Re: a/c switches

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

a power relay or contactor is a mechanical switch operated by an
electromagnet or solenoid.

you feed the relay or contactor say 12 or 24 volts and it moves the contacts
to control your load. they are pretty fast and some get outright expensive.
You can usually find decent motor starting contactors on ebay for 10% of
the new cost.

KEN

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, August 03, 2002 4:45 PM
Subject: Re: a/c switches


> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Beans45601-at-aol-dot-com>
>
> In a message dated 08/03/2002 3:06:47 PM Central Daylight Time,
> tesla-at-pupman-dot-com writes:
>
>
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> >Hi Adam,
> >
> >Don't use 12 volt DC automotive switches.  They are high current but very
low
> >voltage.  AC switches are made to open and break 120VAC (277VAC) safely
> without
> >catching fire or exploding.  That requires special contacts, materials,
and a
> >certain level of quality that many car switches don't have.  You need a
"real"
> >switch for 20 to 30 amps!
> >
> >I can get 20 amp switches from a local shop but a quick look in a few
catalogs
> >did not have them.  The problem is there are many safety standards now
that
> >don't like high power AC hand switches.  Too many people have had them
explode
> >in their hand...  Probably a good thing since they are pretty dangerous
> >really.  Running a light or something is not too bad but if they switch
into a
> >short or big inductive load they can arc and dramatically burn up.
> >
> >Exactly what is hooked to you switch?  If it is inductive or above 20
> amps, you
> >almost have to use a power relay instead.  Check these out from DigiKey
> >
> >http://info.digikey-dot-com/T022/V5/0753.pdf
> >
> >The # Z818-ND  is a DPDT 25 amp 220VAC unit for $11.70.
> >
> >This baby will switch 240 VAC into a dead short and come back for more
:-))
> >
> >The coil is 120VAC so you just wire it up with any low current AC switch
like
> >from Radio Shack to the 120 volts.  You can also pull the relay out of
the
> case
> >to inspect it or make an emergency repair if needed.  That is very useful
if
> >you zap the relay hard and wonder if it was damaged.
> >
> >I would avoid the SPST relays since they cost almost as much as DPDT ones
and
> >the DPDT ones are far more versatile.  You can also wire the contacts in
> >parallel for 40 amps (it really does not work that way, but...)
> >
> .................
> >
> >Cheers,
> >
> >        Terry
>
>
>
>
>
> what exactly does a power relay do?
> Adam
>
>
>