Does the digital controller have a way to prevent an over fire?

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Does the digital controller have a way to prevent an over fire?

Once the kiln is properly calibrated after the test firing, it will fire very reliably for many firings.  The digital controller achieves this reliability by constantly comparing the thermocouple (TC) readings to the program that it is following.  Having multiple TCs in the kiln makes this a redundant operation as well. While calibration issues like firing a little too hot or cool are common, it is very rare to hear that someone seriously overfired a digital L&L kiln.

That said, there are still a few ways to seriously overfire the kiln that the controller cannot prevent. Here are some examples:

Stuck relay

  • The relay is told by the controller when to turn power on and off to the elements. It makes the clicking sound in the control box

  • If the relay sticks closed- fails and stays on all the time- it will not turn off from the lack of a signal from the controller, like it should. Even when the controller says the program is complete or shuts off with an error code because the kiln is climbing so quickly, the temperature in the kiln will continue to climb.  This is only the case in small kilns that have just one relay.
  • Larger kilns and kilns with more than one TC have multiple relays. If one relay sticks closed (on) then the elements will be on all the time in part of the kiln, not the whole kiln. Even having half the elements on all the time is not enough to overfire the kiln.
  • In theory, more than one relay could fail stuck closed (on) at the same time. But the likelihood of it happening would be incredibly small.  Most relays fail open (off) when they fail.

Thermocouples (TCs)

  • If there was just one TC and it was not all the way in the kiln, but in far enough to feel some of the heat- that could overfire the kiln.

  • Most L&L kilns have more than one TC, bolted solidly to the side of the kiln, and the controller will shut the kiln off with an error code if the TC temperature are too different from the program.
  • Another way would be if you had the wrong Type of TC connected to the controller. The controller can be set to read a Type K or Type S TC. As a safety a little jumper on the circuit board itself must be moved to correspond with the K or S setting. An E- 9 error code will result if the jumper and setting do not match. But if the jumper and setting do match say for Type K and you hook up a Type S TC, the kiln will overfire.

Wrong Cone Number or Hold Time

  • While the controller will not allow you to program any cone over cone 10, you could accidentally program Cone 6 when you meant to fire to Cone 06.

  • Or you could put a 10 hour hold at the top temp when you only meant to put a 10 minute hold there. The kiln would be ruined if you held for 10 hours, even for just 1 hour, on a cone 10 firing.
  • Minimally the clay or glass in the kiln would be ruined with too long a hold at a lower temperature.
  • With all this in mind- one can see it is possible, but unlikely a digital L&L will overfire.
  • We highly recommend that the operator monitors the firing and is present when the kiln is to shut off. That way any chance that it might overfire is removed. Overfiring for any reason is not covered by the 3 year factory warranty.

Additional Actions to Take

  1. Make sure you have programmed the kiln properly and it is supposed to be firing.
  2. Read the Operation instructions.
  3. Do a Program Review as soon as you start firing. (For DynaTrols - see this video)
  • Power relays are one of the most important components in your kiln. They execute the will of the computer controller, giving power to the elements only when requested. These power relays are also mechanical switches which will wear out over time. Worn out relays can be the cause of slow or incomplete firings, error codes (E-1, E-d), etc. Other more obvious signs of relay failure are if a zone is lagging behind in temperature considerably or if you notice an entire ring of elements not heating/glowing. 
  • The surest way to test your relays is by using a multimeter to check input, output, and signal voltage. If you do not have access to a multimeter you can run a paper test, which will give you some indication of whether or not you have a relay out.

Process

  1. One way to check the relays (or bad elements) is to check the temperatures of each zone by pressing "1", "2" and "3" in sequence and recording the temperatures of each thermocouple at intervals over the length of the firing. If one zone is consistently firing at a lower temperature then you probably have either burned out elements or a bad relay.
  2. If the relay does not make a soft clicking noise when the kiln is turned on try turning the kiln off and on and then restarting the program.
  3. Remove panel.
  4. Set your multi-meter the approximately 24 volts AC. Check the voltage coming into the coil of the Power Relay. You can tell which wires these are because they will be the small wires coming from the control. This test will tell you if you are getting power to the relay coil which actuates the relay. Unless the relay is actuated by the control you will get no output from the power side of the relay.
  5. With panel plugged in and firing check output from Power Relay with your digital multi-meter. The meter should be set to the next highest voltage above 240 volts AC. Output should be approximately the rated voltage of the kiln when it is supposed to be calling for power to the elements.

