contactor or relay recommendation

[Rich.Andrews]

I am looking for a contactor or relay that has the following characteristics:

1) silent or nearly silent in operation.
2) Be able to handle 20 amps of current.
3) be available in a variety of coil voltages including 120VAC.
4) Cost no more than $30.00 each
5) Rated for continuous duty use.
6) Operable in any position.

Does anyone have any suggestions?

r

 

[CJT]

I am looking for a contactor or relay that has the following characteristics:

1) silent or nearly silent in operation.
2) Be able to handle 20 amps of current.
3) be available in a variety of coil voltages including 120VAC.
4) Cost no more than $30.00 each
5) Rated for continuous duty use.
6) Operable in any position.

Does anyone have any suggestions?

r

What's the "variety of coil voltages" requirement about? Are you
having trouble picking a voltage?

Without (3), I'd suggest you visit your local HVAC supply store.

Or browse the Digikey catalog (although it might be hard to figure
out which ones are quiet from what's there).

I'm surprised you don't say what contact configuration you want --
that seems pretty important.

 

[The Real Andy]

I am looking for a contactor or relay that has the following characteristics:

1) silent or nearly silent in operation.
2) Be able to handle 20 amps of current.
3) be available in a variety of coil voltages including 120VAC.
4) Cost no more than $30.00 each
5) Rated for continuous duty use.
6) Operable in any position.

Does anyone have any suggestions?

r

Lets see, you want a contactor that does everything and cost nothing,
yet you fail to supply any details of the load you are switching?

 

[Rich.Andrews]

Lets see, you want a contactor that does everything and cost nothing,
yet you fail to supply any details of the load you are switching?

The load is a 120 VAC transformer. Having a variety of coil voltages
allows for flexibility in the early design stages. I figured a relay
would be cheaper and that $30.00 was a good figure. Maybe I should allow
two to three times my original dollar figure for the relay? Rarely would
it be switched while under full load.

r

 

[Sam Goldwasser]

The load is a 120 VAC transformer. Having a variety of coil voltages
allows for flexibility in the early design stages. I figured a relay
would be cheaper and that $30.00 was a good figure. Maybe I should allow
two to three times my original dollar figure for the relay? Rarely would
it be switched while under full load.

Check out solid state relays.

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[Rich.Andrews]

Check out solid state relays.

--- sam

Sam,

Solid state relays seem like a good idea but isn't there issues with them?
At one point in time I worked at a hospital that used SS relays to control
the TV sets in the patient rooms. When they got a new batch of TV sets
in, many of the sets failed in less than a month. The SS relays were
blamed and the relays were changed out. We never could figure out what
the issue was with the old ones as they worked fine with the old sets.
The old sets were zenith Chromacolor II and the new ones were Chromacolor
III. The old sets had a transformer and the new ones did not.

r

 

[Sam Goldwasser]

Solid state relays seem like a good idea but isn't there issues with them?
At one point in time I worked at a hospital that used SS relays to control
the TV sets in the patient rooms. When they got a new batch of TV sets
in, many of the sets failed in less than a month. The SS relays were
blamed and the relays were changed out. We never could figure out what
the issue was with the old ones as they worked fine with the old sets.
The old sets were zenith Chromacolor II and the new ones were Chromacolor
III. The old sets had a transformer and the new ones did not.

The specs should tell you what they can drive. SS relays have come
a long way. I don't think controlling a small transformer would
be a problem.

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[Rich.Andrews]

The specs should tell you what they can drive. SS relays have come
a long way. I don't think controlling a small transformer would
be a problem.

I suppose that depends on one's ones definition of small. I would like to
control the power going to two McIntosh MC2500 amps. Each amp weighs
about 138lbs.

r

 

[Sam Goldwasser]

I suppose that depends on one's ones definition of small. I would like to
control the power going to two McIntosh MC2500 amps. Each amp weighs
about 138lbs.

OK, I hadn't noticed that. Still, what you need to determine is their
input characteristics and then see if there is a suitable SS relay.
However, it is hard to beat the price of one or even two 25 A (normal) relays.
Is 25 A enough for one or both? They would just make a distinct click,
nothing totally objectionable and you can always put them in a sound
insulated box that were too loud.

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[Rich.Andrews]

OK, I hadn't noticed that. Still, what you need to determine is their
input characteristics and then see if there is a suitable SS relay.
However, it is hard to beat the price of one or even two 25 A (normal)
relays. Is 25 A enough for one or both? They would just make a distinct
click, nothing totally objectionable and you can always put them in a
sound insulated box that were too loud.

Sam,

A pair of normal 25A relays would probably suffice for my needs. A box
with some sound deadening properties would be sufficient. I think I can
come up with a reasonable time delay circuit so that both amps are not
turned on at once. Do you have a source and part number for the type you
are thinking of?

I was looking at the following and didn't know which way to go:

http://www.newark.com/product-details/text/CD121/4000.html

http://www.newark.com/product-details/text/CD121/12441.html

http://www.newark.com/product-details/text/CD121/3310.html

Is it safe to assume that these mechanical relays can be energized for
hours at a time without issue?

I was looking at the possibility of using SS relays and there are many
design criteria that have to be evaluated. I think the cost savings of an
electromechanical relay offsets the noise factor.

r

 

[tech-guy]

Sam,

Solid state relays seem like a good idea but isn't there issues with them?

A zero crossing solid state relay is a good choice for most
applications. We use solid state relays from power-io.com or
equivalent for switching resistive heaters, cooing solenoids, and
small motors.

For transformer coupled loads (such as on electrical lab furnaces with
special moly heaters), you really need a phase angle firing contactor.
These are more expensive and are electrically noisy since they turn
on mid sinewave.

I do not understand why a properly sized solid state relay should
affect the operation of a standard television.

The issues with solid state relays (or any modern electronics) is that
you have to avoid over-temperature, over-voltage, and over-amperage.