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Sci.Electronics.Basics -> Help needed. Zero crossing with RC snubber problem

There are 33 messages in this thread.
You are currently looking at messages 20 to 33.


Author: Jamie
Date: 19:28 27-02-08

michaelnikolaou@yahoo.com wrote:

> On 27 Φεβ, 03:24, Jamie
> <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
>
>>michael nikolaou wrote:
>>
>>>Hi
>>
>>>I have a 12 v relay driving an large 220 volt AC relay . Across the contact
>>>of the driver relay i placed one RC snubber circut (27NF with 100 R
>>>resisitor in series) to help with some spikes that were influencing the low
>>>voltage driver circuits.
>>>The driver circuit is able to detect mains zero crossing and fire the
>>>driver relay at an angle i choose .
>>>From what i read the best point to switch off the power relay is at zero
>>>crossing . I did that and i show a large spike up to 1 KV at the relay
>>>contact followed by a decaying 500hz waveform to 0 volts . After some
>>>experimentation the best point came exactly when switching off at the peak
>>>of the mains voltage .At this point there is smooth decaying waveform to 0
>>>volt after 5 periods of 500 HZ but no overshoot. The relay presents no
>>>arcing. If i remove the snubber and make the experiment the best place to
>>>switch is zero crossing but i also see large SHARP spikes up to 500 Volts
>>>Peak.
>>>My question is
>>> The switching with snubber must be made at zero crossing or at the peak of
>>>an ac voltage waveform ?
>>>What is the behaviour of the circuit ?.
>>>As i understand any large spikes can harm the X2 capacitor i'm using so
>>>what is the best operating practise ?.
>>
>>>Any help will be appreciated
>>
>>> Michael
>>
>>WHen you say relay, I assume you mean a mechanical contact?
>>
>> if so, It takes time for the contacts the release. If you turn it
>> off at what you detect as the zero crossing point, the contacts most
>>likely will not actually release until some where in some mid point .
>> Many contactors are fast but not fast enough to open before current
>>can get a charge going.
>> That's just my evaluation of what you're doing.
>>
>> By you signaling to turn off the relay at a peak, the contactor will
>>most likely not open until it gets near the zero crossing point.
>>
>>--- Απόκρυψη κειμένου σε παράθεση -
>>
>>- Εμφάνιση κειμένου σε παράθεση -
>
>
> I observe all signals with a scope . I see actually the "driver relay"
> signal .So all my observations
> about timing are correct . My notion was different though .I expected
> to turn off at zero crossing
> voltage and have no arc .Actualy when the transition happents at the
> peak of voltage then i see only a
> decaying waveform ,no overshoot, for which i suspect since i know the
> capacitor and measure the
> frequency one could calculate the total inductance value (cables+relay
> coil). Since its clear that V(emf)=-L*di/Dt
> as pointed out by your emails also then the correct point to switch
> off the driver relay is at peak voltage
> since current lags voltage by 90 deg in any inductor.
> Now i only have to find out how much can a relay type deviate from the
> measurements i have made.
> Thank's for all you help guys
if you're trying to save the contact life you can assist it with a SSR
across the terminals.
The SSR will conduct just prior before the contacts close, this will
create a shunt on the contacts. when the contacts finally make, they
will remove the load from the SSR.
When opening the contacts, the SSR will switch to save the day and
unlatch at the base line. If you decide to employ this, you need to have
a snubber tide across the SSR because of slight delays of the SSR, you
could damage it when the contacts open on a high peak.
Just select a SSR with the same turn on voltage as the contactor and
tie them to the same control voltage.


--
"I'd rather have a bottle in front of me than a frontal lobotomy"

