Re: Switch

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

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

This is what snubbers across the contacts are for... Smallish cap (say, 0.1
uF) in series with a smallish resistor (say 50 ohms) across the contacts.
All it's got to do is absorb enough energy when the contacts first start to
open to keep the voltage down until the contacts get far enough apart to
not spark over.

Watch out if you have a GFI... the snubber can flow enough current to trip
the GFI.

Tranzorbs, MOVs don't seem to work as well in this application, because it
is really a energy storage issue, not a peak clipping one.


Tesla list wrote:
> 
> Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<sundog-at-timeship-dot-net>
> 
> Hi All,
> 
>  Yep.  Ebay is the place to check for large contactors.  I got my contactors
> (500v350A 3P) off Ebay for $36 and change.  Shipping brought it up to
> ~$45-47 (I can't remember exactly.)  They laugh at switching the pole pig,
> and make a very satisfying "CHUNK!* when energized.   The real killer I
> found with small contactors (240v30A) was that they weren't designed with
> this heavy of an inductive load in mind, and there's pretty bad sparking of
> the contacts on opening and closing.  My PFC caps made this a whole lot
> worse.  While it won't be much of a big deal for small coils, it becomes
> problematic on big trannies.  My small contactors (the 240w30A) welded shut
> on me when I used them on the pig at ~20A input. I don't think it was the
> current, but the sparking when they closed.  A quick rap with a screwdriver
> (after I cut the breaker off) and they popped apart.  A stronger spring
> would probably fix it.
>  For a small coil, they work fine though.  You may have to clean up the
> contacts with emery paper once in a while, depending on the quality of the
> contactors (my small ones were cheapies, $2 ea at a flea market, new in the
> box)
> 
>  Keep it safe!
>
                      Shad
> 
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Wednesday, March 28, 2001 1:32 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Switch
> 
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> <Mddeming-at-aol-dot-com>
> 
> In a message dated 3/28/01 12:53:23 AM Eastern Standard Time,
> tesla-at-pupman-dot-com writes:
> 
> >
> > > > Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> > > <Gbjsjg-at-aol-dot-com>
> > > >
> > > > Does anyone have a good location to buy, 50 amp120/240 volts switches,
> > for
> > > > power controller use?
> > >
>   -Max
> 
> I got a 60-Amp 600v dpst knife switch off eBay last year. Very impractical,
> but good for "stage effect". It looks like the type seen in 1930s
> Frankenstein movies. Might try there.
> Matt D.