At 09:37 AM 05/23/07, you wrote:
Hello all,
I'm in the process of rebuilding one of my repeaters and I'm looking
to place a UPS in line for backup.
I'm looking for information on make and models - what's good and
what to stay away from. The VA range is 1300 to 1500, and I'm
willing to spend no more than $200.00.
Thoughts and comments appreciated.
TIA,
Don, KD9PT
For a cheap UPS talk to any of your friend in the IT world. There
are enough uninformed "technicians" (and it use that term generously)
in the IT universe that have no idea as to which end of a screwdriver is
the handle...
When a UPS dies (at about the 3 years point) they just throw it away
and buy a new one. In fact I just recently "re-batteried" a several APC
"Back-UPS PRO 1000" units for a client.
Three comments of warning about APC:
1) They pass all the AC line junk through the unit (via relay contacts)
until there is a brownout (i.e. low AC voltage) or an outage (no AC voltage).
Then the inverter fires up, and the relay switches over. You WILL have an
outage as long as one to two tenths of a second. I've seen desktops and
servers reboot under those conditions (usually mans that the computer
power supply has dying caps, which is a whole 'nother problem).
2) APC runs the batteries hard. Plan on replacing them every 3 years.
3) They over-rate their units. Rarely does any APC give you over
25-30 minutes of run-time. They are designed to provide graceful
shutdown time, not to ride out an outage of any length. Graceful
shutdown means that the server power cord is plugged into the UPS,
and a serial port is plugged into the DB9 jack in the back of the
UPS (via a special cable they sell, one that has a transistorized
circuit buried in one of the molded rubber shells). When the power
fails the UPS sends a signal to the server over the serial port
announcing power fail (they simply change the CD signal from
active to inactive).
In a properly designed network the server messages all the users
and gives them 5 minutes to save the current work and log out.
Then the server shuts down before the battery runs out (or in
large data centers the generator starts up).
The biggest problem with using an IT UPS in a solid state
repeater environment is efficiency. You are running
AC to 12 or 24 or 48V DC and then back to AC into the
repeater power supply which makes 12vDC.
The better way is to simply use the batteries directly on
the repeater - just use a Absorbed Glass Mat battery
(also known as an AGM battery) and float it across the
repeater power buss. The efficiency goes up, if you are
paying the AC power bill your wallet is happier, and you
get zero switchover time.
A compromise design that I've seen has the repeater
power supply and the backup battery diode OR'd to
the repeater itself with 75amp stud-mount diodes
(from a dead fire truck alternator), with an IOTA brand
charger on the backup battery (which was a bank of
glass-cased Exide telephone central office style
batteries - 5 gallons of electrolyte per cell)
So my recommendation, if you have a solid state repeater,
is an AGM battery with a IOTA power supply / charger.
Don't save money on the charger - a good one will last,
a cheap one won't and may take your battery bank with it.
A good IOTA power supply / charger is NOT a waste of
money and a cheap one is false economy.
Mike WA6ILQ
