Maker Pro
Maker Pro

Contactor coil: 50 Hz vs. 60 Hz

J

John S

Jan 1, 1970
0
Root Mean Square does not imply an ac waveform, its jsut most commonly
used for ac waveforms. Every stable waveform has an rms value, even
perfect dc.



I realised it was perhaps not the best phrasing. But... would the dc
component be the average V or the rms?


NT

DC is all of the following: Average, Peak, RMS, Mean, Mode, and most
anything else.

John S
 
P

Paul Conners

Jan 1, 1970
0
Generally, in electronics, "DC component" is defined as the average
value (say, over a period of a periodic waveform). So a 1V peak sine
wave sitting on top of 1VDC would have DC component of 1.0V.
A 1V peak sine wave has a DC component of 0.

The RMS value is the heating value- a 1 ohm resistor with 1VDC across
it will dissipate 1W. A 1 ohm resistor with 1.414V peak sine wave
across it (1 V RMS) will dissipate 1W.

A 1 ohm resistor powered with a 1V peak sine wave sitting on top of
1VDC will dissipate a bit more than 1 watt (RMS value is sqrt(3/2) if
you want to get analytical about it, so about 1.22W).

Thank you SP. Amid all the chest-pounding and playground antics here I can
actually learn something.
 
D

Don Kelly

Jan 1, 1970
0
"NT" wrote in message

I disagree.

Since the relay is open when power is applied to the coil, it's the
open inductance (and the resistance, of course) which will determine
how much current will flow through the coil, that current being what
generates the magnetic field to start the armature on its way.
yup

Then when the relay closes, the closed inductance comes into play and
holds the armature in place until the current through the coil is
reduced to a point where the armature's return spring overcomes the
weakened magnetic field, allowing the armature to open.

yes. I guess in theory both matter, one determines closing behaviour,
the other ensures the relay doesnt overheat. In practice though the
margins are very large, and its normal to simply fix holding current
to suit the relay, and not worry about closing current, which will be
so close as to make no real world difference in all but exceptional
circumstances. But yes, we can consider both if need be.

true with all relays under all ac conditions. Theyre designed to work
that way.
No, its exactly how theyre designed to operate.
Where's the conjecture? I get the feeling you could do with bringing
your skills up to speed on relays.
---
Perhaps.
---
Something like this?
+-----+
120AC>--|~ +|----+
| | |
| | [COIL]
| | |
120AC>--|~ -|----+
+-----+
That would work.

Not in all cases, certainly.

I'd like to see you find one single electromechanical relay that wont
work for.

---
The P&B MR5A I talked about in an earlier post, which has a 240V
50/60Hz coil, a coil resistance of 4800 ohms, an impedance of ~ 6600
ohms at 50 Hz, an open inductance of 14.5 henrys, and a closed
inductance of 16 henrys

But I don't think "typical" is what we're after since we want
something that will _always_ work.

This 2:1 ratio normally is good for relays, and the OP can check his
to see if it conforms to that. If it does, the thing will always work
when subject to this formula.

FWIW, when ac is applied you get puling force plus vibration. With dc
there is no vibration component when its closed, so less holding
current is needed. How much less I've really no idea.

Some relays are fast movers capable of 100s of Hz, some are slow. Ac
relays can always work on dc, but dc ones often dont work ok on ac.

Since current is what's doing the work, my real-world example shows
that 240V 50 Hz RMS impressed across a load with an impedance of 6600
ohms will force 36mA RMS of current through the load.

Then, since it's current that's doing the work, 36mA of DC through the
coil should accomplish the same thing.

Re ripple: If the relay is designed to run on ac 50 or 60Hz, its
designed and rated to live with the current and force variations that
go along with that, 100-120 times a second. Running it on rectified
mains will only serve to reduce the current variations through the
cycle, it wont cause the relay any issues.

Re rms voltage: With my 2:1 figures, rectified 120v is spot on. With
your 174v figure, 120v is well within the 50% margin. Of course for
some uses that margin would need to be confirmed by testing before
production, and reconfirmed if a new relay type is used. Or as you
say, a cap could be added. Or for off brand consumer goods, in it
goes, relays are good for it.

