On Thu, 31 Dec 2020 18:32:12 +0000, Adrian Caspersz wrote:

The 10A relay contacts are probably now some tarnished metal as the
current is too low to keep them 'wet'[*], and probably a better choice
will be one specified to switch signals rather than power.

Or pop the cover off and pull a strip of paper between the contacts
while they are manually pressed together.

--
Cheers
Dave.

"John J" wrote in message
...
On Wednesday, 30 December 2020 at 20:28:18 UTC, Bazza wrote:
On Wednesday, 30 December 2020 at 19:47:03 UTC, Martin Brown wrote:

I think you need to specify what current you want to switch and whether
or not it is an inductive load before any sensible advice it possible.

One company I knew who changed to using solid state relays inadvisedly
managed to have their kit catch fire with monotonous regularity.

You should be asking why are the classical relays are failing first.

Allow me to clarify.

The current I want to switch is negligible because CCTV camera works
on only 12V DC. I want to switch the cameras continuous 12v D/C
output signal to ground by having the relay switch from NO to NC.

The relay on the other side will be activated by a 240volt a/c input.
So a 240v input will switch a 12v D/c to ground

I'm struggling to understand what you are trying to achieve. I'm running
cctv systems around the farm and another in our village hall which record
continuously day and night onto hard disc drives in standard dvr's. The 16
channel hd kits record over 7 days before overwriting while the 8 channel
lower definition units have longer retention times.

The problem with that approach is that you have
to do a lot of work to find when the event you care
about happened, by watching a lot of useless video.

A system which records on a trigger fixes that.

Corse its better to go even further, record everything
and be able to step thru trigger events.

On 31/12/2020 21:11, John J wrote:
On Wednesday, 30 December 2020 at 20:28:18 UTC, Bazza wrote:
On Wednesday, 30 December 2020 at 19:47:03 UTC, Martin Brown
wrote:

I think you need to specify what current you want to switch and
whether or not it is an inductive load before any sensible advice
it possible.

One company I knew who changed to using solid state relays
inadvisedly managed to have their kit catch fire with monotonous
regularity.

You should be asking why are the classical relays are failing
first.

Allow me to clarify. The current I want to switch is negligible
because CCTV camera works on only 12V DC. I want to switch the
cameras continuous 12v D/C output signal to ground by having the
relay switch from NO to NC. The relay on the other side will be
activated by a 240volt a/c input. So a 240v input will switch a 12v
D/c to ground
I'm struggling to understand what you are trying to achieve. I'm
running cctv systems around the farm and another in our village hall
which record continuously day and night onto hard disc drives in
standard dvr's. The 16 channel hd kits record over 7 days before
overwriting while the 8 channel lower definition units have longer
retention times. All the cameras and the recorders are powered by 12
volt dc supplies. The camera signals to the dvr's are 1 volt peak to
peak into 75 ohms. The dvr has its own smps rated at 3A, the cameras
are split over multiple smps units for redundancy but most of the
cameras are well below 1A each

Oh. I'm not struggling. It seems clear that he has some PIR triggered
lights and when they get triggered he wants to start recording.
He wants to use the mains across the lamp to generate a signal that
will pull down a control input to ground, that is fed by a quite high
value pull up resistor from 12V.

The circuits that have been linked to will do *exactly* this.





--
"Women actually are capable of being far more than the feminists will
let them."

On 31/12/2020 22:36, Dave Liquorice wrote:
On Thu, 31 Dec 2020 18:32:12 +0000, Adrian Caspersz wrote:

The 10A relay contacts are probably now some tarnished metal as the
current is too low to keep them 'wet'[*], and probably a better choice
will be one specified to switch signals rather than power.

Or pop the cover off and pull a strip of paper between the contacts
while they are manually pressed together.

I'd go reed switch, but getting a mains coilled one is harder than the
solid state alternative


--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.

In article l.net,
Dave Liquorice wrote:
On Thu, 31 Dec 2020 11:08:22 +0000 (GMT), Dave Plowman (News) wrote:

It would take a true optimist to guarantee a solid state relay will have
a longer life than a traditional one.

Depnds on the application. I doubt a traditional relay would last
long operating with a 7 Hz PWM signal to control the speed of a mains
circulating pump. Might be a tad noisy (acoustically and
electrically) as well. B-)

Why would you use any relay on the output of a PWM generator?

--
*Santa Claus has the right idea. Visit people only once a year.

Dave Plowman London SW
To e-mail, change noise into sound.

On Thursday, 31 December 2020 at 22:41:22 UTC, Rod Speed wrote:
"John J" wrote in message
...
On Wednesday, 30 December 2020 at 20:28:18 UTC, Bazza wrote:
On Wednesday, 30 December 2020 at 19:47:03 UTC, Martin Brown wrote:

I think you need to specify what current you want to switch and whether
or not it is an inductive load before any sensible advice it possible.

One company I knew who changed to using solid state relays inadvisedly
managed to have their kit catch fire with monotonous regularity.

You should be asking why are the classical relays are failing first.

Allow me to clarify.

The current I want to switch is negligible because CCTV camera works
on only 12V DC. I want to switch the cameras continuous 12v D/C
output signal to ground by having the relay switch from NO to NC.

