Next message: Gene Gruender: "Re: lv-ab: Battery Charging: How Charge Large House Bank?"
It depends entirely on the type of load. Most loads (lamps, etc.) are
resistive in nature and do obey Ohm's law. But some loads are "smart"
and make adjustments as necessary to accomplish their tasks. A fridge
is a simple example of a "smart" load -- it is trying to keep the food
compartment at the temperature determined by its thermostat, and makes
whatever adjustments are necessary to accomplish that task. If a lower
power supply voltage means that the motor must run longer (because it is
running less efficiently) then that's what it will do.
Another example of a "smart" load is the UPS (Uninterruptible Power
Supply) that some people use with their computers. These things try to
provide a constant AC voltage to the computer, regardless of the current
voltage at the AC receptacle into which the UPS is plugged. If the
voltage at its input decreases, the UPS draws more current from that
input in order to maintain a constant voltage at its output. And if the
voltage at the input disappears (power outage), the UPS reverts to its
internal battery to keep delivering power to the computer -- at least
for awhile.
Most loads obey Ohm's law. But not all!
wrote:
>
> Randy,
>
> I am at a loss to understand your experience. If the values you cite for your
> reefer are correct, it may have a microprocessor which controls the current
> to the motor so that the machine operates consistently over the typical range
> of voltage which cruisers experience.
>
> The fact remains that if you reduce voltage to a lamp, it will dim. A good
> example is the dimming of headlights when the starter is engaged and pulls
> the battery voltage down.The light output is reduced by virtue of less energy
> (watts) consumed. You'll recall that a load doesn't really "draw" current;
> it's the EMF that forces the electrons to flow through the load. If you
> reduce the EMF, the current will decrease.
>
> I spent years aboard ships which had 120/240VDC systems, and if we increased
> the generator voltage, the current increased, the motors speeded up and the
> lights got brighter; with decreased voltage, the ammeters declined, the
> motors slowed and the lights dimmed. I don't see how anyone can argue with
> that.
>
> Kind regards,
>
> John
> "Truelove"
>
> In a message dated 8/20/1999 5:46:07 PM Eastern Daylight Time,
> writes:
>
> > This is visible to me as my batteries discharge and the fridge, say, is
> running. With a full charge showing something in
> > the neighbourhood of 13V, it draws 9.2A. When my voltage has dropped to 12
> volts (at around 50-60% discharged), its
> > drawing over 10.
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