Project Objective Statement
Deliver a thermal management system for the batteries and motor controller to maintain optimum temperature for competitive performance.Engineering Requirements (Specifications)
Customer Requirements
The full revision history can be viewed here.
Engineering Requirements
The full revision history can be viewed here.
Major Changes: Removed liquid-cooling specs, provided ideal value for max current draw, and added safety specification.
Note: For full mapping of specs and customer requirements, please see the House of Quality document.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 25 mins | 15 mins | 60% |
Finalized Concept Selection
Controller
Possible Mounting Location
- Forced convection over controller and heat sink
- Same location as last year
- Not final location - waiting on information from other subgroups
Note: Heat sink is exposed to air on all sides except for area covered by controller.
Potential Heat Sink Design
Important Design Parameters
- 12" X 12" X 0.25"
- 6061-T6 Aluminium
- Mounting holes for both controller and frame
Batteries
Potential Duct Design Concept
- Body panel design for ducting air done by another performance vehicle team (source)
Important Design Parameters
- Length, width, and height of air intake/duct
- General shape of air intake/duct
Preliminary Battery Box Design
- The green boxes show potential locations for fans (used of 2-4 fans)
- The purple lines show potential locations for vent openings
Important Design Parameters
- Vent width and length (0.23" width or less)
- Fan length, width, and thickness (Approximately 2.5"x2.5"x1" or less)
- Fan RPM/CFM
Fan Circuitry
Wiring Schematic from the Orion BMS Wiring Manual - Full document here
Important Design Parameters
- Battery temperature that turns the thermal management system on
- Relay Coil Current (175mA or less)
- Relay Coil Voltage (9-12VDC)
- Fan Voltage Rating (9-12VDC)
- Fan Current Rating (1A or less)
- Wire Gauge (18-24 AWG)
Proof of Concept
Controller
Justification of Design Parameters
Theoretical Calculations The PDF for the current motor controller heat sink analysis can be found here.
Note: The following analysis was reviewed by Dr. Rob Stevens, a professor in Mechanical Engineering.
The largest assumption made in this analysis was the power dissipated. This parameter is still unknown for the actual system, and the power is based off a proprietary spec sheet from Curtis. Further testing is needed to determine whether this number is accurate. Another number that changed from the last phase is the convection coefficient. An error was found in the previous calculations and has been fixed here.
The worst case scenario is based off the endurance event during competition. In this event, the car is traveling around a track for as long as it can go. There is a significant hill on this course which we determined would cause the biggest load on the controller. The car will be traveling about 9 m/s on this track and the convective coefficient was based off of this speed.
Based on the current calculations, fins will not be required to keep the controller below 85 degrees C, the point at which performance degradation begins. We will validate this assumption in later phases.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 600 mins | 120 mins | 20% |
Simulation
Note: The following analysis was reviewed by Dr. Rob Stevens, a professor in Mechanical Engineering.
Thermal simulation was done in Solidworks Simulation using the results of the above calculations. Simulation was done to confirm the surface temperature results from above, and to get a better idea of the temperature gradient over the plate's surface.
Parameters:
- 400W applied to area the size of motor controller
- h = 82.9 W/m^2K (Convective Coefficient)
- k = 169 W/mK (Thermal Conductivity)
- Ambient Temperature = 18C
- Only top and bottom surfaces affected by convection
The temperature will be highest in the center of the plate, where the controller sits. The lowest temperature is 120F at the edges farthest away from the controller, and 152F in the center.
The steady state temperature range shown by this model implies that the controller’s temperature will never be within 20 degrees of the temperature at which performance begins to degrade (185F).
These results also imply that we don’t need to utilize fins in our design. Although fins will make heat transfer more efficient, they are not necessary to keep our controller within our desired temperature range.
Testing so Far
Wiring Testbench - full pdf here.
Testbench on Dyno
The test plan for running the Hot Wheelz test bench on the RIT FSAE shop dyno can be found here
Several problems were encountered when trying to execute the test plan. The Hot Wheelz program designed specifically for the test bench did not work. To work around this, our team decided to run the dyno manually. During testing, the batteries were measured and found to be gaining voltage, indicating that the electric motor might be acting as a generator. The dyno might have been over-torquing the motor to cause this to happen. Since we were unable to find a SME on the manual mode of the dyno, we could not determine if this was the problem or not. With the phase coming to an end, and the dyno being requested for other teams' projects, testing could not be completed on time.
| Sub Team | Time Spent | Projected Time | Efficiency |
|---|---|---|---|
| Electrical | 4320 mins | 320 mins | 7.4% |
| Mechanical | 1200 mins | 120 mins | 10% |
Testing to be Done
Testing to determine whether the heat sink and airflow speed are effective at removing the heat needed will be important to justifying the system. Designing off of the team specs is good enough for now, but how the heat sink actually performs is what really matters. As dyno testing did not work for this phase, to test the heat sink an external heater will be mounted on it and air will be blown across it, with temperature sensors at various locations. This will be a good intermediary test for the sub system before the entire system is tested on the car for MSD II.
