P12441: Thermoelectric Power Pack for Stove
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Build, Test, Document

Table of Contents

Systems Integration

On May 4th, 2012 the thermoelectric power pack was connected to the next generation stove for testing. The thermoelectric module was able to generate enough power to charge the battery but not run the fan. There are three reasons this was the case. The first is that the fan being used was a 12V 1.7W fan, not a 12V 1.2W as we believed, this is above the specification given to the team and as such we were unprepared. The second reason is that the thermoelectric module only had a 100 degree temperature difference and as such we were not receiving the amount of power we were supposed to. The third reason was that the MPPT did not operate as expected and as such we were not receiving maximum power.

This was an extremely important milestone as this was the first project to achieve successful integration with the stove. Future work will now be focused on improving efficiency and lowering cost.

Evaluation

When the batteries were obtained the arrived fully charged. We had need of both fully charged and discharged batteries. Two of the batteries were drained using a decade box. The resulting data can be viewed here.

The maximum power point tracker (MPPT) is the most crucial part of the thermoelectric power pack design. It is responsible for maintaining maximum power output from the thermoelectric module. The figure below shows the output of the MPPT at different input voltage levels, the output should divide the input voltage by two.
The MPPT divide by two output.

The MPPT divide by two output.

In order to guarantee that the battery is never over charged or under charged a system was implemented to disconnect the battery from charging when it is fully charged, or disconnect it from current draw when it is discharged. The blue trace is the battery terminal voltage and the yellow trace is the output of the comparator, when it is high the system is connected, when it is low it is disconnected.
The high voltage disconnect system operation.

The high voltage disconnect system operation.

The low voltage disconnect system operation.

The low voltage disconnect system operation.

The DCDC switching converters are very sensitive pieces of technology, as such they cannot be prototyped on a breadboard. To prove successful operation evaluation boards were created to prototype the circuits. The evaluation board schematic can be seen here. The evaluation board PCB layout can be seen here. The evaluation board BOM can be seen here.

Test Plans and Results

There are two different categories of tests that must be performed. There are four mechanical tests to be performed.
Rain Test
Humidity Test
Drop Test
Crush Test.
Kick Test.

The electrical test to be performed are simple output voltage and load tests. There are seven electrical test procedures.
MPPT Tracking
Battery Charging
HV/LV Disconnect
Battery Discharge
USB Converter
Fan Converter
MPPT Converter

In order to determine if the customer needs were satisfied a customer acceptance test (CAT) plan was created. The test plan can be viewed here.

A worst case scenario test was carried out to determine how the system would respond to USB charging during the entire cycle with a low battery the data collected can be viewed here.

Functional & Performance Review

The prototype was attached to a TEG test bench in the thermal lab, where a temperature difference was applied to the TEG. From this initial data was collected from the prototype and can be viewed here.

User or Operator Instructions/Manual

Operating the thermoelectric power pack is very simple and consists of 5 steps.
1. Connect the fan to the input marked "fan".
2. Connect the thermoelectric to the input marked "TEG"
3. When you would like to begin cooking flip the switch to the "On" position.
4. Light the stove.
5. When you are finished cooking flip the switch to the "Off" position.

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