Electric Heat Sequence of Operation

Electric Heat Safety Circuits

User initiated control commands to preheat the oil or to start a product cook cycle create a demand for the F5 fryer's electric heat system. Before heat can be applied, the control system checks the electronic fuse, high limit, and heating element tilt switch safety circuits to ensure they are closed. Also, the safety circuits are supplied with voltage in series from electronic fuse, to high limit, to element tilt switch as a method of interlock.

Electronic Fuse

Two electronic fuses (e-fuse) are located on the PMU PCB to prevent excess current draw on the 24 volt DC systems. Classified as logic (primary) and device (secondary), the two 2 A electronic fuses provide protection of different PMU controlled systems. The U7 (logic/primary) e-fuse will open if there is an excess current draw by the PMU and High Limit PCB processors and logic systems. Should there be an excess current draw by the high limit circuit, element tilt switch circuit, safety contactor coil, or heat contactor coil the U9 (device/secondary) e-fuse will open. A closed U9 e-fuse is heat system's first step that must be met.

High Limit

Monitoring of each vat's high limit safety circuit is handled by the High Limit PCB. Input to the High Limit PCB is provided by one or two resistance temperature detector (RTD) probes. The RTD probes are mounted to sense and provide element temperature feedback to the control system. Each high limit RTD probe has a baseline of 100 ohms at 32°F (0°C) with increasing resistance as element temperature rises. Should the element temperature reach the high limit set (trip) point, the safety circuit is then opened and heating of that vat is no longer allowed. Heating of the vat will be allowed once the element temperature is below the reset point, and reset switch pressed by the operator.

One High Limit PCB per vat, full or split
Mounted directly to respective PMU
100 ohm RTD probe(s) for element temperature feedback
Full vat has two RTD probes mounted to element
Split vat has one RTD probe mounted per element

Element Tilt Switch

The electric heating element for each vat is able to be pivoted up for cleaning, or down for cooking. Heat should never be applied when the element is in its upward cleaning position. To verify element position, a circuit runs from the PMU through the mechanical tilt switch and back to the PMU. The tilt switch is a normally open (NO) type, and is actuated closed with the element in its downward cooking position. With the element tilt switch closed, the 24 volt DC signal from the PMU runs through the tilt switch and returns to the PMU. Now the control system will allow heating. Should the element be raised, the safety circuit is then opened and heating of that vat is no longer allowed. Heating of the vat will be allowed once the element is lowered into its cooking position. The element tilt switch safety circuit is not monitored with the control in an OFF state.

One element tilt switch per vat, full or split
Mounted to rear panel near contactors
Normally open mechanical switch
Tilt switch is actuated closed with element in downward cooking position

Electric Heat Control

Safety Contactor

Incoming three-phase line voltage is supplied to one side of the safety contactor. Upon toggling the main power switch on, 24 volts DC is supplied to the coils of all safety contactors. At this time, the safety contactors are closed supplying three-phase line voltage AC to one side of the heat contactor for each vat. The safety contactors will remain closed as long as the fryer main power switch is in the ON position.

Heat Contactor

When heat is demanded by the vat's control system a 24 volt DC signal is sent to the heat contactor which closes the heating element circuit providing three-phase line voltage AC to the heating element. Once the oil temperature set point is reached, the control system no longer sends the 24 volt DC signal to the heat contactor coil, opening the element circuit. The heat contactor will continually cycle open and closed as the control calls for heat.

Heating Element

Heat is applied to the oil through three-phase line voltage AC being supplied to the heating element for each vat. Electric heating elements differ depending on the vat type, three-phase supply voltage, and power output.

Full vat element power output: 14 kW or 17 kW
Split vat element power output: 7kW or 8.5 kW
Typical three-phase line voltage AC: 208-240 V and 380-415 V

Heating Element Resistance and Current Draw Chart

The +/- range is as follows -5%/+10% for all resistance readings on the elements.

