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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. |
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#1
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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 |
#2
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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
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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
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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
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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
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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
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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
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Relay contacts sticking
In article nZZec.123791$gA5.1527613@attbi_s03, masondg4499
@comcast99.net says... "Innes Cathcart" wrote in message news On Mon, 29 Mar 2004 22:50:11 +0000, Kelly E Jones wrote: I've got a relay that controls the submersible pump which supplies water to my house. Relays used to switch inductive loads, such as your pump motor, are prone to arcing when they switch on and off. This is quite normal, and unless some sort of arc suppression (snubber circuit) has been used across the contacts, they will eventually fail. Failure modes are either of two conditions: one is that they stick together, as you have found; the other is that they will fail to make contact at all. The arcing is the cause of both types of failure. -- Used to own a house with a heat pump (basically a reversible air conditioner) in AZ. When the thermostat was switched from cooling to heating, a relay was used to control the reversing coil that switched the direction of freon flow. After several years, the relay would fail to contact, with the result being that the heat pump was still in the cooling mode. I would crank the thermostat up in the winter, and the house would get colder and colder - not very desirable behavior in a heater. Used to replace that relay every few years until I sold the house. -- Jerry Maple General Dynamics C4 Systems Scottsdale, AZ |
#9
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Relay contacts sticking
In article nZZec.123791$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
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Relay contacts sticking
In article nZZec.123791$gA5.1527613@attbi_s03,
Tweetldee wrote: Relays used to switch inductive loads, such as your pump motor, are prone to arcing when they switch on and off. This is quite normal, and unless some sort of arc suppression (snubber circuit) has been used across the contacts, they will eventually fail. Can I buy a snubber somewhere? Can I build one with a few parts from RadioShack? BTW, it seems most people switch their pumps with a pressure switch (as opposed to a relay), and I've never seen a snubber on a pressure switch. Kelly |
#11
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Relay contacts sticking
In article nZZec.123791$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 |
#12
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Relay contacts sticking
"Kelly E Jones" wrote in message
... 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 A snubber is simply a series resistor-capacitor connected dierctly across the contacts. Usual values are 47 ohms and 0.005 uF. I've seen a few relays with MOVs across the contacts. You might try either, or both. The trick is to keep the RC from being burned to a crisp when lightning strikes nearby. I tried that combo on a pressure switch on a pump, but living in FLA, the lightning capitol of the world, it turned out to be more trouble than it was worth. Was having to replace the RC every week or so during the summer months when afternoon storms blew through the area. I finally abandoned the idea and just left the switch contacts alone. Never had any trouble from them aside from the pitting and sticking, which is quite normal for that use. You might try something like that if your area doesn't get a lot of thunder storms. -- Dave M Good judgement comes from experience, and a lot of that comes from bad judgement. |
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