[hpsdr] PicoPSU power supplies

[Dave G4FRE WW2R]

Hi John

A few years ago I was building a pair of atom boards with the PICO PSU for
the rtty computers at MW2I. Reading the manual I also spotted that 13-13.5V
statement and wondered if it excluded 13.8V (which we might need for VHF
portable operation). So I called and asked them. A very curt guy said "cant
you read the manual... if it says 13-13.5V it means 13-13.5V not 13-13.8V"
So I bought the PicoPSU-120-WI-25 12-25V  which I had seen in a car mounted
atom board based audio systems (I kid not!) I have seen running these 2
contest pico-psus have had no trouble with them or the one in my HPSDR since

I also noted that in their "power supply kits" such as "picoPSU-120 + 102W
Adapter Power Kit" they supply a 12.0V PSU, not a 13.8V one

Dave

ww2r


-----Original Message-----
From: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org]On Behalf Of John Ackermann
N8UR
Sent: Saturday, February 04, 2012 1:48 PM
To: Discussion of precise time and frequency measurement; HPSDR List
Subject: [hpsdr] PicoPSU power supplies


***** High Performance Software Defined Radio Discussion List *****

Sorry for the cross-post, but I know this is of interest to some folks
on the HPSDR (high performance software defined radio) list, and I
suspect it may be helpful for some time-nuts as well.

The important message first: the little "PicoPSU" switching power
supplies that plug directly into an ATX socket say they are for 12V
input.  It turns out that they mean it -- the supply will shut down if
the input voltage is more than 13 - 13.5 volts.  So using these in a
typical battery-powered environment is potentially a problem unless you
somehow drop a volt or so.

Here's the sad story...

I recently built several low power Atom-based computers that use the
PicoPSU supplies.  The theory was that I'd run these machines, along
with all the other 12V gear in the basement, off a couple of big
batteries on a float charger.  The battery voltage varies from about
13.5 to 14.2 depending on the charger state.

Built the machine on the bench using an Astron supply, and everything
was cool.  Put on the battery bus in the lab, and things got very funky.
  Sometimes the power LED would come on, but nothing more would happen.
  Take the machine to the bench, everything was fine.  Take it the lab,
didn't work.

I checked all the power connections and found no problems, but the
battery supply simply would not run the computer.

Finally, I found a manual for the PicoPSU on the web, and discovered
that when they say it's a 12V supply, they mean it -- there is an
overvoltage shutdown that's supposed to trip between 13.0 and 13.5
volts.  In practice, it seems that at least some of them are good for a
little bit more than that, because the 13.8V from my bench supply worked
OK.  But when the battery voltage hit about 14.1, that was too much and
the supply shut down.

So, I now have the computers running from an Astron supply that I
adjusted for good measure down to 12.6 volts, and all is well.  For the
long term, I'm considering putting a diode or two in series with each
computer's power lead to drop the voltage that way.

John
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