Magnetic shunt on a relay coil.

[dr pepper]

Further to my recent question on magnetics.

I have this coil from a 230v AC octal industrial relay, actually I've a boxfull.
What is the purpose of the copper D shape piece on the pole, the bit where the relay armature would come to rest, looks like a shorted turn.
I suspect it improves effeciency by reducing eddys or similar (the core is solid not laminated), dc relays dont have these.
I was thinking maybe a circular arrangement of these might make a generator, would I be better keeping the copper piece or losing it.

 

[schmitt trigger]

If I remember properly, it works similar to a shaded pole.......

 

[dr pepper]

H'mm, shaded pole motors were popular on cheaper end turntables, and nowadays seen in microwaves as the cooling fan.
The shaded pole creates a second 'phase' for the rotor.
How that would benefit a relay I dont know, unless theres a magnetic delay and the shaded pole holds the armature during the crossing period of the supply, or at least reduces chattering of the armature.
Not an issue for me, mole grips at the ready.

 

[Ross Craney]

Further to my recent question on magnetics.

I have this coil from a 230v AC octal industrial relay, actually I've a boxfull.
What is the purpose of the copper D shape piece on the pole, the bit where the relay armature would come to rest, looks like a shorted turn.
I suspect it improves effeciency by reducing eddys or similar (the core is solid not laminated), dc relays dont have these.
I was thinking maybe a circular arrangement of these might make a generator, would I be better keeping the copper piece or losing it.

View attachment 74647

DC relays do have these and it is to dampen the flux resulting in slow to operate & slow to release relays. They are (were) very common in telephone exchange switching relay sets

Cancel that , I just had a closer look at the pic. But I would still venture to say that it is some sort of flux conditioning.

 

[tcmtech]

It creates a phase shift, similar to how shaded pole motors work as mentioned earlier Dr P, in the AC magnetic field so the relay is less likely to buzz and chatter.

As the main part of the core magnetic field passes through zero the magnetic field in the shaded part is lagging behind just enough to keep the relay plunger, or what ever version yours uses, in place until the main part has had a chance for its field to reverse and start holding the plunger until the next half of the AC cycle starts again.

 

[dr pepper]

Thanks chaps,
I'd sort of guessed something like that after shaded pole was mentioned.
I've rigged up an led and a diode/cap to the coil, there doesnt appear to be much difference in o/p with or without the shunt, so I'm going to lose it, primarily because I can use the resultant protruding section to glue through the front on an enclosure.
I'm also going to try a low voltage 24v relay, I dont expect a low voltage coil to give as much voltage due to lesser turns.
i have a linear o/p hall effect device, if I could be bothered I could look at the o/p of the coil magnetic flux wise with and without the shunt, but i dont have that much time.

 

[mvs sarma]

It acts like fixed air gap in the magnetic path. Helps to prevent armature sticking for longer time after the drive current is removed.

In telecom we used to have adjustable non magnetic screw with a locknut.

 

[dr pepper]

Hi Mvs, wouldnt that be for DC.
I have some old tele relays and I was thinking after reading post 4 why they didnt have a copper shunt, but you just answered that, there is indeed a screw/locknut, and they look like they are made from invar, non ferritic metal.

 

[mvs sarma]

They were for DC, no doubt.
Even in AC, we might stop a relay at some time irrespective of phase of voltage or current (unless zero crossing methods are adopted), thus remnant magnetism is expected.
if the copper tag shown in photograph is only at the edge as a gap adjustment between core face and armature, purpose is same that i indicated.
of the copper is passing through the inner side of core (below the coil), then it is perhaps to prevent armature chattering to the 60Nz or so frequency. In later case , i humbly feel that the copper foil forms a sort of shorted winding inside to create a level of sluggishness , that we used to call , slow to operate , or slow to release.

I would request the make and model number of the relay and makersname, to help further analysis, please !!

