AW: [sdiy] transformer question

[Czech Martin]

basically : yes.
usually it is sufficient to treat the primary side in the manner you
mentioned.
pitfall here: relay may not come up (undervoltage, or whatever), so 
resistor will burn or circuit will be heavily undervoltaged.
pitfall 2: some relay circuits are not foolproof: fast toggling will again
trip the power fuse.

As for the switching on the secondary side I think that this has no real
benefit, 
it may be even dangerous if the wrong contact will close at the wrong time
(power supply sequencing). One always has to keep that in mind when
designing
circuits with several power and ground pairs. The failure of one pair
should not latch up something else.
Also there are no ideal swithes, contact bouncing may lead to very
disturbing
power supply transients.
So I like the idea of "soft ramp up" much more.

I've constructed a couple of power supplies with/without torroids, up to
400VA,
one with 60000uF/60V, it seemed that they worked...

But I really would like to understand this more, I'll set up a little
circuit simulation
with/without choke coils...

btw.: http://www.geocities.com/SoHo/Museum/4459/circuits/circuits.html

contains some circuits about power supply (some untested!)

m.c.

> -----Ursprüngliche Nachricht-----
> Von: Sowa Roman [mailto:Roman.Sowa at upc.com.pl]
> Gesendet: Donnerstag, 3. Januar 2002 16:31
> An: diy (E-Mail)
> Betreff: RE: [sdiy] transformer question
> 
> 
> just a thought:
> 
> wouldn't be usefull a circuit where transformer is powered up 
> via, say, 1k
> resistors in series with primary windings, and with the load 
> disconnected on
> secondary side, so only rectifier and capacitors are connected. When
> capacitors get charged to full working voltage, a relay 
> shorts those 1k
> resistors and connects the load to the power supply.
> Have anybody tried this?
> 
> Roman
> 
> ""-----Original Message-----
> ""From: jhaible at t-online.de [mailto:jhaible at t-online.de]
> ""Sent: Thursday, January 03, 2002 3:26 PM
> ""To: Czech Martin
> ""Cc: diy (E-Mail)
> ""Subject: Re: [sdiy] transformer question
> ""
> (..snip..)
> ""under load: A transformer which has a higher DC resistance
> ""in its winding has its rated voltage *under nominal load*
> ""(and it will goo higher without load). If you add an external
> ""resistor, the voltage under load will be smaller than the rated
> ""voltage of the transformer, of course.
> ""
> ""So the solution is: Select a toroidal with slightly higher
> ""secondary voltage, and use external resistors to fit your needs.
> ""There are also special rectifiers with considerable resistance,
> ""but I've never used them. I think Harry can tell us about these.
> ""
> ""JH.
> ""
> 
> 
> ---------------------------------------------------------
> This message has been scanned for viruses by MIMESweeper.
> 
> Wiadomosc zostala sprawdzona pod katem wirusow przez
> oprogramowanie MIMESweeper.
>