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Jerry Maple
 
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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