• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Electromechanical Relay

Status
Not open for further replies.

Eran12

New Member
Hello,
Im trying to implement an application that will give me
indication when specific electrical device is turn on.
that device current consumption is around 1 Amp,
and it connected to the wall plug (220VAC).

I tried to used electromechanical relay that will get swithed when
current flow through it, but it didnt work
since the coil of the relay has a relative high resistance (around 7K ohm)
and it does not enable 1 AMP currnt flow through it.
the result was that the switch was turn on but the electrical device
didnt have enough current to turn on.
Does anyone have an idea to resolve this problem?

ill be grateful to get an alternative simple ways to implement this .


thanks.

Eran.
 

Sceadwian

Banned
Is the device turning itself off or is a remote switch of some kind?
 

ericgibbs

Well-Known Member
Most Helpful Member
The voltage rating of the relay coil is 220 VAC.
Connect the relay coil in parallel with the device you want to monitor.

When the device is ON, so will the relay.
 
Last edited:

Eran12

New Member
Thank you very much for the answers.
i tried to connect the it in parallel with small resistance,
but then the relay does not switch on and off since the current
that flows through it is very small.

Eran.
 

ericgibbs

Well-Known Member
Most Helpful Member
Thank you very much for the answers.
i tried to connect the it in parallel with small resistance,
but then the relay does not switch on and off since the current
that flows through it is very small.

Eran.
I didnt say connect it in parallel with a resistance.!

Connect the relay in parallel with the device you want to monitor.

For example if the device is a lamp, then connect the relay in parallel with lamp.

What is the device you want to monitor.?
 

Sceadwian

Banned
I usually just turn my head and look to see if it's on =) You obviously have no idea what you're doing and to check to see if the TV was turned on would require you to wire the relay inside the TV cabinet on the other side of it's main AC switch. If you don't know what you're doing it's very possible to kill yourself playing around inside a TV cabinet.
 

Eran12

New Member
I was planing to connect to the external cable of the TV.
I connected the coil in series to the phase.
I was thinking to connect 220 ohm resistor in series to the coil
to enable current flow of 1 Amp.

i made some calculation and i think it will turn the switch on and off.
Do you think it is possible to implement it by connecting to the TV cable or
just by connecting to TV cabinet ?
 

KMoffett

Well-Known Member
I didnt say connect it in parallel with a resistance.!

Connect the relay in parallel with the device you want to monitor.

For example if the device is a lamp, then connect the relay in parallel with lamp.

What is the device you want to monitor.?
That would assume that the switch was upstream of the power outlet. If the relay is in parallel with the TV's cord it would always be ON, even when the TV was off. Unless the OP put the relay inside the TV, downstream from the TV's power switch.

Or so it seems.

Attached is a design for a Power-On monitor that I saw somewhere. I haven't tried it, but it seems to make sense. The diodes would to be rated for greater than the device current.
ken
 

Attachments

Willbe

New Member
that will give me
indication when specific electrical device is turn on.
that device current consumption is around 1 Amp,
and it connected to the wall plug (220VAC).

I tried to used electromechanical relay that will get swithed when
current flow through it, but it didnt work
since the coil of the relay has a relative high resistance (around 7K ohm)
and it does not enable 1 AMP currnt flow through it.
the result was that the switch was turn on but the electrical device
didnt have enough current to turn on.
You can wind your own current-operated relay using the frame of an existing conventional relay. When cars had electromechanical voltage regulators the coil of the current sensing relay had a few turns of #12 wire.
Nowadays nobody seems to make relays like this, but a junkyard may have one of these.

Or, 1v/1A = 1 ohm (at 2w), and this series sense resistor turns on the base-emitter junction of a xsistor which turns on a relay. 1v out of 220v is negligible. You will then need a wall 'former to power the xsistor ckt.

Digi-Key has relays that operate as low as 1.5vdc or 3vdc, but the contacts may not handle 1A. This would not require a wall 'former.

Commercially available current operated adjustable switches start at $40 or so.
 
Last edited:

ericgibbs

Well-Known Member
Most Helpful Member
That would assume that the switch was upstream of the power outlet. If the relay is in parallel with the TV's cord it would always be ON, even when the TV was off. Unless the OP put the relay inside the TV, downstream from the TV's power switch.
Hi Ken,
This point was assumed. [ie after the switch]

He has been told to put the relay inside the TV.
Seeing how limited the OP's knowledge is, I am concerned that he is out of his depth working on mains devices.
 
Status
Not open for further replies.

EE World Online Articles

Loading
Top