Re: Relays and Contactors

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

Original poster: "Richard Williams by way of Terry Fritz <twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>

Hey (un)Terry, :)

I have 2 contactors, inductive rating is 40 FLA. These are 3-pole. Normally
Open.

LRA -at- 240 is 240
LRA -at- 480 is 200
LRA -at- 600 is 160

Resistive rating is 50 amps

Maximum loads for this project:

120vac -at- 14 amps
240vac -at- 20 amps

The 120vac is single variac controlled.
The 240vac is controlled by two 120VAC variacs in series, common shaft.

So I have 6 contacts altogether.

The series idea sounds good and makes sense since that's exactly what's done
with a rotary gap.
There is no neutral/ground connection to the variacs on the 240VAC line. A
previous schematic showed a connection but due to advicegiven  here that
connection is no longer made. The load, a PT, is connected to the two
brushes.

Soooooo......

In your opinion what is the best contact configuration?

Rick W
SLC




----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, February 07, 2002 8:27 AM
Subject: RE: Relays and Contactors


> Original poster: "terry oxandale by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <toxandale-at-cei-dot-net>
>
> Something I do is take a rated contactor, and then series the contacts
> (using the extra contacts not being used) thus giving a greater total gap,
> but more importantly, it increases the speed of separation. For example,
if
> you series 3 separate contacts per leg, then the total gap per leg is 3
> times that of a single gap, and the contacts total gap thus opens 3 times
> faster. It cuts down on the arcing very nicely. I've tried 3 in parallel,
> but unless the contacts are adjusted to simultaneously open in perfect
> unison, the the last contact to open is going to bear the brunt of
> extinguishing the arc.
>
> (un)Terry
>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Wednesday, February 06, 2002 5:50 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Relays and Contactors
>
>
> Original poster: "Metlicka Marc by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> <mystuffs-at-orwell-dot-net>
>
> Hi Rick,
> Use a good motor starting contactor and the contacts will be made to
> flash as they separate, this prevents them from sticking (ha ha ho ha)
> In constant start\stop\reverse use they do weld shut, but the contacts
> are easily changed. If the load is pushed close to the rating then a
> small capacitor across the coil, this prevents welding due to chatter.
> The contacts will chatter if they arc heavy on closing, this will burn a
> new contact very quickly.
> Use a latching circuit with the auxiliary contacts that run through the
> "E"stop switch, or key switch.
> http://www.fortunecity-dot-com/meltingpot/syria/1210/id34.htm
> Shows one setup that also uses a timer to allow a gap fan or rotary, or
> triggered gap, to come on and up to speed then the main comes in.
> Take care,
> Marc M.
>
>
> Tesla list wrote:
> >
> > Original poster: "Richard Williams by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>
> >
> > Hi list,
> >
> > Ok, I'm new at this sort of thing, high current household voltages,
> 120vac and
> > /or 240vac.
> >
> > I plan to be able to interupt power from the mains using a deadman's
> switch
> > controlling a relay or contactor.
> >
> > During the past I've seen arcing from connections being pulled apart, or
> any
> > situation interupting high currents.
> > The planned current load will be 240vac -at- ~20amps continuous duty. What
> would
> > prevent excessive arcing when the contacts open under full load? Is
there
> a
> > difference between relays and contactors in this respect?
> >
> > I will be using variacs to ramp up power and back down again but if the
> > deadman's switch opens at full power....??
> >
> > Rick W.
> > Salt Lake City
>
>
>
>
>