Date: Thu, 11 Feb 2010 11:54:48 -0500
From: "Gary Schafer" <garyschafer@comcast.net>
Subject: Re: [Amps] Results from new PSUD... resistor b4 the B+ filter
I just looked at PSUD with a 25 ohm transformer, 2500 VAC and 25uf with 8
ohm esr filter cap. No resistor before filter.
The surge current on the first half cycle is around 26 amps. Then peak
current settles down to around 4.5 amps with around 1 amp rms on the load.
With a 25 ohm resistor added before the filter the surge current at startup
is around 22 amps and peak current settles to around 4 amps.
It doesn't look like the resistor does much good as far as startup. Only 4
amps different on peak current on the first half cycle.
It seems to me that a primary step start is a much better way to go, if one
is even needed. As long as the breaker don't trip and the diodes can handle
the peak current.
73
Gary k4FMX
### u are dead on correct. Originally I stated a while back that it took
aprx
500 msec to ramp up to full B+.. with the 22 ohm resistor inserted b4 the
Filter cap. Well, like an idiot, I forgot to shut off the "soft start"
feature on
PSUD !! The real ramp up period is 70 msecs.
## with softy start shut OFF in PSUD... I get essentially the same results
u did. [ I used 22 ohms.... u used 25 ohms] Of course, PSUD keeps coming
up with...."warning... you have just EXCEEDED the 25 A MAX allowable
peak rep current through a 1N5408 diode", and one other parameter was also
exceeded.
### The kicker is... you would have to INCREASE the ..'resistor b4 cap'
value by a HUGE amount.. to make the 'step start' work correctly..
and not blow up diodes ! As soon as you increase the resistor to 50-100
ohms... THEN ur regulation truly does go to hell.
## Personally, I don't like 'thumping' power supplies on, so the
conventional step start, with R in one leg of the 240 line, and shorted
out after XXX sec's, is here to stay. I also don't like changing out diodes
[esp 96 at a time], even if they are cheap. With the 200+ uf filter
cap set ups I use, I have to be real careful how they are initially
started up.
### can someone pse add a line of say 15 x 6A10 diodes to the
Psud fellows on line rectifier form ? 1N5408's are history imo.
6A10's are clearly a better diode.. and drop right in, where a 1N5408
once stood. Both have the same 16 ga [ .051"] leads. Both the same length,
BUT the diam of the 6A10 is bigger. 1 kv @ 6 A CCS... 400-450A Surge.
Most will test at 1400 v piv too. [ reverse current, piv test with hi-pot]
## dahl built all his diode boards, sold commercially, with nothing BUT 6A10's
8 x per board, with a mov across each diode. each board rated for 10 kv piv.
He had em stacked, up to 80 kv, for 3 phase, rated at 18 A CCS.. used for
HD-TV tx. Most other diode board makers also use 6A10's.
later... Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|