solenoid or relay

[AndyStobbs]

Having spent much of the day trying to obtain a part for a piece of plant equipment, I have come across the two words being used to describe the same thing. To me their is a very stark difference between the two, but I wonder what everyone on here thinks.

So people, what would you term a solenoid, and what would you term a relay?

 

[awemawson]

A solenoid is a coil of wire that (usually) has a slug of iron in it's former that can be pulled in when power is applied to make something move.

A relay (usually) contains an electro-magnet (a solenoid with a fixed iron core) that attracts a movable 'armature' that operates electrical contacts.

They are quite different things

Andrew

 

[piman]

Hello Andy,

a solenoid is a coil with an armature that reacts to applied voltage, common items are solenoid valves or starter solenoid on a car (which is really a heavy current relay). A relay is activated by it's solenoid and has various contacts to switch what it is connected to on and off.
Like many terms they get used incorrectly sometimes but are in common use. Much like the term 'alloy wheels', as all wheels are alloy but we recognise that 'alloys' refer to aluminium wheels.

Alec

 

[normspanners]

Solenoid is for heavy current switching IE starting or heavy motor applications ie winch etc but you can have solenoid control hydraulic valves.
A relay is lightish switching up to 80amps ish or for doing what it is called--- to relay a connection.

 

[wookie]

A Solenoid is an coil of wire that when an electric current passes through it creates an electromagnetic force that pushes or pulls a centre metal rod that in-turn operates something else e.g. hydraulic valve, a lever, pulls a cable etc etc

A relay is a solenoid that operates on a set of electrical contacts effectively forming a switch.

So a relay is a solenoid, but a solenoid isn't always a relay

That's my take on it anyway...

 

[rtbcomp]

I suppose starter solenoids are named as such because originally the contacts were closed by mechanical action, pulling a (bowden) cable or pushing a button, usually with the foot.

As cars were dragged into the 20th century the cable/button was replaced by a solenoid and the name "starter solenoid" stuck.

 

[AndyStobbs]

Well I'm glad to see its not just me who believes there to be a difference. Basically the part is a relay from a Hyundai robex. The start signal from the ignition key is fed first onto a relay, which in turn once energized feeds the starter solenoid start connection.
The starter motor is of the pre-engaged type.

Meant to add, I felt this part to be a relay as it has no usable mechanical output. Couldn't comment on how its constructed internally.

 

[madkayaker]

A solenoid is a coil of wire that (usually) has a slug of iron in it's former that can be pulled in when power is applied to make something move.

A relay (usually) contains an electro-magnet (a solenoid with a fixed iron core) that attracts a movable 'armature' that operates electrical contacts.

They are quite different things

Andrew

This is how I view it. It can get very confusing on HV control gear once you start getting back contractors for interlock etc

 

[pedrobedro]

A relay switches a heavier current using a low current, a solenoid throws in a mechanical process like a starter or a winch.

 

[MattF]

A relay switches a heavier current using a low current, a solenoid throws in a mechanical process like a starter or a winch.

They are both low current control, higher current transfer units involving a mechanical process. The post above about the moving core versus contacts magnetically attracted arms/contacts is the one I'd go with as a general definition. A solenoid usually involves a moving core which bridges the gap between two contacts when moved through the application of current. (That's not technically correct, but it seems to be the most common perception of a solenoid). You can also, in theory, change the current handling abilities of a solenoid, through changing the contact surface area and material. Relay contacts are not generally, (never?), changeable.

Anything which doesn't involve mechanical action is a different thing altogether. You're then into solid state switching, namely semiconductors.

 

[puffernutter]

But a solenoid is a key part of an electromagnetic relay! (and it's the word "electromagnetic" that is silent when used with the term relay!

A starter solenoid performs two functions - 1. to mechanically engage the gear in the starter ring and 2. To electrically connect the starter motor to the battery. So it is both a solenoid AND a relay!

Cheers

Peter
(Who used to design railway signalling systems using 1000's of relays)

 

[normspanners]

A starter solenoid performs two functions - 1. to mechanically engage the gear in the starter ring and 2. To electrically connect the starter motor to the battery.

not allways------

 

[AndyStobbs]

not allways------

Thats when it becomes a relay I think.

 

[Robotstar5]

and to add another, what about contactors?

 

[madkayaker]

and to add another, what about contactors?

That's easy there big relays!

 

[normspanners]

A solenoid (from the French solénoïde, derived in turn from the Greek solen "pipe, channel" + combining form of Greek eidos "form, shape"[1]) is a coil wound into a tightly packed helix. The term was invented by French physicist André-Marie Ampère to designate a helical coil.[2]
In physics, the term refers specifically to a long, thin loop of wire, often wrapped around a metallic core, which produces a uniform magnetic field in a volume of space (where some experiment might be carried out) when an electric current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets.
In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion. The term is also often used to refer to a solenoid valve, which is an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid, or a linear solenoid, which is an electromechanical solenoid.


But also on some large vehicles they have starter solenoids to switch the heavy current which can be 80ish amps to the starter terminal on the pre-engage starter solenoid that in turn spins the starter armature to help engage the teeth before the main contactors connect together, then the holding coils which hold the starter in the 'switched on position' take over, to cut the current draw.
In that case the first starter solenoid is actually preforming a relay job.

 

[puffernutter]

Ford is American, they can't spell anyway!