RE: Relays and Contactors

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

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