Need a 120 volt relay

Posted by Mortimer Schnerd on July 2, 2009, 9:44 pm

I'm looking for a cheap 120 volt relay to use with my stereo system.
I've got a receiver that has pre in/main out jumpers and so I've added a
second power amp to it which is a lot more powerful that what's already
built into the receiver. I'm actually powering three rooms of speakers
(8 speakers all told); two sets on the receiver's power amp and 4
speakers in my bedroom off the external power amp.

I want the power to the amp to come on whenever I power up the receiver
but it's a PITA to get to because of the way it's physically installed.

The AC outlet on the back of the receiver is only rated for 100 watts
max. The power amp can draw up to 11 amps so the receiver's AC outlet
isn't going to work.

So what I think I need is a relay. The switched outlet on the back of
the receiver can power the coil and then the relay can handle the power
requirements of the external power amp.

So where can I find such a thing? Ideas?

Mortimer Schnerd, RN
mschnerd at carolina.rr.com

Posted by jeff_wisnia on July 2, 2009, 9:58 pm

Mortimer Schnerd wrote:

> I'm looking for a cheap 120 volt relay to use with my stereo system.
> I've got a receiver that has pre in/main out jumpers and so I've added a
> second power amp to it which is a lot more powerful that what's already
> built into the receiver. I'm actually powering three rooms of speakers
> (8 speakers all told); two sets on the receiver's power amp and 4
> speakers in my bedroom off the external power amp.
>
> I want the power to the amp to come on whenever I power up the receiver
> but it's a PITA to get to because of the way it's physically installed.
>
> The AC outlet on the back of the receiver is only rated for 100 watts
> max. The power amp can draw up to 11 amps so the receiver's AC outlet
> isn't going to work.
>
> So what I think I need is a relay. The switched outlet on the back of
> the receiver can power the coil and then the relay can handle the power
> requirements of the external power amp.
>
> So where can I find such a thing? Ideas?
>
>
>
> Mortimer Schnerd, RN
> mschnerd at carolina.rr.com

Rat Shack has 'em if you don't have any other source. You can prolly
find a socket for one there too, or just cut both ends off an extension
cord leaving a few inches of wire on each and solder directly to the
relay's lugs.

http://www.radioshack.com/product/index.jsp?productId=2049721

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.

Posted by Mortimer Schnerd on July 2, 2009, 10:08 pm

jeff_wisnia wrote:

> Rat Shack has 'em if you don't have any other source. You can prolly
> find a socket for one there too, or just cut both ends off an extension
> cord leaving a few inches of wire on each and solder directly to the
> relay's lugs.
>
> http://www.radioshack.com/product/index.jsp?productId=2049721

That one is only good for 10 amps. My amp can draw 11 so I'm really
looking for one rated for 15-20 amps.

Mortimer Schnerd, RN
mschnerd at carolina.rr.com

Posted by John Gilmer on July 3, 2009, 2:20 am

> jeff_wisnia wrote:

>> Rat Shack has 'em if you don't have any other source. You can prolly find
>> a socket for one there too, or just cut both ends off an extension cord
>> leaving a few inches of wire on each and solder directly to the relay's
>> lugs.
>> http://www.radioshack.com/product/index.jsp?productId=2049721

> That one is only good for 10 amps. My amp can draw 11 so I'm really
> looking for one rated for 15-20 amps.

OK.

Above 10 amps or so, it's call a "contactor."

You can get then at an electrical supply house (with either 24 volte or 120
volt coil). If you are cheap, you can "salvage" them from a microwave oven
or a central A/C. It's kinda fun to take apart a dead microwave oven.
You get a transformer suitable for making your own electric chair among
other things. The magnets are a source of some amusement also.

"Contactors" have either screws connections or a "spade" male leads. You
can get the connectors at R/S. Put the whole thing in a box to keep your
cat from getting fried.

Since you only need 11 amps you can consider getting a two pole relay from
R/S with each pole rated for 10 amps. Wire the poles in parallel and you
have a 20 amp relay.

Posted by cjt on July 3, 2009, 2:41 am

John Gilmer wrote:

<snip>
> Since you only need 11 amps you can consider getting a two pole relay from
> R/S with each pole rated for 10 amps. Wire the poles in parallel and you
> have a 20 amp relay.
>
>

... except that one side will invariably connect/open first, so that the
load won't be equally shared and it'll burn out faster than a device
that's designed for 20 amp service.

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