"Snubber" for electro-mechanical relay?
Sam Mayberry
good luck, sam
"DaveC" <an...@example.net> wrote in message
news:01HW.B76208350...@news.dnai.com...
> I'm going to use a triac to enable a relay, which will handle some higher
> voltage (240 vac) work.
>
> The manufacturer of the control device, a current transformer (with
> incorporated triac)
> < http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR9321 >
> states that for ac use, a "snubber network" must be employed with the
relay's
> coil.
>
> What is this? I'm familiar with the purpose and function of diodes in
> dc-controlled relays; I presume this is an ac equivalent.
>
> Can someone help me select and size components for this? The voltage will
> probably be 24-50 vac (min switching voltage for this device is 24 vac;
I'm
> not comfortable being on the margin of the operating range, so am
considering
> slightly higher voltage). Relay current is -- maybe 50mA (can't find data
> sheet right now...).
>
> Any help with snubber components would be greatly appreciated.
> --
> Note that my return address is corrupted in an attempt to reduce spam. If
you
> choose to e-mail me, please correct my address as described below.
>
> Thanks,
> Dave
> --
> Dave Carpenter
> Sound Logic
> voic...@NOdnai.com
>
> Remove "NO" to reply via e-mail
>
du...@home.com
coil
also an RC network performs similarly
Lizard Blizard
Snubbers reduce overshoot. Usually a cap and a resistor in series, both
across the inductance. The ones in SMPSes are something like 470 pF and
a 100 ohm 1W resistor. But that's for 100 kHz. You probably want more
capacitance for lower freqs.
DaveC wrote:
>
> I'm going to use a triac to enable a relay, which will handle some higher
> voltage (240 vac) work.
> The manufacturer of the control device, a current transformer (with
> incorporated triac)
> < http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR9321 >
> states that for ac use, a "snubber network" must be employed with the relay's
> coil.
> What is this? I'm familiar with the purpose and function of diodes in
> dc-controlled relays; I presume this is an ac equivalent.
> Can someone help me select and size components for this? The voltage will
> probably be 24-50 vac (min switching voltage for this device is 24 vac; I'm
> not comfortable being on the margin of the operating range, so am considering
> slightly higher voltage). Relay current is -- maybe 50mA (can't find data
> sheet right now...).
> Any help with snubber components would be greatly appreciated.
> --
> Note that my return address is corrupted in an attempt to reduce spam. If you
> choose to e-mail me, please correct my address as described below.
> Thanks,
> Dave
> --
> Dave Carpenter
> Sound Logic
> voic...@NOdnai.com
>
> Remove "NO" to reply via e-mail
--
You _MUST_ include NOSPAM in the Subject: line!
My new unmunged and white listed email address is
alond...@hotmail.com - Standard disclaimers apply.
Phil Allison
> voltage (240 vac) work.
>
> The manufacturer of the control device, a current transformer (with
> incorporated triac)
> < http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR9321 >
> states that for ac use, a "snubber network" must be employed with the
relay's
> coil.
>
> What is this? I'm familiar with the purpose and function of diodes in
> dc-controlled relays; I presume this is an ac equivalent.
>
> Can someone help me select and size components for this? The voltage will
> probably be 24-50 vac (min switching voltage for this device is 24 vac;
I'm
> not comfortable being on the margin of the operating range, so am
considering
> slightly higher voltage). Relay current is -- maybe 50mA (can't find data
> sheet right now...).
>
> Any help with snubber components would be greatly appreciated.
> --
The usual snubber for mains voltage ccts is 0.1 uF in series with 100 ohms.
This would be a good stating value for your relay coil. I hope the triac is
continuously triggered as 50mA is getting close to the holding current limit
for most.
Regards, Phil
Malcolm Reeves
wrote:
>the best type of snubber, IMHO is a metal oxide varistor. (MOV)
MOV have limited life times and blow up short circuit then. How many
times will it need to operated is the question. A transzorb or
similar does not have a life limit.
A snubber would also give less EMI as it will slow the edges where as
a MOV will just let it fly off until in clamps. It might be wise to
use both methods, at least at prototype, it case your snubber is not
correct.
Or how about putting the relay inside a bridge rectifier? That way it
has a diode like a dc relay.
...malcolm
--
Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK
(mre...@fullcircuit.com, mre...@fullcircuit.co.uk or mre...@iee.org).
Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power
electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see:
http://www.fullcircuit.com or http://www.fullcircuit.co.uk
NEW - VHDL test bench tool
Phil Allison
> Max off state voltage: 2240 vac RMS
> Min switch voltage: 24 vac RMS
> Max on state current: 1.0 Aac RMS cont.
