[TenTec] DC Power Supply Backup

[W1GOR]

Bill,

By 'floating' a motorcycle, lawnmower, automotive, or R/V battery at 13.8
volts, your transceiver will never 'see' an AC glitch.  When you experience
AC line failures, all that happens is the float charge drops off-line.  The
battery is 'stiff' enough to keep the transceiver operating as if the AC was
still there.  Think about the headlights in your car... With the engine
running, the battery floats at 13.8 volts and the headlights operate at that
voltage.  If you switch off the engine, the alternator stops the float
charge, but the battery still keeps the lights on, and the battery voltage
gradually drops to 12 volts if you wait long enough.

Many remote radio repeaters operate from 12, 24, 36, or 48 volts, directly
from float-charged batteries.  There is no interruption of service whenever
the AC power fails... and when the AC power is restored, the float charge
continues to keep the battery array at the design voltage level.

Be very sure to keep the battery in a well ventilated location, not in any
kind of closed container.  Remember, any discussion of hydrogen gas begins
with the word HINDENBURG..!

As for residual energy in the power supply... Depending upon the load, the
residual energy may last less than a second... You asked about 10 seconds..?
Absolutely not...!   Try placing a dummy load on the power supply equal to
your transceiver in the receive mode... monitor the output voltage and
switch the supply off... watch how quickly the voltage drops to zero...
Fast, isn't it..?  Go with the float-charged battery method.  BTW, there's
nothing wrong with a good, heavy duty UPS... They also operate with an
internal float-charged battery that powers a DC to AC inverter...  Since
your transceiver can operate directly from 12 volts nominal, why power the
AC to DC power supply as well... Basically, if you're using an Astron 13.8
volt power supply, all you need to add is the external battery.  If you can
adjust (increase) the Astron's output voltage to compensate for the forward
voltage drop, add a hefty diode between the Astron and the battery to avoid
discharging the battery back through the Astron supply when the AC power
fails.  In addition, see if the Astron has an over-voltage, or 'crowbar'
circuit to protect your equipment from the effects of failed components
(series regulator transistors) in the Astron power supply... If there is
none built-in, you may want to install one externally... Crowbars are
relatively inexpensive protection against a runaway power supply...!   We
wouldn't want to see a mushroom cloud rising over an Orion...would we..?

73, Larry - W1GOR


----- Original Message ----- 
From: "Bill Tippett" <btippett at alum.mit.edu>
To: <tentec at contesting.com>
Sent: Wednesday, May 21, 2003 10:02
Subject: [TenTec] DC Power Supply Backup


> I've ordered an Orion and for the first time will be
> using an outboard DC supply (a used Astron RS-35M
> is on the way).  I often get short power glitches since I am
> in a rural location and am concerned about getting resets
> on Orion since I understand it takes awhile to reboot (how
> long?)  I'm thinking of getting a small battery (motorcycle)
> to place between the RS-35M and Orion.  This would stay
> fully charged and might help prevent unwanted resets by
> brief power glitches.
>
> Has anyone ever done anything like this?  Is it even
> necessary or is there enough residual energy in the PS
> filter caps that brief interruptions (typically <10 sec) are not
> a problem?  I  don't really want to buy a UPS large enough
> to power Orion but is there a simpler solution?
>
> 73,  Bill W4ZV
>
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