RE: [atlas_craftsman] A bunch of motor questions - single and three phase
- All ,
Richard makes a couple of interesting points , and I think the "slippery
belt" mechanical fuse needs to be more widely publicized .
Something which has not been mentioned in this thread , is the option of
using a 3 phase motor on single phase , with some saving in the upfront
Often surplus 3 phase motors are available considerably cheaper than their
single phase equivalents on the surplus market , and will deliver about 75 -
80& of their rated power on single phase . So a I HP 3 phase motor will
easily yield 0,75HP on single phase . Depending on the configuration often
all that is required is to strap the motor in its Delta configuration , so
that its rated phase voltage equals the applied line voltage and use a 50 -
70 microfarad motor RUN capacitor to the third phase point . Reversing is a
doddle , as all that is required to swop the supply line wire between the
two phase points that the capacitor is connected across , and a simple SPDT
(centre off) switch will suffice ,
If this description doesn't make sense , then try the following -
( This applies to a motor which is rated at 380v 'star' or 220 v 'delta' ,
and is to be used on a 220v single phase supply)
Draw the 3 windings of the motor in the form of a triangle ( referred to as
the 'Delta' connection )
Label the three points of the triangle A, B, and C
Connect the capacitor between B and C .
Connect the Neutral or Common ( 0 v) leg of the supply to A
Connect the Line leg ( 220v) of the supply to B ( forward) OR C (reverse) .
Kind Regards, Carvel
[mailto:email@example.com] On Behalf Of Richard Schaal
Sent: 05 July 2007 05:53 PM
Subject: Re: [atlas_craftsman] A bunch of motor questions
To put it another way, those peak load vs time meters tend to teach your big
consumers to move their peak load to a different time. Example: When I was
AZ, the time between 9PM to 4AM (approx) received a lower rate for energy
the time from 9AM to 4PM.
Regarding the motors, one might presume that if you are only using 1/2 HP of
energy, it wouldn't really matter if the motor was 0.5HP or 5HP. It all
the same... That would be mostly correct as far as the power company goes,
if you make a MISTEAK and start grinding up gears, it will cost you a whole
more at Ebay if you mounted a 5HP motor than the 0.5HP one.
I'm somewhat surprised that you ( the experts here ) didn't apply some sort
proficency (in lathe ops) limiter to the question regarding which motor to
where beginners might use 0.5HP, journeymen could effectively use 0.75HP,
masters could safely use 1HP for the subject lathes.
For me, I've been saved the big bucks on several occasions when my belts
slipping... telling me to make lighter cuts.
Truly, the most expensive substance on the planet is powdered ZAMAC!
- I don't know about the large industrial or commercial installations, but I
am familiar with the time-of-use meters. Our house has a photovoltaic
(solar panels) system installed, as well as a digital time-of-use meter.
For energy used during the peak period, roughly 7:00 AM to 5:00 PM on
weekdays only, we pay a higher rate than normal, 15-20 cents/KWH I think.
The rest of the time, we pay roughly 7-10 cents/KWH. There are two
advantages to this system. First, we use most of the appliances like the
washing machine, dishwasher, etc. during off peak hours anyways since the
peak hours usually happen during work, when nobody is home. Secondly, when
the photovoltaic system generates electricity, it runs the meter backwards
at the time of use rate. In other words, during the middle of the day, we
make electricity at the 15 cent rate when the solar is most efficient but we
use mostly at the lower rate. As a result of the time of use meter, we are
also on the same billing system as the industrial customers, where we get a
monthly statement but only pay the bill yearly, where the generation and the
usage balances out. If we make more electricity than we use over the entire
year, we have just donated this to the power company, but usually
over-generation in the summer is balanced out by usage in the winter (since
the photovoltaic cells don't reach their full 3 KW capacity with the less
sunlight in the winter).
On 7/5/07, xlch58@... <xlch58@...> wrote:
> Richard Schaal wrote:
> > To put it another way, those peak load vs time meters tend to teach your
> > consumers to move their peak load to a different time. Example: When I
> was in
> > AZ, the time between 9PM to 4AM (approx) received a lower rate for
> energy than
> > the time from 9AM to 4PM.
> Actually, there are several different tarrifs. The peak meters, or more
> usually called demand meters look at the highest draw for a
> 5/10/15/30/60 minute interval for the customer during any billing
> period, or sometime year. They are there to encourage the customer to
> reduce their peak draw. So for factories or shops, don't start all of
> your machinery at the same time. For normal offices, stagger your AC
> units so that they don't come on all at once. The power company has to
> size the transformer and lines supplying you for the highest peak
> usage. Time of use rates that you are describing address a similar
> problem, but on a much larger scale. In that case , the power company
> has to have enough generation, transmission and distribution capacity to
> satisfy the peak periods of usage in the day for all of their
> customers. They can give larger customers a break on their charges for
> moving their usage "off peak". Some states have instaitues time of use
> for residential as well. AC HVAC loads are hard to move in a
> residential situation, but you can do things like not run the pool pump,
> or irrigation pumps during the day.
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