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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Relay contacts sticking



 
 
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  #1  
Old March 29th 04, 11:50 PM
Kelly E Jones
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Default Relay contacts sticking

I've got a relay that controls the submersible pump which supplies
water to my house. (For reasons I won't go into, the pressure switch
and the pump power circuit are separated by a great distance, so the
pressure switch supplies a 30V signal to the relay which actually
switches the 240V to the pump). Yesterday, I noticed water coming out
of my overpressure relief valve, and after some frantic
troubleshooting discovered that the relay had stuck 'on' (the contacts
were in the 'on' position despite no juice to the coil). The relay is
being used within the current/voltage for which it is rated. A gentle
push with a screwdriver separated the contacts, and after that they
seemed to work fine.

Any idea what caused this, and how to prevent it in the future?

Thanks,

Kelly

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  #2  
Old March 30th 04, 12:09 AM
Cornelius J Rat
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Default Relay contacts sticking


"Kelly E Jones" wrote
discovered that the relay had stuck 'on' (the contacts
were in the 'on' position despite no juice to the coil). The relay is
being used within the current/voltage for which it is rated. A gentle
push with a screwdriver separated the contacts, and after that they
seemed to work fine.

Any idea what caused this, and how to prevent it in the future?

Any kind of ring/arc supression circuit on those contacts ? I did once come
across a case where the contacts welded lightly shut when the supression
failed.


  #3  
Old March 30th 04, 02:02 AM
Bill Vajk
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Default Relay contacts sticking

Kelly E Jones wrote:

I've got a relay that controls the submersible pump which supplies
water to my house. (For reasons I won't go into, the pressure switch
and the pump power circuit are separated by a great distance, so the
pressure switch supplies a 30V signal to the relay which actually
switches the 240V to the pump). Yesterday, I noticed water coming out
of my overpressure relief valve, and after some frantic
troubleshooting discovered that the relay had stuck 'on' (the contacts
were in the 'on' position despite no juice to the coil). The relay is
being used within the current/voltage for which it is rated. A gentle
push with a screwdriver separated the contacts, and after that they
seemed to work fine.


Any idea what caused this, and how to prevent it in the future?


Age of the relay (they're only good for some large number
of cycles) and/or a relay not designed for starting that
size of a pump. You have to remember that the LRA (locked
rotor amps = starting amps) of a submersible pump motor
is higher than a conventional motor of the same horsepower
rating. (Same goes for refrigeration and all other
hermetically sealed motors.)

It is advisable to go up one size (motor starters are rated
in horsepower) for hermetically sealed motors. If you're
using a "relay" I would, for long term reliability, recommend
replacing it with a regular motor starting contactor with
replaceable contacts and use your 24 volt circuit/relay to
actuate the motor starter. Real motor starting contactors
are lifetime deals, and maybe then some.

One of the nicer features about regular motor starters is
that they are powerful enough to "wipe" the contacts
every time they make and break. It is a matter of geometry
that, as they close, the contacts slide one over the other.
I doubt your 24 volt relay has that capability and since
the contacts always hit on the same one spot they eventually
become damaged enough to weld themselves together when they
connect larger loads, just as you've experienced. They're
relatively inexpensive but then you have the maintenance
and replacement problem recurring much more frequently.

  #4  
Old April 13th 04, 09:49 PM
Innes Cathcart
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Posts: n/a
Default Relay contacts sticking

On Mon, 29 Mar 2004 22:50:11 +0000, Kelly E Jones wrote:

I've got a relay that controls the submersible pump which supplies
water to my house. (For reasons I won't go into, the pressure switch
and the pump power circuit are separated by a great distance, so the
pressure switch supplies a 30V signal to the relay which actually
switches the 240V to the pump). Yesterday, I noticed water coming out
of my overpressure relief valve, and after some frantic
troubleshooting discovered that the relay had stuck 'on' (the contacts
were in the 'on' position despite no juice to the coil). The relay is
being used within the current/voltage for which it is rated. A gentle
push with a screwdriver separated the contacts, and after that they
seemed to work fine.

Any idea what caused this, and how to prevent it in the future?

