> > Why not use a UPS?
>
> Well, there's the old problem of battery life. One of these repeaters
> is the primary Skywarn repeater for the area. The NWS is very
> interested in weather reports from this area since we are the first to
> see what has actually come across Lake Michigan. It needs to be
> operating for sometimes 4-8 hours, depending on the duration of
> watches and warnings. Plus, our Mastr II is not what you'd call--
> "efficient" in it's use of power, even at reduced output. Your idea
> is not without some merit, though, maybe for a 3rd level of AC power,
> operating on exciter power output. h
The other issue with UPS's is that they don't always play nice with
generators. If the "red outlet" is emergency power (i.e. backed up by a
generator), you may find that the UPS may not like the generator-supplied
current, either due to frequency or voltage variations, and refuse to switch
back to "line" power after the generator starts. Higher-end UPS's often
have software-adjustable parameters that get around this problem, but
run-of-the-mill UPS's don't, and my experience has been that many, if not
most, of them aren't very forgiving.
> As far as "installing" something, I think it would be more like
> "plugging it in". I can't disagree with possibly talking to the
> maintenance people about it though. I'll also run-it-past one of the
> other members of our committee, who is an EE, and sells and designs
> emergency generator systems for commercial and industrial customers.
If you want to make something and just "plug it in", I'd get a double-pole
double-throw 20A contactor with 120V coil. Wire the coil and normally-open
contacts to a cord that goes to the white outlet. Wire the normally-closed
contacts to a cord that goes to the emergency outlet. Wire the common
contacts to your equipment. As long as there's power on the white outlet,
the coil will engage the contactor (normally-open contacts will be active),
and current from the white outlet will power your equipment. If you lose
power on the white outlet, the contactor will disengage (normally-closed
contacts will be active), and power from the red outlet will feed your
equipment.
DO NOT tie the neutrals from the two sources together! You should switch
both the hot and neutral using a double-pole contactor per the above.
I make no claims that this is UL, NEC, or AHJ approved...
--- Jeff WN3A
