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'[EE]: Speeding up a relay - zero crossing detecti'
2002\10\28@175937 by llile

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I am trying to get a relay to turn on and off really fast.  I am trying to
reduce the operate and release time to be able to operate or release the
relay during a single half-wave of the 60Hz mains after zero crossing
detection.  Exceeding the 8mS of a half wave cycle causes numerous thorny
headaches that I won't go into here.  Turning it on is pretty easy, I can
get the contacts to close 2mS after I energize the coil, and they quit
bouncing 2mS later for 4mS total.  That is fast enough for my application.


De-energizing the relay, though, is another matter.  It is taking 8mS from
de-energizing the relay to the first contact opening, and 16 mS total for
it to quit bouncing.  In my application it has to operate faster than
that, preferable in less than 8mS.

The spec sheet says this relay will turn off in 2mS, "WITHOUT CATCH DIODE"
(emphasis mine).   According to the specs, this relay will operate fast
enough to close or release during a half-cycle under some test condition.
OK, I am not using a triac for a number of very good reasons which I am
not going to belabor.

Now the mfr (Aromat-NAIS) told me the reason it stays on so long, is there
is a catch diode across the relay.  This backwards diode is designed to
catch the pulse that occurs after opening the relay driver transistor.
Current continues to race around between the coil and the diode for quite
a while.  He recommended trying either a zener in series with the catch
diode, or a resistor.  Unfortunately he didn't have any design hints other
than that, and I am floundering around in the lab trying components.

A 33V zener reduces the  turn-off time to 2 mS, but the bounce time is
about 10 mS, for a total of 12mS, too slow.   I haven't tried a resistor
yet, not having a gfood idea what values might work well.

Anybody else used any of these tricks?


-- Lawrence Lile

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2002\10\28@183754 by Dwayne Reid

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At 04:58 PM 10/28/02 -0600, .....llileKILLspamspam@spam@SALTONUSA.COM wrote:

>A 33V zener reduces the  turn-off time to 2 mS, but the bounce time is
>about 10 mS, for a total of 12mS, too slow.   I haven't tried a resistor
>yet, not having a gfood idea what values might work well.

I think the zener diode is going to give you the best result.  If you want
to try a diode - resistor combination, first determine the maximum spike
voltage your transistor will tolerate, then calculate the series resistor
as that voltage - supply voltage all divided by the steady state coil
current.  Note that you can eliminate the series diode and just put the
resistor across the relay coil if you can tolerate the current consumed by
the resistor (OK for small currents, not good for large currents).

dwayne

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2002\10\28@190539 by Dal Wheeler

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I've never tried this, but could you reverse the drive polarity to the relay
with an H bridge?
----- Original Message -----
From: <EraseMEllilespam_OUTspamTakeThisOuTSALTONUSA.COM>

> I am trying to get a relay to turn on and off really fast.  I am trying to

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2002\10\28@191413 by Dal Wheeler

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(Without the catch diode o'course.)
----- Original Message -----
From: "Dal Wheeler" <@spam@dwheelerKILLspamspaminsightek.net>
> I've never tried this, but could you reverse the drive polarity to the
relay
> with an H bridge?
> ----- Original Message -----
> From: <KILLspamllileKILLspamspamSALTONUSA.COM>
> > I am trying to get a relay to turn on and off really fast.  I am trying
to

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2002\10\29@043809 by Roman Black

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llile@SALTONUSA.COM wrote:
>
> I am trying to get a relay to turn on and off really fast.  I am trying to
> reduce the operate and release time to be able to operate or release the
> relay during a single half-wave of the 60Hz mains after zero crossing
> detection.  Exceeding the 8mS of a half wave cycle causes numerous thorny
> headaches that I won't go into here.  Turning it on is pretty easy, I can
> get the contacts to close 2mS after I energize the coil, and they quit
> bouncing 2mS later for 4mS total.  That is fast enough for my application.
>
> De-energizing the relay, though, is another matter.  It is taking 8mS from
> de-energizing the relay to the first contact opening, and 16 mS total for
> it to quit bouncing.


To get fast relay opening you need to remove
the catch diode or add the zener in series with
it, or even a resistor in series with the diode
may be fast enough.

Typically in the "old days" there were many
mechanical SMPS like this, popular in automotive
uses like the alternator voltage regulator and I
have seen some used in old military equipment like
step-up voltage converters. The most common way
of handling the problem is to use a capacitor in
the circuit across the coil similar to a tank circuit
that resonates the relay. This was also how they
made "personal protection" type HV generators
before the mosfet days. Try a search for "tesla
coil design" or something, you should be able to
get it buzzing very nicely once tuned properly.

The final contact bounce may also be tunable with
some mechanical damping, I have seen weights or
even "blobs" of solder on the relay leafs which were
obviously added as mechanical tuning.

This sounds like quite an interesting application
you are working on?? :o)
-Roman

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2002\10\29@063328 by Russell McMahon

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> I am trying to get a relay to turn on and off really fast.  I am trying to
....
> De-energizing the relay, though, is another matter.  It is taking 8mS from
> de-energizing the relay to the first contact opening, and 16 mS total for
> it to quit bouncing.  In my application it has to operate faster than
> that, preferable in less than 8mS.
>
> The spec sheet says this relay will turn off in 2mS, "WITHOUT CATCH DIODE"

The answers so far have been along the right lines.
You need to understand what is happening that is affecting the turn off time
if you want to intelligently attack the problem. (Some times unintelligent
attack works better though :-) ).

These MAY not help you as you MAY already be down to the minimum mechanical
time, but reading this MAY give you ideas.

The energy required to activate and hold the relay on is "stored" in a
magnetic field. This field must be removed to allow the relay to release.
The activate field is almost always lower than the "hold in" field.

When the current supplied to the relay coil is removed with the intention of
deactivating the relay, the energy stored in the field must be dissipated.
The collapsing magnetic field has the effect of attempting to maintain the
current that was flowing at the time of deactivation. This effect will
continue indefinitely if the energy is not dissipated. nature arranges for
ways to ENSURE that the energy will be dissipated. This tendency for the
current to continue to flow at its turn off value was labelled by an old
Cockney lecturer I had years ago as "the law of natural cussedness". If you
provide a path for the current generated in the coil by the collapsing field
to flow in, the energy dissipated as the current flows will cause the
current to decrease until the field reaches a level where the relay will
"drop out".

Your task, should you accept it, is to dissipate this energy in as short a
time as possible.