The relay on the other side will be activated by a 240volt a/c input.
So a 240v input will switch a 12v D/c to ground

I'm struggling to understand what you are trying to achieve. I'm running
cctv systems around the farm and another in our village hall which record
continuously day and night onto hard disc drives in standard dvr's. The 16
channel hd kits record over 7 days before overwriting while the 8 channel
lower definition units have longer retention times.
The problem with that approach is that you have
to do a lot of work to find when the event you care
about happened, by watching a lot of useless video.

A system which records on a trigger fixes that.

Corse its better to go even further, record everything
and be able to step thru trigger events.

I take your point but it's perfectly possible to use a more or less standard system to generate alarm messages to a phone. Having received a message the timing is readily available. Still you pays your money and you takes your choice.

In article ,
Martin Brown wrote:
Lifetimes for relay based logic running a few daily tasks should be of
the order of 30 or 40 years if properly designed. That is about how long
my oil burner controller lasted before relays started to fail.

Quite. I have an el cheapo mains coil relay switching my AV system via the
amp on off switch and aux mains output. As the aux mains output is limited
to an amp or so.

It is an open frame no name device bought from Maplin in the 70s or 80s.
Obviously fitted in an enclosure for safety. Used at least every day and
on for hours. Still works just fine.

Cars have relays too that can outlast the car. Not always, of course.

--
*Forget the Joneses, I keep us up with the Simpsons.

Dave Plowman London SW
To e-mail, change noise into sound.

Paul wrote:
Bazza wrote:
Apologies for not explaining the electrical details in a professional
manner and maybe I should have found a forum for CCTV matters. I'm not
an electrician but an elderly and pretty capable DIYer.
As I said earlier I have been using old style (coil) relays
specifically the MY2NJ type and they have worked with the 5 cameras I
have.
I use a 240v PIR sensor that sends 240v to the relay when it is
activated. The relay, when activated, makes or breaks contact in the
camera. This triggers the camera to start recording. Here is an
extract from the manual..........
"""Trigger This is the cause or stimulus which defines when to trigger
the Network Camera. The trigger source can be external digital input
devices. This option allows the Network Camera to use an external
digital input device or sensor as a trigger source. Depending on your
application, there are many choices with digital input devices on the
market which help detect changes in temperature, vibration, sound,
light,"""

They make 12V PIR sensors, which could run off the 12V supply feeding the camera.
Some experimentation undoubtedly required, but the nice thing is, you're
no longer fiddling with mains voltage.

https://www.youtube.com/watch?v=XR8Bfcyofog

Paul

On Fri, 01 Jan 2021 12:38:31 +0000 (GMT), Dave Plowman (News) wrote:

It would take a true optimist to guarantee a solid state relay
will
have a longer life than a traditional one.

Depnds on the application. I doubt a traditional relay would last
long operating with a 7 Hz PWM signal to control the speed of a
mains
circulating pump. Might be a tad noisy (acoustically and
electrically) as well. B-)

Why would you use any relay on the output of a PWM generator?

So a micro controller can be isolated from, and switch, mains power?
Doesn't take a true optimist to guarantee a SSR will last longer than
a traditional relay in this application.

--
Cheers
Dave.

On 02/01/2021 12:43, Dave Liquorice wrote:
On Fri, 01 Jan 2021 12:38:31 +0000 (GMT), Dave Plowman (News) wrote:

It would take a true optimist to guarantee a solid state relay
will
have a longer life than a traditional one.

Depnds on the application. I doubt a traditional relay would last
long operating with a 7 Hz PWM signal to control the speed of a
mains
circulating pump. Might be a tad noisy (acoustically and
electrically) as well. B-)

Why would you use any relay on the output of a PWM generator?

So a micro controller can be isolated from, and switch, mains power?

Of course it can. Opto isolators or double wound transformers - all of
these meet very high isolation specs. As can of course the relays.


Doesn't take a true optimist to guarantee a SSR will last longer than
a traditional relay in this application.

Nope.

Relays have their place. If they are off, there is no leakage and there
is true isolation

But in switching awkward loads everyone has gone MOSFET these days Not
even triacs, much really not even GTOs

semicoinductors do in fact get better from year to year.






--
Any fool can believe in principles - and most of them do!

In article l.net,
Dave Liquorice wrote:
On Fri, 01 Jan 2021 12:38:31 +0000 (GMT), Dave Plowman (News) wrote:

It would take a true optimist to guarantee a solid state relay
will
have a longer life than a traditional one.

Depnds on the application. I doubt a traditional relay would last
long operating with a 7 Hz PWM signal to control the speed of a
mains
circulating pump. Might be a tad noisy (acoustically and
electrically) as well. B-)

Why would you use any relay on the output of a PWM generator?

So a micro controller can be isolated from, and switch, mains power?

Most would isolate the mains input to the device - not its output?

Doesn't take a true optimist to guarantee a SSR will last longer than
a traditional relay in this application.

Well, yes. But then not many used a hammer where a screwdriver is needed.

BTW, would you guarantee your SSR on the output of the PWM device will
provide total galvanic isolation when off - in the same way as a
mechanical relay would?

--
*You know you're a redneck if your home has wheels and your car doesn't.

Dave Plowman London SW
To e-mail, change noise into sound.