Bunn My Cafe AP Technical Training Manual page 16

The tank is initially filled upon startup and is monitored by a refill or level probe. When commanded by the large or
small brew button, the CBA will activate the fill solenoid allowing the regulated water to enter the inlet of the flow
meter and exit out the flow meter going to the fill tube located on top of the tank. The paddle within the flow meter
created an input signal to the CBA, the CBA generates a logical number on the display during a brew dispense called
Flow Counts. The flow count is the calibrated volume of brew water entering the tank, rising past the level probe.
The brewer will display a series of informational screens during the brew process while the brew pump is activated
to draw the calibrated water from the tank through the check valve, sprayhead, coffee pod, pod holder, stream guide
and into the receiving cup. The brew pump will deactivate when the water drops below the level probe and the cofffee
air pump will turn on creating a minimal amount of pressure above the coffee pod to push out any remaining coffee,
reducing drip out time.
The brewer will begin heating the water back to set temperature. Once temperature is achieved and the heater turns
off, the refill circuit will activate and fill the tank with water until it reaches the level probe.
Heating Circuit
The heat circuit consists of:
(A) - Temperature Sensor
(B) - Limit Thermostat
(C) - Tank
(D) - Tank Heater 1425 watt, 120vac
(E) - Control Board with Hybrid Heating
Components
(F) - Vent Valve
The vent valve is located above the water tank and is
normally open to allow venting during heating. The heat-
ing element is protected when the brewer is powered on
to prevent dry firing of the tank element, which occurs
when there is no water in the tank. The fill probe must be
satisfied with water before the CBA activated the heating
element. Once the fill probe is satisfied, the CBA moni-
tors the tank thermistor/temp sensor (resistance/voltage)
and will activate the heater triac (TH1) and pass power
through the limit thermostat and to the heating element.
The limit thermostat is used as a precautionary device in the event of a tank over heating. The limit is rated to open
at a temperature of 230º F. and will reset around 170º F.
Hybrid Heating Circuit
A relay and a triac are connected in parallel so either can switch power to the tank heater. The relay
carries the current when the water temperature is more than two degrees lower than the target range.
The triac is used under two conditions:
1. Every time the relay contacts open or close, the triac switches on for a fraction of a second
before the open or close and stays on for a fraction of a second after the open or close. This
prevents the relay contacts from carrying any surge current on closure and prevents any arcing
of contacts on opening. This greatly increases relay contact life.
2. When the water temperature is within two degrees of target, the relay contacts open and the
triac pulsed at a low duty cycle to reach and maintain the target temperature with extreme
accuracy. The need for a keep-warm blanket is eliminated.
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My Caf é AP Training Manual
F
A
B
C
D
E