I'll use a 12v relay here but that is for example only.
If you place a "reverse biased" diode across the coil (so that current does
not flow in it when activating voltage is applied, then the generated
current will flow through this diode when the activating voltage is removed.
The energy loss in this diode is small (Vdiode-drop x I) and the main energy
loss will usually be in the relay coil (I^2 x Rrelay-coil). eg for a 12 volt
relay coil rated at 50 mA coil current the relay will have a R=V/I = 12/50
mA = 240 ohm coil. At turn off, instantaneous diode loss = 0.6v x 20 mA = 12
mW. Instantaneous coil loss = (20 mA)^2 x 220 = 88 mW. These rates of
dissipation will fall as the current falls. Turn off time will depend on
stored energy which depends on coil inductance but, as you have seen, this
can be 10's of mS (or 100's with suitable design). If the voltage across the
dissipative element (here = the diode) can be increased the energy loss will
go up and the relay will drop out sooner. As the relay voltage drop is 12v
initially and resistance is 240 ohms, we can get equal dissipation to the
relay coil losses by placing a 240r in series with the diode. Now the R and
the relay coil will have about 12v across EACH of them initially. ie the
voltage across the coil will double essentially instantaneously at turn off
to satisfy the law of natural cussedness and maintain the initial current.
We can expect relay release time to approximately halve. I said "essentially
instantaneously" above as the stray capacitance (wiring plus coil self
capacitance) can not be instantaneously stepped in voltage (just as an
inductor cannot be stepped in current) so there will be a SMALL rise time as
this stray capacitance charges.

If we increase the resistor to 720r in this example the voltage will rise to
48v (12 across relay, 36 across resistor) for about 4 x initial energy
dissipation rate. We can hope (but not expect :-) ) that relay release time
is now down to about 2 mS.

If instead of a resistor we use a 36v zener then the voltage rises to 36v
not only initially but throughout the time that current flows so dissipation
will be faster. A zener will therefore be faster than a resistor for a given
maximum allowable rise in voltage, as the resistor will rise to this value
initially and then decay whereas the zener will hold the voltage until
essentially all energy is gone.

Clearly (a dangerous term) the higher the voltage the coil is allowed to
rise to, the quicker the energy will dissipate. This voltage will USUALLY be
set by your switch voltage limits.

I say USUALLY because there is a secondary effect which will take over in
limiting cases. If you use no back diode etc at all and just turn off the
coil the current will desperately seek somewhere to go. Not finding a low
resistance path the law of natural cussedness (aka electromagnetic induction
and collapsing field etc) will generate a rapidly rising voltage. If the
insulation resistance can withstand this, voltage rise will ultimately be
limited by the energy becoming stored in the stray capacitance. Much of the
initial L x I^2 energy will now be stored in 0.5 x C x V^2 energy. At the
top of the voltage hill it will look around and start on back down (as it
were). We have a ringing underdamped (probably) tuned circuit. The
oscillatory current will flow through the coil resistor and slowly dissipate
the available energy. as the only dissipative element is the coil resistance
we will not release especially rapidly but the ringing voltage will add em
noise and odds on will damage your switching element with a voltage of
perhaps thousands of volts. As we have all found from time to time :-).

Several people mentioned mechanical resonance and damping I think and ?Roman
mentioned weighted contacts etc. I *suspect* that optimum effect may be
achieved by aiming at a discharge time constant around the mechanical
release time of the contacts. Also, arranging for a slightly underdamped to
critically damped discharge may assist. This is easily checked for
empirically. Use large voltage zener and observe achieved release time with
bouncing. Now adjust zener and or resistor discharge so that the coil
voltage decays in around this sort of time. See if this has any affect on
contact bounce as you vary it somewhat. (If not, give up ? :-) )

Relay release may be speeded by reducing the current once operated from the
pull in value to just above the drop out value. Circuit complexity may not
allow but it seems probable that a judiciously applied pulse (or perhaps
more complex waveform) late in the release may cushion the falling contacts
against a hard and bouncy landing. Consider - usually you are effectively
"dropping:" the contacts and associated actuation hardware from the on
position to a mechanical rest off position. Bouncing on arrival is a natural
consequence. Application of some retro rockets (or the relay coil
equivalent) which slow the descent at just the right time, may serve to
reduce this bouncing.

Do you have to use this relay ? Probably yes, but there are many which
operate far faster than this. Notably reed type which tend towards low
current capabilities.

________

- Knowing more about the "'real problem" would probably assist us in
tailoring the answer.

- Using both electronic and mechanical switches in parallel can solve some
problems. The electronic switch is turned on just before the mechanical
switch turns off so there is NO contact bounce at this stage. The electronic
switch is then turned off. The electronic switch needs handle current for
only a very small period and the mechanical switch sees NO switching
transients and has the Rdson (aka mechanical contact resistance) of a VERY
large FET.


What about using series opposed MOSFETs ?
Gate drive is interesting but not impossible.


           Russell McMahon

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2002\10\29@064635 by Siiskonen, Pekka

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> -----Original Message-----
> From: Russell McMahon [spamBeGoneapptechspamBeGonespamPARADISE.NET.NZ]
[a lot of intersting text snipped]
> - Using both electronic and mechanical switches in parallel
> can solve some problems.

If the "pull" speed is acceptably fast, why not use two relays in series,
cut the path with another relay w. normally closed contacts  -- provided the
close-open process needs not repeat too soon to have time to release the
relays in good order.

Pekka Siiskonen

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2002\10\29@081305 by Spehro Pefhany

picon face
At 04:58 PM 10/28/02 -0600, you wrote:

>A 33V zener reduces the  turn-off time to 2 mS, but the bounce time is
>about 10 mS, for a total of 12mS, too slow.   I haven't tried a resistor
>yet, not having a gfood idea what values might work well.
>
>Anybody else used any of these tricks?

Yes, you'll probably get the fastest operation with no catch diode and
either a high enough voltage driver that the parasitic capacitance limits
the voltage or with an avalanche-rated MOSFET. I don't know if your cost
constraints will permit these options. The release operation is more
complex than it looks (not just a simple inductor-resistor model)
because the moving iron induces a voltage in the coil. Try scoping the
relay coil with it driven by a reed relay to see what kind of voltages
you get. Unfortunately this takes you out of the realm of guaranteed
performance of the relay, so design changes *could* lead to problems
in production, though if you stay with one (real) manufacturer or
two that have been qualified it should not be much of an issue.

