Lance Philip Strugar on sat 18 oct 97
Regarding electric kilns, Lisa Skeen asked:
> 1. Do I need a 3 phase or a 1 phase kiln? I don't know what the phase
> part means.
The electricity that we obtain from our power companies is alternatinc
curent.
The voltage on our 120 volt outlets begins at zero, climbs to about +170
volts,
then falls to zero, then to minus 170 volts, and back to zero. This is
repeated,
in the United States, 60 times each second. Plotting the voltage on graph
paper results in a sine function (remember, from high school trig?). The
120
volts refers to RMS value; root mean squared. If you were to connect the
elements of a kiln to 120 volts DC, the heating effect would be the same as
connecting them to 120 volts AC RMS.
The above description applies to a single phase circuit. This is the kind
of
circuit you'll find in American homes. Homes are usually supplied with dual
120 volt circuits, which provide 240 volts where required. Most electric
kilns run on 240 volts.
In commercial applications, three phase circuits are employed. The sine
waves present in the three circuits still trace out the same pattern 60
times
a second, but the starting points of the three are separated by an eaual
amout of time. Using a circle to describe this, the first phase begins at
zero volts and zero degrees on the circle. At 120 degrees on the circle,
the
second phase starts. At 240 degrees, the third phase starts. This circular
pattern results in very efficient motor operation in a three phase system.
It is irrelevant however, for kilns which produce only heat, not rotational
work.
Three phase service is usually not available in homes in the U.S. (Over-
seas is a different matter.) If you obtain a kiln that was used in a three
phase environment, you should be aware of the potential differences
involved in home installation. (Yes, it was intended.) The voltages that
are typically available in three phase are: 120, 208, 277, 440. Note
that 240 is *not* available. The closest is 208.
The point is that you should check the voltage rating of the kiln, and
make sure it matches your house supply. Adjustments are usually
possible.
This is probably more than you wanted to know about the subject, but
I hope it's helpful.
Lance Philip Strugar
Senior Project Engineer, Boeing (St. Louis)
Jeff Lawrence on sun 19 oct 97
Lisa Skeen was asking about electric kilns and mentioned L&L, Skutt, and
Olympic.
I have a big oval Olympic, a three others that are 28 1/3 wide and X27"
deep: a Crusader, an Aim and a Skutt, which I fire to ^04 2-3 times per week
each.
For me the biggest factor is the difficulty/ease of changing the elements.
The Aim seems more solid in its electrical connections than either the
Olympic or the Crusader. The screw connectors are a breeze to disconnect and
reconnect as opposed to the Olympic crimp connections, which require a
manlier grip than I can generate without coronary risk.
The Crusader is a veteran with a funky clay plate insulater which was broken
into many pieces (some missing) and therefore allows the connectors to short
out on the casing from time to time. Last time I nestled them in some fiber
scraps and havent had the problem more.
The Olympic is a workhorse, but I've changed its connectors for screw-type
ones and wish that its electric housing felt a little less tinny. The only
real problem I've experienced is that 48 Amps is very slow to get to ^5 or
^6. Maybe the new ones have better insulation or pull more juice.
I bought the Skutt new last month and delight in how tight a new kiln is.
That computer controller tempts me with its possibilities -- always wanted
to try some of Conrad's crystalline formulae. The other three I've moved
myself twice, after getting them used. They have seen heavy action and show it.
My bet is that if you get one new and never let muscle-headed movers treat
it like just the brick they think it is, you'll be happy with any brand.
Jeff
Jeff Lawrence
jml@sundagger.com
Sun Dagger Design
Rt 3 Box 220
Espanola, NM 87532
ph 505-753-5913
fax 505-753-8074
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