Oven Controls Build

[ed_denu]

This thread is intended to document an electrical control panel build for use with a powder coat oven.

Legal Disclaimer:

Warning – All wiring projects involving AC voltage are inherently dangerous and can cause serious injury or death if done improperly. You assume all responsibility for the electrical work that you perform and the dangers involved therein. If you are at all unsure about completing any aspect of this or any other wiring project, consult a qualified electrical contractor to perform the service(s) for you.

Always follow electrical code requirements specific for your location. Before undertaking any electrical project contact your local electrical authority and your insurance company to ensure that you comply with all policies, regulations and authorities concerning this work.

I’m using a PID, Timer, SSR, alarms, switches, etc. Some of the steps are obvious, but this step by step procedure may provide some guidance for anyone considering their own oven control build.

Before purchasing components determine what capabilities you desire in the operation of your oven.

Do you need ramp/soak capabilities from the PID controller which would allow you to control the rate of temperature rise in the oven ?
Do you desire a built-in timer function that will turn off the oven elements after the cure cycle is complete?
Do you want internal lights and or a recirculating fan, high temperature or timer expiration alarms?
Do you prefer an SSR or Contactor relay to control the oven elements?
Have you determined the wattage necessary for the planned oven size?

These are all questions you need to answer before purchasing components and starting construction of the control unit.

Purchasing considerations: When purchasing, the first consideration is to make sure all components are compatible.

PIDs - Most of the lower priced PIDs such as the TET-612, JLD-612, TC-408, Auber SYL-2362 are capable of driving either an SSR or contactor and have 2 sets of output relay contacts for alarms. However, if any of these models are used to drive a contactor(versus an SSR), then one set of output contacts is consumed for use by the contactor.

Ramp/Soak controllers such as the Auber SYL-2342(contactor model) and SYL-2352(SSR model), only have one set of output contacts for alarms.

Higher end controllers such as the Watlow Model 93’s are configurable in many designations, so before purchasing one of these models be certain that it is configured to suit your requirements. One nice advantage of using a Watlow is that they are made in the USA and can be repaired if they malfunction, unlike the Asian offerings.

Most PIDs, regardless of the model, can support (2) SSRs or (4) contactors if multiple relays are necessary for your configuration.

SSR’s and contactors - The decision of which type relay to use is a personal choice imo. Some sort of relay is necessary as the PID controller internal circuitry is not capable of directly switching the amperage loads of a typical oven heating element(s).

SSRs by design are capable of switching multiple times per second and have a switching life usually in the millions of cycles. They have no moving parts and accomplish the switching by use of semiconductors. The switching process generates heat so a good heat sink is necessary. They can fail either open or closed so if overheating is a concern then use of a high temperature alarm could be considered.

SSR’s typically switch only one leg of a 240 volt power requirement for elements so be certain to disable the electrical mains power supply prior to working on the elements.

SSRs can be found in either AC or DC input voltage models, with the DC version being the most common.

Computer fan/heatsink combinations work well for cooling but these fans will require a 12VDC power source(discussed more in the build section).

Contactors are electro-mechanical relays that open and close contacts using an electromagnet coil. Their switching produces an audible click/clack sound and their life expectancy is normally in the hundred thousand cycles.

Contactor models can be found with input coil voltage requirements in many variations of AC or DC voltages so be certain to get one that matches your intended power supply. A 120VAC coil contactor is probably the most commonly used type in Powder Coating ovens.

Contactors also come in various pole or contact sets. For a 240 volt oven a 2 pole is most commonly used. If you have a higher amperage load requirement the element loads can be broken up and switched over a 4 pole contactor of a lesser amperage rating than what would be required if using a 2 pole model.

When using a contactor, the PID parameter controlling cycle time must be reduced to slow the on/off cycling process or the contactors life expectancy will be reduced.

Timer, toggles, alarms, etc. - In the build section I will discuss a number of components I have found to work well. This is not an all inclusive list and there are many choices of components. At the very end of the build I will list some sources I’ve found for various components.

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Construction of the Control Box:

After you have acquired the components for the oven build lay them out and determine the size necessary for the physical housing. If you have access to a drawing program these can be very useful in creating a scaled drawing for layout of the control box.

I’ve chosen to place the physical controls(PID, timer, switches, etc.) on the side of the control box rather than the lid or door. There are two advantages I see in this choice. By placing them on the side they are visible from the oven front so side access to the controls is not necessary. The other advantage is that if these components are not placed on the door, then there is no danger the wiring will be pinched by opening/closing the door.

The square cutouts for the PID and similar instruments can be made using a Dremel with small cutout wheels. Round openings are most easily made using step drills.

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Once the openings are cut, fit the components into place. Then layout the internal components giving thought to the wire routing. The recycled control box I found didn’t have an internal mounting plate so I constructed one from sheet metal and mounted it to the control box using standoffs.



I like to use appropriate colored wiring. I use multi-strand red and black for the hot feeds, white for neutral, and blue for all low voltage DC wiring. Wiring internal to the control box can be 14 or 16 gauge for all pid and timer power, light, fan wiring, etc. Once wiring exits the box into conduit runs then NEC rules apply for wire gauge and maximum allowable conductors within a conduit. Wire gauge for the circuit wiring powering the elements thru ssr’s and contactors needs to be sized appropriate to the element load. Larger gauge wire is marked with colored tape.

