[Amps] Soft Start

[Bryan Swadener]

The 10 Ohm resistors only limit the inrush current. They have zero to do with the delay. 
The delay is set by the R/C values in the coil circuit. R includes the relay coil itself.
The delay only needs to be long enough to limit the current pulse. Adding more delay gains nothing. 

vy 73, 
Bryan WA7PRC 

________________________________ 
From: Arnie Pfingst 
To: Bryan WA7PRC 
Sent: Wednesday, December 27, 2017 1:06 PM 
Subject: Re: [Amps] Soft Start 


When the cap let go it scared the S #% T out of me! Several people told me about how the "un charged" cap bank draws a huge current at start up and maybe thats why the cap let go, (they all have been changed since) the same kind of thing happens to a tube fil, without all of the pyrotechnics. Jim why did you select 10 ohm resistors over something higher giving a slightly longer delay? 
Arnie 

-------- Original message -------- 
From: Bryan WA7PRC 
Date: 12/27/17 12:34 PM (GMT-08:00) 
To: amps at contesting.com 
Subject: Re: [Amps] Soft Start 

FWIW, Mike WØBTU put this together, s'plaining the "Miller-Larson Effect": 
http://www.w0btu.com/miller-larson_effect.html. 


Though, in some cases (such as in the SB-220), there's little/no benefit, 
as the filament transformer limits the current. In those cases, you're 
mainly extending the life of the ON/OFF switch from yuuuge inrush current 
caused by overly large HV filter capacitance. 

vy 73, 
Bryan WA7PRC