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Re: [TowerTalk] Shack wiring

To: <>, "Pete Smith" <>
Subject: Re: [TowerTalk] Shack wiring
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Mon, 24 Jan 2005 11:07:03 -0500
List-post: <>
> My entire shack is on a single 110V circuit (separate 220
for the
> amplifier).

You mean 120. The USA standard (last time I looked) was

Recently I have begun to get low voltage warnings (104.5
> volts) from my UPS in the morning, and so have put a
digital voltmeter on
> the circuit.  With no load except for the computers (2),
the UPS and the
> table light, voltage right now is 108.7.

Too low. Almost everything is cenetered around 120v  +- 5%
Mine is 123 or so normally.

 My two radios (on receive) cause
> the voltage to drop about .4 volts.  When the voltage is
running low, I
> typically see 104.7 or 104.8 without the radios, so adding
them to the load
> sets off the UPS.

Wow. I would guess a typical HF radio might draw an amp or
less from the mains on receive. That would mean you have an
ESR of .2 ohms in the mains. That's pretty bad.

> Two questions, I guess -- is the voltage drop with loading
I describe above
> roughly what you'd expect?  If necessary I can dig out the
standby power
> requirements for the two radios.  And second, what is the
US spec for line
> voltage?  The power company is coming out to investigate
and I'd like to
> know where I stand.

For capacitor input supplies, you need to measure PEAK
voltage....not RMS. I got into a frustrating thing with the
ARRL lab when they reviewed an AL1200 amp. They used an RMS
metering and regulating system, and they had terrible peak
clipping caused by soft power lines and a bad regulator in
the lab. It took forever (after the review was published) to
get the ARRL to understand how power lines work. It was
worse than dealing with a layman, because they kept telling
me "we paid $30,000 for our regulator, and it is rock solid"
or something equally stupid.

When dealing with a capacitor input supply, you need a true
peak reading meter. When dealing with things that respond to
heating like tube filaments and lamps, you need to know the
true RMS.

The same meter (and the same voltage regulator or monitor)
won't work for both.

I don't know what your UPS is actually measuring and
watching, but odds are it is nether peak nor RMS. It
probably, like most cheap (and some very expensive things),
is not reading what it should actually read.

So you need two meters need to measure the true
peak and you need to measure the true RMS. Capacitor input
supplies run off the peak, and are more sensitive to line
ESR at a  given power load than resistive loads like choke
input supplies or filaments.

73 Tom


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