[ARC5] [Milsurplus] If You Need a Regulated Low B+ Supply

[Dennis Monticelli]

Actually DC/DC switching regulators are mostly non-isolated.  But the little
modules you see in surplus stores are often from the telecom industry which
is the chief user of isolated power and for good reason considering the huge
ill-defined ground loops that would otherwise result in a big telco central
office.

Do be careful about how high you stack them because they were not designed
for that.  Extra insulation in the case mounting area is a good idea and
also antiparallel diodes across the output to prevent inadvertant current
backfeeding.  No guarantee these supplies will all power up in the right
sequence and could easily force current into their slow-to-come-up brothers.

I had some Lamda 100V AC/DC bricks (isolated) that I tried stacking even
though I could not find a hard spec on their voltage floating ability.  I
did real well up to 400V and then blew out the "top" brick when I went for
500V. Like the hams say, "If your antenna survived the winter, it wasn't
tall enough!"

Dennis AE6C

On Thu, Feb 11, 2010 at 9:48 PM, Mike Feher <n4fs at eozinc.com> wrote:

> Switching regulators are inherently isolated, unless, they make an effort
> to
> connect the input common to the output common. I have never seen one like
> that, which does not mean they do not exist, HI. 73 - Mike
>
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ 07731
> 732-886-5960
>
>
>
>
> -----Original Message-----
> From: milsurplus-bounces at mailman.qth.net
> [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
> Sent: Friday, February 12, 2010 12:43 AM
> To: 'Discussion of AN/ARC-5 military radio equipment.'; 'Old Tube Radios';
> milsurplus at mailman.qth.net
>  Subject: Re: [Milsurplus] If You Need a Regulated Low B+ Supply
>
> Some folks have asked where I got the converters.
> It was a local surplus house in Carrolton, Texas,
> called "Tanners."  We call it the "candy store."
> Lots of good stuff but, alas, none of these remain in stock.
> You find them often on Ebay.  Check with any local
> surplus houses you know, because these kind of
> DC/DC converters are becoming pretty common.
> You can get them for all kinds of voltages out.
> If you look at some, be sure they have an isolated output
> (i.e the input and output negatives are not common).
> All of them I've seen in surplus are isolated, but some are not.
> One caution:  Many of these can source better than an amp.
> It's easy to look at these little bricks and think of
> safe, cute 12-volt plastic radios, and get careless.
> When you start stacking them,
> they ain't "play-prettys" no more.
> An amp at 300 volts will kill you mos'-very-buncha dead.
> Be careful.
> 73 Dave S.
>
> p.s. I don't know if the case insulation will stand really high voltages,
> since they were designed to never be more than 30 volts above ground.
> I don't allow the cases to contact ground.  Haven't had a problem
> so far at the 90-volt level, but I've stacked them to 300 and
> I think that might be a bit "dicey."  I'm going to stick with 90 to 120
> volts and be happy.
>
>
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