Build, Test, Document
Table of Contents
Build, Test, and IntegrateIterative activities to validate functionality and performance at the sub-system and system level.
The ink was fabricated by Intrinsiq Materials. It is copper based ink that is designed to be highly conductive. The ink layout was printed onto three 14” glass panels using the custom screen. After being hand-printed, the ink was baked using a hand-held heat gun. The glass was then transported to Intrinsiq Materials where it was laser-sintered. All steps were completed by hand due to the unusual size of the panel, which resulted in numerous imperfections throughout the process. The laser-curing was completed using multiple passes over specific traces, in order to create “nodes” to put the vertical traces in parallel with on another. Each of the three panels were prepared with the intent to have different resistances, in order to create a range of testing conditions. The overall measured resistances of the two of the three panels measured 3.3ohms, 9.8ohms. The last one was damaged durring the sintering process which led to poor ink adhesion and conductivity. There were many imperfections and inconsistencies in the final ink layouts due to the custom nature of the process. Directly after being printed, two of the three panels had notable imperfections in the ink pattern. The resistances of the individual heating traces on each panel also varied, leading to a variance in voltage and current at different areas of the trace. All of these imperfections led to poor performance of the ink and reduced efficiency in heat spread. Furthermore, the ink was required to have a lifetime of 25 years. A realistic way of testing for the ink lifetime wasn’t able to be determined, but it is assumed that this requirement would not be met, due to the lack of robustness exhibited since the ink was printed.
The ink layout was chosen based upon hand-calculation and ANSYS tests of head spread across glass. Several ink layouts were theoretically analyzed, with traces at various locations across the panel. The final design needs to be efficient at spreading heat across the panel, while also not obstructing the solar cells. There are gaps between the cells and are bus-bars running down the center of the cells, so ideal ink placement is on top of either of the previous areas, because it allows for complete exposure of the solar cells. The ink trace dimensions need to be minimized in order to allow for minimum cost. Both hand-calculations and ANSYS testing used a thermal conduction value of 1.4W/mk for glass. The convection coefficient was varied from 5 to 28 W/m2k, to be representative of typical winter wind conditions in Rochester. The ANSYS calculations assumed that convection on the back of the panel could be neglected. After analyzing multiple ink layouts, both the hand-calculations and ANSYS testing agreed on a pattern which minimized the required amount of ink, allowed for completed exposure of solar cells, and maximized heat spread across the glass. The final configuration along with the configuration printed on glass can be seen in the figures below.
The system was constructed according to the layout determined in MSD I. Each subsystem was connected and integrated into the prepared enclosure. An image of the complete system integration is shown in the figure below
Test Plans & Test Results
An all encompassing document was created to keep track of all subsystem testing and results. This document also includes a final evaluation of the project that judges the success/failure based on the completion of the engineering specifications.
The most important requirements of the system are its ability to melt snow while using a minimal amount of power. Without these requirements being met, the system cannot be a viable marketable product. Several rounds of heat testing were conducted under varying conditions, which included different voltages and different operating temperatures. A list of conducted tests can be seen below.
Testing was done on two different ink trace layout. Testing at room temperature was done on a layout with a resistance of 9.8 ohms. This layout was able to reach higher power output points and a more drastic change in temperature then the other ink trace. However this one had more issues with the ink braking down during testing. There were burn marks seen as the voltage reached 9V.
The second trace was tested at freezing temperatures. This ink didn't have much change in temperature throughout the glass. There were small changes right at the ink trace but farther away there was no change observed. This trace, with a resistance of 3.3 ohms was not able to achieve higher power outputs. Burning was also NOT observed during testing with this trace. Testing data can be found at Ink Test Data.
Complete System Testing
After successfully testing all subsystems, the complete system was assembled. Testing was accomplished in indoor ambient conditions and consisted of three main steps:
1) Modifying the set points
The sensor output voltages were probed with a voltmeter to record current conditions. Accordingly, the set points were slightly changed in the conditioning circuitry using the adjustment pots to be slightly above or below those voltages [AT -> Lower ; AL -> Higher ; PV -> Higher (Due to the inverting nature of the PV conditioner)].
2) Applying various artificial stimuli to simulate a "melt" condition
With environmental conditions compensated for, artificial stimuli that would normally be seen in a working environment were applied. These consisted of shielding the Panel to simulate snow cover, chilling the ambient temp sensor in ice water to simulate cold conditions, and shining light on the ambient light sensor to simulate ample sunlight for power production. Once and only when all three stimuli were observed by the conditioning circuitry would the panel theoretically turn on. Successful awakening and operation was observed.
3) Removing various stimuli to simulate a "no melt" condition
Individual stimuli were removed and then reapplied one at a time to check for system sleep and reawaken operation. Each functioned as intended. Successful operation was observed indicating the system performs as intended
S1: Power Consumption
Based on the voltage, amperage, and temperature conditions recorded during testing, it was shown that the system currently does not meet the requirement of utilizing less power than the extra power that the panel would be generating. Heat output rate needs to be improved.
S2: Supply Voltage
The system was designed to half a 12V supply voltage. The battery used is a 100Ahr 12V battery.