http://webpages.charter.net/jamie_5";
Author: Fred Bloggs
Date: 11:02 28-02-08





> Thank guys for your replies .Some of them i have to study first
>
> Let me make some things clear about the circuit and values chosen
>
> 1. I've measured turn-on , turn-off delay at 3.3 ms for the driver relay.All
> results are
> after calculating this delay .So what is see on the scope is at the moment
> i'm explaining
> 2. the arc is across the driver relay .The power board is inside a control
> unit box so
> i have to leave with small distances and cpu disturbances.Its actually a
> microcontroller
> having the problem .Driver relay contact current rating is 5A at 220V
> .Power relay coil is rated is 6
> watts consumption at 220V.
> 3. Using large value capacitors over 33 nf was causing sometimes latch of
> the power relay so i have
> value limitation here
> 4. The capacitors i've chosen are X2 self healing 275VAC. With no ZC control
> they are blown
> to 0 nf value (some of them) after 10-12 months of operation.
> 5. I don't have the space or budget to use large sized capacitors rated at
> higher voltages or SSR .
> The idea was to use ZC to avoid using expensive and large size protection
> snubber
> So the question is .
>
> Does the relay On/OFF time differs with time .If it's 10% it's not a
> problem since again
> the arc will not be so high .Since its the current break that causes the
> arc i must switch off at Peak of the
> ac voltage .This is what my reading confirmed .In this case switching a
> resistive load must i change the driver
> algorithm ???
>
> Any helpful comments will be apreciated
>
>

The circuit below simulates fairly well. You don't want to use a
conventional snubber across the contacts because on opening the relay
coil voltage reverses and adds to the 220VAC source. Placing a snubber
in shunt with the coil with peak current limiting resistor as shown
increases operating power by about 10% but tends to maintain the contact
voltage and results in a very slew rate limited 0.5V/us contact voltage
peaking in the 450V range. There should be no arc at all with this
circuit, with or without zero crossing logic. K1 are the 12V relay
contacts and K2 is the 220VAC coil. I did not consider contact bounce on
closure, will leave that to you.
View in a fixed-width font such
as Courier.


.
.
.
.
. 220VAC
. o o
. | |
. | |
. | - K1
. | -
. | |
. | |
. | R 100R, 1.5W
. | |
. | |
. | +-----.
. | | |
. | - |
. | |\| |
. | K2|\| ===
. | |\| | 47nF
. | |\| |
. | - |
. | | |
. | | |
. '------+-----'
.
.
Author: legg
Date: 11:36 28-02-08

On Thu, 28 Feb 2008 11:02:31 -0500, Fred Bloggs <nospam@nospam.com>
wrote:


>
>The circuit below simulates fairly well. You don't want to use a
>conventional snubber across the contacts because on opening the relay
>coil voltage reverses and adds to the 220VAC source. Placing a snubber
>in shunt with the coil with peak current limiting resistor as shown
>increases operating power by about 10% but tends to maintain the contact
>voltage and results in a very slew rate limited 0.5V/us contact voltage
>peaking in the 450V range. There should be no arc at all with this
>circuit, with or without zero crossing logic. K1 are the 12V relay
>contacts and K2 is the 220VAC coil. I did not consider contact bounce on
>closure, will leave that to you.
>View in a fixed-width font such
> as Courier.
>
>
> .
> .
> .
> .
> . 220VAC
> . o o
> . | |
> . | |
> . | - K1
> . | -
> . | |
> . | |
> . | R 100R, 1.5W
> . | |
> . | |
> . | +-----.
> . | | |
> . | - |
> . | |\| |
> . | K2|\| ===
> . | |\| | 47nF
> . | |\| |
> . | - |
> . | | |
> . | | |
> . '------+-----'
> .
> .
Placing impedance in series with the working solenoid could produce a
reduction in speed/dropout performance in the armature of the relay
switching the main working load. (not shown in the above drawing)

I'm not sure how you modelled the relay coil, but if it used a linear
inductor, it will not likely reflect actual performance. A relay
drive coil is coupled to a mechanically changing magnetic circuit.

As the OP already has a cost-free solution involving programmed timing
adjustments, perhaps it's best to let the issue drop?

