Indictive currents on relay contact

J

Joe G (Home)

Guest
Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

What other switching methods would you suggest.


Regards
Joe.
 
Oh,

Supply is 110V AC

JG
"Joe G (Home)" <joe.g@optusnet.com.au> wrote in message
news:42db9083$0$25702$afc38c87@news.optusnet.com.au...
Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

What other switching methods would you suggest.


Regards
Joe.
Click to expand...
 
One day Joe G (Home) got dressed and committed to text

Oh,

Supply is 110V AC

JG
"Joe G (Home)" <joe.g@optusnet.com.au> wrote in message
news:42db9083$0$25702$afc38c87@news.optusnet.com.au...
Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

What other switching methods would you suggest.


Regards
Joe.
Click to expand...
Is the arcing causing a problem ??

--
Regards ..... Rheilly Phoull
 
"Joe G (Home)" wrote:

Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.
Click to expand...
Suck it and see ? 0.1uF and 100R in series is a classic off the shelf
combination.


What other switching methods would you suggest.
Click to expand...
Triac.

Graham
 
This is prelim design thinking.
JG
"Rheilly Phoull" <Rheilly@bigpong.com> wrote in message
news:42db957a$0$18646$14726298@news.sunsite.dk...
One day Joe G (Home) got dressed and committed to text

Oh,

Supply is 110V AC

JG
"Joe G (Home)" <joe.g@optusnet.com.au> wrote in message
news:42db9083$0$25702$afc38c87@news.optusnet.com.au...
Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

What other switching methods would you suggest.


Regards
Joe.

Is the arcing causing a problem ??

--
Regards ..... Rheilly Phoull
Click to expand...
 
Oh - I see like RC snubber networks for triac's.
JG
"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42DB96FF.65F0CE39@hotmail.com...
"Joe G (Home)" wrote:

Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

Suck it and see ? 0.1uF and 100R in series is a classic off the shelf
combination.


What other switching methods would you suggest.


Triac.

Graham
Click to expand...
 
On Mon, 18 Jul 2005 12:48:15 +0100, in sci.electronics.design Pooh
Bear <rabbitsfriendsandrelations@hotmail.com> wrote:

"Joe G (Home)" wrote:

Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

Suck it and see ? 0.1uF and 100R in series is a classic off the shelf
combination.


What other switching methods would you suggest.


Triac.

Graham
A useless suggestion.... quantum tunneling capsules from peratech.
Click to expand...

This is a particularly badly designed site so
http://www.peratech.co.uk/pills.htm
or
http://www.peratech.co.uk/pdfs/p001v004.pdf

some of the stuff is available from Maplin


martin
 
quantum tunneling capsules from peratech:
http://www.peratech.co.uk/pdfs/p001v004.pdf
Click to expand...
Interesting. When I was a kid we did similar things with carbon
microphones from old phones. Of course there I don't think it was a
quantum tunneling effect, just that it conducted better when you
squeezed everything together.

Tim.
 
On Mon, 18 Jul 2005 21:20:38 +1000, "Joe G \(Home\)"
<joe.g@optusnet.com.au> wrote:

Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.
Click to expand...
A 1N4004 diode across the inductive motor, so that, when the relay
contact is closed, the diode is reversed biased, and when the contact
is open, the inertia of the inductive current still finds a path to
flow, through the diode. The diode should be as close as possible to
the relay (not to the motor). With this, you can completely eliminate
the spark.

What other switching methods would you suggest.
Click to expand...
MOSFETs.

Regards
Joe.
Click to expand...
 
Sorry, now I read your supply is AC.

Best is to turn on and off when i=0. A TRIAC solves for you half of
the problem (it always turns off when i=0). If you want to also turn
on when i=0, you need to detect it yourself. Even if you do all that,
you still may need a snubber to avoid unwanted triggering of the TRIAC
(due to excessive dV/dt, when the switch opens). A series RC network
will do the job.
 
On Mon, 18 Jul 2005 21:31:44 +1000, "Joe G \(Home\)"
<joe.g@optusnet.com.au> wrote:

Oh,

Supply is 110V AC

JG
"Joe G (Home)" <joe.g@optusnet.com.au> wrote in message
news:42db9083$0$25702$afc38c87@news.optusnet.com.au...
Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.
Click to expand...
None. AC is self-quenching.

John
 
On Mon, 18 Jul 2005 14:56:51 +0200, Mochuelo wrote:

Sorry, now I read your supply is AC.

Best is to turn on and off when i=0. A TRIAC solves for you half of
the problem (it always turns off when i=0). If you want to also turn
on when i=0, you need to detect it yourself.
Click to expand...
You could use something like a MOC3030, opto-triac, with a zero-cross
detector built in, to get v=0 turn-on.
http://www.optoinc.com/optocouplers1.html

Even if you do all that,
you still may need a snubber to avoid unwanted triggering of the TRIAC
(due to excessive dV/dt, when the switch opens). A series RC network
will do the job.
Click to expand...
Just trying the snubber across the relay contacts could help.

Cheers!
Rich
 
Beware of voltage leakage through snubber circuit.
You may want to consider snubberless triacs like ST T820W. They have
high dv/dt ratings
 
Joe G (Home) wrote:

Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

What other switching methods would you suggest.


Regards
Joe.


use a solid state relay, most of them turn off
Click to expand...
at or near the base line (zero crossing), but that
time the back flow should be reduced to a min..
you could also use some TVS diodes.


--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
 
Joe G (Home) wrote:
Oh - I see like RC snubber networks for triac's.
JG
Click to expand...
(I see why others complain about top-posting now)

yes, exactly like that.

Beware, however, the type of resistor you choose. If contact is made at
the peak of AC line voltage (156V) and the capacitor is discharged, the
100R resistor "sees" all 155V, so the peak power is

Ppeak = (155V^2)/100R = 243W

which will exponentially decay to zero with a time constant of 10us, for
the suggested 0.1uF + 100R snubber. If you picked 10R, the peak power
would be 10 times higher, but the time constant would be ten times shorter.

Make sure the resistor has a suitable voltage rating, and can cope with
the peak pulse power (whatever that works out to be).

Also, the start-up current of the AC motor may be quite a bit higher
than its operating current.

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:42DB96FF.65F0CE39@hotmail.com...


"Joe G (Home)" wrote:


Hi All,

I have a relay with 3amp contact current rating that is powering an
inductive motor at 700mA.

Q1
What additional subber components would you suggest
to reduce the spark quench after contact opening.

Suck it and see ? 0.1uF and 100R in series is a classic off the shelf
combination.



What other switching methods would you suggest.


Triac.

Graham
Click to expand...
 
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