You may want to consider reversing the N.O. and N.C. contacts and
the drive logic, if that works for you. The bounce on release is almost
nonexistent in most relay designs.

Best regards,




>-- Lawrence Lile
>
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2002\10\29@092155 by llile

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I thought of the H-bridge and decided that was one of my more radical
approaches I'd try later.


-- Lawrence Lile





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       Subject:        Re: [EE]:  Speeding up a relay - zero crossing detection


(Without the catch diode o'course.)
{Original Message removed}

2002\10\29@094334 by llile

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Hmmm, Roman, this capacitor idea has come up more than once.  It sounds
like dangerous medicine, ringing is generally something to be avoided, but
a little RC network near the coil might just ring once (like the postman)
and then quit.  I am using a 2n5551 to drive this thing, which is a high
voltage transiostor, so I can tolerate quite a lot of spike without
damaging the transistor.   Right now, I am going to try a resistor in the
circuit.  I reason thusly:  the resistance of the coil is 1600 ohms and
rated voltage is 24 volts.  So the moment I turn it off, a 1600 ohm
resistor in parallel would produce a 24V negative spike.  If I double the
resistance, this voltage should go up by twice.  Quadruple it, and I might
get a 100V pulse out of the thing.  Since a 33V zener (which I tried
yesterday) did a lot of good but not enough, this might just do the trick.
I'll try 6400 ohms and see what that does.

Under ideal conditions this relay is supposed to turn off in 2mS, which
would be peachy, but I fear that means it produces a 250V kickback pulse
in the process!

Yes there is a PIC in this thing.  The whole problem with the relay is, if
I don't turn off in less than one half  60HZ AC cycle, I get big noise
pulses off the relay contacts which get into everything including my PIC
power supply.  Eventually one of these pulses either resets the PIC or
makes it do wierd things.

Imagine the NO and NC contact of a relay.  When the relay is firing, an
arc is drawn from the NC contact.  If there is 120V from the NO to the NC
contact, as this arc ionizes the air in the gap, and some inductance
somewhere, the arc continues as the contacts move across the gap and these
contacts are momentarily shorted together!  Yes this really happens, and
yes it happens every time a relay is fired.  Look it up in Aromat (NAIS)
technical literature.  In my circuit, the relay is choosing between
half-wave and full-wave power.  As long as I fire during the correct phase
of the AC cycle, there is only a diode drop voltage across my relay
contacts. If I fire the relay during the wrong half, it momentarily shorts
the NO and NC contacts, generates a huge pulse of energy at 2.5megacycles
and about 1500 watts, and this literally goes everywhere.  Imagine trying
to work your PIC on the same board as a 1500 watt AM station.  I think the
FCC will not be happy about this either. No amount of shielding or
decoupling seems to fix it.  After loading a blunderbuss full of
capacitors and firing them at my circuit board, I decided this problem
would be solved by subtler and more devious means.  Thus trying to fire a
relay on a zero crossing, a quixotic quest at best!


-- Lawrence Lile






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       Subject:        Re: [EE]:  Speeding up a relay - zero crossing detection




To get fast relay opening you need to remove
the catch diode or add the zener in series with
it, or even a resistor in series with the diode
may be fast enough.

Typically in the "old days" there were many
mechanical SMPS like this, popular in automotive
uses like the alternator voltage regulator and I
have seen some used in old military equipment like
step-up voltage converters. The most common way
of handling the problem is to use a capacitor in
the circuit across the coil similar to a tank circuit
that resonates the relay. This was also how they
made "personal protection" type HV generators
before the mosfet days. Try a search for "tesla
coil design" or something, you should be able to
get it buzzing very nicely once tuned properly.

The final contact bounce may also be tunable with
some mechanical damping, I have seen weights or
even "blobs" of solder on the relay leafs which were
obviously added as mechanical tuning.

This sounds like quite an interesting application
you are working on?? :o)
-Roman

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2002\10\29@094825 by llile

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Russell,

An excellent treatise on the problem - some points of which I had already
thought through, others not.  At this stages I am locked into a particular
relay, and the spec sheet says it will turn off fast enough for this
application(2mS), just doesn't say how that is accomplished!   I am
switching 12 amps, so light duty fast reed relays aren't being tried.  My
switch can tolerate quite a high pulse, so I think we can probably
eventually come up with something that will create a rather large pulse
but shut this thing down fast enough.  Off to the lab!


-- Lawrence Lile
Senior Project Engineer
Toastmaster, Inc.
Division of Salton, Inc.
573-446-5661 voice
573-446-5676 fax

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2002\10\29@095239 by Bob Ammerman

picon face
Lawrence,

Is this for a piece of test equipment of some sort, where costs are not that
critical, or is it to be buried in some sort of high tech toaster?

Bob Ammerman
RAm Systems

{Original Message removed}

2002\10\29@100216 by Bob Ammerman

picon face
Do I correctly guess this is part of a microwave oven?

I understand your need to switch the relay during the correct half-cycle of
the AC wave.

However, you are not turning it on and then off again within the same 8.3 ms
time, are you?

Bob Ammerman
RAm Systems

{Original Message removed}

2002\10\29@100452 by Spehro Pefhany

picon face
At 08:40 AM 10/29/02 -0600, you wrote:

>Yes there is a PIC in this thing.  The whole problem with the relay is, if
>I don't turn off in less than one half  60HZ AC cycle, I get big noise
>pulses off the relay contacts which get into everything including my PIC
>power supply.  Eventually one of these pulses either resets the PIC or
>makes it do wierd things.
>
>Imagine the NO and NC contact of a relay.  When the relay is firing, an
>arc is drawn from the NC contact.  If there is 120V from the NO to the NC
>contact, as this arc ionizes the air in the gap, and some inductance
>somewhere, the arc continues as the contacts move across the gap and these
>contacts are momentarily shorted together!  Yes this really happens, and
>yes it happens every time a relay is fired.  Look it up in Aromat (NAIS)
>technical literature.  In my circuit, the relay is choosing between
>half-wave and full-wave power.  As long as I fire during the correct phase
>of the AC cycle, there is only a diode drop voltage across my relay
>contacts. If I fire the relay during the wrong half, it momentarily shorts
>the NO and NC contacts, generates a huge pulse of energy at 2.5megacycles
>and about 1500 watts, and this literally goes everywhere.

