Tom Buck on wed 8 may 02
Martin Rice, of Costa Rica:
just in case no one else replied: there are three types of switches
commonly used on pottery kilns with their high current demand.
the simple on/off switch that will handle 15+ amperes; generally
used for one circuit only, that is, ONE element loop (loops). called heavy
duty switches by electricians.
three-way switches. an extension of the one-way switch. the
settings are Low, Med, High. and a switch usually handles TWO elements.
LOW means the two elements are connected together in series (hence, higher
resistance, lower current draw); Med means ONE element only (the kiln
builder/designer chooses which one); and High means both elements in
parallel, or maximum current draw in both elements.
and the "infinity" type switch which is actually a "rheostat" or
"potentiometer" that controls the resistance of the circuit such that the
current in the element will vary from zero to maximum. ONE element only.
if you have five elements and five switches, then chances are
that each is an "infinity" type.
til later, Peace. Tom B.
Tom Buck ) -- primary address. "alias"
or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
Snail Scott on wed 8 may 02
At 10:54 AM 5/8/02 -0400, Tom wrote:
> and the "infinity" type switch which is actually a "rheostat" or
>"potentiometer" that controls the resistance of the circuit such that the
>current in the element will vary from zero to maximum.
A rheostat is one type of infinite switch,
but I don't think I've ever seen a kiln with
rheostat-type switches. A true rheostat will
give continuous power, but at varying levels.
The only type of infinite switch I've seen in
kilns is the sort that always delivers full
power, but at intervals of varying length.
(That's the 'clicking' noise.)
Are there really kilns with rheostat switches
out there?
-Snail
Tom Buck on thu 9 may 02
Ah me!
George Wendt is right, my use of the word rheostat was unwise, a
poor choice....comes from studying Electricity & Magnetism too long ago.
The infinity type switch does indeed use a reed (bimetallic strip)
to control the current flow. It does so by setting the time the current is
on at each setting of the switch, as in a kitchen range. and it does so in
the manner George described.
If your kiln is in a quiet place, you can hear the "hum" when
power is flowing through the element; and hence hear when the "hum" stops.
later. Peace. Tom B.
Tom Buck ) -- primary address. "alias"
or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
Michael Wendt on thu 9 may 02
The switches used on most kilns today are the same in principal as those
used to control the elements on the range top. I took one apart after it
quit working and found a bi-metallic strip that works like a thermostat in
response to heating due to current flow. When the switch is set low, the
internal contact breaks early in the heat cycle.The current to the elements
is off until the switch closes again. At higher settings, the switch takes
longer to break contact. On the Cress kilns I have worked on, the switches
control high power relays that actually do the element control switching.
One note of interest, I have used high power solid state controls on small
kilns like the one I am building for my dilatometer project, but even they
switch the power on and off , just at 60 cycles per second.
Rheostats would need to be enormous to pass the wattage a kiln uses andwould
be very wasteful since a rheostat uses electrical resistance to impede
current flow and thus generates heat.
Regards,
Michael Wendt wendtpot@lewiston.com
Wendt Pottery
2729 Clearwater Avenue
Lewiston, Idaho 83501
1-208-746-3724
wendtpottery.com
others wrote:
At 10:54 AM 5/8/02 -0400, Tom wrote:
> and the "infinity" type switch which is actually a "rheostat" or
>"potentiometer" that controls the resistance of the circuit such that the
>current in the element will vary from zero to maximum.
A rheostat is one type of infinite switch,
but I don't think I've ever seen a kiln with
rheostat-type switches. A true rheostat will
give continuous power, but at varying levels.
The only type of infinite switch I've seen in
kilns is the sort that always delivers full
power, but at intervals of varying length.
(That's the 'clicking' noise.)
Are there really kilns with rheostat switches
out there?
-Snail
| |
|