Vat Type	Power Rating (kW)	Voltage Rating (VAC)	System Voltage (VAC)	System Wiring	System Wiring Type	Resistance Phase-Phase(ohm)	Resistance Phase-N(ohm)	Current Draw (A)
Full	14	208	208	3 Wire Wye	3+G	11.77	-	38.86
		220	220	3 Wire Wye	3+G	13.18	-	36.74
		240	240	3 Wire Wye	3+G	15.68	-	33.68
		220	380	4 Wire Wye	3NG	-	19.76	21.27
		230	400	4 Wire Wye	3NG	-	21.59	20.21
		240	415	4 Wire Wye	3NG	-	23.51	19.48
Full	17	208	208	6 Wire Wye	3+G	14.54	-	47.19
		220	220	6 Wire Wye	3+G	16.27	-	44.61
		240	240	6 Wire Wye	3+G	19.36	-	40.90
		220	380	4 Wire Wye	3NG	-	16.27	25.83
		230	400	4 Wire Wye	3NG	-	17.79	24.54
		240	415	4 Wire Wye	3NG	-	19.36	23.65
Split	7	208	208	3 Wire Wye	3+G	11.77	-	19.43
		220	220	3 Wire Wye	3+G	13.18	-	18.37
		240	240	3 Wire Wye	3+G	15.68	-	16.84
		220	380	4 Wire Wye	3NG	-	19.76	10.64
		230	400	4 Wire Wye	3NG	-	21.59	10.10
		240	415	4 Wire Wye	3NG	-	23.51	9.74
Split	8.5	208	208	6 Wire Wye	3+G	14.54	-	23.59
		220	220	6 Wire Wye	3+G	16.27	-	22.31
		240	240	6 Wire Wye	3+G	19.36	-	20.45
		220	380	4 Wire Wye	3NG	-	16.27	12.91
		230	400	4 Wire Wye	3NG	-	17.79	12.27
		240	415	4 Wire Wye	3NG	-	19.36	11.83

Preheat

To maintain oil life, a slow Preheat mode is used when oil temperature is below 180°F (82°C). In the Preheat mode, the F5 control system pulses heat demand to slowly raise oil temperature until it reaches the exit point of 180°F (82°C). Afterwards, constant heating of the oil is performed up to the set point. Preheat mode is not available if the oil temperature is above 180°F (82°C).

Rapid Heat

Occasionally, a user may want to exit the preheat mode to raise oil temperature as fast as possible. Rapid Heat mode exits the Preheat mode when oil temperature is below 180°F (82°C), and the control system provides a constant heat demand until the set point is reached. Rapid Heat mode is not available if the oil temperature is above 180°F (82°C).


Rapid Heat Off	Rapid Heat On

Set Point

Each programmed product has a set point temperature which the F5 heat system must achieve before a cook cycle timer can be started by the user. If the oil temperature is below the product set point, then heat will be applied by the control system. Should the oil temperature be above the product set point, then heat will not be applied by the control system, allowing the oil to cool.

Cook Cycle

During a product cook cycle, the F5 control system applies heat in a varying duty cycle depending on the oil temperature readings. Generally, full heat is applied for a period at the beginning of a cook cycle to anticipate the effect of product lowering oil temperature. After the full heat period, a variable heat duty cycle is applied pulsing heat on and off depending on the difference between oil temperature and the product set point.

Energy Save

Energy Save mode reduces the vat's set point temperature to conserve electrical power consumed by the heat system. Energy save mode may be entered manually by swiping up and tapping the icon, or with an extended period of inactivity by the control system. Once in Energy Save mode, the set point is reduced to a default value of 280°F (138°C) and heating of the oil is performed thermostatically. Energy Save mode parameters may modified in the Settings > Advanced menu.


Energy Save Off	Energy Save On

Energy Save Oil Temp: 280°F (138°C) default temperature (with Auto Activate ON)
Auto Activate: enables energy save mode once Activate After period of vat inactivity
Activate After: 15 minutes default period (with Auto Activate ON)

Energy Save mode is exited once a product is chosen on the control screen. At that time, the F5 control system will raise the oil temperature to match the chosen product's set point.