[Amps] Re: 12V 120A Switching Power supply?

[Steve Katz]

> Quiet?  Not the FCC Class B telecom units I've been playing with.  These
> beasts put out relatively low noise differentially between output V and
> its
> ground but put out a lot of noise "common mode" between the output pair
> and
> the case (green wire ground), between the input leads and case, and
> between
> the input return and output return.
> 
> I've been measuring these things at work and currently see 2V peak to peak
> impulses at the 75 KHz switching frequency followed by 10-20 cycle of
> ringing at about 50-100 MHz.
	  

	::Clearly, it depends a lot on the specific power supply.  You
wouldn't be measuring 75 kHz impulses from the MagneTek MG3 model, for
example, since its switch frequency is 500 kHz.
	-WB2WIK/6


> From what I can tell, the manufacturers pass FCC EMI testing by putting a
> resistive load on the outputs that's not connected to anything, just
> resistors floating in air.  This minimizes the tendancy for the output
> ground noise to pump back into the input lines.  But once we connect the
> outputs to our equipment (and it's chassis ground), the input conducted
> noise rises by 20-30 dB and we that far out of spec.
> 
> jeff, wa1hco
> 
> ----- Original Message -----
> From: "Steve Katz" <stevek@jmr.com>
> To: "'Phil Levin W2GE'" <w2ge@arrl.net>; <Amps@contesting.com>
> Sent: Monday, April 01, 2002 6:27 PM
> Subject: RE: [Amps] Re: 12V 120A Switching Power supply?
> 
> 
> >
> >
> > > Uh....  Did not know that!
> > >
> > > Curiously, How much does one of these 120 amp switchers cost and are
> > > they RF quiet?
> >
> > ::Like most modern switch mode power supplies in the 500W+ class,
> > they run about a dollar per Watt.  I would say they are _very_ RF quiet,
> > since their primary applications are powering large telecommunications
> > systems which need to meet not only FCC Part 15 Class (B) but also Part
> 68
> > and a variety of other certification requirements.  We use 'em all the
> time.
> >
> > 73 de Steve, WB2WIK/6
> >
> >
> >
> > > Phil W2GE
> > >
> > > -----Original Message-----
> > > From: amps-admin@contesting.com [mailto:amps-admin@contesting.com] On
> > > Behalf Of Steve Katz
> > > Sent: Monday, April 01, 2002 6:10 PM
> > > To: 'Doc Johnson'; amps@contesting.com
> > > Subject: RE: [Amps] Re: 12V 120A Switching Power supply?
> > >
> > > There's been a great deal of speculation and advice on here regarding
> > > this,
> > > but in reality, a simple answer to the simple question has been
> > > provided.
> > > There are absolutely 12V, 120A "off the shelf" power supplies readily
> > > available and currently for sale.  If someone wants one delivered
> > > tomorrow,
> > > he could have it.
> > >
> > > The MagneTek MG3 product is one I've used for a few years now, in
> > > exactly
> > > this category.  Delivery is a few days or less, and it's a solid,
> > > certified
> > > product.  Not large or heavy, and a twin MG3 pack provides 12V
> regulated
> > > at
> > > 200A continuously.  There's a 48v version of the same product.
> > >
> > > Unipower, TDI, NMB, Todd and others make similar stuff.  Nothing
> unusual
> > > about the requirement at all, although evidently the ham community
> seems
> > > to
> > > think so...
> > >
> > > WB2WIK/6
> > >
> > > "Each success only buys an admission ticket to a more difficult
> > > problem." --
> > > Henry Kissinger
> > >
> > > > -----Original Message-----
> > > > From: Doc Johnson [SMTP:bluescreen@comcast.net]
> > > > Sent: Monday, April 01, 2002 2:42 PM
> > > > To: amps@contesting.com
> > > > Subject: [Amps] Re: 12V 120A Switching Power supply?
> > > >
> > > > Why not build the amp out of 48 volt transistors? I have a dozen 300
> > > watt
> > > > 48 volt power transistors that I have been saving for such a
> project.
> > > This
> > > >
> > > > should reduce the current requirements and hopefully make the power
> > > supply
> > > >
> > > > lighter?
> > > >
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