I use crimp terminals for all wiring being placed under terminals. The multistrand wire does not work well under screw terminals without terminal ends attached. The power block connections do not require terminals. Smaller switches and indicator lights work best by having the wire soldered to the connector tabs.

Power to the box is first routed thru the Master Disconnect at the top of the control box. A master disconnect is important imo as it removes all power to the oven when not in use. Alternately you could use a plug and receptacle or use the service panel breaker as a disconnect.

When I started this construction the disconnect switch panel mount kits weren’t available so I improvised and made my own panel mount(see picture below). The output from the disconnect routes to the power distribution block. From there, the various power connections can be made. I like the power blocks versus terminal strips as they typically take less space within the control box. I’ve added a main power indicator light to alert me that the main power is enabled to the controls. The flexible power cord is a Service Cord of the appropriate wire gauge from McMaster Carr.

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I’m using two fuses. A small ½ amp fuse is used to protect the Watlow and Omron. The other is a 30A fuse adding additional protection for the element load. My load is around 22A so the 30A fuse should be adequate. The oven is connected to a 30A circuit wired with 10 gauge and a double pole 240 volt breaker.



The light/alarm buzzers I’m using have 120VAC inputs. One is used for the timer expiration event and the other is a high temperature alarm controlled by the PID.

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The toggles for the light and fan have internal lights incorporated into them. It shows you at a glance if the light and/or fan are enabled.

The PID I’m using is a Watlow model 93AA-1CD0-00RR. It’s a ramp/soak model for use with an SSR and has a single electromechanical relay that will be used to drive the high temperature alarm. I’m using a computer heat sink with fan to keep the SSR cool. I drilled 2 small holes in the heat sink base to mount the SSR. Make sure to apply the dielectric grease before mounting the SSR. The SSR/heatsink components are mounted on a pvc plastic base to isolate it from the control box.

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The heatsink cooling fan requires a 12VDC power source. I’m using a Radio Shack stepdown transformer and a small regulated rectifier power supply built on a bread board to convert the transformer’s AC current to DC. Another option would be to use a plug-in charger typically used to charge small battery powered appliances. Just check the output voltage to ensure it conforms to the fan’s specifications.

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The timer is an Omron H3CA-8 model. It is a countdown timer capable of timing from 0 to 0000 seconds/minutes/days. These timers come in various models(seconds, minutes, days) so be sure to get one that meets your requirements. It has (2) sets of output relay contacts. One is used to drive the DC input signal from the PID to the SSR(this allows the timer to turn off the element heating function) and the second is used to sound an alarm at the expiration of the timed event.



The (on/off/on) switch adjacent to the Omron timer allows for manual or timed mode. In the off position the elements are disabled but the PID is energized for parameter changes and temperature readouts. In the manual mode, the PID engages the SSR and will manage to the set point. You can then monitor part metal temperature prior to starting the timed cure cycle. Switching to the timer position begins the timed cure cycle based on the timer’s setting. At expiration of the timer, the elements are disabled and the audible alarm sounds. Switching the toggle to the off position silences the alarm.



Toggle/Timer operational notes: The toggle is wired so that in the off position the PID remains powered on, but has no control over the elements. If the toggle is switched to either manual or timed mode, then the DC power feed from the PID is fed thru the Timer Relay 1 NC contacts to the SSR and the PID can manage to the Set Temperature. The Timer relay contacts change relationship(NO/NC) at expiration of the timer, therefore when the timer expires, the Relay 1 switches to the NO position and the DC power feed from the PID to the SSR is opened. The high temperature alarm functions in a similar manner as it is connected to the NO contacts, so when the Timer expires the Relay 2 contacts change from NC to the NO position and the alarm sounds.

The (on/on) switch adjacent to the pid is used to switch between (2) TC’s. One TC has a clip-on probe(to monitor part temp) and the other is a more typical TC monitoring oven temperature. Routing two TC’s thru a switch doesn’t appear to materially affect the temperature reading of the TC.

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I’ve also added an ammeter to the controls. It’s certainly not a requirement but it can give me amperage reading at a glance to verify all elements are working. The ammeter comes with a shunt that needs to be included in the element circuit. The meter only functions when the momentary switch wired into the circuit is pushed. It’s not practical to have the ammeter wired for constant readout as it would be flashing rapidly between zero and the high amperage readings once the set temperature is approached and the PID begins cycling the elements on/off.

I will post pictures later of the control box mounted to the oven. I hope to have this complete in the next week or two.


I hope this information is helpful to anyone contemplating a control penal build.

[ed_denu]

The forum software only appears to allow 2 pictures per post. Here are a couple of additional pictures of the component layout and the beginning of the wiring.

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Here is a picture of the ammeter with shunt and a picture of the base and mounting bracket for the Omron. The Watlow also requires a mounting bracket to hold the PID within the cutout. The base and mounting brackets can often be found with the units, or can be ordered separately.