Coffee Makers
© 2006 Dr. Ray Franco, PhD., PE r.a.franco@ieee.org
Case History: Exemplar Mr. Coffee, Drip, 4 Cup, Coffee Maker Purchased at Wal-Mart in 2006 for $19.94.
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Exemplar Mr. Coffee, Drip, 4-Cup, Coffee Maker ($19.94).
External Components of a Drip Coffee Maker.
The Manufacturer's Data is Stamped into the Bottom Plate of the Coffee Maker. Mr. Coffee is Owned by Sunbeam.
Manufacturer's Tag - Model NLX5, SN: X069SX
120 VAC, 600 Watts, UL Listed 668N.
Water Leaves the Reservoir Through the One-Way Valve and Enters the Heating Tube. Boiling Bubbles Push the Water into the Brew Basket.
Brew Heating Tube Temperature: 242 °F. Warmer Heating Tube Temperature: 260-313 °F. Duty Cycle: ON = 10 sec.; OFF = 127 sec.
The Water in the Heating Tube Starts to Boil, and a Column of Water Rides Upward on Top of the Bubbles to the Brew Basket.
Bottom of Coffee Maker. The 12 VAC Transformer Supplies Power to the Clock/Timer, and the Relay Switches 120 VAC to the Heater Element.
Thermal Transfer Compound is Used between the Warmer Plate and the Heater Element.
600 Watt Heater Element.
Front of Clock/Timer Printed Circuit Board.
Back of Clock/Timer Printed Circuit Board.
Measured Resistance of Heating Element: 24.4 Ω.
Using 24.4 Ohms, the Calculated Wattage is 590 Watts.
Test with Thermostat and Cutoffs Removed. The Aluminum Heating Tube Melted and the Heating Element Opened before the Plastic Caught Fire.
Some Melting of Plastic, But the Heating Element Opened Before the Plastic Caught Fire.
Hot Spot on Bottom Steel Plate after Test with Thermostat and Cutoffs Removed.
Case History: Evidence Examination Case #: F06-026.
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Burnt Coffee Maker from Case # F06-026.
Mr. Coffee, Model No.: NLX5.
Comparison of Exemplar and Burnt Coffee Makers.
Mirror Images.
Both the Water Heating Tube and the Heater Element were Intact.
Measured Heater Element Resistance: 24.2 Ω.
Ruber O-Ring Still Intact.
Electrical Arcing (Copper Beads) was Present on the Stranded Wire Power Cord.