S3: Heat Output Rate
During heat testing, the ink began to degrade, resulting in a much higher actual resistance in the ink than was originally measured.
S4: Temperature Output
The system was unable to output the levels of temperature that were needed to successfully melt the snow and clear the panel.
S5: Rate of Snowmelt
Testing was not conducted using actual snow. However, due to poor ink performance, resulting in the lack of heating and heat spread as predicted, based on calculations for power consumption and heat output rate, it was shown that the snowmelt rate was far from meeting spec.
S6: Ink Lifetime
There was no feasible way to test whether this ink would last 25 years within the scope of this project. However, during testing alone, the ink showed an extreme lack of robustness. The ink was easily damaged and broken when connections were soldered to it and also was significantly damaged after the panel was gently transported for Imagine RIT. Furthermore, the ink began to degrade and sometimes burn during mere minutes of heat testing. Therefore, it can be assumed that the ink would not realistically be able to last any amount of time comparable to multiple decades.
S7: Climate Operational Temperature
The system was not able to function at freezing temperatures. The ink degrades and is not able to carry the required amount of amperage.
S8: Ink Trace Dimensions
Although a high priority wasn't placed on measuring exact ink trace dimensions, the overall ink dimensions were minimized in order to keep costs low. The width of the ink traces was constrained by the widths of the bus-bars, resulting in very narrow heating traces.
The customer set a budget of approximately $1000. The final BOM added up to $854.76, when not including the battery that was donated by Renewable Rochester. If the cost of the battery is considered in the cost, the total increases to $1,122.66. This is still within reasonable range of where the customer wanted the budget to be.
S10: System Response Time
As observed when testing the system as a whole, the system response time (i.e. time between interrupt signal and melt signal) was so quick that it was immeasurable by the methods available. As such, it can be determined the response time is below the requirement of .5 seconds or less.
S11: On/Off Mechanism
The system includes a functioning manual on/off switch which allows the user to turn the system off if they want. There is also a "melt" switch, which allows the user to force the system into melting mode, even if the sensors aren't reporting ideal conditions.
S12: Heat Energy Not Transferred to Snow
Because the heat testing didn't utilize actual snow, it wasn't possible to quantify how much of the energy would be lost to the environment and how much would actually be utilized to melt snow.
S13: Heating Time of Ink
The ink was desired to reach it's desired temperatures within 300 seconds. During testing, the temperature of the trace reached steady state within 300 seconds. However, because the panel didn't heat up as much as was desired, meeting this spec is overall irrelevant. Once a new ink formula is developed, further testing can be developed in order to
S14: Sense Snow
The system was tested for functionality at identifying ideal conditions for snow melt - low temperature, high ambient light, and low panel voltage. These three conditions, when met simultaneously, constitute snow on the panel. The integrated sensor system was able to monitor all three of these parameters accurately, identify when the conditions were ideal, and initiate a melt sequence in the system.
The system was tested in hardware using a function generator and an oscilloscope. The function generator was programmed to output a triangle wave with range equal to that of the sensor output. These generated functions, as well as the comparator outputs, were captured with the oscilloscope in the same image. These captures are located in the Test Plan directory (linked below).
Unfortunately, due to the timing of the project, the weather was not ideal for our testing purposes (the prototype was not complete until April). Therefore, the system was not actually tested in an actual winter environment. As such, the team coded S14 yellow, so as to indicate that, while the system was functioning, we were not able to demonstrate explicitly that it could 'sense snow'.
Externally, the system is very simple with a total of only 4 Input/Output peripherals (An On button, Heat button, Panel Voltage Input, and Heat Output). Each are clearly labeled for easy of hookup and use. For assembly and operation, the user only needs to ensure the battery is properly installed and the peripherals are securely connected.
Opportunities/Suggestions for Future WorkTechnical:
- Do more research on how a car defroster works
- Testing the situation where a small layer of snow is melted and the rest of the snow slides off.
- Optimize power output vs. ink durability
- Use cad program with DRC(Design Rule Check)/LVS
(Layout versus Schematic)
- Less crowded board is better for testing (Less Noise)
- Bypass Capacitors are critical
- Use socket mounts for early prototyping
- Make sure part footprints are correct on board
- Hole size/spacing
- Double and triple-check connections to avoid damaging
- Purchase spare parts in event of failure
- Ink is not durable and will probably not survive a
- Next group should do more work and research into the ink
- Ink needs to have a lower resistance to be able to achieve power levels needed to melt snow.
- Heat Testing
- Putting thermocouples right on the ink traces causes and issue in reading values. The thermocouples should be put right next to the traces.
- Painters tape doesn’t hold the thermocouples very well at cold temperatures
- Too much current caused the ink to burn in some places
- If the project started spring semester for the design phase, there would be snow to test with outside for the fall semester
- Seek more assistance from professors
- Keep edge updated throughout
- Pay attention and try to stay on schedule
- Large time buffers does not mean things can be put off
- Expect unexpected problems to occur so start testing as soon possible
- Agree on a clear goal with the customer before the project starts so there is no confusion
- Make sure the test plans and subsystem tests are very detailed so there is no surprises when the full system is put together