Any fool can overbuild a product. Good engineers know when to stop,
> and good engineers get paid good money to get it right.
> 73, Bill W6WRT
Agreed. We are paid to do good but not ridiculous engineering. Leave that for
Hollywood. Or Star Wars (the project, not the movie).
For serious high power (3 kW to Terrawatts), three phase service is the
recommended design. With a simple 6 rectifier bridge, the ripple is down to
4.2% RMS, and with a 12 pulse Delta-Wye connected dual secondary transformer,
1%.
The need for large capacitors is eliminated, and a simple LC or just C filter
is enough. This eliminates the hazardous stored energy that takes a lot of
expensive parts and design care to prevent damage to amplifiers and cables.
73
John
K5PRO
### Some books say 5%... some say 4.8% ripple for a 6 rectifier bridge.
[dahl sold a lot of em.. all using 6A10 diodes]. That's with NO filter at
all... VS 48-50% ripple for single phase + no filter. That's great IF you
have
208/360/480/600 vac 3 phase power available. With any 3 phase, 6 x rectifier
bridge, the caps get.."topped up" 360 x per second VS 120 for single
phase FWB... and only 60 for a doubler. I only have 240/120 vac
single phase available.. and long drop line into the house. Part of the high
C concept / experiment was to eliminate ripple at 120hz + all harmonics, plus
improve dynamic regulation. Sorta like a quasi brute force regulated B+ supply.
The big caps all reside in their own steel cab. We found that with a CORRECT
type and sized B+ fuse PRECEDING the correct type and sized 50 ohm glitch R,
that any short from B+ to chassis, grid, etc, was not an issue, regardless
of whether 34 uf was used... or 250 uf. Fault current value is still the
same. 7700 vdc / 50 ohm glitch = 154A fault current..... which will open off
a 3A rated HV fuse in < 2 msecs. All B+ wiring BEFORE the 50 ohm glitch R IS
a concern,
and precautions HAVE to be taken. So is follow on energy.
## In the case, where multiple banks of caps are in parallel, individual HV
fuses are used at the INPUT of each bank of caps. Each bank gets it's own HV
meter. If the input hv fuse to any individual bank is removed, or goes open,
the Hv meter for that bank will drop to zero. There is only one teflon hv
wire, running from FWB.. over to B+ fuse, that feeds the 50 ohm glitch R.
There is only one real heavy duty teflon wire, running from the input of the
same B+ fuse, b4 the glitch R.....that goes external, to the box full of caps.
This external teflon hv wire terminates on the input buss, that is just cu
strap running across the top of hv insulators. Fuse clipS sit right on top of
the same strap. NO hv connectors used anywhere, it's all hardwired.
## plate xfmr, contactors, FWB, + glitch R {and it's fuse] , etc... reside in
one box. Caps reside in a 2nd box. RF deck is in a 3rd box. All box's
have a B+ meter. The box of caps, gets separate B+ meter's for each bank of
caps. All 3 x box's bonded together, via a star grnding system. There is
really little chance of the B+ accidently being grnded out.
The individual fuses for the inputs to each bank, alone won't limit current,
but will facilitate adding/deleting banks. Everybody has been telling me for
yrs, that anything over 40 uf is a waste of time, and you will soon reach the
point of 'diminishing returns' . Well I had the caps on hand, so proceeded
with the experiment to find the point of diminishing returns. I haven't
found it...yet.
Later... Jim VE7RF
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