[time-nuts] Favorite DC power Supply?

Neon John jgd at johngsbbq.com
Sat May 3 00:33:19 EDT 2008

On Sat, 03 May 2008 08:58:58 +0930, Matthew Smith <matt at smiffytech.com> wrote:

>I am building two GPS-driven devices, an NTP server based on an ancient 
>single board computer and a Nixie clock.  Our power here is not what one 
>might call reliable - we are stuck on a spur of a very long 19kV, single 
>wire, earth return supply which plays up a) when there is a thunderstorm 
>within 200 miles and b) when it feels like it.

Does your power system STILL use ground return?  Are you sure there isn't a
neutral return on the primary feed?  If not then WOW.  I bet it's interesting
walking around the earth ground in dry weather.  A shocking experience.

>My thought was to integrate a UPS component into the design by 
>connecting these to 12V 7Ah sealed lead acid batteries, which I can get 
>for just over $20 AUD a piece.  If I were to do this, would it be 
>sufficient to power the units from a 13.8V supply?  I believe this to be 
>within the voltage range for float-charging the batteries so was 
>guessing that this may be a simple way to provide uninterrupted power to 
>my gear.

Change that voltage to whatever float voltage your batteries want and it'll
work peachy.  That is effectively the way I had my homemade UPS connected -
the two big honkin' 100 amp supplies connected to a pair of trolling
batteries.  Also connected to the trolling batteries was a non-switch-mode,
pure square wave inverter, a Tripplite 1kw unit.  Yep, with about 2 dozen
2N3055 TO-3 transistors bolted down each side and about 60 lbs of iron and
copper in the transformer.  A simple power blocking oscillator design with the
*deluxe* frequency control board, a 555 timer running at 60hz
injection-locking the power oscillator.  It had no concept of overload
shutdown so it was good for much more than 1kw short term until the whole unit
got hot enough to boil eggs!  Seems like that sucker cost around $600.

Everything that everybody said wouldn't work on a square wave inverter did.
Second generation HP laserjet, 386 vintage computer power supplies, CRTs,
smart terminals, TrailBlazer modems (remember those?), etc.

I started one of the very first for-pay ISPs (dixie.com).  It was hosted on a
33mhz 386 PC with 12mb of RAM ($$$) and an actual gig of full height 5.25"
hard drives ($$$$$$$$$$) running Interactive Unix ($2k just for the OS).  That
machine supported 2 developers plus 16 2400 bps dial-up modems and a couple of
Trailblazers for news feeds.  Demonstrates just what a pig winders is!  Had a
hell of a time getting that Bell B*tch to drag a T-1 line to my basement where
all this stuff was operated from.

I later added a second machine and modem rack and another homemade UPS. Same
architecture except that I couldn't find any more 100 amp supplies on a
moment's notice.  I instead used a 150 amp unregulated supply that came out of
a Univac mainframe.  A motor-operated variac ahead of the transformer
"regulated" the voltage.  At the operator's console was a voltmeter and a
momentary on-off-on toggle switch.  Whomever was sysop at the time had the
duty to watch the voltage and run the variac up and down as needed.  We always
intended to build an automatic regulator but never got a round tuit.

At $20 a month per subscriber I just couldn't make the numbers work for the
long term so just about the time Mosaic hit the scene, I shut everything down,
sold most of the hardware, let the registration on dixie.com expire and left
the computer field to open a restaurant.  *sigh*.

Back to the present.  Here in the US, inverters are so cheap that one could be
applied to each load.  No idea what conditions are there but here I can get a
750 watt inverter for under $50 and a 2000 watt unit from Harbor Freight for

John De Armond
See my website for my current email address
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
It isn't Global Warming.... It's Jerry Falwell arriving in hell.

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