Re: where can i get a 20 amp relay?

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I think the original poster was referring to the real starter relay (as used
to be used in Fords (at least in 60's and 70's) and my airplane) that really
is designed to carry the full starter motor current of hundreds of amps.
They have a big solenoid that pulls down what looks like a big copper washer
onto two electrodes. There is also some clever mechanical stuff that rotates
the washer each actuation, so that the contact area is spread out (and so
that if you get a "bad spot"... you can just "bump the starter" again and
get a new spot).

I'd wonder, though, about the AC voltage rating... They are, after all,
designed to switch 24VDC, at most... a far cry from 300+ peak volts on a
240VAC line.

And, the coil in these things is NOT designed for continuous operation. It
will get hot if run off 12V continuously.  You could work out a "spike and
back porch" type drive for it to solve that problem.

Periodically, one sees real contactors around with dual coils that would be
ideal.  They have a low resistance coil to "pull in" the relay, and then a
higher resistance coil that does the "holding". The low resistance coil is
in series with a microswitch that automatically disconnects it when the
relay armature pulls in.

I'd check air conditioning supply/repair places.  There's a fairly large
relay in an a/c that typically runs off 24VAC to control power to the
compressor.

----> >If you don't mind a little overkill, you could try
 > >using an automotive start relay...
 >
 >          An interesting thought, lets run thru it.
 >
 > >those contacts are good for a couple of hundred amps DC
 >
 >          Generally a lot less.
 >          The relay does not control the starter.
 >          It switches 10A or so to control a _solenoid_
 >          (solenoid switch, actually) and THAT switches the 100s
 >          of A.
 >
 >
 > >(should do ok on AC as well).
 >
 >          However there is an added question:
 >          What _voltage_ will the contacts see?
 >          I Assume 120vac or thereabouts.
 >          The automotive units are designed for 12vdc on
 >          the contacts (1k: more like 15vdc...)  This is
 >          About 8x UNDER spec for 120VAC control.
 >
 > >And the coil is 12 volts like you need.  From what I've
 >
 > >seen, they're relatively cheap as well.
 >
 > >  > -----Original Message-----
 >