Re: a/c switches

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

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