RL
Author: Fred Bloggs
Date: 12:51 28-02-08



legg wrote:
> On Thu, 28 Feb 2008 11:02:31 -0500, Fred Bloggs <nospam@nospam.com>
> wrote:
>
>
>
>>The circuit below simulates fairly well. You don't want to use a
>>conventional snubber across the contacts because on opening the relay
>>coil voltage reverses and adds to the 220VAC source. Placing a snubber
>>in shunt with the coil with peak current limiting resistor as shown
>>increases operating power by about 10% but tends to maintain the contact
>>voltage and results in a very slew rate limited 0.5V/us contact voltage
>>peaking in the 450V range. There should be no arc at all with this
>>circuit, with or without zero crossing logic. K1 are the 12V relay
>>contacts and K2 is the 220VAC coil. I did not consider contact bounce on
>>closure, will leave that to you.
>>View in a fixed-width font such
>> as Courier.
>>
>>
>> .
>> .
>> .
>> .
>> . 220VAC
>> . o o
>> . | |
>> . | |
>> . | - K1
>> . | -
>> . | |
>> . | |
>> . | R 100R, 1.5W
>> . | |
>> . | |
>> . | +-----.
>> . | | |
>> . | - |
>> . | |\| |
>> . | K2|\| ===
>> . | |\| | 47nF
>> . | |\| |
>> . | - |
>> . | | |
>> . | | |
>> . '------+-----'
>> .
>> .
>
> Placing impedance in series with the working solenoid could produce a
> reduction in speed/dropout performance in the armature of the relay
> switching the main working load. (not shown in the above drawing)
>
> I'm not sure how you modelled the relay coil, but if it used a linear
> inductor, it will not likely reflect actual performance. A relay
> drive coil is coupled to a mechanically changing magnetic circuit.
>
> As the OP already has a cost-free solution involving programmed timing
> adjustments, perhaps it's best to let the issue drop?
>
> RL
>

He was working with a largely resistive 8KR coil, the 100R has no effect
on pull-in or hold-in. The programmed timing can be dropped, what
happens at line loss, does his controller lock up because things didn't
go exactly as planned, you tell me.
Author: legg
Date: 15:23 28-02-08

On Thu, 28 Feb 2008 12:51:29 -0500, Fred Bloggs <nospam@nospam.com>
wrote:


>>
>> Placing impedance in series with the working solenoid could produce a
>> reduction in speed/dropout performance in the armature of the relay
>> switching the main working load. (not shown in the above drawing)
>>
>> I'm not sure how you modelled the relay coil, but if it used a linear
>> inductor, it will not likely reflect actual performance. A relay
>> drive coil is coupled to a mechanically changing magnetic circuit.
>>
>> As the OP already has a cost-free solution involving programmed timing
>> adjustments, perhaps it's best to let the issue drop?
>>
>> RL
>>
>
>He was working with a largely resistive 8KR coil, the 100R has no effect
>on pull-in or hold-in. The programmed timing can be dropped, what
>happens at line loss, does his controller lock up because things didn't
>go exactly as planned, you tell me.

I've asked for this information, but still see only the reference to a
6W AC coil in the relay doing the work. Larger AC working relay coil
current is seldom determined by the DC impedance of the coil. You can
refer to the Leach tutorial on this issue, and their catalog, though
they don't seem to supply relays or contactors with low frequency AC
coils, at present.

For example, a 115V 400Hz coil in a 4W series, is listed as consuming
90mA. This indicates that the DC resistance of the coil must be less
than half an RDC value that would produce the specified current, in
order to keep combined power loss from coil and armature poles to the
value expected.

The losses in AC activated coils is typically 5 times that for DC
rated ones, in simpler commodity forms like OMRON MGN.

http://components.omron.com/components/web/webfiles.nsf$FILES/family.html?ID=CNEN-6TJQPU

But that wasn't always the case.

Older SquareD parts anticipate coil current ratios of more tha 4:1
between closed and open armature, with different values expected for
50 and 60Hz dedicated parts..

http://ecatalog.squared.com/catalog/173/html/sections/21/17321026.html#1013844

The same relationship shows up in lower-powered parts:

http://catalog.tycoelectronics.com/TE/bin/TE.Connect?S=21426&M=FEAT&P=86596,8051
7&U=&BML=10576,16354,16453&LG=1

