PROJECT TITLE: Testing Document (version 1.0)

Project: Wind-Powered DC-DC ConverterDate(s):04/07/2013Prepared by: Jonathan Juges, Dalibor Vitkovic and Jonathan Davis

Document status: _Draft _x_ Proposed __ Validated __ Approved

Introduction

The Wind-Powered DC-DC Converter test plan will be executed in multiple stages. Our project has multiple components- a power source (wind turbine), a charge-controller circuit, a 12-V battery, a DC-DC converter, and USB I/O interface between the converter output and the DUT (smart phone). We will be tested each component upon their completion in order to ensure desired performance. We have a wind turbine that gives us enough power to charge our battery a charge controller-circuit that controls the charging of our 12-V battery to prevent wearing down of the battery. We also have a functioning DC-DC converter that takes the standard 12V output from a car plug and steps it down to the required 5V and 1A that we need for the desired performance specification. Our testing procedure will be comprised of ensuring design specifications for each component. Afterwards, the final testing will be done once the individual components are validated as a complete assembly. Upon successful completion of these tests, our product will prove we can utilize renewable wind energy and apply it to power a mobile device.

Test Plan

Wind Turbine- In order to know our optimal conditions for performance, we will need to find the point of maximum power transfer for our turbine. The point of maximum power transfer is where our turbine will be delivering the most power to our assembly.

Charge-Controller Circuit- We will want the charge controller circuit to charge the battery when it drops below a certain voltage (13.5 volts) and prevent charging when the battery voltage exceeds a certain amount (14.4 volts). This will help the life of the battery. In order to test this, we will look at the current coming out of the charge controller once the turbine is applied to its input and the output of the charge controller is being fed to the battery.

DC-DC Convert Circuit- Our DC-DC converter circuit must be able to operate through a range of specified inputs and achieve a specified output level. Therefore, we will be looking at the input/output conditions in order to validate our design.

Test Procedure

Wind Turbine- We will use a leaf blower to simulate the wind. When testing the wind turbine, we will be considering three factors in particular: leaf-blower speed, leaf-blower distance, and the load. In order to find out what sort of output range the turbine is capable of, we must vary these parameters. The leaf blower has two-different wind speed settings and we can further adjust the air speed by moving the leaf blower between 2 and 4 feet from the face of the turbine. Within this 2-4 foot range, the leaf-blower is capable of speeds between 21-31 MPH on the low setting and 25-25 MPH on the high setting. We will also be utilizing a string of resistors in order to easily change the load resistance that is seen by the turbine (resistance values are the following: 50, 100, 110, 120, 130, 140, 145, and 150 ohm). The picture shown below shows an example set-up for testing the turbine. The steps are as follows:

1) Attach the turbine to a structure for stability.2) Attach an anemometer to the structure, behind the turbine blades to measure wind

speed.3) Set the leaf blower up at some distance x from the face of the turbine (x varies from 2 to

4 feet in our case).4) Plug the leaf blower into an outlet for power.5) Obtain your string of resistors (shown at the bottom of the picture).6) Place the turbine output across a resistor (or set of resistors).7) Turn the leaf blower on (choose the setting).8) Use the multimeter to measure the voltage the turbine generates across the string of

resistors.9) Repeat the procedure for desired distances, leaf-blower settings, and load values.

Charge-Controller Circuit- For our charge-controller circuit, we will be measuring the performance by using a power supply, oscilloscope, and capacitor (to simulate the battery). The capacitor behaves like a very low capacity battery so it enables us to check the operation of the charge controller quickly in seconds rather than wait hours for the battery to charge and discharge. The picture below shows the set-up we used to test the charge-controller circuit by itself.

1) Attach the leads of the DC power supply to the input of the charge-controller circuit.2) Turn on the supply at desired voltage level. 3) Turn on the oscilloscope.4) Calibrate probes.5) Attach the probes to the output of the charge controller circuit.6) Attach the probes across the capacitor (battery).7) Look at the measured response on the oscilloscope.8) Pull out one of the output cables from the charge-controller circuit and plug a wire

into that spot.9) Now using a multimeter in current mode, attach one of the multimeter connectors

to the wire that is now in the spot of the output cable and the other connector onto the corresponding lead on the capacitor (battery).

DC-DC Converter Circuit- For the DC-DC converter testing, we will look at the input and output measured values. In order to test the converter circuit we will need the circuit, DC power supply, multimeter, oscilloscope, and probes. The picture below shows the circuit and attached measuring tools.