Oh, why don't you just advance the switching to the relay by a few ms so
that switching takes place at the right time? It only has to be
*repeatable*, correct?  You have more than +/-4msec to play with on a 60Hz
line.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
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2002\10\29@100857 by Roman Black

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face
llile@SALTONUSA.COM wrote:
>
> Hmmm, Roman, this capacitor idea has come up more than once.  It sounds
> like dangerous medicine, ringing is generally something to be avoided,

Sorry I misunderstood. I thought you needed to
oscillate the relay EVERY mains cycle, ie in
a synchronous fashion.


> Under ideal conditions this relay is supposed to turn off in 2mS, which
> would be peachy, but I fear that means it produces a 250V kickback pulse
> in the process!

An RC snubber on the coil might be a viable
solution, taking just enough energy to keep the
back-emf voltage peak down but allowing fast
turn off?


> Imagine the NO and NC contact of a relay.  When the relay is firing, an
> arc is drawn from the NC contact.  If there is 120V from the NO to the NC
> contact, as this arc ionizes the air in the gap, and some inductance
> somewhere, the arc continues as the contacts move across the gap and these
> contacts are momentarily shorted together!  Yes this really happens, and
> yes it happens every time a relay is fired.  Look it up in Aromat (NAIS)
> technical literature.

This could be part of your problem. When I was an
apprentice working on DC cranes my maintenance job
was to file smooth the copper contacts on large
(hundreds of amps) contactors. I got to see a lot
of high current relay systems and normally they are
designed to break the current flow very quickly.
Putting a large current through the NC contacts of
most relays is *very bad* as these contacts break
as the relay starts to pull in, which happens
slowly due to armature magnetic inefficiency at the
start of the pull, inductance, armature inertia etc.

The main current should always be through the NO
contacts so the break occurs under spring tension
which is highest when the relay is closed and the
break will be very quick.

Have you considered using the NO contacts for the
major current, or maybe using two relays if you
need a changover effect which is how some high
current systems work?
-Roman

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2002\10\29@102433 by Roman Black

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Russell McMahon wrote:

> If instead of a resistor we use a 36v zener then the voltage rises to 36v
> not only initially but throughout the time that current flows so dissipation
> will be faster. A zener will therefore be faster than a resistor for a given
> maximum allowable rise in voltage, as the resistor will rise to this value
> initially and then decay whereas the zener will hold the voltage until
> essentially all energy is gone.


Hi Russell,
Are you saying ALL the energy is dissipated by the
zener (excluding the diode for simplicity)??

I have believed that only the *peak* of the back emf
is conducted, which seems backed up by my experience
seeing a zener of 45v dissipate a lot less heat
than say a 20v zener on a 12v coil which is switched
at a set frequency. Obviously the time of conduction
is a lot less with the 45v zener but if you are
correct we are talking about a standard unit of
energy dumped each time the coil switches at a set
freq so there would be no difference in dissipation
with differing zener voltages...

Also on the cro I have seen the zener clip the peak
and still leave the lower exponential decay of the
wave (with the zener not conducting), judging from
the area under the curve NOT conducted by the zener
it would be the bulk of the energy, explaining why
a 45v zener will run stone cold and a 20v one cooks.
Or am I missing something here as usual at 2:30am?? ;o)
-Roman

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2002\10\29@103300 by Michael Rigby-Jones

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> -----Original Message-----
> From: Roman Black [SMTP:fastvidSTOPspamspamspam_OUTEZY.NET.AU]
> Sent: Tuesday, October 29, 2002 3:19 PM
> To:   spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU
> Subject:      Re: [EE]:  Speeding up a relay - zero crossing detection
>
> Or am I missing something here as usual at 2:30am?? ;o)
> -Roman
>
Coffee, and lots of it :o)

Mike

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2002\10\29@114045 by llile

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        To:     KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU
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       Subject:        Re: [EE]:  Speeding up a relay - zero crossing detection

Roman sez:


>The main current should always be through the NO
contacts so the break occurs under spring tension
which is highest when the relay is closed and the
break will be very quick.

I think this is the arrangement I am using. There are some safety reasons
(which are too complex to go through here) that I need the main current in
the NO contact, so this is lucky.


>Have you considered using the NO contacts for the
major current, or maybe using two relays if you
need a changover effect which is how some high
current systems work?
-Roman

I haven't considered two relays yet, nor Triacs in parallel with relay
contacts.  This might be a way to control this current precisely without a
big triac heat sink, turn off the relay contacts whenever then turn off
the triac precisely.  But I will consider these excessively complex
solutions after exploiring simple ones.

A 5.6Kohm resistor in series with the catch diode gave me a response about
like the 33V zener.  I am going to try a 51V zener I just happen to have
laying around and see how that works.

--Lawrence


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2002\10\29@114831 by llile

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Sphero Sez:

>Oh, why don't you just advance the switching to the relay by a few ms so
that switching takes place at the right time? It only has to be
*repeatable*, correct?  You have more than +/-4msec to play with on a 60Hz
line.


Good idea.  Unfortunately on release the contacts continue bouncing for
much too long.  With just a catch diode, the release time is plenty long,
too, and I am not sure how repeatable it is.  I am hoping that releasing
the relay more quickly will help the bounce time.  If I can't get the
bounce time down to 2mS like it is on  energizing the relay, then I'm
screwed and will have to go to plan B whatever that is.

So far I have got the total release time (delay plus bounce) down from
16mS to about 12mS by putzing around putting things in series with the
catch diode.  If I can shave off another 4mS then I am within my 8mS
window that I am shooting for.  Also, so far Zeners seem to do the best
job.  Back to the lab for more experiments!

--Lawrence

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2002\10\29@115042 by llile

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No, just turning it on for a while (tens of seconds) then turning it off.


Keep guessing, it is not a microwave.  If you guess correctly, we'll have
to shoot you.  I'll reveal what it is when the patent is issued. ;-)

-Lawrence





Bob Ammerman <.....rammermanspam_OUTspamADELPHIA.NET>
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10/29/02 08:56 AM
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Do I correctly guess this is part of a microwave oven?

I understand your need to switch the relay during the correct half-cycle
of
the AC wave.

However, you are not turning it on and then off again within the same 8.3
ms
time, are you?

Bob Ammerman
RAm Systems

{Original Message removed}

2002\10\29@115045 by llile

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Yes, I am trying to keep costs low.  That's why I haven't tried exotic
solutions like H bridges or such yet.


-- Lawrence Lile





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Lawrence,

Is this for a piece of test equipment of some sort, where costs are not
that
critical, or is it to be buried in some sort of high tech toaster?