RL
Author: Fred Bloggs
Date: 16:09 28-02-08



legg wrote:
> On Thu, 28 Feb 2008 12:51:29 -0500, Fred Bloggs <nospam@nospam.com>
> wrote:
>
>
>
>>>Placing impedance in series with the working solenoid could produce a
>>>reduction in speed/dropout performance in the armature of the relay
>>>switching the main working load. (not shown in the above drawing)
>>>
>>>I'm not sure how you modelled the relay coil, but if it used a linear
>>>inductor, it will not likely reflect actual performance. A relay
>>>drive coil is coupled to a mechanically changing magnetic circuit.
>>>
>>>As the OP already has a cost-free solution involving programmed timing
>>>adjustments, perhaps it's best to let the issue drop?
>>>
>>>RL
>>>
>>
>>He was working with a largely resistive 8KR coil, the 100R has no effect
>>on pull-in or hold-in. The programmed timing can be dropped, what
>>happens at line loss, does his controller lock up because things didn't
>>go exactly as planned, you tell me.
>
>
> I've asked for this information, but still see only the reference to a
> 6W AC coil in the relay doing the work. Larger AC working relay coil
> current is seldom determined by the DC impedance of the coil. You can
> refer to the Leach tutorial on this issue, and their catalog, though
> they don't seem to supply relays or contactors with low frequency AC
> coils, at present.
>
> For example, a 115V 400Hz coil in a 4W series, is listed as consuming
> 90mA. This indicates that the DC resistance of the coil must be less
> than half an RDC value that would produce the specified current, in
> order to keep combined power loss from coil and armature poles to the
> value expected.
>
> The losses in AC activated coils is typically 5 times that for DC
> rated ones, in simpler commodity forms like OMRON MGN.
>
>
http://components.omron.com/components/web/webfiles.nsf$FILES/family.html?ID=CNEN-6TJQPU
>
> But that wasn't always the case.
>
> Older SquareD parts anticipate coil current ratios of more tha 4:1
> between closed and open armature, with different values expected for
> 50 and 60Hz dedicated parts..
>
> http://ecatalog.squared.com/catalog/173/html/sections/21/17321026.html#1013844
>
> The same relationship shows up in lower-powered parts:
>
>
http://catalog.tycoelectronics.com/TE/bin/TE.Connect?S=21426&M=FEAT&P=86596,80517&
amp;U=&BML=10576,16354,16453&LG=1
>
> RL

I'm aware of that. Generally AC coils with predominantly reactive
impedance are rated in VA and the so-called impedance limited coils with
impedance dominated by coil wire resistance are rated in Watts. The OP
is working with a 6W impedance limited coil.
Author: legg
Date: 16:22 28-02-08

On Thu, 28 Feb 2008 16:09:22 -0500, Fred Bloggs <nospam@nospam.com>
wrote:

>
>
>legg wrote:
>> On Thu, 28 Feb 2008 12:51:29 -0500, Fred Bloggs <nospam@nospam.com>
>> wrote:
>>
>>
>>
>>>>Placing impedance in series with the working solenoid could produce a
>>>>reduction in speed/dropout performance in the armature of the relay
>>>>switching the main working load. (not shown in the above drawing)
>>>>
>>>>I'm not sure how you modelled the relay coil, but if it used a linear
>>>>inductor, it will not likely reflect actual performance. A relay
>>>>drive coil is coupled to a mechanically changing magnetic circuit.
>>>>
>>>>As the OP already has a cost-free solution involving programmed timing
>>>>adjustments, perhaps it's best to let the issue drop?
>>>>
>>>>RL
>>>>
>>>
>>>He was working with a largely resistive 8KR coil, the 100R has no effect
>>>on pull-in or hold-in. The programmed timing can be dropped, what
>>>happens at line loss, does his controller lock up because things didn't
>>>go exactly as planned, you tell me.
>>
>>
>> I've asked for this information, but still see only the reference to a
>> 6W AC coil in the relay doing the work. Larger AC working relay coil
>> current is seldom determined by the DC impedance of the coil. You can
>> refer to the Leach tutorial on this issue, and their catalog, though
>> they don't seem to supply relays or contactors with low frequency AC
>> coils, at present.
>>
>> For example, a 115V 400Hz coil in a 4W series, is listed as consuming
>> 90mA. This indicates that the DC resistance of the coil must be less
>> than half an RDC value that would produce the specified current, in
>> order to keep combined power loss from coil and armature poles to the
>> value expected.
>>
>> The losses in AC activated coils is typically 5 times that for DC
>> rated ones, in simpler commodity forms like OMRON MGN.
>>
>>
http://components.omron.com/components/web/webfiles.nsf$FILES/family.html?ID=CNEN-6TJQPU
>>
>> But that wasn't always the case.
>>
>> Older SquareD parts anticipate coil current ratios of more tha 4:1
>> between closed and open armature, with different values expected for
>> 50 and 60Hz dedicated parts..
>>
>> http://ecatalog.squared.com/catalog/173/html/sections/21/17321026.html#1013844
>>
>> The same relationship shows up in lower-powered parts:
>>
>>
http://catalog.tycoelectronics.com/TE/bin/TE.Connect?S=21426&M=FEAT&P=86596,80517&
amp;U=&BML=10576,16354,16453&LG=1
>>
>> RL
>
>I'm aware of that. Generally AC coils with predominantly reactive
>impedance are rated in VA and the so-called impedance limited coils with
>impedance dominated by coil wire resistance are rated in Watts. The OP
>is working with a 6W impedance limited coil.

