirling

Jan 1, 1970
0
SA Dev said:
Hi,

I've got a 19" monitor that I want to power on and off automatically.
If modern, it may support this already.
If it's connected to a PC, look for a software setting to turn it off.
Interrupting the syncs should turn it off.
 
S

SA Dev

Jan 1, 1970
0
John,
For long life and low noise, solid state relays are very good, though
you may have to parallel the monitor with a night light bulb, to
achieve the holding current necessary to keep them on, since the
monitor supply will draw pulses of current only at the peaks of the
cycle.

Ok. I don't understand what you mean about the night light bulb? The input
voltage would not be coming from the monitor, but from a PC. Do I still
need the night light? Why?

SA Dev
 
J

John Popelish

Jan 1, 1970
0
SA said:
John,


Ok. I don't understand what you mean about the night light bulb? The input
voltage would not be coming from the monitor, but from a PC. Do I still
need the night light? Why?

SA Dev

The power switch in an AC solid state relay is pulsed on at every line
voltage zero crossing. The TRIAC switch needs a minimum load current
to stay latched on for the rest of the half cycle. Any device powered
by a DC supply with a capacitor energy storage filter will draw
significant current only near the peak voltage each half cycle, so
there is no holding current to keep the TRIAC switch on from the line
voltage zero crossing to the peak. Adding a small resistive (or
resistor in series with a capacitor, to draw more current as the
voltage rises toward the peak) provides the holding current. With
some relays, this can be as simple as a 2 watt resistor of 100 ohms or
so in series with a microfarad (or less) of capacitance rated for
across the AC line voltage. But a 7 watt bulb is simpler. Paint it
black if the light bothers you.
 
J

John Popelish

Jan 1, 1970
0
SA said:
John,


Ok. I don't understand what you mean about the night light bulb? The input
voltage would not be coming from the monitor, but from a PC. Do I still
need the night light? Why?

SA Dev

The power switch in an AC solid state relay is pulsed on at every line
voltage zero crossing. The TRIAC switch needs a minimum load current
to stay latched on for the rest of the half cycle. Any device powered
by a DC supply with a capacitor energy storage filter will draw
significant current only near the peak voltage each half cycle, so
there is no holding current to keep the TRIAC switch on from the line
voltage zero crossing to the peak. Adding a small resistive (or
resistor in series with a capacitor, to draw more current as the
voltage rises toward the peak) provides the holding current. With
some relays, this can be as simple as a 2 watt resistor of 100 ohms or
so in series with a microfarad (or less) of capacitance rated for
across the AC line voltage. But a 7 watt bulb is simpler. Paint it
black if the light bothers you.
 
S

SA Dev

Jan 1, 1970
0
Ian,
If modern, it may support this already.
If it's connected to a PC, look for a software setting to turn it off.
Interrupting the syncs should turn it off.

It is not a standard computer monitor, but an arcade monitor. It has no
physical power switch and also does not turn itself off even if not plugged
into a computer. It is on when plugged in, off when unplugged.

What I plan to do is tap a 5v or 12v signal from the PC power supply to run
to a relay of some type to turn the monitor on or off by applying or
removing its AC power.

When doing this, do I need to get a relay that has 2 positions, so it can
connect and disconnect the common and hot AC line? Does the ground line
always remain connected?

Thanks,

SA Dev
 
S

SA Dev

Jan 1, 1970
0
John,
The power switch in an AC solid state relay is pulsed on at every line
voltage zero crossing. The TRIAC switch needs a minimum load current
to stay latched on for the rest of the half cycle. Any device powered
by a DC supply with a capacitor energy storage filter will draw

I guess I'm still confused, I am *not* electrically brillaint. I am used to
mechanical relays where you apply some electricity (I would use 12V DC from
a power supply) and then it connects some terminals. Is this AC solid state
relay different?

Thanks,

SA Dev
 
I

Ian Stirling

Jan 1, 1970
0
SA Dev said:
Ian,


It is not a standard computer monitor, but an arcade monitor. It has no
physical power switch and also does not turn itself off even if not plugged
into a computer. It is on when plugged in, off when unplugged.

What I plan to do is tap a 5v or 12v signal from the PC power supply to run
to a relay of some type to turn the monitor on or off by applying or
removing its AC power.

Ok, in that case, the simplest way is probably to use a conventional
(not solid state) relay.
Practically any relay will do.
You want one with a 5V/12V coil, able to swich 110/220V (or whatever
the monitor voltage is) at the rated current of the monitor.)
(ideally you should double this current or so.)


You only run the live wire through it, connecting one end to the moving
contact, and one to either the normally open or normally closed (depending
on whether you want the monitor on when the relay has or has power to the
coil).
 
S

SA Dev

Jan 1, 1970
0
Ian,
You only run the live wire through it, connecting one end to the moving
contact, and one to either the normally open or normally closed (depending
on whether you want the monitor on when the relay has or has power to the
coil).

Which wire is the live wire? If I'm looking at an AC recept, I see a longer
slot, shorter slot, and hole (ground). Is the shorter slot the live wire
(black)? Then the longer would be the common (white)?

Thanks,

Alan
 
N

N. Thornton

Jan 1, 1970
0
A standard mechanical relay wil do the job nicely - you must add a
diode across the coil to avoid damage to the transistor driving it.

Part numbers - find one yourself.


Regards, NT
 
I

Ian Stirling

Jan 1, 1970
0
SA Dev said:
Ian,


Which wire is the live wire? If I'm looking at an AC recept, I see a longer
slot, shorter slot, and hole (ground). Is the shorter slot the live wire
(black)? Then the longer would be the common (white)?