Bob Ammerman
RAm Systems

{Original Message removed}

2002\10\29@120836 by Tom Messenger

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face
Lawrence,

You probably have looked at this and rejected it for some reason... or
maybe you haven't.

You mentioned that you are essentially going from full wave to half wave
rectification for power control purposes. This can be done by using 2
diodes in the full wave bridge and 2 SCR's for the other two.  Gate 'em on,
full power. Remove gate drive, half power. No relay.

Tom M.

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2002\10\29@125610 by Steve Smith

flavicon
face
I assume you are using a fet or transistor to turn on the relay ! Try an
R-C network as you only need to limit the voltage returning from the
relay to VCEO - Vsupply if the inductance of the relay is measured the
number of stored joules can be calculated and this can be limited to a
peak voltage less than the fet withstand voltage. I had the same problem
with  a contactor coil (500mA / 110v) and I used a 1u0 250 plastic cap
in series with a 22R resistor and an 800v fet the speed improvement
compared with a catch diode was a factor of about 5 (the bounce time
does increase) It's the same princable as a flyback switch mode to limit
the Dv / Dt. Bear in mind all things are a compromise limit the voltage
slow down the relay. With no diode at all it is in thery possible for
the voltage to escape to infinity assuming the resistance of the coil is
nil  but it is the fastest release you will get.


Jus my 2p  Steve....

{Original Message removed}

2002\10\29@131519 by Peter L. Peres

picon face
Normally when setting up a relay that fast you use a push-pull or
polarised relay. The first has two coils and the second has a magnet in
the armature and will be operated by reversing the polarity of the current
in the coil.

One way to speed up your relay is to use a push-pull driver and drive the
'upper' side (the one that replaces your diode) with a very short pulse.
This will kill the field or part of it and leave the rest to make a safe
voltage pulse (that is lower than your Vceo).

Another is to use a drive transistor with very high Vceo and no diode. If
the manufacturer is not lying it should work. I've used BF457 like this
once but not for speed reasons (I needed the high voltage pulse). BF457 is
rated to 250V I think. You can use any of the many final video amplifier
NPNs that are mass manufactured for the color TV and monitor market.

Imho for a mass market application this is something that you will regret.

Peter

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2002\10\29@131538 by Peter L. Peres

picon face
The capacitors across the coil in a vibrator mostly suppress the arcing on
the contacts and in certain types of vibrators supply the necessary energy
for the armature to go through to the 'other' side. The tuning is entirely
mechanical.

Peter

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2002\10\29@132805 by Wagner Lipnharski

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face
What about using two relays?

The first idea was to feed power to the load only when Relay#1 is not
energized and Relay#2 is energized, power would flow by both relays
contacts, so, energizing Relay#1 (that you can do in 4ms), will cut power
to the load and would release Relay#2 from auto-sustain.  This would be
something like Set/Reset flip-flop using relays. But here you need a
zero-crossing detector to sync the operation.

The second idea was to use the Relay#1 to switch Relay#2 coild feed power
from DC to AC rectified non filtered lower voltage, so, when Relay#1
energizes, the Relay#2 will still energized (auto-sustainned) as long the
semi-senoid holds power to it.  When the senoid drops its voltage to a very
low level (around 160 degrees or less), Relay#2 will release armature and
also will interrupt its own sustain. With some sort of luck it could
release power from the load very close to zero-crossing without any
external sync.  You could call this a "line sync shut off".

W46NER

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2002\10\29@160322 by Barry Gershenfeld

face picon face
>Yes there is a PIC in this thing.

If you have a PIC and you know where the zero crossings are, you
ought to be able to start the relay in "early".  Having it
close _at_ the zero crossing would get you fewer sparks as
well.  Then you have the whole 8 ms to get it de-energized
again.  Or do you have a minimum closed time?

You have the most interesting projects.   Must be the work
you do.  You lab would be fun to work in :)

Other simple-minded idea:  Bigger, nastier spring on the
relay, and more drive current to pull it in.

Barry

>generates a huge pulse of energy at 2.5megacycles
Old timer!

>Imagine trying
>to work your PIC on the same board as a 1500 watt AM station.  I think the
>FCC will not be happy about this either.

Filter it, license it, go on the air!

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2002\10\29@164234 by Russell McMahon

face
flavicon
face
> A 5.6Kohm resistor in series with the catch diode gave me a response about
> like the 33V zener.  I am going to try a 51V zener I just happen to have
> laying around and see how that works.

A resistor in parallel with a zener may give you a better result.
Roman questioned my comment about a higher voltage zener giving a better
result. His real world observations obviously make sense. In an ideal world
where there is no stray capacitance I think what I said holds as the voltage
will rise to whatever value it needs to to dissipate the energy. But, as I
noted, the stray capacitance will  store energy as the voltage rises and you
then get an oscillatory decaying waveform once the peak voltage reached is
less than the zener voltage. If you have say a 27v zener and a resistor in
parallel with it that is HIGHER in resistance than one that would drop 27v
initially then the zener will initially dissipate more energy than the
resistor alone would but the resistor will continue once the voltage drops
to below Vzener.
example to make this less clear :-)
100 mA initial current.
20v zener
R effective = V/i = 20/100mA = 200R.
Place say a 1000r in parallel with zener.
When zener conducts the 1k will conduct 20/1000 = 20 mA or only 20% of the
initial 100 mA so the zener is taking most of the energy BUT the resistor is
not allowing the voltage to rise as high as it otherwise would. Energy in
core is L x I^2. When I drops to 20 mA resistor will take it all at 20v so
below this zener will drop out. But by then current is 0.2 of initial and
energy is down to 4% of initial. Hopefully (what's the bet) relay will have
dropped out by now. The resistor damps the otherwise long term oscillatory
tail.

Passing thought:     Custom relays can be built with eg brass or copper head
and/or tail end slugs to tailor operate and release response times and
shapes but that's a whole new arcane world.


       Russell McMahon

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2002\10\29@172756 by Dwayne Reid

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At 10:35 AM 10/30/02 +1300, Russell McMahon wrote:

>A resistor in parallel with a zener may give you a better result.

That is essentially the same as the suggestion I made.  However, my
original reasoning still stands: you want the magnetic field to decay as
fast as possible which means that you want ZERO current to flow.  That
means allowing the voltage to rise as high as possible before allowing
current flow - the zener does this.