Sorry, but I don't see a resistance limited coil described in any
correspondence from the OP.

The most common ( old P&B now Tyco ) contactor for high current that
still offers AC coils and a fair description of their impedance and
wattage expectations:

http://tinyurl.com/3845jx

RL
Author: Fred Bloggs
Date: 03:43 29-02-08



legg wrote:
> On Thu, 28 Feb 2008 16:09:22 -0500, Fred Bloggs <nospam@nospam.com>
> wrote:
>
>
>>
>>legg wrote:
>>
>>>On Thu, 28 Feb 2008 12:51:29 -0500, Fred Bloggs <nospam@nospam.com>
>>>wrote:
>>>
>>>
>>>
>>>
>>>>>Placing impedance in series with the working solenoid could produce
a
>>>>>reduction in speed/dropout performance in the armature of the relay
>>>>>switching the main working load. (not shown in the above drawing)
>>>>>
>>>>>I'm not sure how you modelled the relay coil, but if it used a
linear
>>>>>inductor, it will not likely reflect actual performance. A relay
>>>>>drive coil is coupled to a mechanically changing magnetic circuit.
>>>>>
>>>>>As the OP already has a cost-free solution involving programmed
timing
>>>>>adjustments, perhaps it's best to let the issue drop?
>>>>>
>>>>>RL
>>>>>
>>>>
>>>>He was working with a largely resistive 8KR coil, the 100R has no effect

>>>>on pull-in or hold-in. The programmed timing can be dropped, what
>>>>happens at line loss, does his controller lock up because things didn't
>>>>go exactly as planned, you tell me.
>>>
>>>
>>>I've asked for this information, but still see only the reference to a
>>>6W AC coil in the relay doing the work. Larger AC working relay coil
>>>current is seldom determined by the DC impedance of the coil. You can
>>>refer to the Leach tutorial on this issue, and their catalog, though
>>>they don't seem to supply relays or contactors with low frequency AC
>>>coils, at present.
>>>
>>>For example, a 115V 400Hz coil in a 4W series, is listed as consuming
>>>90mA. This indicates that the DC resistance of the coil must be less
>>>than half an RDC value that would produce the specified current, in
>>>order to keep combined power loss from coil and armature poles to the
>>>value expected.
>>>
>>>The losses in AC activated coils is typically 5 times that for DC
>>>rated ones, in simpler commodity forms like OMRON MGN.
>>>
>>>http://components.omron.com/components/web/webfiles.nsf$FILES/family.html?ID
=CNEN-6TJQPU
>>>
>>>But that wasn't always the case.
>>>
>>>Older SquareD parts anticipate coil current ratios of more tha 4:1
>>>between closed and open armature, with different values expected for
>>>50 and 60Hz dedicated parts..
>>>
>>>http://ecatalog.squared.com/catalog/173/html/sections/21/17321026.html#10138
44
>>>
>>>The same relationship shows up in lower-powered parts:
>>>
>>>http://catalog.tycoelectronics.com/TE/bin/TE.Connect?S=21426&M=FEAT&;
P=86596,80517&U=&BML=10576,16354,16453&LG=1
>>>
>>>RL
>>
>>I'm aware of that. Generally AC coils with predominantly reactive
>>impedance are rated in VA and the so-called impedance limited coils with
>>impedance dominated by coil wire resistance are rated in Watts. The OP
>>is working with a 6W impedance limited coil.
>
>
> Sorry, but I don't see a resistance limited coil described in any
> correspondence from the OP.
>
> The most common ( old P&B now Tyco ) contactor for high current that
> still offers AC coils and a fair description of their impedance and
> wattage expectations:
>
> http://tinyurl.com/3845jx
>
> RL