There's no such thing as "rms dc voltage",

RMS can be applied to any and every waveform, dc included. Its very
relevant when working with rectified ac, semismoothed or unsmoothed.
and if the relay is
designed to operate on AC with a certain RMS current in its coil, how
can it possibly overheat if that current is DC?

With the same current it wont, with higher curren ti will. IIRC you
proposed using 174v rms, that would be ok on your specific relay, but
not a universal solution.

NT
-----------------------
I sense a bit of cross confusion in this thread.

a)Do not the AC/DC ratings refer to the contact rating rather than the coil
rating? As with any switch, there is a big derating of contacts designed for
AC use but applied to DC- Example a typical 120V 15 A light switch would
fail at 15A 120V DC- it might work at 15A, 12V. Older switches with good
snap contacts do much better.

You indicate experience for the factor of 2:1- but is this something that
translates across the AC/DC barrier?

b) John indicates 174VDC giving 0.036A would be OK- for closing. However
when closed, the holding current will be 0.031A and this is the steady state
current that is involved in heating when the relay is closed. For DC the
voltage would need to be about 150VDC [ (174*0.031/0.036)^2]. So it
remains to be seen if that is sufficient to close the relay. According to
you- it would be more than adequate. From John's 80% criterion it is
inadequate.- so point (c).

c) The peak force is related to the square of peak flux For AC, this is
proportional to (Vrms/f)^2 independent of the magnetic medium. The magnetic
medium determines the corresponding peak current. While a DC current of
0.036A corresponds to an rms current of the same magnitude, and the average
force is the same, at that current, as the average force in the AC case, it
is well below the peak force (about a factor of 2, ). This may have have a
bearing on the relay's operation- just a conjecture.


Don Kelly
cross out to reply
 
D

Don Kelly

Jan 1, 1970
0
"NT" wrote in message
-----------------------
I sense a bit of cross confusion in this thread.

a)Do not the AC/DC ratings refer to the contact rating rather than the
coil
rating? As with any switch, there is a big derating of contacts designed
for
AC use but applied to DC- Example a typical 120V 15 A light switch would
fail at 15A 120V DC- it might work at 15A, 12V. Older switches with good
snap contacts do much better.

No, I'm talking about coil voltage ratings.

You indicate experience for the factor of 2:1- but is this something that
translates across the AC/DC barrier?

I'm not 100% clear what you mean there. In short, many relays only
have one coil voltage rating, and its for just one of either ac or dc.
The various ones I've seen that have coil 2 ratings, one for ac one
for dc, have consistently had the dc coil rating be half the ac
voltage rating.

b) John indicates 174VDC giving 0.036A would be OK- for closing. However
when closed, the holding current will be 0.031A and this is the steady
state
current that is involved in heating when the relay is closed. For DC the
voltage would need to be about 150VDC [ (174*0.031/0.036)^2]. So it
remains to be seen if that is sufficient to close the relay. According to
you- it would be more than adequate. From John's 80% criterion it is
inadequate.- so point (c).

c) The peak force is related to the square of peak flux For AC, this is
proportional to (Vrms/f)^2 independent of the magnetic medium. The
magnetic
medium determines the corresponding peak current. While a DC current of
0.036A corresponds to an rms current of the same magnitude, and the
average
force is the same, at that current, as the average force in the AC case,
it
is well below the peak force (about a factor of 2, ). This may have have
a
bearing on the relay's operation- just a conjecture.

Don Kelly
cross out to reply

Peak force would come into play when dealing with stiction, but a
relay would have to be on its very last legs for stiction to be
significant in practice.


NT

Thank you.

Possibly the DC rating is lower because of the lower impedance (In the
example, with the coil closed the resistance cited is about 60 % of the 60
Hz impedance and the same current is wanted.

Don Kelly
cross out to reply
 
E

ehsjr

Jan 1, 1970
0
NT said:
If you want to go get some specs of other relays, you can. This is
starting to get silly.

