[GreenKeys] To snub or not.

[Keith Lueck]

 Ack.  Never mind.  If you're using a hv supply and a resistor, the zener idea obviously wouldn't work...  
    On Tuesday, June 25, 2019, 10:39:23 AM CDT, Keith Lueck <kwlueck at swbell.net> wrote:  
 
  Indeed.  Before rectifiers existed, a snubber was the only choice. ;-)
BTW, another solution is to use a back to back pair of high voltage zeners.  You can spitball the amount of time the field will take to collapse (and thus the required voltage); the energy stored in the inductor is 1/2*L*i^2, so, 1/2*4*.06^2 = 7.2 mJ.  If you use, say, a 47V zener, the field will collapse in 7.2 mJ / (47*.06) J/s, or 2.55 ms, about the same amount of time as a snubber...  
Keith
    On Tuesday, June 25, 2019, 9:52:41 AM CDT, Peter Gottlieb <kb2vtl at gmail.com> wrote:  
 
 They had engineers back then too, and some very good ones. No doubt they had this under control and working nicely. 


Peter

> On Jun 25, 2019, at 10:49 AM, Jeffrey D Angus <jdangus at att.net> wrote:
> 
> Image 1: this is the reverse EMF kickback when you open the
> contacts. A negative spike close to 120 v. This will usually kill
> a keying transistor.
> Image 2: Putting a reverse diode across the coil, clamps the
> spike to near zero volts, but the reverse current through the
> coil is long enough to miss the Spacing signal.
> Image 3: Using a series RC snubber will cut down the reverse
> spike, but still allows the coil to correctly act like there is a
> Space signal. It also cuts way down on arcing on mechanical
> contacts.
> 
> Oddly enough, Western Union had all this figured out over
> a hundred years ago. ;-)
> 
> 
> -- 
> Jeff-1.0
> wa6fwi
> http://www.foxsmercantile.com
> 
> 
> 
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> <120 v no snubber.jpg>
> <120 v with diode.jpg>
> <120 v with snubber.jpg>
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