That link proves my point, the AC coils are specified in Volt-Amps and
the listed DC resistance of those coils is ~20% of the reactance. The
fact that the OP describes his coil as AC and 6W means it's impedance
limited.
Author: legg
Date: 10:39 29-02-08

On Fri, 29 Feb 2008 03:43:59 -0500, Fred Bloggs <nospam@nospam.com>
wrote:


>>>I'm aware of that. Generally AC coils with predominantly reactive
>>>impedance are rated in VA and the so-called impedance limited coils with
>>>impedance dominated by coil wire resistance are rated in Watts. The OP
>>>is working with a 6W impedance limited coil.
>>
>>
>> Sorry, but I don't see a resistance limited coil described in any
>> correspondence from the OP.
>>
>> The most common ( old P&B now Tyco ) contactor for high current that
>> still offers AC coils and a fair description of their impedance and
>> wattage expectations:
>>
>> http://tinyurl.com/3845jx
>>
>> RL
>
>That link proves my point, the AC coils are specified in Volt-Amps and
>the listed DC resistance of those coils is ~20% of the reactance. The
>fact that the OP describes his coil as AC and 6W means it's impedance
>limited.

Could you post a link to a data sheet for any device meeting this
description? I am unable to find a relay in this coil power range that
even has an AC-operated rating specified in W, never mind one
operating at this power level resistively.

I see some smaller ones that come close to 45 degrees, but are still
on the inductive side. I guess it's hard to avoid, being a magnetic
component.

I appreciate that there's some confusion here, but I have a suspicion
that it is most likely to originate with poor characterization by the
OP. I see no reason to carve the misunderstanding into electronic
stone on the news server.

RL
Author: Fred Bloggs
Date: 11:36 29-02-08



legg wrote:
> On Fri, 29 Feb 2008 03:43:59 -0500, Fred Bloggs <nospam@nospam.com>
> wrote:
>
>
>
>>>>I'm aware of that. Generally AC coils with predominantly reactive
>>>>impedance are rated in VA and the so-called impedance limited coils with

>>>>impedance dominated by coil wire resistance are rated in Watts. The OP
>>>>is working with a 6W impedance limited coil.
>>>
>>>
>>>Sorry, but I don't see a resistance limited coil described in any
>>>correspondence from the OP.
>>>
>>>The most common ( old P&B now Tyco ) contactor for high current that
>>>still offers AC coils and a fair description of their impedance and
>>>wattage expectations:
>>>
>>>http://tinyurl.com/3845jx
>>>
>>>RL
>>
>>That link proves my point, the AC coils are specified in Volt-Amps and
>>the listed DC resistance of those coils is ~20% of the reactance. The
>>fact that the OP describes his coil as AC and 6W means it's impedance
>>limited.
>
>
> Could you post a link to a data sheet for any device meeting this
> description? I am unable to find a relay in this coil power range that
> even has an AC-operated rating specified in W, never mind one
> operating at this power level resistively.
>
> I see some smaller ones that come close to 45 degrees, but are still
> on the inductive side. I guess it's hard to avoid, being a magnetic
> component.
>
> I appreciate that there's some confusion here, but I have a suspicion
> that it is most likely to originate with poor characterization by the
> OP. I see no reason to carve the misunderstanding into electronic
> stone on the news server.
>
> RL

Here is one that does MUCH MUCH better in my original snubber circuit
that you, in your infinite wisdumb, cut.
http://www.components.omron.com/components/web/PDFLIB.nsf/0/109B19860C4214F385257201007D
D570/$file/G2R_0607.pdf
Author: legg
Date: 12:56 29-02-08

On Fri, 29 Feb 2008 11:36:51 -0500, Fred Bloggs <nospam@nospam.com>
wrote:

