I have a site where for many years the only load was a battery charger feeding
a battery to power up the equipment. For many years the power meter DID NOT
MOVE! It started moving when I substituted a GE Mastr II base station power
supply with backup battery.
My theory (correct me if I am wrong) is that the very short duty cycle current
pulses drawn when the sine wave is at the crest of the cycle (when the diodes
conduct) is why the meter was not moving.
The GE Power supply is ferro resonant and draws current over the whole cycle
although the power factor is pretty bad. The GE supply also uses a filter
choke which reduces the current pulsing when the diodes conduct to a minimum.
73 - Jim W5ZIT
--- On Tue, 9/16/08, Bob M. <[EMAIL PROTECTED]> wrote:
From: Bob M. <[EMAIL PROTECTED]>
Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
To: Repeater-Builder@yahoogroups.com
Date: Tuesday, September 16, 2008, 10:31 PM
Thank you Eric. This was the explanation I was looking for. The UPS
is saving me money when drawing 181 Volt-Amps, yet the electric meter is only
recording and charging me for 31 Watts. I wonder if APC did this on purpose. I
don't know how much current is actually being fed to the batteries; they've
been in there for a couple of months and should be fully charged by now, so it
should just be trickling them (eight 12V 7A SLA cells in series/parallel for
48V).
Bob M.
======
--- On Tue, 9/16/08, Eric Lemmon <[EMAIL PROTECTED] net> wrote:
> From: Eric Lemmon <[EMAIL PROTECTED] net>
> Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
> To: Repeater-Builder@ yahoogroups. com
> Date: Tuesday, September 16, 2008, 9:21 PM
> Albert,
>
> You are forgiven, because you pose an important question!
>
> The spinning aluminum disk in the kilowatthour meter found
> on most
> residential service-entrance panels measures true power in
> kilowatts versus
> time, which equals energy. Thus, your electric utility
> charges you for the
> true power you use, not for volts times amperes- known as
> reactive power.
> Although the utility must provide the capability to supply
> all of the
> amperes you need, some of those amperes are "given
> back" to the utility due
> to a lower than unity power factor. That is why many
> utility companies
> charge a "kVAR Penalty" to certain industrial
> power users whose volt-ampere
> demands far exceed their watt demands, meaning that the
> power factor is low.
> Industrial power users strive to keep their power factors
> at 0.95 or above,
> to avoid some really painful penalties! The power factor,
> or PF, is simply
> watts divided by volts time amperes.
>
> The issue of power factor is why large Diesel generator
> sets have ratings
> such as 1000 kW/1250 kVAR. In simple terms, any AC
> generator requires
> torque (engine horsepower) to meet true power demands, and
> excitation (field
> flux intensity) to meet reactive power demands. When the
> generator load is
> reactive, that is, it has a power factor less than unity,
> the generator must
> not only have the horsepower to supply the energy in watts,
> but it must have
> excess capacity to handle the additional current required
> by motors and
> other low-power-factor loads. In a nutshell, that is why a
> 1000 watt
> generator may be unable to keep running a refrigerator that
> uses only 900
> watts; the fridge may require 1200 VA to operate because it
> has a low power
> factor, and the small generator has no ability to handle
> such loads.
> Because of its relatively small amount of spinning mass,
> such a small
> generator probably could not even handle the
> refrigerator' s starting
> current- which is about 5 to 6 times its running current.
>
> 73, Eric Lemmon WB6FLY
>
> ___
