Jim,
I've seen these used, but they were used in smaller DC supplies. I
have several books on the subject and will look it up. That value
though seems way to much at 35 uF for this. Placed across the primary
leads, it will start looking like a short or a leak if big enough.
That's why your seeing an increased current. The cap is causing more
current to be drawn or mag I + cap I. All transformers have
magnetizing current which is low compared to their output power.
However, the larger the transformer, the more this will be. Also, the
higher the flux density its ran at, the higher it will be. For this
type transformer service, the power factor should be about 0.95 or
so. If the ripple is low where you want it, I wouldn't worry about
adding anything else that may draw more current.
Best,
Will
--- In ham_amplifiers@..., "pentalab" <jim.thomson@...>
wrote:
Gents
My buddy tried this... said it worked. He gave me a 32 uf cap
to
try it myself. It gets installed directly in parallel with the
pri of the plate xfmr. [this is for a C input HV supply].
I didn't see any improvement... but I may well have easily had the
wrong value. What I did notice was the magnetizing current went
up on the pole pig... from 1.8A to 2.3A ! The magnetizing
current is why the step start never allows you to charge the caps
up
to max V. [u always have current flowing through the drop resistor]
The plate xfmr is always sucking magnetizing current... even with
nothing connected to the secondary.
Dahl himself said the concept won't work. Seems to me it
would work on TX... and be the wrong value cap on RX... because
of
load. The idea I had was to use a small possibly sped up vac
relay... tied into the T/R set up... to open/close... one leg of
the
cap.
I also noticed that the new 253 lb Dahl draws only 1.6 A of
magnetizing current. I thought it would be double that of the
smaller 120 lb pole pig.... it's not. The smaller pole pig draws
1.8 A. My electrician buddy sez they never oversize vault
transformers... the idea being you don't want to be drawing excess
magnetizing current.
I take it the magnetizing current is in addition to the normal
load ??
If my electrician buddy is correct... then why does the bigger
Dahl draw LESS magnetizing current than the smaller 120 lb pole
pig ??
1.6 A is nothing to sneeze at... = 384 Va. 2.3 A = 552 Va
Magnetizing current is one thing.... power factor is another.
These
xfmr's typ have a .9 pwr factor... and even worse with a bigger HV
C input filter. Maybe I'm confused here... but it appears the
load
is not the XL load of the xfmr... but the HV C filter on the sec
side ?
Power factor correction caps work great on motor's and probably
xfmr's.. depending on the type of filter used.. C or resonant
choke.
Who's the expert on this ? Maybe Dahl is right.. and it might
be
fruitless....... or maybe it works on TX... but correction cap has
to be switched out on RX. IF it works... how do you go about
sizing the correction cap ?.... and how much current flows through
the correction cap ???
Later... Jim VE7RF
