[Amps] Re Direct rectification of AC mains to derive the

[Jim Thomson]

Date: Wed, 18 Sep 2013 18:43:02 +0200
From: peter chadwick <g8on at fsmail.net>
To: Manfred Mornhinweg <manfred at ludens.cl>, amps at contesting.com
Subject: Re: [Amps] Re Direct rectification of AC mains to derive the
amp, VDD, supply


Manfred, 

I am afraid you are missing my point. What you can do safely as a professional engineer is not the same as the average amateur building at home. For example, getting the necessary spacing between PCB tracks, making an RF transformer which meets a 2kV breakdown - these are things (and not the only ones) that the average homebrewer could get into trouble with. Especially if they take any short cuts such as deciding to earth the neutral. 

Many years ago now, there was an article in QST entitled "Just like the QST article except...": it went into how people made minor changes to the published design and had problems. 

I could see the same article being required again......

While to see one result of an inadvertent earthing      http://www.railwaysarchive.co.uk/documents/MoT_Barnham1962.pdf

73

Peter G3RZP

##  I believe in the UK, one side of the 230 vac line is grounded.  That means you have UNbalanced 230 vac coming into the home.   IE: one side of the 230 line is neutral.
Here in NA, the 240 line at the pole pig xfmr out in the street has a CT...and only the CT is grounded.   In the main 200A panel, the neutral is bonded to ground  / earth. 
Meanwhile the 14.4 kv feeding the pri of the same pole pig  is UNbalanced...one side of the 14.4 kv line is grounded to dirt...and also looped with a short wire to the CT of the sec. 

##  Now if one was to take the BALANCED  240 vac line..and rectify it,  with a FWB you end up with  339 vdc no load.   As long as each side of the 120 line is fused..and  a RVS connected safety diode is wired
across the B+  / VCC filter cap, there should not be any problems. 

##  Look in some old  arrl books. They used doublers and triplers and quadruplers  across the 240 vac line,  to obtain B+  for  sweep tube amps and the like.   Apparently, tokyo hi power uses  500 vdc rated devices 
in their 2.5 kw SS amps. 

##  back to reality for a moment.  50-60 vdc  3.3 kw  switching supplies are dirt cheap these days, even brand new. All telcos and cell sites are using them by the truckload, literally.  Unity PF at all phase angles.  They barely
run luke warm while sucking 63A CCS  from them.  They will operate on anything from 170-315 vac  and any freq from 40-70 hz.   At the telco I worked at, we would put 6 of em in a 25 inch shelf = 20 kw CCS. 
Then stack the shelves.  Lose any single or more supplies, and the rest just take up the slack, and at all times, the load current is split up dead even between the remaining supplies.  Heck, you can even jack em
in / out hot.   One controller ran the entire mess.   each 3.3 kw supply is only  6-7 inchs tall   x aprx 12-14 inchs deep.   Each one is 4 inchs wide.  They don’t weigh much either.  $475.00  each. 

##  The unity PF is a winner.  Line V can sag or surge all it wants, the output vdc never changes.   Ditto with the freq, so if using an emergency gen set, 58-59 hz has no effect on it.   They can also be strung in series,
but I can’t remember how far you can go with that.   Just one of these switching supplies would be plenty for a 1.5 kw amp...even with 50% eff PA section.   Out of >  1200  we installed, I have yet to see one fail. 
You could use two in parallel, and if one died, the 2nd one would take up the slack...and you are still on the air. 

later... Jim  VE7RF