[Hammarlund] HQ-150 Line Bypass Caps Needed

[Robert Nickels]

  On 8/22/2010 12:49 PM, Al Parker wrote:
> Is the concern just (mostly?) power consumption of the capacitor 
> across the line?  If my math is correct, a 0.01 uf cap across a 125v 
> line draws 0.03 watts.  I suppose the greenies are looking at gnat 
> hairs, but if that's so, why not just put it across the line AFTER the 
> on/off switch, not before as in the diagram on that page?

Hi Al,

Since I opened this can of worms I probably should explain in more 
detail.   (There are ap notes on the referenced website for anyone who 
wants to know more).

As we know, virtually all modern electronic products use switch-mode 
power supplies, which generate a certain level of EMI that can be 
conducted along the AC power line. While the reason has changed (our 
boatanchor designers were more concerned about filtering our 
interference TO the receiver) - the remedy is the same - capacitors are 
commonly placed directly across the AC input terminals to reduce 
differential mode EMI.   To insure a safe failure mode, "X" type 
capacitors are now specified for line-to-line ("Y" types are used from 
Line-to-Neutral).

To effectively filter this newfangled noise, these caps can be quite a 
bit larger than the .01 uF  (aka 10 nF) that we're used to seeing, and 
safety agencies mandate that capacitance values above 100 nF be 
discharged automatically with a time constant of <1 second in order to 
prevent a charged-up cap from producing a shock or spark at the plug of 
an un-plugged device.  The traditional way of complying with this 
requirement is to add resistors that act as bleeders (usually two 
resistors in series in order to meet safety agency "single point 
failure" requirements).

This is where the "green problem" occurs -  the constant current drain 
of the bleeder resistors can cause the device to  exceed the quiescent 
or standby power level called for by new energy efficiency regulations. 
   Thus, the CAPZero devices were developed to act as "smart bleeder 
resistors" to safely discharge the filter caps without adding to the 
standby power consumption.   A product that helps manufacturers meet one 
rule without breaking a different one!

As I said, this is not relevant to our boatanchor radios which of course 
"blow the budget" for lots of other reasons but I thought it was 
interesting to pass along, given the times we live in.

73, Bob W9RAN

PS:  Good signal on the VSB net Al, been using the KWM-1 here - great radio!