Worth investigating, to me. JF gave a specific relay & numbers. I
tried to find a relay to support the idea that an AC/DC relay would
be happy with DC voltage about 50% of AC rating. Can you please
provide a reference?

Meanwhile, what I did find was an ap note from Tyco entitled
"Operating DC Relays from AC and Vice-Versa" .
http://relays.te.com/appnotes/app_pdfs/13c3250.pdf

It does not agree with the DC at ~50% of AC rating idea. It uses
the example of a KR series relay coil. Their example uses a 12
volt AC relay fed by DC. The example states that the "DC voltage
cannot exceed 9.8 volts", and "should not be lower than 7.35 volts".
Thus the DC range would be ~61%(minimum) to ~81% (maximum) of the
12VAC rating.

Extrapolating, it does agree with the idea of BR+C fed by 120 for
the 240 volt relay, insofar as the DC voltage:
~146VDC min to ~194VDC max, which makes the midpoint ~170VDC.
That's very close to ~168 from the BR+C

Regarding coil ratings, I've worked with DC relays, and I've worked
with AC relays, but I haven't worked with AC/DC coil relays, so
I can't speak from experience with them, and I haven't found
anything yet specifically dealing with that, other than the
link I found to Tyco. So a specific link or links would be
most helpful.

Thanks,
Ed
 
J

Jamie

Jan 1, 1970
0
ehsjr said:
Worth investigating, to me. JF gave a specific relay & numbers. I
tried to find a relay to support the idea that an AC/DC relay would
be happy with DC voltage about 50% of AC rating. Can you please
provide a reference?

Meanwhile, what I did find was an ap note from Tyco entitled
"Operating DC Relays from AC and Vice-Versa" .
http://relays.te.com/appnotes/app_pdfs/13c3250.pdf

It does not agree with the DC at ~50% of AC rating idea. It uses
the example of a KR series relay coil. Their example uses a 12
volt AC relay fed by DC. The example states that the "DC voltage
cannot exceed 9.8 volts", and "should not be lower than 7.35 volts".
Thus the DC range would be ~61%(minimum) to ~81% (maximum) of the
12VAC rating.

Extrapolating, it does agree with the idea of BR+C fed by 120 for
the 240 volt relay, insofar as the DC voltage:
~146VDC min to ~194VDC max, which makes the midpoint ~170VDC.
That's very close to ~168 from the BR+C

Regarding coil ratings, I've worked with DC relays, and I've worked
with AC relays, but I haven't worked with AC/DC coil relays, so
I can't speak from experience with them, and I haven't found
anything yet specifically dealing with that, other than the
link I found to Tyco. So a specific link or links would be
most helpful.

Thanks,
Ed
You must remember that AC coil relays are wound a little different,
its not just induction here. Inter pole windings help keep the AC coil
from chattering the armature. I am sure under DC operation, this may
effect the calculations.

There are some AC coil relays that do not do this and thus the 50%
voltage for DC should come close, but then again, DC R in the coil also
plays a role in this.

Jamie
 
E

ehsjr

Jan 1, 1970
0
Jamie said:
You must remember that AC coil relays are wound a little different,
its not just induction here. Inter pole windings help keep the AC coil
from chattering the armature. I am sure under DC operation, this may
effect the calculations.

There are some AC coil relays that do not do this and thus the 50%
voltage for DC should come close, but then again, DC R in the coil also
plays a role in this.

Jamie

Your post contains nothing specific and does not address
my question.

I am looking for a specific link or links that shows a datasheet,
ap note, or example of a relay that NT has in mind. Do you have one?

I want specifics, like John Fields posted; the specs that NT
said you could get: "If you want to go get some specs of other
relays, you can." The specs I have been able to find so far
do not demonstrate what NT was talking about, thus my post
asking for a reference.

Ed
 
J

Jamie

Jan 1, 1970
0
ehsjr said:
Your post contains nothing specific and does not address
my question.

I am looking for a specific link or links that shows a datasheet,
ap note, or example of a relay that NT has in mind. Do you have one?