Thanks,

Kelly


Not too sure what caused it, and unless you can find the cause and
eliminate it I'll bet it will happen again. What make/model of relay are
you using? Perhaps a sealed one would be better. good luck,

Innes
  #5  
Old April 13th 04, 09:49 PM
Innes Cathcart
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Posts: n/a
Default Relay contacts sticking

On Mon, 29 Mar 2004 22:50:11 +0000, Kelly E Jones wrote:

I've got a relay that controls the submersible pump which supplies
water to my house. (For reasons I won't go into, the pressure switch
and the pump power circuit are separated by a great distance, so the
pressure switch supplies a 30V signal to the relay which actually
switches the 240V to the pump). Yesterday, I noticed water coming out
of my overpressure relief valve, and after some frantic
troubleshooting discovered that the relay had stuck 'on' (the contacts
were in the 'on' position despite no juice to the coil). The relay is
being used within the current/voltage for which it is rated. A gentle
push with a screwdriver separated the contacts, and after that they
seemed to work fine.

Any idea what caused this, and how to prevent it in the future?

Thanks,

Kelly


Not too sure what caused it, and unless you can find the cause and
eliminate it I'll bet it will happen again. What make/model of relay are
you using? Perhaps a sealed one would be better. good luck,

Innes
  #6  
Old April 13th 04, 11:38 PM
Tweetldee
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Posts: n/a
Default Relay contacts sticking

"Innes Cathcart" wrote in message
news
On Mon, 29 Mar 2004 22:50:11 +0000, Kelly E Jones wrote:

I've got a relay that controls the submersible pump which supplies
water to my house. (For reasons I won't go into, the pressure switch
and the pump power circuit are separated by a great distance, so the
pressure switch supplies a 30V signal to the relay which actually
switches the 240V to the pump). Yesterday, I noticed water coming out
of my overpressure relief valve, and after some frantic
troubleshooting discovered that the relay had stuck 'on' (the contacts
were in the 'on' position despite no juice to the coil). The relay is
being used within the current/voltage for which it is rated. A gentle
push with a screwdriver separated the contacts, and after that they
seemed to work fine.

Any idea what caused this, and how to prevent it in the future?

Thanks,

Kelly


Not too sure what caused it, and unless you can find the cause and
eliminate it I'll bet it will happen again. What make/model of relay are
you using? Perhaps a sealed one would be better. good luck,

Innes


Relays used to switch inductive loads, such as your pump motor, are prone to
arcing when they switch on and off. This is quite normal, and unless some
sort of arc suppression (snubber circuit) has been used across the contacts,
they will eventually fail. Failure modes are either of two conditions: one
is that they stick together, as you have found; the other is that they will
fail to make contact at all. The arcing is the cause of both types of
failure.
The solution to your problem is to replace the relay, or if they are
separately replaceable, the contacts themselves. Then enjoy your water
until the contacts fail again. That's just a fact of life when you live in
the boonies, as I do.

Cheers!!!!!!
--
Dave M

Good judgement comes from experience, and a lot of that comes from bad
judgement.


  #7  
Old April 13th 04, 11:38 PM
Tweetldee
external usenet poster
 
Posts: n/a
Default Relay contacts sticking

"Innes Cathcart" wrote in message
news
On Mon, 29 Mar 2004 22:50:11 +0000, Kelly E Jones wrote:

I've got a relay that controls the submersible pump which supplies
water to my house. (For reasons I won't go into, the pressure switch
and the pump power circuit are separated by a great distance, so the
pressure switch supplies a 30V signal to the relay which actually
switches the 240V to the pump). Yesterday, I noticed water coming out
of my overpressure relief valve, and after some frantic
troubleshooting discovered that the relay had stuck 'on' (the contacts
were in the 'on' position despite no juice to the coil). The relay is
being used within the current/voltage for which it is rated. A gentle
push with a screwdriver separated the contacts, and after that they
seemed to work fine.

Any idea what caused this, and how to prevent it in the future?