I *think*.

dwayne

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2002\10\29@174049 by Russell McMahon

face
flavicon
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> >A resistor in parallel with a zener may give you a better result.
>
> That is essentially the same as the suggestion I made.  However, my
> original reasoning still stands: you want the magnetic field to decay as
> fast as possible which means that you want ZERO current to flow.  That
> means allowing the voltage to rise as high as possible before allowing
> current flow - the zener does this.
>
> I *think*.

Not quite. A capacitor cannot "allow" an instantaneous change in voltage. An
inductor cannot "allow" an instantaneous change in current. At turnoff the
coil current will continue and the voltage will rise to whatever level is
required to support this. With no clamp components the current flows into
the stray capacitance !

You are correct about it being better for voltage to rise as high as
possible (subject to capacitive storage second effects). Higher voltage x
initial current = higher energy dissipation.



       RM

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2002\10\29@195854 by Dwayne Reid

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At 11:38 AM 10/30/02 +1300, Russell McMahon wrote:
> > >A resistor in parallel with a zener may give you a better result.
> >
> > That is essentially the same as the suggestion I made.  However, my
> > original reasoning still stands: you want the magnetic field to decay as
> > fast as possible which means that you want ZERO current to flow.  That
> > means allowing the voltage to rise as high as possible before allowing
> > current flow - the zener does this.
> >
> > I *think*.
>
>Not quite. A capacitor cannot "allow" an instantaneous change in voltage. An
>inductor cannot "allow" an instantaneous change in current. At turnoff the
>coil current will continue and the voltage will rise to whatever level is
>required to support this. With no clamp components the current flows into
>the stray capacitance !

I thought that was what I said.

But the point I'm trying to make is that you want the magnetic field to
collapse as quickly as possible - that requires getting the current to fall
as quickly as possible.  That in turn requires allowing the voltage to rise.

Note: when I say "allow the voltage to rise as high as possible", I mean
just that: allow the voltage to rise as high as the switching device will
allow.

dwayne

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2002\10\30@095444 by llile

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Well guys, this has sparked a lively discussion. I think this proves there
is more than one way to skin a cat, and maybe there are a dozen ways.


Here is the result:  I tried various zeners (33V and 51V) with 1n914
diode in series, various resistors, combinations of diodes and resistors,
capacitors, and combinations of capacitors and resistors.

Without anything in parallel with the coil, the contacts were able to
close in 2 mS and bounce for about 8mS.  The peak voltage on the coil rose
to 244V. My driver transistor is rated at 180V, so that is a bit too much
for it but it didn't blow (this time).

The fastest closing and bounce time was achieved by just a resistor in
parallel.  Resistor plus diode was slower, as was a capacitor (I have no
idea what the resonant frequencies were, having no idea of the inductance
of the coil)  of various values, and various zeners.  Another fun day
goofing around in the lab.

I'm using a 6.8K resistor in parallel with a 1.6K ohm coil.  It limits the
peak voltage on the coil to about 109 volts, plenty low to stay in spec
with my driver transistor.  The higher this peak is, the faster everything
works.  My contacts close in about 3.5mS, and bounce time is still about
8mS.  These times seem to be quite repeatable, but we are going to test it
on 30 real production units before we are satisfied it is going to work.

I pre-time firing the relay so that it actually closes a few hundred
microseconds after the positive zero crossing, and then it spends most of
the positive AC cycle bouncing.  After a dozen tries, the PIC hasn't
gagged on any dirty power like it did before I synchronized the switching.
I am going to do  a more extensive test on it today.


-- Lawrence Lile








Russell McMahon <RemoveMEapptechEraseMEspamspam_OUTPARADISE.NET.NZ>
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> >A resistor in parallel with a zener may give you a better result.
>

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2002\10\30@123851 by Peter L. Peres

picon face
I have a double suggestion: swap the relay for a lower voltage one of the
same type and use a series resistor and no suppression. This may fix the
problem. If not, maybe add a small value capacitor (1nF ?) in parallel
with the coil.

Peter

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2002\10\30@135926 by hard Prosser

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One idea that may improve things is to drop the coil current back to a
hold-in value (possibly 25% of that to pull the relay in) once the relay is
connected. Then when you want to disconnect you have only about 1/8th the
energy to dissipate.

I did some simulations yesterday of your problem & the zener/resistor
combination certainly gave the best results.

Richard P





Well guys, this has sparked a lively discussion. I think this proves there
is more than one way to skin a cat, and maybe there are a dozen ways.


snip..

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2002\10\30@152326 by Olin Lathrop

face picon face
> I thought of the H-bridge and decided that was one of my more radical
> approaches I'd try later.

That sounds like a bad idea, at least without current feedback.  You want
the current to go to 0, not negative.  The force on the relay arm is
proportional ABS(current).


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2002\10\30@153259 by Olin Lathrop

face picon face
> Re: [EE]: Speeding up a relay - zero crossing detection

One thing I haven't seen mentioned yet (just got back and found 200 PIC
list messages) is the relay current just before turnoff.  This should be
reduced as far as possible to the "holding" current after the initial
switch to on.


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2002\10\30@170355 by Olin Lathrop

face picon face
> One idea that may improve things is to drop the coil current back to a
> hold-in value (possibly 25% of that to pull the relay in) once the relay
is
> connected. Then when you want to disconnect you have only about 1/8th
the
> energy to dissipate.

Actually 1/16 the energy if the current is dropped to 1/4.


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2002\10\31@080658 by Chris Loiacono

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> Well guys, this has sparked a lively discussion. I think this
> proves there
> is more than one way to skin a cat, and maybe there are a dozen ways.

Hi Lawrence:
I suggest that instead of the cat skinning allegory, this is a 'cant see the
forest for the trees' thing.

Since this is only to switch 12A, and the switching is somewhat
time-sensitive in the application, what is the reason that a silicon switch
could not be used? With some simple, inexpensive, off-the-shelf devices, you
could power your load for exactly one half cycle, and you could choose pos
or neg. This method would always switch at or so near zero that there would
be no noise generated to cause th PIC side to hiccough. It sounds like your
relay will switch gazillions of times, and probably wouldn't last long.
It would require just a bit more effort to do this with an inductive load,
but only because a random crossing trigger would be needed, and you would
have to calculate the current zero point and have the PIC output then
instead of the voltage zero. OK, I'll stop tying to guess....

