Electric Forklift Battery Cooling

The goal of the project is to assist in the replacement of Internal Combustion (IC) Engines with Lithium-Ion battery powered electric motors. This will be done by designing and prototyping a more efficient cooling system to eject excess heat produced by the batteries while under load.

=Problem Definition=

Background
Hyster-Yale produces a variety of lifting trucks. In an effort to be more globally responsible and eco-friendly, they are working on producing a line of electric forklifts. This creates an excess of heat that needs to be removed to allow the batteries and motors to operate at optimal efficiency. With the current setup, the system is effectively operable up to an ambient temperature of approximately 30°C. However, in many locations the ambient temperature can reach 40°C.

Deliverables

 * Proof on Concept Prototype
 * Prototype to cost less than $1000 per unit to produce.
 * Solid Model
 * The prototype model is to be modeled in SolidWorks.
 * The model is to include a heat transfer and airflow analysis.
 * Heat transfer Calculations
 * Calculations done to represent total energy removed from the battery module under given conditions.

Functionality

 * The heavy-duty cooling system should be able to remove 100 Watts of heat from each battery module.
 * The heavy-duty cooling system should cool the battery during charge/discharge at a rate of 1C.
 * The heavy-duty cooling system will replace the standard cooling system for equipment operated in ambient temperatures of up to 40.
 * The heavy-duty cooling system should be able to remove 100 Watts of heat from each battery module.
 * The cooling system is expected to maintain internal battery cell temperatures at or below 55 °C by removing heat from the batteries modules.

Spatial
The cooling system needs to fit within the compartment behind the battery assembly and in front of the forklift counter weight.


 * The heavy-duty cooling system dimensions will be:
 * Height < 502 mm
 * Width < 652 mm
 * Depth < 272mm

Mounting

 * The heavy-duty cooling system needs to mount in the same position as the current cooling system.
 * Cooling system components will be mounted using the same mounting hardware as the current cooling system.
 * Additional heat transfer equipment will possibly mount in the 10mm slots between battery cells.
 * The mounting system shall be able to withstand vibrations from daily equipment operation.

Cooling System Operational Specifications

 * During operation, the cooling system supply voltage shall remain at 12 Volts DC.
 * During operation, the system shall draw no more than 15 amps.
 * During operation, the system shall use no more than 180 watts.

Battery Unit Specifications

 * The individual battery voltage is 51 Volts.
 * The individual batteries are rated at 174 Amp-hours.
 * The individual battery units have a high-speed discharge rating of 350 Amps.

Environmental

 * The cooling system is expected to operate in environments with ambient temperatures between -10°C and 40°C.
 * The heavy-duty cooling system shall resist water ingress, rust and corrosion on components and in connectors.
 * The system shall withstand normal equipment cleaning procedures including pressure washing.

=Design Considerations=

=Project Learning=

Thermal Studies
A solid model was created using SolidWorks to represent the battery configuration. Conduction and convection analyses were run on the model to figure out what temperature and velocity the incoming air needed to be at to maintain the desired internal temperature.

Heat Pipes


Heat pipes are a passive way of moving heat from one location to another. They are an evaporator-condenser system contained inside of a pipe, generally copper. Heat pipes would be used to move the heat from the walls of the batteries to a location with more space so that the heat could be rejected easier. They can be very quick and efficient, however, they work better at shorter lengths. Seeing as our battery modules are rather long they are not a very viable option. Here is some of the research on heat pipes:
 * [[File:ATS_info.pdf]]

Peltier Modules


Peltier modules are a thermoelectric device that operates on 12 volts. They have one hot side and one cold side. For the purpose of cooling down the batteries, we could use the modules in two different ways. The first would be to attach the cold side directly to the wall of the batteries, but this would still leave the hot side just radiating into the gap. The second way of using them would be to set them up at the intake so that the cold side would cool down the air, and the hot side could be vented into the atmosphere more easily. Here is some more information on Peltier modules:
 * [[File:Thermonamic_Module.pdf]]
 * [[File:Peltier_Cooler_Information.pdf]]

Refrigeration Cycles


Refrigeration cycles have four main parts: an evaporator, compressor, condenser, and expansion valve. The function of the evaporator is to absorb heat and boil the refrigerant, usually R-134a. The phase change is what allows the evaporator to absorb heat (any substance takes in energy when changing from a liquid to a gas). From the evaporator the gas is drawn in to the compressor and then compressed to a point where the gas is at higher pressure and temperature. Next the refrigerant is pushed into the condenser where the gas releases heat and changes back into a liquid. The expansion valve allows the refrigerant to expand causing a pressure drop. Then the refrigerant is returned to the evaporator and the cycle repeats. This system can be modeled as an ideal compression cycle. After sizing and selecting components, the component efficiency can be added to the model and accurate predictions about the system can be made.

=Final Design=

=Validation=

=Team Members=

=Additional Documentation=

Project Schedule



Meeting Minutes



Presentations