CAUTION: LIVE ELECTRICITY IS INVOLVED WITH SOME OF THESE TESTS. This test should only be done by an experienced person familiar with electricity.

  1. Carefully examine thermocouple tip. This is the exposed welded joint at the end of the thermocouple that is not covered up by the ceramic tube.
  2. To do this you will have to remove the thermocouple from its protection tube (if it is a kiln that has one of our protection tubes). You can do this with the kiln disconnected from power.
  3. Look for corrosion - especially if it severe. These thermocouple tips will oxidize and otherwise corrode over time. That is normal. There is some point, however, at which the corrosion affects the ability of the tip to work (thermocouples work by generating a small voltage at the tip caused by two different metals reacting to each other).
  4. Corroded thermocouple tip

  5. Make sure the two wires are securely joined. One of the things that can cause an intermittent problem is a bad weld. If the two wires touch each other (even if they are not welded) they may work temporarily. However, if the weld is not secure then the wires could separate when the kiln heats up and cause an intermittent failure.
  6. If the thermocouple tip looks healthy then test the control board.

  1. Unplug kiln or turn off circuit breaker if the kiln is wired direct to your power supply. If you can not physically be sure the power is disconnected (for instance is you see that the cord is unplugged you KNOW there is no power coming into the kiln) then check the voltage at the power connection pluck with your multi-meter.
  2. Open up the control panel. This will be a little different on each kiln series.
  3. Remove or open the panels that cover the element connections.
  4. Look at internal wiring.
  5. Images burned wires in a kiln

  6. Check the tightness of all connections. Do this by wiggling the connector to make sure nothing is loose.
  7. Make sure all wires are connected to their proper connection point. You may have to compare the kiln to the wiring diagram to be sure of this. This step would be particularly important if a wire has come loose.
  8. Specifically look at wires going from power connection block to the on/off switch, then to the control fuse, and finally to the control transformer.
  9. Make sure all wires inside control panel are connected.
  10. Look for any burned spots or deteriorating wire.
  11. Look for any short circuits. This might be caused by a wire losing its insulation and touching another component for instance. Typically if there are any short circuits there will be some evidence of a burn on the metal the wire touched.
  12. Look for dirt or foreign material. Some material can be an electrical conductor and could cause a short circuit. Clean out any dirt.
  13. Pull off and reseat all spade connector connections of power wires to remove oxides and ensure good connection.

CAUTION: Turn power off to kiln from the circuit breaker or unplug the kiln.

  1. Unplug kiln.
  2. Remove the control box and the insulation panel.
  3. Remove the wires to the relay.
  4. Remove the nuts from the studs that hold the relay in place. Remove old relay and replace with new one.
  5. Visually inspect the wire connectors. Do they look corroded or "cooked"? Are the wires frayed? Any corrosion on the wire itself? If any of this is questionable you should replace the appropriate wires.
  6. Reconnect all wires. Visually inspect to make sure the spade connectors are down as far as they can go and feel to see that they are tight (a gentle tug should not remove one). If they are loose for some reason remove the wire and slightly squeeze the spade connector with pliers to tighten it.

IMPORTANT: The slip on wire connectors cannot be loose or corroded. If there is a bad connection then heat will be generated and the component that they slip onto (relay, terminal strip, etc) may overheat and fail. If you squeeze the slip on terminal to make it tighter–be sure to squeeze it evenly so that one side is not tight and the other loose. If there are any doubts about the integrity of the wire or the connector replace the whole wire or harness.

 

How to check a relay in an Easy-Fire Kilns

  1. Similar in any L&L automatic kiln.
  2. Follow proper electrical safety practices.

Parts

  1. See this page for the 12 Volt 30 Amp relay we use for most kilns.
  2. See this page for the 240 Volt 30 Amp relay we use as a control relay for 480 volt kilns.
  3. See this page for all contactors and relays.

 

How to change a relay in an Easy-Fire Kilns

  1. Be sure to keep the wires on in the right sequence when changing a power or control relay in an Easy-Fire, Easy-Fire XT, School-Master or eQuad-Pro Kiln.
  2. The configuration is similar in a Jupiter panel or as control relay in a DaVinci, Hercules, or Easy-Load panel.
  3. Make sure kiln is unplugged or locked out and tagged out at the circuit breaker or fused disconnect switch when doing this maintenance.

Parts

  1. See this page for the 12 Volt 30 Amp relay we use for most kilns.
  2. See this page for the 240 Volt 30 Amp relay we use as a control relay for 480 volt kilns.
  3. See this page for all contactors and relays.