 

[dr pepper]

The copper tag is just at the edge, it isnt a physical gap adjustment, more a shorted turn.
From earlier replies I summise that it does a similar job as the shunts do in a shaded pole motor and creates a lag in the magnetic flux, and as I understand it this smooths out the pull on the armature.
As a generator using a neo magnet there doesnt appear to be any difference with or without the tag.
Theres no manufacturer on these relays, however from the equipment I'd say it was made by teledyne in the late 70's, its a plasma treament machine for paper and board, well was its now been scrapped.
Heres a better pic for those interested, theres also a full relay as well as another coil with copper 'D' and core removed.
I might have some 415v ones somewhere, might try one of those tonite.

 

[mvs sarma]

dr pepper, i don't see any photo or a link. OK i do understand an old product, but we can perhaps get a mechanical diagram or datasheet for the same. please indicate the relay # and little more details as shown on the metal / plastic cover.

 

[mvs sarma]

dr, pepper, now i see that photo.
let me study for similar relays , as we also have similar ones made in India by O/E/N and PLA

 

[mvs sarma]

could you please see whether the info in link here helps to appreciate,
**broken link removed**

 

[dr pepper]

Interesting, thanks for the link.
I think we've covered pretty much all I need to know, esp as I'm going to hack the relay for its winding.
Having read that I might try the shunt on the inboard or as they refer to the heel end of the core and see if that makes a difference, according to the thread on the link it speeds up the response of the relay.

P.S. on accaision the only way I can upload a picture is if I first create the thread and then edit the text to incluse the picture, I think its something to do with the parental controls on the computers here at work.

 

[mvs sarma]

I am happy that the link i gave , helps you to some extent , at least.
i get you,
no photo is needed.
but try to give some links , if you have.
if there is a datasheet or code number written on the relay , it might also help us.

 

[kinarfi]

it changes the hysteresis loop to being nearly square so that as the magnetic field reverses, it reverses so fast that the momentum of the coil holds it in place, if you cut it or lose it, there is a good chance your relay will start to buzz,
kinarfi
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/hyst.html#c1

 

[dr pepper]

Yes I think I've established that it quietens the relay.
Seeing as I was thinking of making a humble little dynamo to generate a few ma at 6v I dont think I'll be needing the little piece of copper.

 

[MrAl]

Hello guys,


"One test is worth a thousand expert opinions" sometimes, so the simple answer is, operate the relay a few times with the copper in place and operate the relay a few times without the copper in place and see if you can notice a difference. If you feel like getting deeper into it, you can test the average response of the relay with and without the copper by looking at the closures (and openings) on a scope using a resistor and bias voltage.

A photo of the relay 'across the flat' part of the armature would help us to judge the distance from the top of the copper to the top of the metal pole of the armature. Is it lower or higher, or nearly equal to the height of the top of the pole when it is installed properly. It would have to be a perfect cross section view however.

 

[kinarfi]

it changes the hysteresis loop to being nearly square so that as the magnetic field reverses, it reverses so fast that the momentum of the coil holds it in place, if you cut it or lose it, there is a good chance your relay will start to buzz,
kinarfi
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/hyst.html#c1

EDIT: PS this is practical experience from working with various relays, the stronger the return spring, the more likely to get a buzzing relay, not having the hysteresis ring is not a guarantee of a buzzing relay.

 

[MrAl]

Hi,

Just to introduce a little theory here. If the copper ring does represent a shorted turn, then it could introduce a delay.

If we could have a perfect transformer with a coupling factor of exactly 1 and zero ohm windings and we energized the primary with a source and then removed the source and shorted out one of the windings (even just a one turn winding), it would take forever for the magnetic field to collapse. Since a perfect coupling is not possible and certainly not how this relay is made, we'll see just a delay while the field is collapsing. The reasons for this is in the definition of the inductor where the voltage across the inductor plays a huge role in how fast the energy stored in the field decreases. With 2v across a winding if it takes 2 seconds to decrease to some small level, then with only 1v across that winding it would take 4 seconds to decrease. With 0.5v it would take 8 seconds, and so on. When we get to zero volts (a shorted turn of a perfect zero ohm winding) the time delay is infinite.
So the net effect in the real life coil is a filtering effect or a delay effect. So that could be the main purpose of the copper.