Re: Contactor question, Arc Suppression

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Terry,

Yep, that would work with a simple zero crossing detector, but for it 
to work, the electromechanical energize time from rest to contact 
must be "monkey'd" with. It would take a zero crossing detection and 
delay to the next half cycle to time out the energize vs. current 
crossing scenario. Obviously, a pot on the delay would be worthwhile 
to fine tune the delay time required, and hopefully, a consistent 
energize time on the coil (questionable). However, if you can simply 
suppress the arc, this timed situation becomes null and void (but a 
cool approach nevertheless)!

Take care,
Bart

Tesla list wrote:

> Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> There is a "trick".  I am not sure it is worth all the trouble...
>
> You make a circuit the monitors the current and voltage along with 
> some delay electronics.  The idea is to only open the contactor when 
> the current passes through zero.  Close it as the voltage passes 
> through zero...
>
> Then, the contacts only have to take the nominal current rather than 
> peak or break situations...  But the circuit and all the trouble it 
> takes to make it has to be balanced against just getting a really 
> big contactor in the first place...
>
> It can be done with some simple stuff in very controlled situations, 
> but it is sort of an "art form"...
>
> An alternate is to get contactors with fail safe switches that 
> detect a failed contact.  If it welds closed, a warning goes out...
>
> Contactors weld closed all the time...  Probably their #1 failure mode....
>
> Maybe best to use really big hydraulic circuit breakers...  They 
> know how to hand the big currents ;-))
>
> Cheers,
>
>     Terry