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element life and slow cooling: now relays, long

updated sat 13 nov 10


William & Susan Schran User on fri 12 nov 10

On 11/12/10 12:08 AM, "David Martin Hershey" wrote:

> FWIW, I've had very good element life
> on my heavily used vented Skutt KM 1027.
> I've fired down on almost all firings,
> bisque ^04, and glaze ^5-6.
> I don't stuff the kiln full every time.
> That may be helping.
> However, I've not been so lucky
> with the relays. Don't know if it's related
> to the firing schedule, or what.
> After the last failure,
> Skutt sent me a re-designed relay package.
> We'll see how they hold up.

On a crystalline glaze forum there has been lots of discussion about SSR's,
Solid State Relays. Those doing crystalline firings really abuse our kilns
and elements. One of the forum members is building and retrofitting kilns
specifically for the demands of a crystalline firing cycle, including a
reducing capability! I know one kiln manufacturer has built some proto-type
kilns with the SSR's and they are out on trial with crystalline glaze
potters to see how they stand up.

Here's a posting from the forum about using SSR's:

"For a 3 zone kiln you will need three SSR=3DB9s their rating must be 120% =
than you expect to draw through each relay, and must have a heat sink.

I use the Bartlett control board, which is common here in the States.
It uses 12Vdc for the outputs.
Assuming you kiln is like our typical hobby Kiln with a Bartlett controller=
most 10 to 12 sided kilns use from 15amps to 20amps per zone or section.

Each section will require one 25amp SSR ( 20 X 120% =3D3D 24amps ) or a 25 =
I expect the relay will be in the control box and it will be warm in there.
To ensure long life assuming 50=3DB0 to 60=3DB0c inside the control box you=
need a
larger than normal Heat Sink.
Start with a Heat Sink with a dissipation rating: 1.0=3DB0C/W and add a coo=
fan. If you know that the ambient temperature is less than 40=3DB0c the fan=
not required.
Here is a typical wiring of a SSR.
Connection 3 and 4 is the Control voltage (12vdc) from the board Positive
and Negative must be observed.
Connection 1 and 2 is the AC line voltage. One side of the AC line (a phase=
connects to one end of the elements; the other end of the elements connects
to the SSR at connection 1, connect AC line (b phase) to connection 2,
that=3DB9s all it takes for a simple set up. "

The author of this forum thread contends using SSR's will extend element
life and that is why there are a few test kilns out there. We shall see.

William "Bill" Schran