Date: Tue, 23 Feb 2010 22:42:35 -0500
From: "herzog@frontiernet.net@frontiernet.net"
<herzog@frontiernet.net>
Subject: [Amps] Step Start circuit - needed or not?
We got around to discovering the why;
so subsequent commercial transmitters had the step start added.
The inrush current varies. depending upon the magnet memory of the core
when it was shut off, and the voltage of the sine wave upon
contactor/relay closure.
A par 30 amp inrush could be 900 amps every hundredth turn-on.
This manifested itself in several fronts:
Fuses in the mains quit.
misc-unexplained HV rectifier diode failures.
AND MOST IMPORTANTLY: welding of a hv contactor/relay, causing
intermittent hv to come on with vibrations closing the other side of the
stuck-on relay; fortunately caught before someone had to die!!!!
## agreed. My buddy has fried a total of 4 x on/off switch's on his
Drake L4B. It's just a 10A slide switch [rocker activated]. 2650 vdc
no load.. and has 25 uf filter cap. We added external step start,
[25 ohm ww in one leg of 240 line] which also step starts the fil.
ZERO problems after that. I fried 2 x on/off switch's on my own
drake amps. Added step start to all of em.
## Back in 1976, I had a 4-1000 amp, with 4800 vdc no load supply,
and 35 uf oil filter cap. NO step start, and 1N5408's. I used a P+B
PRD-11ago series DPST 30A relay to apply the 240 vac. Also had
2 x 80 lb Hammond [identical] plate xfmrs, with sec's in Parallel, and
8 ga wire back to main panel !
## welded the contacts 25% of the time. A tiny jab with the eraser
end of a pencil would free it easily enough. It got so bad, that after
6 x months there wasn't enough contact material left, for contacts to
even make contact! Contacts were blowing themselves apart on each
turn on. In one ssb SS contest,the B+ would not even come on. Quick
fix was to jam some folded AL foil between contacts, turn on breaker,
then turn on the relay ! Worked, with the usual blue flash. Relay was
replaced, nothing left at all of the contacts, just like you ground em
down to the armature. Then added a 2nd relay, and step start resistor.
Step start relay was manually activated after XXX sec's. At the
VE7ZZZ MM contest station, in desparatation, we used a breaker to
manually shunt the step start R, that works too. At the telco I just
retired from, everything now has 'soft start'. No more slamming on
6 x -52 vdc @ 800A rectifiers.
later... Jim VE7RF
A step-start relay with fusible resistors, instead of the huge relays
collinbs used, saved all these BG problems, and I damn near learned too
late about the why. Wil Herzog K2LB
=========================RE:
To: <HeathKit_HFAmps@yahoogroups.com>, <amps@contesting.com>
It is not necessary but if it makes you feel good then do it. You will
s also help the economy.........
Many ignore the fact that the power and filament transformers or
windings when combined, offer more than sufficient inrush protection.
Instead they ignore those items in the calculations.
The SB-1000 requirement was established years ago when the designer
stated that inrush was not necessary and only included in later
Ameritron amps to satisfy the Nervous Nellies that believe every thing
that is published in ham rags by uninformed people. The SB-1000 is an
AL-80 clone for the most part and was sold to Heath by Ameritron.
Ameritron also offers parts support even today.
Carl
KM1H
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