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Tom Bloyd
01-31-2012, 09:08 AM
I'm looking to put an over temp limit on a new kiln. Any suggestions?

Pete VanderLaan
01-31-2012, 10:50 AM
I'm looking to put an over temp limit on a new kiln. Any suggestions?
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We wire it in with the door kill switch both of which control the main relay. If either of them breaks the circuit, it goes down. I would do it through an ice cube relay since the draw on the controller will be an issue.

Tom Bloyd
01-31-2012, 11:45 AM
Sorry I meant for an annealer. I've seen a seperate cube from watlow, but can't seem to find it. I want it to shut off about 1100 in case a relay sticks on. It's going on a mechanical relay 220 30 amp unit.

Pete VanderLaan
01-31-2012, 12:25 PM
We used the overlimit controller from watlow and would still do it the same way Tom. Ice cubes are certainly available from Graingers A kill circuit is a kill circuit. What you want to do implies two relays to me. One usually open all the time, the other managing the on off requirements of the annealer. I would use the ice cube to drive the normally open mechanical relay unless the soleniod requirements are under .2 Amp. Messy.

Tom Bloyd
01-31-2012, 12:35 PM
Thanks Pete. Yeah, I was thinking two relays. I'll talk to watlow and see what they come up with. I saw one that was like a hockey puck that had it's own thermocouple and a preset limit built in it, that was normally open. This was ten years ago. Thanks for the help

Scott Novota
01-31-2012, 02:07 PM
I feel like I totally misunderstood this question.

Nothing new there. So I will just remove my clearly out of scope post.

Tom Bloyd
01-31-2012, 02:43 PM
Scott. I was to vague. I know better than to post first thing in the morning before I've had any coffee.

Tom Clifton
01-31-2012, 03:10 PM
an annealer..... It's going on a mechanical relay 220 30 amp unit.

Pardon the intrusion of a newcomer. On the assumption that you are talking about a 220v annealing kiln, you can use nearly any modern ramp/soak controller - Watlow, Partlow, Fuji etc. (your choice depends largely on the service you receive from the tech guys more than cost) Drive your primary load heating elements off a pair of hefty Solid State Relys for the annealing process but stick with the mechanical relay on the alarm output. Be sure to have it fail open in the event of a power loss to the controller as the 110v control circuit may well be separate from the 220 power.

If you want an absolute fail safe - use a separate controler for the over temp from the process control.

Pete VanderLaan
01-31-2012, 03:23 PM
The purpose here is to keep a load of glass in the lehr from melting down. The trouble with mechanical relays is that when they fail, they almost always fail open with welded points which says that the 240V needs to be cut at another source since this relay is one stuck puppy. It implies a second master relay which almost never gets thrown and should run the fail safe. MDR is a lot safer than Mechanical, but are getting hard to come by.

What to watch out for here is using the alarm or overtemp to run a solenoid on a relay that draws too much amperage. The controller really usually wants to handle no more than .2 amp and will fry if you try to push too much through it. Why, you might ask do I know this? Thus, the icecube relay which has this teensy solenoid in it. .

Tom Bloyd
01-31-2012, 03:37 PM
Yeah I'm stuck with this mechanical relay, because that is how this Digitry is set up. I know they like to fail on, so I'm trying to figure a way to make this work. I'm using this annealer for a special project. This system usually runs my pickup oven so it's never running when I'm not around.

Tom Clifton
01-31-2012, 04:15 PM
It implies a second master relay which almost never gets thrown ... MDR is a lot safer than Mechanical, but are getting hard to come by.


I quite agree about a second relay and that was the intention of my remark. I'm going to stop at that as every time I get sarted talking about the operational cycle life of Mechanical, Mercury and Solid State Relays, Power relays vs control relays I don't quit and I really get annoying.

Keep your glass hot. Tom

Pete VanderLaan
01-31-2012, 05:37 PM
You are certainly welcome in your observations Tom. When I really think about it, MDR's on my lehr's have lasted about 20 years. I went through a period where they failed a bunch around the year 2000 on some I bought from a surplus place. I do not trust low end mechanicals at all even for short periods. The Cutler Hammer 150 AMP ones I use for the molys are very nice.

The irritant I have and I don't know if other controllers do it, but LOVE will, if sitting after running a program, reverse their program if there is a power failure. It means you have to be really careful about leaving the lehr door open after emptying it. If I am leaving the shop for any length of time, I have to turn off the power completely to it.

And if you're not annoying, you're not participating.