Theoretical Models
The heat sink motor controller resistance model (shown above) developed for this phase will be used for testing the heat sink. The power will change based on how much heat the external heater is producing and the h value if we decide to run different speeds of air across it. We will calculate surface temperature based on these parameters to validate that the heat sink works like we predict it will.
If it is found during testing that the heat sink alone is inadequate, theoretical models for the resistance needed to remove the heat will be needed. This in turn would be used to purchase fins that would add the right amount of resistance. Another option would be to use this data to design fins, and a model would need to be developed to explore this option. However, this can not be determined until more testing is complete.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 180 mins | 60 mins | 33% |
Benchmarking
- Can monitor temperature via controller programming language
- Also have ability to monitor motor temperature if desired
- Set defined values as parameters in program
- Output a signal to a relay that powers a fan
Decided to not pursue further research on the topic until further analysis was done on heat sink / fins.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 60 mins | 45 mins | 75% |
Batteries
Justification of Design Parameters
Preliminary Airflow Design
Preliminary Airflow Design Justification - File
There are two possible options to duct air into the battery box. The first option is the place an air intake/duct near the top of the main roll hoop and direct the air in through the top of the battery box. The second option is to place air intakes/ducts within the body side panels to direct the air in through the sides of the battery box.
One concern with the main roll hoop concept was that there would not be enough available space to mount a duct since it cannot come into contact with the driver's head and there is a warning light mounted on the top of the roll hoop. However, after checking with the solidworks model, there would be approximately 4-7 inches of available space.
The other concern with the main roll hoop concept was how effective the airflow would be by entering through the top of the box. The first components the airflow would encounter would not be the battery cells. Also, due to Formula Hybrid Rules EV2.3.4 (listed below) would require the BMS to be sectioned off from the rest of the battery box. Any directed air into the top of the box near the BMS would get trapped in this section and never reach battery cells.
EV2.3.4: The accumulator container may not contain circuitry or components other than the accumulator itself and necessary supporting circuitry such as the AIRs, BMS, and pre-charge circuitry. Note 1: The purpose of this requirement is to allow work on other parts of the tractive system without opening the accumulator container and exposing (always-live) high voltage. Note 2: It is possible to meet this requirement by dividing a large box into an accumulator section and a non-accumulator section, with an insulating barrier between them. In this case, it must be possible to open the non-accumulator section while keeping the accumulator section closed, meeting the requirements of the “finger probe” test.
- The green boxes show potential locations for fans (used of 2-4 fans)
- The purple lines show potential locations for vent openings
Due to the preliminary duct design, fans will most likely be required to induce airflow for the battery cells near the top and rear of the battery box. If fans are located here, it would be reasonable to assume that vent openings should be located on the front face of the battery box to allow the air to exhaust out. Vent openings would need to be required on the sides of the battery box as well to allow the air from the side ducts to enter.
Preliminary Fan Design
Preliminary Fan Design Justification - File
A full speed fan system would be simpler than a variable speed system which would help ensure that the team meets CR7: System is easy to install and service. A simpler system would also aid the team in meeting CR12: System is built and tested in time for competition. A MOSFET device has never been used by the team before and will add complexity to the thermal management system which could require more troubleshooting and testing.
The team is also aiming to only utilize the thermal management system when the batteries reach a critical temperature before they start to degrade. At this point in time, it may be necessary to have a fan blowing at full speed to ensure the batteries stay under the degradation temperature.
Testing so Far
- Formula Hybrid GM Mentor offered to perform temperature testing on cells
- Sent 4 cells to GM Battery Lab
- Should arrive this week
- Tests include temperature data at 2C (endurance) and 10C (acceleration) discharge rates
- Testing could take 1-2 weeks, depending on availability of equipment & personnel
Testing to be Done
- Theoretical Models to be Considered:
- Thermal analysis on the battery cells
- CFD analysis on the airflow within the battery box
- Tests to be Considered:
- Fan testing to verify that it matches its specifications
- Measure the current draw of the fan system
- Waterproof test on fans and vents
- Vehicle testing to verify that the system turns on based on set temperature
Theoretical Models
Battery Cell Heat Generation/Temperature Rise
A detailed working document can be viewed here.
The MATLAB script can be viewed here.
- Purpose: This theoretical model aims to roughly estimate the amount of heat a battery cell can generate during two different competition scenarios. Since the new battery cells are not in-house and the testing by GM has not been completed yet, this information will give a general idea for how much the temperature rise of the battery cell will be and how much heat the system will have to remove to maintain a desired temperature.