Since this is another top-secret mission of yours, and you already have
about a dozen people to share the future patented project's proceeds with,
I'll leave it like this for now. My gut is telling me that if you stick with
the relay and patent this thing - someone will come along, read the patent
and produce a better mouse-trap without the relay. If you want to get this
to market faster and would like to eliminate the weak (reliability) relay
link, I'm sure I (or many others herein)could get you there.

Chris

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2002\10\31@195521 by llile

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       Subject:        Re: [EE]:  Speeding up a relay - zero crossing detection


>>Since this is another top-secret mission of yours, and you already have
about a dozen people to share the future patented project's proceeds with,
I'll leave it like this for now.


LMFAO!  Another top secret mission!   We certainly wouldn't want Russian
Spies seeing our toaster plans!  (muffled guffaws)  I hope Vasili or
somebody else from that end of the world isn't reading any of this! (he
said with a chuckle)

I'll take your suggestions seriously (after I stop laughing at your
comment and at myself. )

--Lawrence

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2002\10\31@195925 by llile

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Dropping the relay holding voltage was a good idea, but it didn't reduce
the contact bounce time on release in practice.  I verified this with a
scope and then with a data sheet, they predict only about 20% less bounce
time with wide variations in coil voltage for one particular relay.    A
guy from Aromat was on this problem today, and we are starting to look at
different relays with different bounce characteristics.  They are really
reluctant to specify bounce time for some reason, esp. in a power relay.
So far we haven't been able to find one that meets all the requirements.

The reason these relays bounce so much on release, is they are released by
a spring only.  At the end of it's travel it's spring force is lightest,
and it can't control the armature so well at that end.  They do make
relays which are actuated by a coil and released by a coil plus a
permanent magnet.  If I could find one of these then it might work fast
enough.  Back in the glory days of relays this would have been available.
But nowadays, relays are made as simply and as cheaply as possible, and
electronics cleans up the mess they make.

So far I've rejected triacs because of too much heat.  I'll be taking a
closer look at them tomorrow.


-- Lawrence Lile





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> One idea that may improve things is to drop the coil current back to a
> hold-in value (possibly 25% of that to pull the relay in) once the relay
is
> connected. Then when you want to disconnect you have only about 1/8th
the
> energy to dissipate.

Actually 1/16 the energy if the current is dropped to 1/4.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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'[EE]: Speeding up a relay - zero crossing detecti'
2002\11\02@032410 by Peter L. Peres
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On Thu, 31 Oct 2002, .....llile@spam@spamEraseMESALTONUSA.COM wrote:

*>The reason these relays bounce so much on release, is they are released by
*>a spring only.  At the end of it's travel it's spring force is lightest,

It bounces so much because it is actuated by a LINEAR spring. Faster
devices use a mechanical or magnetic hysteresis element to speed up
'decision'. In other words, find a better relay ...

Peter

*>So far I've rejected triacs because of too much heat.  I'll be taking a
*>closer look at them tomorrow.

You said you will be actating it now and then. A triac used in this role
would not get hot. You could put it in parallel with the relay. The relay
would switch for continous operation and the triac for pulses. Also one
could use the scheme that uses the triac as breaker to avoid arcing on the
relay.

Peter

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2002\11\02@035337 by Steve Smith

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Take a little example from the UPS industry they use hybrid static
switches in some of the smaller models of ups consisting of either two
triacs and a pair of relays all the way up to very large static switches
with parellel pairs of thyristors and moterised circuit breakers as
noted below the triac is only used to get the zco operation uasally
without a heatsink and a slave mechanical contact to reinforce it after
it has opperated this gives a no bounce switch and limited power
disapation due to the relay reinforcment. The simplest form I have seen
is a relay driven at twice its normal coil voltage (capacitor
storage)and a single triac across its n/c contact the operation is then
drive the relay on fast with a high coil voltage and use the triac to
bypass the n/c until it has released properly. It may be worth
investigating

Regards Steve...

{Original Message removed}

2002\11\02@130739 by Wagner Lipnharski

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Peter L. Peres wrote:
> I have a double suggestion: swap the relay for a lower voltage one of
> the same type and use a series resistor and no suppression. This may
> fix the problem. If not, maybe add a small value capacitor (1nF ?) in
> parallel with the coil.
>
> Peter


Supposing it could be possible, what would happens if you wrap a secondary
coil (with the diode) around the actual relay coil?
All the magnetic collapsing field would be drained by this secondary coil
in short (by the diode), with few energy generated at the primary coil, is
this correct or not?  How this work in a regular transformer where the
secondary has a shorting reversed diode and you interrupt the primary
current?  The "current still flowing under field collapsing" is correct,
but only when you don't have any other way to drain the energy. The
secondary in short (by the diode) could minimize the induced energy at the
primary.

W46NER.

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2002\11\02@210702 by Dave Tweed

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Wagner Lipnharski <wagnerEraseMEspam@spam@USTR.NET> wrote:
> Supposing it could be possible, what would happens if you wrap a secondary
> coil (with the diode) around the actual relay coil?
> All the magnetic collapsing field would be drained by this secondary coil
> in short (by the diode), with few energy generated at the primary coil, is
> this correct or not?

Although the shorted secondary would effectively "kill" the inductance of
the primary for the switch-off transition, eliminating the voltage dump
into the switching device, the pulse of current in the secondary would
create a magnetic field of its own (opposite in polarity from the original)
until it decays. The actual turn-off time of the relay would be essentially
unchanged, and this is what we were trying to improve.

-- Dave Tweed

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2002\11\03@061027 by Roman Black

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Dave Tweed wrote:
>
> Wagner Lipnharski <spamBeGonewagnerKILLspamspam@spam@USTR.NET> wrote:
> > Supposing it could be possible, what would happens if you wrap a secondary
> > coil (with the diode) around the actual relay coil?
> > All the magnetic collapsing field would be drained by this secondary coil
> > in short (by the diode), with few energy generated at the primary coil, is
> > this correct or not?

> The actual turn-off time of the relay would be essentially
> unchanged, and this is what we were trying to improve.


Exactly, and the easiest way to get the fastest
coil field collapse is to just use no catch diode
and have a switching transistor rated for the
250v spike that the coil produces.

The only faster way to get the field to collapse
is to reverse the *current* at turnoff by
applying a voltage, which would in effect "squash"
the field as someone mentioned before.

