Re: AC/DC power supply


Joe Zeglinski
 

Hi Rick,


Yes, I was on my way to get that same PS-15KX like yours, but then decided to try the switched mode version. I asked the dealer if there were any other manufacturers of similar product (yes, there are a lot of lab power supply makers) - and in particular a PS-15KX like unit but with an "ammeter and voltmeter" with at least one cig lighter socket. I would even settle for an ammeter and an LED indicator triplet for voltage levels, in case of power droop. Or, they should be smart enough to have a single "switchable meter" for amps/volts. Looks like Pyramid has cornered the low end market, and only a couple of their units have the convenient sockets. I had considered punching an extra hole in the panel and adding my own socket to this supply since two sockets should be a bare minimum. Surely the 10 amp capacity could typically handle more than just one cig lighter accessory.

Sorry to extend this thread so far, but having the right power supply for our AP mount, and menagerie of accessories, seems important enough to stray this far off topic.
Joe

----- Original Message -----
From: "Rick Wiggins" <rickwiggins@...>
To: <ap-gto@...>
Sent: Thursday, March 20, 2008 3:12 PM
Subject: [ap-gto] Re: AC/DC power supply


Hi Joe,
Probably either one will work fine. Most of the switchers in the 12V
range are used by HAM operators to run thier equipment. I prefer
linear ads they generate less electrical noise. Obviously, batteries
are the most pure (electrically) suppply as there is nearly no
electrical noise, linear supplies are the next in line as they only
have the residual AC noise and usually that is heavily filtered,
with switchers being the highest electrical noise although again,
the oputput is usually heavily filtered to remove this noise.
Switchers run at very high frequencies and generate lots of RF noise
that can couple on other lines through inductance and radiation. It
is probably not a concern, but why take that chance. Switchers are
usually more expensive also; however, they are lighter, so if weight
is a mojor concern (10 lbs vs 3 lbs) in the size we are using, this
may be your choice.
Here is my favorite portable unit at a nice price:
http://www.etronics.com/p-23875-pyramid-ps-15kx-12-amp-power-supply-
wcigarette-adapter.aspx
Here is a complete line of supplies:
http://etronics.resultspage.com/search?w=pyramid+power+supplies

Hope this helps,
Rick

--- In ap-gto@..., "Joseph Zeglinski" <J.Zeglinski@...>
wrote:

Hi,

Pyramid power versus switch mode supply from a brick ...

I was going to get another Pyramid today - the "regulated" 10
amp unit
with the cig lighter socket this time - but on the way, I came
across a
huge Motorola (HPN4002B) power brick at another electronics shop.
From what
I have seen on the web, these are used to power the boom boxes in
today's
street hot rods - glad to provide a "good, quiet, use" for these.
Unlike the
Pyramid's which are LINEAR supplies, this is a 14 vdc, 10
amp, "switch mode"
brick. Looks very nice, although it only has an plain automotive 2-
pin DC
connector (like there is for a trailer hitch, or to hook up your
rear lights
in the car trunk), rather than a lighter socket of course.

Are there any potential problems with using a "switch mode"
supply
instead of a Linear?
The 10 amp Pyramid weighs 4.5 KG - about 10 lbs which I assume is
mostly
transformer iron, while the 4 inch square by one foot long !!!
power brick
is a featherweight. The power cord weighs about as much as the
entire
brick - a lot easier to haul out into the yard :-)

I wonder if using a switch mode supply will have a clean
enough waveform
compared to a Linear supply, and if it might generate electronic
noise in
the vicinity of a CCD or DSLR camera system. Could plugging in my
DSLR into
the supply (tapped, of course), produce herringbone patterns in
the sensor
image. If not directly induced from the DC supply line, is there a
potential
of EMI induced noise from a switch mode supply within a few feet
of the
scope and camera?

I would appreciate any advice on using this. At $35 each, I
decided to
buy a couple, and make my own power box - probably using the
Marine DC
sockets and plugs. The 10 amp Pyramid alone was going to be $85 in
a local
store, so I thought getting a couple of bricks to handle a total
of 20 amps
for less than that, seemed like a better deal. Should handle the
AP-900, a
few Kendrick dew heaters, the laptop, TCF focuser, and an STL-
11000 with no
sweat, with enough juice left over to keep the coffee warm in the
12 vdc
mug, I hope.

Finally, assuming two bricks can be used, is it wise to wire
the two DC
output jacks together in parallel - to potentially supply a total
of 20 amps
(rather than two separate buses) - or is the switch mode supplies,
common
wired output, going to buck? Then again, just like the early PC
power
supplies, I suppose they could shut down, if there isn't enough
load, from
the tracking motor alone.

Thanks,
Joe


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