- Assumptions:
- Vehicle will run for 35 minutes during endurance event based on last year's results
- Vehicle will run for 7 seconds during acceleration event based on last year's results
- Continuous current through the batteries is 30A (2C discharge) for endurance event based on battery specs
- Continuous current through the batteries is 150A (10C discharge) for acceleration event based on battery specs
- Worst case value for the specific heat capacity of the battery cell is 825 J/kg-C; (page 16, table 2.3 in this source)
- Linear relationship between heat generated over time and temperature rise
- Analysis Equations
- Results
Airflow in Battery Box
A theoretical model has not been developed as of yet to model the airflow to be expected in the battery box based on the preliminary design. Working towards a theoretical model for the airflow is a task for the next phase.Benchmarking
The full working document can be viewed here.Relays
Fans
Efficiency for Battery Box Proof of Concept
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 600 mins | 240 mins | 40% |
System Design Layout
Functional Decomposition
Concepts/specs have not been finalized so this was not changed.
System Architecture
Full revision history here.
Detailed Design of System, Subsystem, and Parts
Controller
Heat Sink Design
Electrical Schematics
Full PDF here.
Batteries
Airflow through Box
- For preliminary design, the size of the duct and the airflow it can produce still needs to be determined
- Will need to work alongside Aerodynamics Subgroup to identify space available and to communicate space needed for duct
Electrical Schematics
PDF Electrical Schematic - File
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 30 mins | 10 mins | 33% |
Procurement
Controller
Manufacturability
- 12" X 12" is a standard size - material would not need to be cut
- Mounting holes can be machined on a mill or drill press
If fins need to be added
We determined through analysis that fins are not necessary. If testing proves that we do need fins, they can be added in the following way:- A finned plate can be purchased through our GM mentor or obtained from a professor.
- Drill holes through finned plate and heat sink, tap holes in heat sink to secure the plates together, place thermal paste between them.
- Weld plates together, depending on material of finned plate and thickness.
Assembly
The updated heat sink will be mounted to the frame the same as the previous version. The following will need to be completed again- Weld mounting tabs to the frame. If possible the same mounting tabs from the last vehicle, but these might need to be removed/changed.
- Mill heat sink to size. This can be done with a 3 axis mill. The sides and top and bottom will be milled parallel.
- Drill holes for mounting. This can be done with a 3 axis mill. The holes will be through holes for easy bolting to the mounting tabs.
- If fans are needed, mounting brackets will be welded to the frame to attach the fans to the vehicle.
- Wires associated with fans will need to be secured with non-conducting mounting wire. They will be attached to the frame.
Batteries
Manufacturability
- Manufacturing plans for the duct system will be decided during the next phase. Still need to decide if the body work will act as the duct or if a duct will be mounted inside the body work.
- Have verified with Electrical Mounting & Isolation Subgroup that vent openings can be cut into the box at specified locations. Will have to discuss further with this group to create more detailed manufacturing plans for next phase.
- Openings will also have to be cut into the battery box if fans are to be mounted within the box. Will create more detailed manufacturing plans to accomplish this during the next phase.
Assembly
- There is the potential to mount ducts within the body side panels if this option will be used going forward.
- Fans can be mounted in the battery box. If not in the battery box, locations on the frame around the battery box will have to be identified.
- Fan circuitry (relay) can be mounted in or around the battery box in its own container or in a container that holds other low-voltage electrical components. Another option would be to mount the relay on a side panel on the vehicle with the other relays and determine waterproofing method.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 120 mins | 45 mins | 38% |
Bill of Materials
Controller
A full revision history can be found here
The estimated total cost of all components in the controller assembly is $83. Although we have not sourced all of the components, we are confident that we will fall well within our $2000 budget.
We are unsure of what the fins will actually cost. Various suppliers have fins that meet our size and material requirements ranging from $35 to $100. Many websites also require a quote to get a more accurate price. We can also obtain fins through one of out GM mentors for a discounted cost.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 45 mins | 20 mins | 44% |
Batteries
A full revision history can be found here.
Yellow cells are estimations and assumptions and will be finalized during the next phase.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 60 mins | 20 mins | 33% |
Test Plans
Controller
Heat Sink Validation
The link to the motor controller heat sink test plan is here
This test will be able to gather temperature data of the motor controller heat sink sub system under an induced load independently of any other components. This will be verification that the design works as predicted.
| Time Spent | Projected Time | Efficiency |
|---|---|---|
| 120 mins | 60 mins | 50% |
Batteries
Test plans will be created during the next phase when a more concrete design for the battery box cooling has been determined.Risk Management
Risk Management Update
A working document can be found here.
Plot of Total Risk Importance
Note: Since previous phase focused mostly on dyno testing, not many of the importance values changed since the last review.
Addressing High Risks
The full mitigation plan can be viewed here.
Project Plan & Budget
Project Schedule
Full PDF here.
Work Breakdown Structure
Actual from Phase 3 - full PDF here.
Projected for Phase 4 - full PDF here.
Projected Costs
- $2000 budget
- Components not finalized but should be within budget based on components
- Projected Cost from Controller: $83
- (Highest) Projected Cost from Batteries: $430
- Highest Overall Cost: $513
Action Items from Review
See full document of notes and action items here.
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- Node updated 2016-11-08 13:38 by mam1664