I want specifics, like John Fields posted; the specs that NT
said you could get: "If you want to go get some specs of other
relays, you can." The specs I have been able to find so far
do not demonstrate what NT was talking about, thus my post
asking for a reference.

Ed
Don't be anal, they make relays that will do AD/DC because they have a
diode imbedded in them. The voltage ratings are the same. The coil is
actually of DC type.. They also have relays with shunt diodes built into
them, for those you need to insure the polarity is correct and are
strictly DC only.

We also deal with solenoids to operate in the same manner..

Scroll down and read about AC coils, I am sure if you're looking for
some more detailed information you can find it, but this will explain
some of the differences.

http://www.ehow.com/about_6498402_difference-ac-dc-relay-coil.html


Jamie
 
J

Jamie

Jan 1, 1970
0
The said:
First you tell him not to be anal then you lube him up really good
then you ram your howdy doody linkage , what's up kiddo?
BOOWAHAHA...I JUST HAD TO, YOU HAD TO:) LOL
MOST UNIVERSAL MODELS ARE SOMEWHAT ERRATIC & DUBIOUS.
EUROS AND AMERICANS WILL ALWAYS BE THEMSELVES, BEST CAN BE DONE IS PUT
TO USE A CONVERTER DEVICE HARMONIC WITH BOTH WAVES PHI's. OR FREQUENCY
TO OR FROM THE INSTINCTIVE DEVICE BE IT AC OR DC PLAIN COIL OR
CONTACTOR WHICH IS HIS CONUNDRUM.

PLEASE SEND YOUR ARGUMENTS TO WHO GIVES A FLYING ****.COM :)

TGITM
You must? You read and replied to it. It didn't concern you one bit how
ever, you were interested enough to push those fat fingers along while
burning all those calories sitting on your fat ass, just to post your
dumb shit..


You are taking up valuable space, move on and allow some one more
deserving to fill that gap.

Jamie
 
J

Jamie

Jan 1, 1970
0
The said:
YOU THINK YOU KNOW SOMEONE MORE DESERVING?
**** YOU CUMSHOT..GO POP YOUR LOAD SOMEWHERE ELSE.
TELL YOUR FAT ASS FATHER I AM POSTING HIS NAME AS A REFERNCE ON A
HAUNTED HOUSE I HAVE MY EYES ON......BOOWAHAHAHAHA!
AND DONT ASK ME TO BILL THE GROUP FOR MY SERVICES EITHER.
THIS IS HOW WE DO IT.
PATECUM
TGITM
Useless pond scum..

jamie
 
J

John S

Jan 1, 1970
0
I may be able to obtain a very small 2-pole 240 vac contactor I need rated
for 50 Hz only.

If I install it in N. America, what's the implication? Is the hold-in
magnetism less than if it were 60 Hz? Just noisy?

Hi, Dave -

Magnitisim is less.

Noisy depends on many things.
Please don't ask or suggest other sources. This is a very specific device and
I've not been able to locate other than this.

Thanks,
Dave

You should look at the manufacturer's specifications. The 50/60 Hz will
not matter much except for one thing: the coil current will be reduced
to ~50/60 of its nominal value (~83.3%) because of the coil inductance
(it has to do with total impedance, but this is a best guess without
knowing more about your contactor). Usually, the manufacturer will list
the minimum voltage the coil can handle.

At this point, my best guess is that the coil will suffer a 15% loss of
excitation voltage. If the mfr says that's too low, you may be in
trouble at low line.

Cheers,
John
 
J

Jamie

Jan 1, 1970
0
John said:
---
If you're saying that half-wave rectified 12VAC will cause the
armature of a relay with a 12VDC coil to close, instead of chatter,
then I'd have to ask for proof since I have empirical evidence which
refutes your assertion.

Years ago, Larkin and I had the same argument here.

He took your position and lost the argument.

Well, then he lost unfairly.

Never heard of core hysteresis?
---
What does that have to do with driving DC coil relays with rectified
AC, or driving AC coil relays with DC?

