Re: Short circuit/Control Panel - 220 V relay coils

Subject:     Re: Short circuit/Control Panel - 220 V relay coils
      Date:  Thu, 12 Jun 1997 00:55:00 GMT
      From:  jim.fosse-at-bjt-dot-net (Jim Fosse)
        To:  Tesla List <tesla-at-pupman-dot-com>
References:  1

>Subject:     Re: Short circuit/Control Panel - 220 V relay coils
>       Date: Wed, 11 Jun 1997 06:29:05 -0700
>       From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>Organization: Stoneridge Engineering
>         To:  Tesla List <tesla-at-pupman-dot-com>
> References: 
Hi Bert,
        I like the idea (wish I'd thought of it;)

For running a lower voltage coil on a higher voltage a tungsten lamp
would also work. Use the 10Xish hot to cold resistance of it's
filament to supply the surge current needed and then limit the hold
current. This method would work for AC too. I'd try a 40W light bulb
to start with and go to larger wattage bulbs if the 40W didn't pull
in. (I'm assuming a 110V supply and a 24V coil).

>I agree with your analysis. Sooo....
>How about using an electrolytic capacitor charged through a power
>resistor from the DC source. The cap would initially be charged to the
>full AC Peak value to supply the initial surge of pull-in current
>required. Once the initial current surge has energized the contactor,
>the holding current would be set by the sum of the power resistor and
>contactor coil resistances (R1+Rc). Might take a bit of trail and error,
>but should be a usable approach.
>                                   | 
>               R1               -------
>   ---------/\/\/\//\------------o   o--------O
>   +                      |                   O
>                        + |                   O 
>                        -----                 0  Rc
>  DC                    -----                 0  
>                          |                   O
>   -                      |                   O
>   -------------------------------------------- 
>We used to use a similar approach to rapidly brake AC motors by
>disconnecting the motor from the AC and switching it over to a charged
>capacitor through a contactor to bring it to a _screeching_ halt.
>Safe contactin' to ya!
>-- Bert --