Kelly Savino on sun 15 nov 09
This is very useful info from Michael Wendt and belongs in the clayart arch=
ives. Thanks for taking the time, Michael!
http://www.primalpotter.com (website)
http://primalmommy.wordpress.com (blog)
http://www.primalpotter.etsy.com (store)
--- Begin forwarded message:
From: Michael Wendt
To:
Subject: Re: Dirty voltage?
Date: Sun, 15 Nov 2009 15:40:25 -0800
Kelly,
I am writing you directly because so many people complain on
clayart about having to skip over or delete information they
do not want to know. Share it with clayart if you find it of
use to you.
If you will check to see if the wiring is otherwise adequate
for your kilns, I propose an easy fix:
replace your 240 volt elements with standard 208 elements.
Here is a chart of the values I created in Lotus 123
spreadsheet
kiln's total
voltage resistance amperage
wattage
208 5 41.6
8653
215 5 43
9245
220 5 44
9680
230 5 46
10580
240 5 48
11520
From this chart , you can see that the reason you cannot
reach temperature is your elements have too much resistance.
I simply plugged various values of resistance into the
spread sheet until I got the same wattage at 208 volts that
the original 240 volt design was meant to produce.
At 3.7 ohms, here is the result:
208 volts / 3.7 ohms =3D 56.2 amps
208 volts x 56.2 amps =3D 11,693 watts compared to the
original 11,520 watts at 240 volts.
Be aware that these are hot resistance values and the cold
values ( 4.625 ohms ) are higher. This is the required
design value for the entire kiln and since there are 3
elements in parallel, they each have 3 times the resistance
cold (4.625 X 3 =3D 13.875 ohms ).
If the circuit will not support that amperage, you can do as
I suggested earlier and disconnect the bottom elements and
raise the bottom of the kiln higher by lining it with
insulating firebricks topped with kaowool. I've done this
before when I needed to fire a small load and it works well.
Write me if you need more info. Regards,
Michael Wendt
mwendt@wendtpottery.com
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