> Max off state leakage current: 50 ua @ 240 vac
> Peak surge current (non-repetetive): 8.0 Aac for 1 cycle @60 hz
>
> See any problems with this?
> --
Looks fine to me, the SCR is shown as having a bridge rectifier around it so
it works like a triac.
Regards, Phil
Malcolm Reeves
>The current switch (actually uses an SCR, not a triac; my error) has these
>specs (rated at 60hz only):
>
>Max off state voltage: 2240 vac RMS
>Min switch voltage: 24 vac RMS
>Max on state current: 1.0 Aac RMS cont.
>Max off state leakage current: 50 ua @ 240 vac
>Peak surge current (non-repetetive): 8.0 Aac for 1 cycle @60 hz
>
>See any problems with this?
SCRs are rectifies, so does it have two, back to back? The spec does
not list holding current (which has been mention before I know). If
the SCR is trigger with a pulse and then stays on all by itself the
current has to be above the holding level to guarantee this happens.
With just a relay for load will it?
If the relay load look significantly inductive then the voltage and
current will be out of sink. If the SCR(s?) are pulse driven at say
the zero crossing then the phase lag voltage to current could be a
problem.
Daniel Narvaes
Malcolm Reeves wrote in message
<0adtjtokc0fk4a0eo...@4ax.com>...
>On Fri, 29 Jun 2001 16:24:44 -0400, "Sam Mayberry" <za...@sgi.net>
>wrote:
>
>>the best type of snubber, IMHO is a metal oxide varistor. (MOV)
>
>MOV have limited life times and blow up short circuit then. How many
>times will it need to operated is the question. A transzorb or
>similar does not have a life limit.
What is a trabzorb?
David Emrich
"Sam Mayberry" <za...@sgi.net> wrote in message
news:tjporvf...@corp.supernews.com...
> the best type of snubber, IMHO is a metal oxide varistor. (MOV)
> good luck, sam
Not really. MOV's aren't rated for repetitive surges. Admittedly in this
particular case (50mA 24VAC) no MOV worth its reputation would fail. But
the theory doesn't extend up to reasonable currents at, say, 240VAC.
I've just been through this very exercise switching a 1horse 240VAC motor
with a regular relay.
For lowish voltages and currents like these, a Tranzorb (the bidirectional
version) would probably be the go, since they ARE designed to deal with
repetitive surges (as long as they're mounted properly, coz the smaller ones
rely on the leads for conducting any transient heat build-ups away).
For full-on mechanical switching of 240V mains, I used a 275V (150Joule?)
MOV across the load, paralleled with a 100R/0.1uF snubber. I also stuck a
100R/0.1uF snubber across the relay contacts just to make sure. This was
the result that worked after several cranks through the "cycle" involving
reference designs and discussions with reps from relay, MOV and snubber
manufacturers. *sigh*.
The theory goes like this. The MOV shunts some fraction of the energy in
the load when it's switched off. The MOV really only gets "used" when the
load is switched off at the worst part of the cycle (wherever that may be),
which happens relatively rarely in a randomly switched load. (that's why the
MOV is rated at 275V, rather than, say, 250V). The snubber across the load
deals with anything that remains after the MOV has done its trick. The
snubber across the relay contacts cleans up anything due to lead or wiring
inductances, or not capped by the other two devices.
But, as ususal with anything you read on the Internet, "your mileage may
vary".
David.
S Ungstad
Steve
DaveC wrote:
>
> I'm going to use a triac to enable a relay, which will handle some higher
> voltage (240 vac) work.
>
> The manufacturer of the control device, a current transformer (with
> incorporated triac)
> < http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR9321 >
> states that for ac use, a "snubber network" must be employed with the relay's
> coil.
>
> What is this? I'm familiar with the purpose and function of diodes in
> dc-controlled relays; I presume this is an ac equivalent.
>
> Can someone help me select and size components for this? The voltage will
> probably be 24-50 vac (min switching voltage for this device is 24 vac; I'm
> not comfortable being on the margin of the operating range, so am considering
> slightly higher voltage). Relay current is -- maybe 50mA (can't find data
> sheet right now...).
>
> Any help with snubber components would be greatly appreciated.
> --
Phil Allison
S Ungstad <sung...@clsp.uswest.net> wrote in message
news:3B400197...@clsp.uswest.net...
> The R-C thing can work, but a MOV is better for AC applications.
> Steve
An RC snubber has the advantage over a MOV that it slows the rise time of
any back emfs while a MOV only clips the spike after it reaches a certain
voltage.
A triac or SCR can be re triggered if the dv/dt of the spike is fast enough
and so not turn off.