Do you have a multimeter?
Measure the resistance from live at the plug to the monitor connections.
(You could also use a double pole relay, and disconnect both live and
neutral, ground is left connected.)ZZ
 
J

John Popelish

Jan 1, 1970
0
SA said:
John,


I guess I'm still confused, I am *not* electrically brillaint. I am used to
mechanical relays where you apply some electricity (I would use 12V DC from
a power supply) and then it connects some terminals. Is this AC solid state
relay different?

Thanks,

SA Dev

Yes. it is turned on by applying a low voltage DC to an internal
light emitting diode in series with an internal resistor or other
current regulating mechanism. Most of the ones on the catalog page I
sent operate with any DC voltage applied between between 3 and 32
volts. The light beam turns on the electronic switching circuit,
instead of connecting metal contacts.

If you prefer an electromechanical relay, there are lots of them that
will do the job, but they take more drive current so you will have to
build a transistor driver to boost a logic level signal to drive them,
and put a diode across the coil to prevent a high voltage spike when
you turn them off.
 
S

scada

Jan 1, 1970
0
SA Dev said:
Ian,


Which wire is the live wire? If I'm looking at an AC recept, I see a longer
slot, shorter slot, and hole (ground). Is the shorter slot the live wire
(black)? Then the longer would be the common (white)?

Thanks,

Alan

Be sure to use a diode across the relay coil, reverse biased. If not, you
run the risk of destroying the PC power supply, or mother board! The relay
coil can produce hundreds of volts when turned off, the diode suppresses
most of that voltage. The + side of the coil wire goes to the "Cathode"
the - to the Anode. Use something with a high "PIV" rating, the 1N4007
should do nicely (PIV 1000V). I would use the 12V line (used mostly for
motor drive: CD, HD, etc.), not the 5V. I'm not saying you won't still fry
something in the PC! Do it at your own risk! If I were to do it, I would use
the 12V as a signal to an external "Box" that was independently powered to
do the deed!
 
S

SA Dev

Jan 1, 1970
0
Hi,
Be sure to use a diode across the relay coil, reverse biased. If not, you
run the risk of destroying the PC power supply, or mother board! The relay
coil can produce hundreds of volts when turned off, the diode suppresses
most of that voltage. The + side of the coil wire goes to the "Cathode"
the - to the Anode. Use something with a high "PIV" rating, the 1N4007
should do nicely (PIV 1000V). I would use the 12V line (used mostly for
motor drive: CD, HD, etc.), not the 5V. I'm not saying you won't still fry
something in the PC! Do it at your own risk! If I were to do it, I would use
the 12V as a signal to an external "Box" that was independently powered to
do the deed!

How/Why does the coil produce so much voltage? I was planning on using the
PC power supply just to send the 12V, which should only be about 75ma. The
AC will not be coming from the power supply at all. Does this still pose an
issue?

Thanks for the help!

Alan
 
J

John Popelish

Jan 1, 1970
0
How/Why does the coil produce so much voltage? I was planning on using the
PC power supply just to send the 12V, which should only be about 75ma. The
AC will not be coming from the power supply at all. Does this still pose an
issue?
No. The diode is needed only if the relay coil is disenergized by a
switching device. If it is disenergized by a decaying power supply
that it stays connected to, it cannot produce any voltage. Its
magnetic energy will just hold up the supply for a few extra
microseconds. A nonevent.
 
M

Michael A. Terrell

Jan 1, 1970
0
SA said:
Which wire is the live wire? If I'm looking at an AC recept, I see a longer
slot, shorter slot, and hole (ground). Is the shorter slot the live wire
(black)? Then the longer would be the common (white)?

Thanks,

Alan

If you are talking about the standard US 15 Amp 120 Volt AC outlet,
yes, the long pin "SHOULD" be ground. That is, if it is wired properly,
and not fed from a three phase source where neither side is grounded. In
other words, don't depend on it, unless you check every outlet you plan
on using before plugging it in.


--
We now return you to our normally scheduled programming.

Take a look at this little cutie! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida
 
S

SA Dev

Jan 1, 1970
0
John,
No. The diode is needed only if the relay coil is disenergized by a
switching device. If it is disenergized by a decaying power supply
that it stays connected to, it cannot produce any voltage. Its
magnetic energy will just hold up the supply for a few extra
microseconds. A nonevent.

So I'm safe in doing this:

Get a 12V DC relay that is rated at 120VAC 10A.

Connect a power connector from my PC power supply to the 12V DC coil part of
the relay.
Connect the monitor AC hot line to the normally open poles of the relay.

When I turn on my PC, the relay will connect, connecting the monitor's
power.
When I turn off the PC, the relay will release, disconnecting the monitor's
power.

Is this right? Any other gotcha's?

Thanks so much for the help,

Alan
 
S

SA Dev

Jan 1, 1970
0
Hi Michael,
If you are talking about the standard US 15 Amp 120 Volt AC outlet,
yes, the long pin "SHOULD" be ground. That is, if it is wired properly,
and not fed from a three phase source where neither side is grounded. In

The long round pin = ground, right?

Then the wider slot is common (if looking at a recept with the ground
underneath the two slots, it is the left wider slot).

Then the narrower slow is the hot (if looking at a recept with the ground
underneath the two slots, it is the left wider slot).

Is this right?

Thanks,

Alan
 
J

John Popelish

Jan 1, 1970
0
SA said:
John,


So I'm safe in doing this:

Get a 12V DC relay that is rated at 120VAC 10A.

Connect a power connector from my PC power supply to the 12V DC coil part of
the relay.
Connect the monitor AC hot line to the normally open poles of the relay.

When I turn on my PC, the relay will connect, connecting the monitor's
power.
When I turn off the PC, the relay will release, disconnecting the monitor's
power.

Is this right? Any other gotcha's?

Thanks so much for the help,

Alan

That should work, fine.
 
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