[RFI] DC Power supplies

Doug Powell dougp01 at gmail.com
Wed May 4 15:34:21 EDT 2016


I have worked in regulatory product compliance for many years and the
information you seek is not readily available on most manufacturer's data
sheets.  As you probably already know, having a UL, CSA or ETL mark is no
guarantee either.  If I were to start on such an endeavor, I would first
start by looking at all the candidate power supply rating labels (wall
wart, line lump, brick or open frame types) and look for either FCC,
European CE marking or other such markings.  If the power supply has this,
then you have narrowed the list somewhat.

Using anecdotal information from an online forum to compile a list is risky
at best and if your information is relied upon for some mission critical
application, you may be taking on some level of liability as well.  The key
is to get hard data from a standardized setup at an accredited EMC lab.
Sometimes manufacturers will publish their test results, especially if they
have really good minimum passing margins.  If a manufacturer has a passing
result but only marginally, then they may not be willing to publish.  This
happens more often than you might suspect.  In the end, this power supply
is a component intended to be used in a larger system.  This larger system
must in turn comply with interference rules, for both emissions and
immunity.  Manufacturers often have a "conditions of use" statement that
says something on the the line of "must be used in such a way as to not
cause interference..."  In other words, by using a standardized test setup,
they passed the tests and anything that is done to make use of the power
supply may inadvertently cause less than ideal RF results.  The real world
is seldom standardized, so your mileage will indeed vary.

All this said, I do think it is a good idea to publish a list of reputable
manufactures that are known to have a good track record.  I myself have had
good results from Mean Well USA, Power One, Advanced Power Solutions, XP
Power, TDK lambda and so on.  Nevertheless, the final result will only be
known after a particular device is selected and is paired up with whatever
piece of gear you are powering.

best of luck,  ~ Doug

On Wed, May 4, 2016 at 12:51 PM, <charlie at thegallos.com> wrote:

> Hey Gang,
> We all know about buying old analog wall warts for power supplies to cut
> down on RFI, but sometimes, that is NOT going to happen
> With the proliferation of things like LED strip lights, which by
> themselves are usually fairly quiet, BUT the power supplies they are
> hooked to are often horrid noise bombs, the question becomes
> Where can we recommend to someone who put in (or wants to put in)
> something like LED strip lights get a power supply?  MOST of the supplies
> we will need to replace use a C7 connector on the input (that is the one
> that looks like an infinity or an 8) and will need a barrel connector on
> the output (typical female).  The output isn't that big a deal if it needs
> to be changed, but think about the "hot" side
> They typically draw between 3-6 amps/meter of strip at 12V
> Believe it or not, I actually see some "line lump" type supplies being
> advertised as "No RFI" fairly cheap, but being they are out of China, for
> some reason, I trust them about as far as I can throw my tower AFTER it
> was installed
> I think it might be a real good idea if we could come up with a list of
> various "Line lump" (so they can be wired in) type power supplies at
> various power ratings that are KNOWN to be good, and sources for them
> I'd be more than happy to collect the list and put it up on my web site
> 73 de KG2V
> Charlie
> www.thegallos.com
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Douglas E Powell

dougp01 at gmail.com

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