From my experience, those diodes are used in order to return the
coil's inductive turn-off transient to the positive supply in order to
keep E = LdI/dT from ruining a relay driver's day, and to save the
user the expense of an extra part and the PCB real estate needed for
its implementation.
Why?. You don't understand why, I guess?

I was going to make a whole page for you to read, but I know how you
carry on with JL, I won't be another one of your imaginary conquest.

Not saying that don't know what your doing but you tend to over look
a few things that have been done in the field over the years.


Jamie
 
E

ehsjr

Jan 1, 1970
0
Jamie said:
Don't be anal, they make relays that will do AD/DC because they have a
diode imbedded in them. The voltage ratings are the same. The coil is
actually of DC type.. They also have relays with shunt diodes built into
them, for those you need to insure the polarity is correct and are
strictly DC only.

We also deal with solenoids to operate in the same manner..

Scroll down and read about AC coils, I am sure if you're looking for
some more detailed information you can find it, but this will explain
some of the differences.

http://www.ehow.com/about_6498402_difference-ac-dc-relay-coil.html


Jamie

I don't know how to make it clear enough for you to understand.
While I do appreciate your attempt to help, I must say it misses
the point.

I want a *specific* link to an *AC/DC* relay of the type *NT*
had in mind, or to an ap note or reference that discusses a relay
coil that is rated for *both* AC and DC as he indicated.

Do you have a link to what NT was talking about? Here's what
he said:
"The various ones I've seen that have coil 2 ratings, one for ac one
for dc, have consistently had the dc coil rating be half the ac
voltage rating."

I _do not_ need generalizations, hand waving and condescending
responses. You mentioned a relay that will "do" DC because it
has an imbedded (sic) diode and say "The voltage ratings are the
same." That is *NOT* what NT said. He talks about the dc
coil rating being half the ac rating.

Ed
 
J

Jamie

Jan 1, 1970
0
ehsjr said:
I don't know how to make it clear enough for you to understand.
While I do appreciate your attempt to help, I must say it misses
the point.

I want a *specific* link to an *AC/DC* relay of the type *NT*
had in mind, or to an ap note or reference that discusses a relay
coil that is rated for *both* AC and DC as he indicated.

Do you have a link to what NT was talking about? Here's what
he said:
"The various ones I've seen that have coil 2 ratings, one for ac one
for dc, have consistently had the dc coil rating be half the ac
voltage rating."

I _do not_ need generalizations, hand waving and condescending
responses. You mentioned a relay that will "do" DC because it
has an imbedded (sic) diode and say "The voltage ratings are the
same." That is *NOT* what NT said. He talks about the dc
coil rating being half the ac rating.

Ed
Is this what you're looking for ?

http://relays.te.com/appnotes/app_pdfs/13c3250.pdf

It explains operating AC coils on DC and AC coils using
the internal DIODES for shading rings design.

These are just some examples out there.

I don't know what "NT" had in mind, if this isn't what
you're after, than I'll stand down. ;)

Btw.
P&B got bought out, in case any one didn't know.


Jamie
 
J

Jamie

Jan 1, 1970
0
John said:
John Fields wrote:




Well, then he lost unfairly.


---
Instead of blathering on about something of which you obviously have
little knowledge, why not try it?

That is, get a few relays with DC coils, drive their coils with
half-wave rectified AC, and post back with the results.
---

Never heard of core hysteresis?


---
Sure, but for relays it's usually defined as the difference between
the must-make and must-break voltage instead of this:

http://www.google.com/imgres?imgurl...xBqTvXvFJSCsALa6bmOBg&ved=0CCEQ9QEwAQ&dur=468
Now we both know!
---

Why?. You don't understand why, I guess?


---
Well, although a case might be made for:

.AC>---[DIODE>]--+-------+
. | |K
. [COIL] DIODE
. | |
.AC>-------------+-------+


I've never heard of a DC solenoid being converted to AC by using a
shunt diode, have you?

If so, why not give us the benefit of your knowledge by elaborating on
the subject?
---

I was going to make a whole page for you to read, but I know how you
carry on with JL, I won't be another one of your imaginary conquest.


