[Amps] Resistor before the cap redux.

[Jim Thomson]

From: TexasRF at aol.com
Subject: Re: [Amps] resistor before the cap redux
 
Jim, did you test using the Mag transformer with the larger AC wiring?

##  No, i wanted to, but my friend said it was going to be tough,
since we would have to re-locate the smaller xfmr, and then
kludge the  wiring into place.



 Did you test using the Dahl transformer using the smaller AC wiring?

## No,  and that would have been a complete waste of time,
with 100% predictable results. 




In other words, how much of the problem is caused by the 12 ga  wiring?

## IMO... a bunch.   With a 6 v drop..... to reduce the drop by 1/2,would
require going down by 3 wire ga's  [ down to 9 ga].   To reduce  in 1/2
again.. would require  going down to  6 ga.   Even then, you still have a
1.5 v drop.   PEAK drop will be  3-5  X  that much  per psud.   To really
get the drop  way down.... I'd use  1-0   cu.   That.. or   move xfmr
closer to the main panel... then  extend the  B+  and B-.... via
GTO  HV wire.... to the RF deck.. which is probably cheaper. 
It was a LONG run of 12 ga wire.   



 
Has anyone determined that a 22 ohm resistance in series with the secondary 
 is enough to actually take care of the turn on surge? I ask this because 
many I  have measured some of the Dahl secondary windings at about 25 ohms. 
Adding  another 22 ohms only reduces the charging current by about half. In 
my  experience, the charging current needs to be much lower than that.

##  I finally [ with some help and tips  from GM3SEK]  loaded the 
latest version of PSUD onto the new laptop.  Huge improvement
over what I had on my old laptop.

###  using PSUD... and  my small 46 dahl... and a 25 uf  filter cap,it
works out to .55  sec to charge caps up to max! 3079V, NO LOAD !

###  IMO...  550  msec  is probably enough to do the job... THEN
short the 22 ohm resistor out.. with a vac relay... more on that
to follow.  






 
You mention pri magnetizing current: I am not familiar with that term and  
am guessing there is a 1.9 A current flow in the primary with no load on the 
 secondary. If so, there is about 450 watts of loss just sitting there.  
Seems the transformer would get pretty warm when this happens. Am I  
understanding this correctly?

###  yes...  and that's  for a 120 lb, 10 kva  hypersil pole pig,
240 pri / 4800 vac  sec.   On a 253 lb dahl, it's  just  1.6 A 
Nothing heats up any where..just sitting there.  However,
my big dahl fil xfmr's WILL  heat  up, with no load on the sec! 
With  a load on the sec, the fil xfmr  runs barely luke warm.
And that fil xfmr has no benefit of cooling air from the tube's blower,
since fil xfmr is not in the air plenum.   Dahl told me that is normal,
on his  EI  wound  fil xfmr's.


##  I have not  yet measured mag current on the 46 lb dahl. 
BTW... if you stuff  120 vac into the 240 vac pri.... the mag current
will NOT  drop in 1/2.  It will  drop down to almost nothing ! 

 
I went through a voltage drop witch hunt in my shack a few years back and  
also found that 12 ga wiring for the power amplifiers is entirely 
inadequate. I  ran a temporary length of 4/0 three conductor cable from the breaker 
panel to  the amplifier area and that blasted cable is still there and in the 
way! I just  have to get it out of there one of these days.

##  agreed.    I had my electrician ham buddy  run  a 100A  sub panel
in for me... fed with 3 ga  cu.   Then  really short runs of 10 ga  wire
<10'.... to each L4B.   A  10' run of  10 ga  wire.. amounts to a 20' loop.
Sub panel on other side of wall of ham gear.   Main 200A panel, is 30'
away  from sub panel. 

later... Jim   VE7RF




 
73,
Gerald K5GW