1) Attach the DC supply leads to the input of the converter.2) Turn on the supply.3) Use the multimeter to measure the output voltage.4) Measure the output while varying the supply through the converter input voltage range

of 10 to 14 volts to ensure stability.5) Attach the oscilloscope probes to the output of the converter to look at the output

waveform and measure the voltage ripple. 6) Plug the smart-phone cable USB into the USB interface at the output of the converter.7) Ensure that the phone recognizes the converter and is charging.

Complete Car Charger Assembly- In order to test the car charger model of our circuit, you need only:

1) Plug the car adapter input of the converter into the outlet of a car.2) Plug the smart-phone charging cable into the USB interface at the output of the

converter circuit module. 3) Plug phone into the charging cable.4) Ensure the phone is charging.

Complete Wind-Turbine Assembly- In order to test the entire assembly, we will need: turbine (with structure), leaf blower (with structure), anemometer, charge-controller circuit, battery, DC-DC converter circuit, phone cable, smart phone, multimeter, and any necessary cabling to power the leaf blower and make necessary connections between the assembly units.

1) Set-up the turbine with anemometer attached to the structure.2) Set-up the leaf blower at desired distance from the face of the turbine.3) Connect the output of the turbine to the input of the charge-controller circuit. 4) Connect the output of the charge-controller circuit to the leads of the battery.

5) Use dual-sided alligator clip cables to connect the leads of the battery to the input of the DC-DC converter.

6) Plug your phone cable into the USB interface at the output of the converter circuit. 7) Turn on the leaf blower at the desired setting.8) Ensure the smart phone is charging. 9) You can measure the individual element values in the same manner as in the individual

testing phase of the components.

1. Wind Turbine Results

In order to test for the point of maximum power transfer, we varied several factors: leaf-blower speed, leaf-blower distance, and the load. The results of which are shown below in figure 1 for average power vs load. As we can see from the graph, we achieve maximum power transfer by setting the leaf blower 3 feet away and on the high setting. Table 1 shows the varying speeds the turbine experiences from the leaf blower depending on the distance and setting of the leaf blower. These wind speeds were measured by using an anemometer attached to the turbine support right behind the turbine.

50 100 110 120 130 140 145 1500

0.5

1

1.5

2

2.5

2 Feet, Low3 Feet, Low4 Feet Low2 Feet High3 Feet, High4 Feet, High

Figure 1- Maximum Power Transfer

Distance (feet) Leaf-Blower Setting

Wind Speed (MPH)

2 Low 313 Low 254 Low 212 High 353 High 31

4 High 25Table 1- Leaf-blower Speed

2. Charge-Controller Current

When testing the charge-controller circuit we simply wanted to measure the varying charging currents the battery receives with varying supply (wind speed). The results are shown below in table 2. Therefore, we can expect 60-140 mA depending on wind speed and distance for our testing scenario.

Distance (Feet) Setting Wind Speed (MPH) Current (mA)2 Low 30 803 Low 25 724 Low 21 602 High 35 1403 High 31 1304 High 25 110Table 2- Charging Current

3. Output Circuit (Step-Down DC-DC Converter) Results

For our DC-DC converter, we have certain desired I/O specifications that are displayed in table 3 below. Table 4 shows the values that were actually measured from our completed circuit. Here, we see that the voltage range is narrower than in our specification. This is because we are using a battery to power our converter circuit and this battery has a charge-controller circuit that will keep the battery within 13.5-14.4 volt range. Therefore, the measured values are within specification. Also, the 10 to 14 volt range is applicable to our car-charger model, where the supply will be a car battery.

Topology Buck Regulator (No isolation required)

Input Voltage Range 10 to 14 volts

Output Voltage 5 volts +/- 0.1 volts

Output Current 1 amp

Switching Frequency 500 kHz (set by the PWM chip)

Output Voltage Ripple 50 mV p-p

Table 3- DC-DC Converter Specs

Input Voltage (Volts) 13.8-14.2

Output Voltage (Volts) 5.06Output Current (Amps) 1.64Output Voltage Ripple (mV) 50Table 4- Measured Values

Conclusion

The DC-DC converter circuit that we designed is versatile in that it can be utilized along with a wind turbine, charge-controller, and battery assembly anywhere there is wind or as a stand-alone converter in a car. This provides the user with some flexibility in being able to charge their phone in a variety of situations with a desirable performance (being that of the AC-DC units).