DTB4824 temp controller

I am using a DTB4824 controller on an oven. I have a type J thermocouple. There is 240VAC at terminal 1 & 2. I have my control wires hooked to terminal 7 & 8. This excites a coil on the contactor that draws less than 0.05 amps. Why does the controller not last more than 3 months? Am I not connecting it properly? Is there a set of terminals that would be better to connect to for the output on the contactor?

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What’s the full part number of your controller? The extended digits specify output types etc. which might be relevant. Also, what are the symptoms of failure? Are they coincident with any other sort of event that you’ve noticed?

My first guesses at a cause might be nastiness coming in on the power supply, or damage to the output from a reactive load–speaking of which, what sort of contactor is being driven?

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DTB4824RR if full part number. Contactor is a Square D 60Amp 3 pole 240VAC Coil. Have not been having other issues with the oven. The contacts between terminals 7 & 8 remain open even when the controller is asking for more heat. I have the heating differential set to 30degrees F on the controller. Jake

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Hello Jake,

Welcome to the DigiKey community.

This is my understanding of your oven using the Delta DTB4824RR temperature controller:

Potential issues, in no particular order, include

  • mechanical vibration
  • moisture
  • excessive enclosure temperature
  • relay contact wear / pitting
  • damage to logic board
  • damage from incoming power

My intuition says to use an interposing relay between the Delta controller and the primary contactor. This would reduce the stress on the controller’s contacts. However, I’m not 100% convinced this is the issue. It may also be appropriate to modify the equipment to use an SCR based controller instead of the mechanical contactor.

Could you please provide answers to the following questions to help isolate the issue:

  1. What is the approximate duty cycle for this mechanism? For example, in a 10 minute period, how many times does that primary contactor engage? I see you have the differential set to 30 F which would reduce the cycling, but it may still be excessive.

  2. Describe the enclosure with respect to temperature, humidity, and dust intrusion.

  3. Are there any large motors in the vicinity that could cause power line spikes?

  4. What am I missing? Other DigiKey member may have additional questions.

Best Wishes,


P.S. Out of curiosity, have you attempted to switch and then reprogram to use terminals 9 and 10? Forgive me it this is not possible, as I have not programmed this particular controller.


Note that the RR suffix indicated relay and relay for outputs for channels 1 and 2 respectively.

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Hello. Approximate duty cycle for this oven would be 1 on/off cycle in a 10 minute period. It is a very clean, low humidity, no dust environment with an average temp of 90 - 100 degrees F with the oven running. The largest motor in the kitchen/bakery there would be a 1hp 1ph motor. As far as switching to terminal 9 & 10 I would like that and think it is possible but cannot make the controller do what I think it should and get those terminals to work. Could you give me the sequence to make those terminals work? Jake

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Hello Jake,

That doesn’t seem excessive. However I wouldn’t rule out contact destruction. To be sure, the unit’s contacts are rated at 5A. However, that assumes a resistive load. That heater contactor is sure to have a large inductive kick that causes pitting of the contacts every time they open.

Perhaps we should take a look at the interposing relay another day. However, that does not solve your immediate issue of the broken oven.

\color{red}\Huge \fbox{WARNING}

For readers who are new to industrial controls, we should take a moment to recognize the serious nature of our actions. A mistake could cost money, production time, damage to equipment, fire, or even hurt a person.

As a starting point for all work that involves modifications to equipment there are some critical stipulation:

  • you are qualified to perform the work
  • you understand the risk associated with the modifications
  • you have informed your supervisor about non-standard modifications or operation of a piece of equipment
  • you, along with your supervisor and other essential personnel, perform a risk assessment and safety analysis prior to performing the work
  • you have proper Lock Out Tag Out (LOTO) processes in place
  • you follow all applicable employer, state, and federal guidelines

With that said, I may have found a way to use the group 2 contacts. In involves placing the controller into dual loop control and then shifting to use reverse control. The essential text is highlighted in this excerpt from the datasheet.

Please let us know if you were successful. Assuming this works it will be interesting to see if the controller life extends past 3 months.

Best Wishes,


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