Regards Phil
Sam Mayberry
really need much of a snubber at 24 or 48 volts. we put ours in starting in
1972 and had no significant failures. maybe you're using a larger relay.
note also the ssr he's using is rated at 1 amp, if i recall. that aint much
to run a big relay so i'm assuming (always questionable) the relay is small.
yes, he could put all kinds of stuff on it. from off-group discussions i
sense he's not an experienced user. we've had racks of hundreds in service.
best wishes, sam
"David Emrich" <dem...@ihgtech.com.au> wrote in message
news:9hoi0n$5gh$1...@yeppa.connect.com.au...
Sylvan Butler
> For full-on mechanical switching of 240V mains, I used a 275V (150Joule?)
> MOV across the load, paralleled with a 100R/0.1uF snubber. I also stuck a
> load is switched off at the worst part of the cycle (wherever that may be),
> which happens relatively rarely in a randomly switched load. (that's why the
> MOV is rated at 275V, rather than, say, 250V). The snubber across the load
How odd. How does a 275V MOV survive on a 240V-RMS line? I would
have expected the MOV to be at least 350V.
sdb
--
| Sylvan Butler | Not speaking for Hewlett-Packard | sbutler-boi.hp.com |
| Watch out for my e-mail address. Thank UCE. #### change ^ to @ #### |
They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety. --Benjamin Franklin, 1759
"Don't Tread On Me!"
Phil Allison
Sylvan Butler <Znospam+...@hpb13799Z.Zboi.hpZ.com.invalid> wrote in
message
news:slrn9k1ein.7ed.Z...@hpb13799Z.Zboi.hpZ.com.invalid...
> On Mon, 2 Jul 2001 09:16:05 +0800, David Emrich <dem...@ihgtech.com.au>
wrote:
> > For full-on mechanical switching of 240V mains, I used a 275V
(150Joule?)
> > MOV across the load, paralleled with a 100R/0.1uF snubber. I also stuck
a
> ...
> > load is switched off at the worst part of the cycle (wherever that may
be),
> > which happens relatively rarely in a randomly switched load. (that's why
the
> > MOV is rated at 275V, rather than, say, 250V). The snubber across the
load
>
> How odd. How does a 275V MOV survive on a 240V-RMS line? I would
> have expected the MOV to be at least 350V.
>
> sdb
>
MOVs are usually labelled with their nominal AC rms voltage. At this voltage
they draw virtually no current. I know some types have the nomimal DC
voltage marked on them - very confusing.
Regards, Phil
Skipp
Just go to a motor supply or rebuild shop and buy one. Snubbers are most
often a resistor in series with a capacitor, the values selected for the
type of operation required.
I have selected values I use for AC Motor Circuits and different values
for the output of audio amplifiers.
You can often buy them in premade packages, when said are not available, I
just build them myself.
Hope that helps.
cheers
sk...@pilot.ucdavis.edu
http://sonic.ucdavis.edu
Sam Mayberry
120 vac. best wishes, sam
"Sylvan Butler" <Znospam+...@hpb13799Z.Zboi.hpZ.com.invalid> wrote in
message
news:slrn9k1ein.7ed.Z...@hpb13799Z.Zboi.hpZ.com.invalid...
David Emrich
"Phil Allison" <bi...@bigpond.com> wrote in message
news:QGT%6.18639$e5.4...@newsfeeds.bigpond.com...
>
> S Ungstad <sung...@clsp.uswest.net> wrote in message
> news:3B400197...@clsp.uswest.net...
>
> > The R-C thing can work, but a MOV is better for AC applications.
> > Steve
>
> An RC snubber has the advantage over a MOV that it slows the rise time of
> any back emfs while a MOV only clips the spike after it reaches a certain
> voltage.
Also, a RC subber is designed to take repetitive hits,... a MOV isn't.
Rather critical in the intended application...
David.
David Emrich
"Sylvan Butler" <Znospam+...@hpb13799Z.Zboi.hpZ.com.invalid> wrote in
message
news:slrn9k1ein.7ed.Z...@hpb13799Z.Zboi.hpZ.com.invalid...
wrote:
> > For full-on mechanical switching of 240V mains, I used a 275V
(150Joule?)
> > MOV across the load, paralleled with a 100R/0.1uF snubber. I also stuck
a
> ...
> > load is switched off at the worst part of the cycle (wherever that may
be),
> > which happens relatively rarely in a randomly switched load. (that's why
the
> > MOV is rated at 275V, rather than, say, 250V). The snubber across the
load
>
> How odd. How does a 275V MOV survive on a 240V-RMS line? I would
> have expected the MOV to be at least 350V.
It's an RMS voltage rating. :-)
David.
Phil Allison
> Also, a RC subber is designed to take repetitive hits,... a MOV isn't.
>
> Rather critical in the intended application...
>
> David.