---
Aw... Poor baby.

Afraid of making and having to own up to an error, are you? ;)
---

Not saying that don't know what your doing but you tend to over look
a few things that have been done in the field over the years.
No error, you're the one with egg on the face loser, and this will be
my last to you. I will not be another JL stick for you to crack your
false sense of victory with.

http://relays.te.com/appnotes/app_pdfs/13c3250.pdf

Just because you haven't seen it or think it shouldn't be done means
every one else should bend over to your rule? Sorry sucker, this is why
people move on and those like yourself are left holding the bag.


And while your reading that doc, if you even do, the comment about
unfiltered DC where the armature might experience movement, they don't
say it will. That is because it depends on the mechanical design of the
relay and type of system in place.

Further more, I guess you've never seen the old trick of operating a
small DC relay with half wave to force the unit to slightly vibrate, not
enough to actually see it how ever, when doing this, you could force the
contact surface to keep themselves cleaner and thus cheap relays would
be used to pass reference signals through. This would be evident over
time from apparent ware on the contacts from mechanical movement and no
arc which would otherwise do the wetting process via the plasma process.

By and have a good life..


Jamie
 
J

Jamie

Jan 1, 1970
0
The said:
YOU SUCK.....STAY OFF USENET DUDE.
YOU'RE ON BORROWED WAVELENGTH AS IT IS.
GO HUNT DOWN SOME TERRORISTS OR DO SOMETHING HELPFUL INSTEAD.
CHANGE YOUR NAME, TRY COOKIE MONSTER.
BOOWAHAHAHAHA,.....YOU FINK !
PATECUM
TGITM
You know what's even funnier than your stupidity? Your lack of
ability to convey over what you really want to say in english,
it's hilarious..

Jamie


"Just for you:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
"
 
E

ehsjr

Jan 1, 1970
0
Jamie said:

Geeeez. I posted that link in my _first_ post in the thread, and
you replied to that post. I guess you either didn't read the post
properly, or didn't understand it. The ap note does not agree with
the DC at ~50% of AC rating idea - details are given in that post.
It explains operating AC coils on DC and AC coils using
the internal DIODES for shading rings design.

Yup. To operate an AC relay on DC, (the Tyco ap note says
doing so is impractical, but that you can do it in an
emergency) you should install a residual and you must lower
the voltage below the AC rating. An AC rated coil needs DC
in excess of 61% of the ac rating on the minimum side, and
less than 82% of the ac rating on the maximum side, per the
example given in the ap note.
 
J

Jamie

Jan 1, 1970
0
ehsjr said:
Geeeez. I posted that link in my _first_ post in the thread, and
you replied to that post. I guess you either didn't read the post
properly, or didn't understand it. The ap note does not agree with
the DC at ~50% of AC rating idea - details are given in that post.
Sorry, I didn't see that.

No, that wasn't a hack as far as the diodes goes, that is a practical
design in a family of relays, We use large contactors with the dual
coil and diodes in them. You don't see this from the out side world but
they are incased in the encapsulation. Those particular types can have
DC going directly to them. It's just the way they are with obvious
reasons.
Yup. To operate an AC relay on DC, (the Tyco ap note says
doing so is impractical, but that you can do it in an
emergency) you should install a residual and you must lower
the voltage below the AC rating. An AC rated coil needs DC
in excess of 61% of the ac rating on the minimum side, and
less than 82% of the ac rating on the maximum side, per the
example given in the ap note.



The app note is pointing equivalent power dissipation, as you
know relays will pull in at a lower current So I don't see a problem
here.


Why don't you put a few AC types on the bench and test them yourself?

I think you'd be surprised in what you find. Lab testing tells a lot
about what you can do.

The only problem I have found with this practice of using AC on DC is
that some AC units use material that has a high hysteresis and the
AC will help keep this down. They do this in cases where they don't use
the dual coil system. In DC operation, I've seen it over magnetize the
core and cause a little slow release on the contacts. But that may not
be such a big deal in most cases.

Have a good day.

Jamie
 
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