Date: Mon, 16 Apr 2012 09:11:38 -0500
From: Rob Atkinson <ranchorobbo@gmail.com>
Subject: Re: [Amps] Filter Capacitors
To: Jim Thomson <jim.thom@telus.net>
.
>
> ## ?when playing with conventional choke input supplies, not the resonant
> types that
> henry radio used, ?you are in for an eye opener. ?When you 1st turn it on,
> ?you get this
> huge ?yo-yo oscillation on the P-P ?v waveform, that finally settles down. ?
> what psud wont
> simulate is a varying load, like ssb-cw. ?Once the supply is up and running,
> and no more
> soft start involved, is when the trbl starts up. ? ? Every time you hit the
> key, ?you are slamming this
> big load on it...and you end up toggling between full and no load. ? Every
> time you hit the key,
> that oscillation starts up, and P-P V is sky high, till it settles down. ? On
> cw, that?s next to impossible.
You have to use bleeder resistors so there is always a load on the
supply, or swinging choke on the input.
### I realize that. Put a scope across the B+ and B- and you will get a real
surprise
when keying on CW. Even with a massive bleeder load, they don’t work right.
I suspect modern day amp manufacturers avoid using a two stage LC
filter because the iron costs more and adds weight. Nowadays even
good 330 uF electrolytics, a string of 8 let's say, is cheaper and
smaller. I think that once you start getting above 50 uF @ 3 KV the
stored energy gets high enough to IED on a fault. CW rigs used choke
input filters for years--actually the handbooks say you can get by
with more ripple with a CW rig--maybe it was okay because they were
class C? I'll find out eventually--I have a single 813 with a 1500 v.
supply from a pair 866As and dual LC filter to try out.
73
rob
K5UJ
## any 2 x stage LC filter in a power supply these days is plane nuts. Any $$
spent on
fixed and swing chokes is a complete waste of $$ imo. Even the resonant
chokes used in the
henry amps is a waste of effort.
## For XXX amount of $$$ spent, you are much better off to just buy the
biggest hypersil
C core xfmr you can get your hands on.....or an EI type with real low loss
plates. Then use enough
C to get the ripple down to at least 1% or less. Then you end up with superb
regulation, both static and
dynamic. On a 2 x GS35B 6m amp my buddy built, he tried using the bigger
plate xfmr, and just changed the
taps on it. With 5 kw CCS CXR out on 50.125 mhz, the B+ drops exactly 50
vdc between RX and TX.
Ripple is real low, like .3% with the 162 uf total C used. Ripple is zip on
120-240-360-480 hz.
The combo of high C + a bigger plate xfmr will result in good V regulation.
The low ripple is just the side effect of the high C...and amounts to a free
lunch. And no, it wont cook your xfmr either.
## You wont get any IED effect with any fault either. The 50 ohm glitch
simply limits the fault current to a safe value.
The HV fast fuse in the B+ lead will open off in less than 2 msecs. The
filter C + 50 ohm glitch R will result in a
RC time constant. The RC time constant is long enough to do some serious
damage.... hence the use of the HV fuse.
3600 vdc divided by a 50 ohm glitch R = 72 A of fault current. And 72A will
open off a fast 1A rated HV fuse pretty
quick. Believe me, you can cro-bar this thing all day long if you want with
no ill effects. HV fuse opens up, event over .
Replace HV fuse, and repeat until you run out of HV fuses.
later... Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|