Thanks,

Kelly


Not too sure what caused it, and unless you can find the cause and
eliminate it I'll bet it will happen again. What make/model of relay are
you using? Perhaps a sealed one would be better. good luck,

Innes


Relays used to switch inductive loads, such as your pump motor, are prone to
arcing when they switch on and off. This is quite normal, and unless some
sort of arc suppression (snubber circuit) has been used across the contacts,
they will eventually fail. Failure modes are either of two conditions: one
is that they stick together, as you have found; the other is that they will
fail to make contact at all. The arcing is the cause of both types of
failure.
The solution to your problem is to replace the relay, or if they are
separately replaceable, the contacts themselves. Then enjoy your water
until the contacts fail again. That's just a fact of life when you live in
the boonies, as I do.

Cheers!!!!!!
--
Dave M

Good judgement comes from experience, and a lot of that comes from bad
judgement.


  #8  
Old April 14th 04, 12:15 AM
Jerry Maple
external usenet poster
 
Posts: n/a
Default Relay contacts sticking

In article nZZec.123791$gA5.1527613@attbi_s03, masondg4499
@comcast99.net says...
"Innes Cathcart" wrote in message
news
On Mon, 29 Mar 2004 22:50:11 +0000, Kelly E Jones wrote:

I've got a relay that controls the submersible pump which supplies
water to my house.



Relays used to switch inductive loads, such as your pump motor, are prone to
arcing when they switch on and off. This is quite normal, and unless some
sort of arc suppression (snubber circuit) has been used across the contacts,
they will eventually fail. Failure modes are either of two conditions: one
is that they stick together, as you have found; the other is that they will
fail to make contact at all. The arcing is the cause of both types of
failure.


--

Used to own a house with a heat pump (basically a reversible air
conditioner) in AZ. When the thermostat was switched from cooling to
heating, a relay was used to control the reversing coil that switched
the direction of freon flow. After several years, the relay would fail
to contact, with the result being that the heat pump was still in the
cooling mode. I would crank the thermostat up in the winter, and the
house would get colder and colder - not very desirable behavior in a
heater. Used to replace that relay every few years until I sold the
house.

--

Jerry Maple
General Dynamics C4 Systems
Scottsdale, AZ
  #9  
Old April 14th 04, 12:15 AM
Jerry Maple
external usenet poster
 
Posts: n/a
Default Relay contacts sticking

In article nZZec.123791$gA5.1527613@attbi_s03, masondg4499
@comcast99.net says...
"Innes Cathcart" wrote in message
news
On Mon, 29 Mar 2004 22:50:11 +0000, Kelly E Jones wrote:

I've got a relay that controls the submersible pump which supplies
water to my house.



Relays used to switch inductive loads, such as your pump motor, are prone to
arcing when they switch on and off. This is quite normal, and unless some
sort of arc suppression (snubber circuit) has been used across the contacts,
they will eventually fail. Failure modes are either of two conditions: one
is that they stick together, as you have found; the other is that they will
fail to make contact at all. The arcing is the cause of both types of
failure.


--

Used to own a house with a heat pump (basically a reversible air
conditioner) in AZ. When the thermostat was switched from cooling to
heating, a relay was used to control the reversing coil that switched
the direction of freon flow. After several years, the relay would fail
to contact, with the result being that the heat pump was still in the
cooling mode. I would crank the thermostat up in the winter, and the
house would get colder and colder - not very desirable behavior in a
heater. Used to replace that relay every few years until I sold the
house.

--

Jerry Maple
General Dynamics C4 Systems
Scottsdale, AZ
  #10  
Old April 14th 04, 01:46 AM
Kelly E Jones
external usenet poster
 
Posts: n/a
Default Relay contacts sticking

In article nZZec.123791$gA5.1527613@attbi_s03,
Tweetldee wrote:

Relays used to switch inductive loads, such as your pump motor, are prone to
arcing when they switch on and off. This is quite normal, and unless some
sort of arc suppression (snubber circuit) has been used across the contacts,
they will eventually fail.


Can I buy a snubber somewhere? Can I build one with a few parts from
RadioShack?

BTW, it seems most people switch their pumps with a pressure switch (as
opposed to a relay), and I've never seen a snubber on a pressure
switch.

Kelly

 




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