To measure how much electricity a single home appliance uses:
1. We know there are ammeters, which show the amount
of current used instant by instant (as a speedometer shows
the speed of a car;)
2. But is there also a device that cumulates usage, the
way a mileometer totals distance traveled? What would
this be called?
3. And is this a $500 electrician's instrument or a $25
gadget anyone can safely use?
For plug in appliances the kill-a-watt is pretty good. For bigger
stuff you need a clamp on amp meter. Simple appliances can be pretty
easy but bigger things vary more based on other factors. Like your
fridge will use a lot less power while you are on vacation verses at
home as well as possibly different weekday verses weekend. Heating
and cooling will depend on the outside conditions.
On Mon, 14 Mar 2011 07:17:56 -0700 (PDT), jamesgangnc
You ned more than a clamp-on ammeter to get the information the OP is
requesting. You need a power meter. I had (likely still have
somewhere) an old utility meter that I used to measure the amount of
power consumed by the charger for my electric car.
It was a conversion of a 1975 Fiat 128L Sport coupe, running an
aircraft generator for a motor, through the 4 speed tranny with a
simple resistor start, dual voltage power controller with field
weakening.. It started on 24 volts through a stainless steel ribbon
resistor, which was then shorted out feeding full current, then
switched to 48 volts with the resistor back in the circuit for about 1
second, then shorted back out. Putting the accellerator down further
weakened the shunt feild of the compound wound motor, causing it to
speed up. The dual voltage setup was a series parallel arrangement
using a single contactor and a diode set.
8 GC2H golf cart batteries drove it about 30 miles at 50mph, or 50
miles at 30mph, on a single ($0.25 at the time) charge. That was
roughly equivalent, cost-wize, to 200 MPG at 30MPH with gas at about
a buck a gallon.
On Mon, 14 Mar 2011 21:50:34 -0400, email@example.com wrote:
Have you noticed, at least it's my impression, that when they give mpg
for current hybrid cars, they totally ignore the electricity? AFAICT,
they just take the miles driven and divide by the gallons of gasoline
used. Or do they do it right and just not explain it?
My wife's car is the prius.
There is no savings by charging the batteries from the engine. Not to
say it doesn't ever do that. You can see the charge direction when
braking. They all recomend for maximum gains that you plan your stops
so that you can slow down gradually. When you put your foot on the
brake lightly it does the braking with the electric motor acting as a
brake/generator. You can feel it. I try to do that. If you stop
hard it still generates but also has to use the regular brakes. Some
of the savings also comes from shutting the gas engine down when ever
there is an opportunity. If you stop at a red light it will turn the
engine off. When you take off the electric motor starts you moving
and also starts the engine. When you are maintaining a consistent
speed like out on the highway it will shut the gas engine off on
slight downhills and use just the electric motor to maintain speed.
It's pretty impressive that they are able to bring the gas engine in
and out of the drive train without it being noticable. You really
have to pay attention to tell when it happens. It pretty consistently
gets around 50mpg no matter what the trip is. Even on the highway
running at 75mph. I was surprised at that as the highway doesn't have
much oppotunity for charging.
The Prius has an Atkinson cycle gas engine, a major feature for high
mpg. The exhaust stroke is, in effect, longer than the intake stroke.
That makes the engine more efficient. But it gives you less horsepower
in the same size engine. The engine has variable valve timing. I have
not seen a good explanation, but I think they can shift the engine back
toward a 'normal' engine for higher HP when needed. The engine HP can be
smaller (as with any hybrid) because when high HP is need both the gas
engine and electric motors are used. With a smaller engine you are
operating in a more efficient RPM range.
It uses a "hybrid synergy drive". It is a planetary drive that connects
the gas engine, 2 motor/generators, and the wheels. There is no
mechanical change for forward, reverse, high, low. The "drive" allows
charging the batteries while driving, powering the drive electric motor
from the other motor/generator (combined with gas engine - necessary at
the high end of the speed range), and generally manipulating the "drive"
so the gas engine runs in the efficient RPM range. When the batteries
are charged from the engine while driving, the engine is at an efficient
RPM. The engine throttle is totally controlled by computer.
Regenerative braking, as above, captures much of the kinetic energy that
would be lost as heat in the brakes. It must work pretty well - the city
mpg is close to the highway mpg. I assume this is a major feature of all
Obviously it all works, as you mpg indicates.
Having the engine stop at a red light is kinda strange at first.
The efficiency of a gas engine varies widely with operation conditions
as seen in the faster you go the more gas you use. This is the big
advantage that an electric motor has as its efficiency remains
relatively constant regardless of speed and operating conditions. In a
gas car you waste energy every time you brake. Braking occurs
obviously when you apply the brakes but also occurs every time you let
up on the gas. In an electric car a lot of this brake energy
especially the latter is recovered. In an electric car the motor
control unit acts a a continuously variable transmission that keeps
the power closely matched to the required load in a gas vehicle all
you have is a few preselect ratios from the transmission to select
from. Actually you only have one to select from under typical driving
regenerative braking puts roughly the same amount of energy back in
as was required to accellerate the car to speed in the first place, or
to take it up the hill if you are coming back down. Not 100%, for
sure, but likely better than 75% on today's sophisticated hybrids.
On Tue, 15 Mar 2011 17:30:52 -0400, firstname.lastname@example.org wrote:
Considering the efficiency of an electric motor, I'd say 75% is *way* high.
Remember, you lose energy in both directions and you can't recapture it all
anyway (or there would be no need for conventional brakes).
The nice thing about the concept of an electric car is that there is the
possibility of eliminating the need for fossil fuel to operate it. Yes, you
still need a souce of energy to provide the electricity, but that source can
be derived from hydroelectric, nuclear, wind, or solar sources.
They also do not put out any pollution from the tailpipe, and are quieter.
On 3/15/2011 2:08 PM, email@example.com wrote:
What happens every time a Conservative business group tries to build a
nuclear power plant or hydroelectric dam? I seem to recall a woman
drowning Democrat blocking construction of an offshore wind farm because
it would spoil his view of the ocean. I'm sure some left field
religious group will file suit against a solar power plant because it
steals the life energy from The Sun God. Tell me, how do you store the
power from a wind or solar power plant in a practical manner for later
use or for when there is no wind or sunshine?
All laudable effects, but the electric car devotees are missing the point.
The market for a car that only goes 80 miles on a full charge is minuscule.
My vehicle gets more than 250 miles on a tank of gas and I can "recharge" it
in five minutes at any of scores of "filling stations" encountered during
that 250 miles.
If someone drives 30 miles to work with the lights and A/C on, there's a
good chance he won't make it home.
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