[sdiy] Power Supply Questions

[Oscar Salas]

Hello,

> whenever you plan to max out more than about 80% of the
> rated the power.

Talking of modern transformers... Do the manufacturers calculate that 80%?

> construction of the transformer, so you'd need to consult
> the data-sheet

http://www.myrra.fr/technical/technical.html
http://www.myrra.fr/documentation/catalogue_myrra_int_2011_site.pdf

It is the Myrra 44383

> the regulator you would get a slightly smaller DC
> current.  

Yes , before regulator I read slightly more current, It would same before the diode ring?




--- On Wed, 3/16/11, ASSI <Stromeko at nexgo.de> wrote:

> From: ASSI <Stromeko at nexgo.de>
> Subject: Re: [sdiy] Power Supply Questions
> To: synth-diy at dropmix.xs4all.nl
> Date: Wednesday, March 16, 2011, 8:07 PM
> On Wednesday 16 March 2011, Oscar
> Salas wrote:
> > In a 2X18 30VA transformer, so each secondary (15VA)
> is current rated
> > 0.83A at 18V, how much current rated will be in each
> secondary after a
> > regulator that provides 15V?
> 
> The VA figure includes the core and winding losses, but
> also depends on the 
> max. ambient temperature.  Small transformers are
> often surprisingly 
> inefficient.  Also, the load regulation is getting
> poorer the smaller the 
> core and you may not have enough drop-out voltage left for
> the regulation if 
> you pull the maximum power.  This all depends a lot on
> the actual 
> construction of the transformer, so you'd need to consult
> the datasheet 
> whenever you plan to max out more than about 80% of the
> rated the power.
> 
> > It is 1A... or it can not be considered after the
> regulator and remains
> > 0.83A?
> 
> It is 0.83A, or the stuff before your load must not get
> warm at all. :-)
> 
> But note that this is a an RMS current for resistive
> load.  You will 
> actually have a very impulsive current that provokes higher
> losses, so after 
> the regulator you would get a slightly smaller DC
> current.  So if you want 
> 1A current from each secondary, you should get a larger
> transformer.  The 
> next size up is probably around 50VA rated and that should
> give you enough 
> room not to worry about the fine print on some data sheet.
> 
> 
> Achim.
> -- 
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