Next message: (no email): "lv-ab: Garmin sux"
The compressor in a refrigeration system obeys Ohms law. It has a
certain amount of
work to do. You put warm food in the fridge and those btu's must be
removed. This
takes power. Power is measured in watts and a given amount of watts is
going to be
needed to remove a given amount of btu's. This total amount may vary
from one
system to another, depending on efficiency and ambient temperatures.
P=IxE
therefore 120 watts = 10 amps x 12 volts or 120 watts = 12 amps x 10
volts. We did
the same amount of work but, used more amps in the second example.
Motors do not
like to do this and will begin to get hot at lower voltage and high
amps. Small
compressors usually have an internal overload device that opens the
circuit before
the windings burn out.
As far as the amps dropping on the boat when the generators were slowed
and the
voltage dropped, I would suggest that you were not doing the same amount
of work
and less power was used. A bulb that is dim is not generating as much
light energy
as one that is bright and does not use the same power. A fixed
resistance of 1 ohm
will cause a current of 100 amps at 100 volts of applied voltage. Apply
200 volts
and the current goes to 200 amps. Ohm's law states I = E/R. The
confusion here is
the difference between a fixed load, like a light, and a variable load,
like a
motor. If you apply the proper voltage to the bulb you will get the same
amount of
light at the same amperage. This is what we want the light to do. A
motor is
expected to do varying amounts of work. Your compressor will draw less
amperage on
a cool day when head pressures are low and more amperage on a hot day
when it must
pump against a higher head pressure. On either day if you reduce the
voltage the
amperage will go up because it still will be trying to do the work.
Tom Duane
>
> >
> > 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"
> >
> >
___________________________________________________________________________
|| The Live-Aboard List : send a "subscribe" or "unsubscribe" request ||
|| in body of message to: ||