>
The intended application was a 24 volt AC relay being switched by a small
SCR (inside a bridge rectifier). Back emfs arise at each switch off which
would be at the SCR min holding current, only a few milliamps. The SCR gate
drive system is unknown but likely to be rectified AC from the current
transformer since the response times of the sensor are slow, 100s of
milliseconds.
Wouldn't any MOV worth its salt cope with a low milliamp pulse a few times a
day?
Regards, Phil
Spehro Pefhany
> Since this is going to be used so many times per day, is it the consensus of
> the contributors here that an MOV may be too little protection?
Consider a bidirectional TVS rather than a MOV or RC network.
Best regards,
--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Spehro Pefhany --"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.BlueCollarLinux.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
David Emrich
Oh sure, it's fine for this application. I should've been a bit clearer.
My warning was intended to mean that the RC snubber solution scales up to
where it's a multi-amp pulse at full mains voltages and above, several times
an hour. However, MOV's don't scale up that well. :-)
Sorry for the confusion.
David.
David Emrich
"Spehro Pefhany" <sp...@interlog.com> wrote in message
news:_Ry07.88135$Mf5.25...@news3.rdc1.on.home.com...
> In sci.electronics.components DaveC <an...@example.net> wrote:
>
> > Since this is going to be used so many times per day, is it the
consensus of
> > the contributors here that an MOV may be too little protection?
>
> Consider a bidirectional TVS rather than a MOV or RC network.
Aka Transorb isn't it Spehro?
David.
Spehro Pefhany
>>
>> Consider a bidirectional TVS rather than a MOV or RC network.
> Aka Transorb isn't it Spehro?
Right. Or is it Transzorb? Anyway that's a trade name for a line of TVS
products. Lots of suppliers of them such as Diodes Inc. and Microsemi.
Jim Adney
wrote:
>On Mon, 2 Jul 2001 09:16:05 +0800, David Emrich <dem...@ihgtech.com.au> wrote:
>> For full-on mechanical switching of 240V mains, I used a 275V (150Joule?)
>> MOV across the load, paralleled with a 100R/0.1uF snubber. I also stuck a
> ...
>> load is switched off at the worst part of the cycle (wherever that may be),
>> which happens relatively rarely in a randomly switched load. (that's why the
>> MOV is rated at 275V, rather than, say, 250V). The snubber across the load
>
>How odd. How does a 275V MOV survive on a 240V-RMS line? I would
>have expected the MOV to be at least 350V.
Some manufacturers sell their varistors by RMS voltage and some sell
them by the peak. These were probably by RMS.
-
-----------------------------------------------
Jim Adney jad...@vwtype3.org
Madison,Wisconsin USA
-----------------------------------------------
Richard Erlacher
question, i.e. "WHAT IS IT?"
It's the classic case of telling the guy how to build a clock, when
all he wants to know what is time it is.
I'm kind-of curious what a "snubber" is, in the general case, myself.
Dick
On Tue, 3 Jul 2001 23:01:52 -0700, DaveC <an...@example.net> wrote:
>On Fri, 29 Jun 2001 19:40:18 -0700, Lizard Blizard wrote
>(in message <3B3D3C12...@private.rsccd.org>):
>
>> Jeez, what's with all the crossposting!!
>
>Well, I'll tell you what's with it.
>
>All these wonderful replies, all the great discussion and cross-discussion
>wouldn't have happened if I'd posted to 1 or 2 groups. Response probably
>would have been limited to a third of all that I've gotten. This is a topic
>that many people can (and did) contribute to.
>
>To borrow a phrase, "Cross-posting isn't criminal." *Off-topic* cross-posting
>should be.
Jim Thompson
wrote:
|If only all the "wonderful" replies would answer the original
|question, i.e. "WHAT IS IT?"
|
|It's the classic case of telling the guy how to build a clock, when
|all he wants to know what is time it is.
|
|I'm kind-of curious what a "snubber" is, in the general case, myself.
|
|Dick
|
"Generally" speaking, a snubber is an R/C network applied across an
inductive load to limit the voltage that occurs when the inductor is
suddenly disconnected from the source.
Specifically, if I had an inductor with 1A flowing in it and I wanted
to limit the voltage to 100V I would choose R = 100ohms. (1A*100ohms
= 100V). The C would (generally) be chosen to create an RC time
constant somewhat larger than the L/R time constant, otherwise the
voltage will ring below ground. (This *may* not be a problem is some
applications.
There are more complicated "snubbers" that utilize diodes and
inductors as well. These are used to "snub" in only one direction, or
to tailor load lines for switching power supplies.
(If replying by E-mail please observe obscure method of anti-spam.)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
For proper E-mail replies SWAP "-" and "_".