But if the field collapsing into an open circuit
produces 250v, wouldn't forcing it to collapse
quicker by using a reverse current source cause
this back-emf voltage to spike even higher??
And doesn't that mean the reverse current source
must have a voltage greater than 250v to have an
effect?
-Roman

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2002\11\03@090048 by Dave Tweed

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Roman Black <fastvidspam_OUTspam@spam@EZY.NET.AU> wrote:
> But if the field collapsing into an open circuit produces 250v, wouldn't
> forcing it to collapse quicker by using a reverse current source cause
> this back-emf voltage to spike even higher?? And doesn't that mean the
> reverse current source must have a voltage greater than 250v to have an
> effect?

Exactly right. dI/dt = V/L no matter how you cut it.

-- Dave Tweed

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2002\11\03@144113 by hard Prosser

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But if the field collapsing into an open circuit
produces 250v, wouldn't forcing it to collapse
quicker by using a reverse current source cause
this back-emf voltage to spike even higher??
And doesn't that mean the reverse current source
must have a voltage greater than 250v to have an
effect?
-Roman

Yep!
Richard P

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2002\11\04@175146 by llile

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>Exactly, and the easiest way to get the fastest
coil field collapse is to just use no catch diode
and have a switching transistor rated for the
250v spike that the coil produces.

I found this to be true in the lab, Roman.  I could get almost the same
speed with nothing in parallel with the relay, and also with a 6.2K in
parallel with the relay but with signifigantly less pulse, about 100Volts.


But, sadly, there is no way to turn off this relay fast enough due to
excessive bouncing.  I changed the relay topology around signifigantly, so
that the relay shorts across the power diode to achieve full wave or half
wave power.  voila!  Very little noise on switching.  Didn't have to
resort to even more extreme measures like parallel triacs.

The key point here is, when a mechanical relay switches, the NO and NC
contacts are MOMENTATILY SHORTED TOGETHER.  This causes a great amount of
noise if they are at different voltages and also both in low impedance
power circuits.  I am talking like
playing-polo-on-the-antenna-of-a-commercial-radio-station kind of noise,
that I could not ever filter out of my power supply with any sane
measures.  When I changed the topology so that the NO and NC contacts
weren't at different voltages (one of them isn't connected to anything)
suddelny I was able to see but a tiny blip on the scope when the relay
switches and no bounce.

If you don't believe the momentarily shorted together bit, consult the
details of a relay technical catalog.  One contact draws an arc which
continues to conduct as it approaches the other contact.  If a high
current can flow at that time, BOOM! it does for one half cycle until the
arc is extinguished.  OTOH, once the NO contaact finally closes, it, too
can draw an arc and remain closed.  If both contacts are involved in an
arc, look out FCC here we come transmitting noise! This is especially true
at higher voltages and when there is a big inductance anywhere nearby.

-- Lawrence Lile





Roman Black <spamBeGonefastvid@spam@spamEZY.NET.AU>
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Dave Tweed wrote:
>
> Wagner Lipnharski <.....wagnerspamRemoveMEUSTR.NET> wrote:
> > Supposing it could be possible, what would happens if you wrap a
secondary
> > coil (with the diode) around the actual relay coil?
> > All the magnetic collapsing field would be drained by this secondary
coil
> > in short (by the diode), with few energy generated at the primary
coil, is
> > this correct or not?

> The actual turn-off time of the relay would be essentially
> unchanged, and this is what we were trying to improve.


Exactly, and the easiest way to get the fastest
coil field collapse is to just use no catch diode
and have a switching transistor rated for the
250v spike that the coil produces.

The only faster way to get the field to collapse
is to reverse the *current* at turnoff by
applying a voltage, which would in effect "squash"
the field as someone mentioned before.

But if the field collapsing into an open circuit
produces 250v, wouldn't forcing it to collapse
quicker by using a reverse current source cause
this back-emf voltage to spike even higher??
And doesn't that mean the reverse current source
must have a voltage greater than 250v to have an
effect?
-Roman

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2002\11\04@180714 by Jim

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 "The key point here is, when a mechanical
  relay switches, the NO and NC contacts are
  MOMENTATILY SHORTED TOGETHER."

I guess this would be *true* for a relay used
in an open-to-the-air environment where a PLASMA
forms (from the 'sparcing' in the air which then
is conductive) between the contacts -

- as opposed to the use of a vacuum relay which should
not be subject to such a phenomonon?

RF Jim

{Original Message removed}

2002\11\05@114143 by llile

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Yup.  A vacuum relay, oil-filled relay, reed relay, or a big power
contactor with very large air gaps would not exibit this behaviour.  The
relays that do this are the compact, cheap  PC mounted type that are
ubiquitous in  oven controllers and the like.  Also, a relay switching
lower voltage would probably not do this, and a relay switching lower
power.

-- Lawrence Lile





Jim <jvpollspam@spam@DALLAS.NET>
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       Subject:        Re: [EE]:  Speeding up a relay - zero crossing detection


 "The key point here is, when a mechanical
  relay switches, the NO and NC contacts are
  MOMENTATILY SHORTED TOGETHER."

I guess this would be *true* for a relay used
in an open-to-the-air environment where a PLASMA
forms (from the 'sparcing' in the air which then
is conductive) between the contacts -

- as opposed to the use of a vacuum relay which should
not be subject to such a phenomonon?

RF Jim



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2002\11\05@164317 by Russell McMahon

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> Yup.  A vacuum relay, oil-filled relay, reed relay, or a big power
> contactor with very large air gaps would not exibit this behaviour.  The
> relays that do this are the compact, cheap  PC mounted type that are
> ubiquitous in  oven controllers and the like.  Also, a relay switching
> lower voltage would probably not do this, and a relay switching lower
> power.

Also can get "magnetic sniggers" and arc "ladders" (can't remember correct
name) which cause arc to rise thermally and extend its length to cause it to
extinguish. You could fit several hundred toasters inside some of those :-)


       RM

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2002\11\07@031130 by Michael Rigby-Jones

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> -----Original Message-----
> From: Russell McMahon [SMTP:spamBeGoneapptechspam@spam@PARADISE.NET.NZ]
> Sent: Tuesday, November 05, 2002 9:39 PM
> To:   RemoveMEPICLISTspam_OUTspamMITVMA.MIT.EDU
> Subject:      Re: [EE]:  Speeding up a relay - zero crossing detection
>
>
> Also can get "magnetic sniggers" and arc "ladders" (can't remember correct
> name) which cause arc to rise thermally and extend its length to cause it
> to
> extinguish. You could fit several hundred toasters inside some of those
> :-)
>
>
Usualy called "Jacobs Ladders" IIRC.

Mike

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