>
>
>legg wrote:
>> On Fri, 29 Feb 2008 03:43:59 -0500, Fred Bloggs <nospam@nospam.com>
>> wrote:
>>
>>
>>
>>>>>I'm aware of that. Generally AC coils with predominantly reactive
>>>>>impedance are rated in VA and the so-called impedance limited coils
with
>>>>>impedance dominated by coil wire resistance are rated in Watts. The
OP
>>>>>is working with a 6W impedance limited coil.
>>>>
>>>>
>>>>Sorry, but I don't see a resistance limited coil described in any
>>>>correspondence from the OP.
>>>>
>>>>The most common ( old P&B now Tyco ) contactor for high current that
>>>>still offers AC coils and a fair description of their impedance and
>>>>wattage expectations:
>>>>
>>>>http://tinyurl.com/3845jx
>>>>
>>>>RL
>>>
>>>That link proves my point, the AC coils are specified in Volt-Amps and
>>>the listed DC resistance of those coils is ~20% of the reactance. The
>>>fact that the OP describes his coil as AC and 6W means it's impedance
>>>limited.
>>
>>
>> Could you post a link to a data sheet for any device meeting this
>> description? I am unable to find a relay in this coil power range that
>> even has an AC-operated rating specified in W, never mind one
>> operating at this power level resistively.
>>
>> I see some smaller ones that come close to 45 degrees, but are still
>> on the inductive side. I guess it's hard to avoid, being a magnetic
>> component.
>>
>> I appreciate that there's some confusion here, but I have a suspicion
>> that it is most likely to originate with poor characterization by the
>> OP. I see no reason to carve the misunderstanding into electronic
>> stone on the news server.
>>
>> RL
>
>Here is one that does MUCH MUCH better in my original snubber circuit
>that you, in your infinite wisdumb, cut.
>http://www.components.omron.com/components/web/PDFLIB.nsf/0/109B19860C4214F385257201
007DD570/$file/G2R_0607.pdf

This is a 400mw/0.9VA relay coil.

RL
Author: Lostgallifreyan
Date: 04:44 01-03-08

Fred Bloggs <nospam@nospam.com> wrote in news:47C834A3.2050100@nospam.com:

> wisdumb

Cute. *Saves for future use.
Author: LVMarc
Date: 16:00 17-04-08

michael nikolaou wrote:
> Hi
>
> I have a 12 v relay driving an large 220 volt AC relay . Across the contact
> of the driver relay i placed one RC snubber circut (27NF with 100 R
> resisitor in series) to help with some spikes that were influencing the low
> voltage driver circuits.
> The driver circuit is able to detect mains zero crossing and fire the
> driver relay at an angle i choose .
> From what i read the best point to switch off the power relay is at zero
> crossing . I did that and i show a large spike up to 1 KV at the relay
> contact followed by a decaying 500hz waveform to 0 volts . After some
> experimentation the best point came exactly when switching off at the peak
> of the mains voltage .At this point there is smooth decaying waveform to 0
> volt after 5 periods of 500 HZ but no overshoot. The relay presents no
> arcing. If i remove the snubber and make the experiment the best place to
> switch is zero crossing but i also see large SHARP spikes up to 500 Volts
> Peak.
> My question is
> The switching with snubber must be made at zero crossing or at the peak of
> an ac voltage waveform ?
> What is the behaviour of the circuit ?.
> As i understand any large spikes can harm the X2 capacitor i'm using so
> what is the best operating practise ?.
>
> Any help will be appreciated
>
> Michael
>
>
Hello,


Two comments:


If the load is not purely resistive, there will be a voltage current
shift, aka Eli ICE Man... therefore in this case zero voltage crossing
is not at all zero current crossing and you may be creating more problem
by switching at the worst (or just a bad) time) .

BY looking at the signal that the rc snubber is trying to "tame" , you
adjust RC unitl you get a "critically damped response. you can dampen
more, but at the cost of higher stand by leakage via the RC, as it
becomes a part of the load too!

Good luck, this is an often asked problem, and the ability to visualizes
on scope and make changes and observations, will help you forever. This
is a re-occcuring problem and it is the variations in the load that
cause engineers to have to re-visit the solutions

Best regards

Marco
1 2


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