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Developing a Custom Battery Pack with Limited Information

Anton Beck
Written by Anton Beck
Posted on June 3, 2020 at 9:31 AM

Creating an application or product requires designs, drawings, and recommendations regarding the function of the application, materials to use, and the dimensions. In addition, a manufacturer also must consider how to power it. Many applications require a portable battery source that can be recharged numerous times and stored safely without future damage.

Just like when designing an application, a customer will need to think about certain factors regarding the battery pack. However, you may not know where to start. Small manufacturers may not have electronic engineers available who are versed in battery chemistries, and you may be unsure of whether you have any information to provide to a battery pack manufacturer.

Here at Epec Engineered Technologies, we've worked with manufacturers at all levels of the design process to help them determine the right type of battery pack, size, and chemistry that is required. Even when they don't have any idea on where to start and only have limited information, Epec will help them iron out all the details so that we can provide the battery pack that is suitable for the application. Some factors to consider include mechanical, hardware, and software requirements as well as the chemistry type, cell size, and industry regulations. In addition, materials and the overall product budget will help to decide the battery pack manufacturing process.

Learn How to Reduce Battery Pack Costs and Lead Times of Your Final Product

When having limited information, a customer wants to consider the following factors of enclosure design, battery chemistry, cell amount, and certifications. We will discuss these factors (and many others) with you as we will send out a questionnaire to target your battery pack requirements. Our technical and engineering teams will also set up meetings to talk about these factors.

Enclosure Design

If this is the customer's first time in creating a custom battery, one of the most important things to figure out is the enclosure where the battery pack will be housed in the application. The enclosure exterior can be made from either plastic or metal as it will have a cover that may need to be accessible during the charging, discharging, or when removing the battery pack for long-term storage. The enclosure will also have to protect the battery pack from extreme temperatures, humidity, and water entry.

So, a customer will need to figure out how the cover will close and attach so that the battery pack stays securely in place without having the connection accidentally terminate due to vibrations, shocks, or other environmental impacts. The customer should consider all specialty connections inside the enclosure and the contact points with the battery, the cables used to monitor the battery chemistry to ensure safe use, and wire harnesses.

Battery pack manufactured with custom enclosure and BMS

Battery pack manufactured with custom enclosure and battery management system (BMS).

The enclosure may be housed entirely inside the product, or in may be attached externally onto the product and work as a mechanical function in the application. When there is limited information and there are no drawings of the enclosure exterior, we will need to understand where the enclosure will be located as well as the color, materials to use, finish, and how the pack will be charged if it will consist of rechargeable batteries. Possible battery enclosure design considerations:

  • Shrink Wrap:This is method can be used when the battery will be completely enclosed in the product and you are looking for the least expensive and simplest method. This process may be ideal when the battery will experience little environmental conditions inside the product.
  • Vacuum Formed Plastic:In some cases, the battery will be enclosed inside the product yet still may be susceptible to certain environmental conditions as vacuum formed plastic may be used.
  • Injection Molded Plastic:This is a common process for battery pack enclosures. It can be used when the battery is encased in the product or when the enclosure will form an outer area of the product.
  • Vented Enclosures: Vented enclosures may be desired when there will be thermal effects that will cause the batteries to swell due to generated heat and gases over a long period of time as this feature allows for air flow.

Metal enclosures may also be used for the battery pack. When selecting a metal material, a customer should take into consideration the type of material that may increase the weight to the product or may not be compatible with other materials used for the product's components.

Battery potting may also be desired to provide shock and vibration resistance, and to increase flame retardant properties and electrical insulation capabilities. The enclosure will be placed into a resin consisting of polyester, epoxy, acrylic, urethane, and silicone.

A drawing of the enclosure exterior is normally preferred when a customer contacts a battery pack manufacturer, as it provides greater dimensions and functions in regard to the enclosure exterior. If 3D drawings are not applicable, then a 2D drawing will be acceptable.

Chemistry Considerations

Deciding on the battery chemistry will require the customer to know the power requirements of the application or product during specified lengths of time. Some applications may need short bursts of power to start a set of processes, while others require low power over a longer time frame. Chemistry types that we will talk about with the customer will include:

  • Alkaline
  • Nickel Metal Hydride (NiMH)
  • Nickel Cadmium (Ni-Cd)
  • Lithium

When working with limited information, there are certain key factors that we consider. This process will help us narrow down the type of chemistry that will work with your budget and time to market.

  • Battery pack size: Size does matter when it comes to battery packs, as it will have to fit into the product without hampering the product's functions. For example, lithium-based batteries come in very small sizes when compared to NiMH.
  • Costs: When it comes to costs, lithium-based batteries will be more expensive than alkaline, Ni-Cd, and NiMH. One thing to keep in mind when figuring out your budget is to consider both the battery pack development costs as well as the retail sales price of the finished product. You do not what to overprice the product for the particular market where it will become unsaleable.
  • Energy Density and Power Density: Energy density and power density may sound similar. Yet they consist of two different factors for battery packs. Energy density consists of the amount of energy that a battery chemistry can store within the specific mass and size. Power density comes into play based on the amount of power that the battery can deliver.

So, a battery pack with a high energy density can provide a lower amount of power for a longer time before needing to be recharged. Meanwhile, a customer developing a small RC car toy will require a smaller battery that provides a higher power density for it to function. Examples of energy density and power density in certain battery chemistries are:

  • Ni-MH: It has a power density of 1.5 to 4 megawatt per cubic meter (MW/m3) and an energy density of 70 to 100 kilowatt per cubic meter (kWH/m3)
  • Lithium: It has a power density of 0.4 to 2 megawatt per cubic meter (MW/m3) and an energy density of 80 to 200 kilowatt per cubic meter (kWH/m3)
  • Voltage: The voltage of a specific battery chemistry will impact the number of cells that will be required. Each cell will have a specific voltage, such as a Ni-MH battery chemistry having a 1.2 voltage. If you require more of a voltage, additional cells will need to be added, or the customer may need to switch to a different battery chemistry that offers a higher voltage in each cell if the enclosure size is small.
  • Specific Energy and Specific Power: The specific energy of the battery is based on how much capacity there is based on the weight of the battery, which can be a factor if the product has to come in a certain weight for it to function. The specific power of the battery indicates the amount of loading that the battery provides. So, the product may require high specific power, such as portable power tools, but will have lower specific energy capacity due to the lightweight requirements of the battery.

All these factors will need to be taken into consideration when developing a battery pack. These key aspects will impact the battery pack size, weight, charging requirements, discharging requirements, and cost feasibility.

Number of Cells

Once a battery chemistry is decided, we will need to know the number of cells and the arrangement of the cells to provide the right current and capacity for the product. The enclosure's dimensions will have an impact on these battery cell aspects. The number of cells that will be required will be decided by both the customer and our engineers to get the right arrangement as well as to make the battery pack more physically attractive when inside the product. Possible configurations include:

  • Linear cells (F-type): straps are placed on the top when there is an even number of cells. When there is an odd number of cells, there will be one strap on the top and one on the bottom.
  • Multi-row cells: Multi-row cells are cubic or composite F-type as they are packed evenly based on the number of cells available.
  • Nested type cells: Nested cells are packed so they take the least amount of space as possible.
  • Circular type cells: This process involves packing the cells in a circular tube. Anywhere from 2 cells up to 91 cells can be packed in tubes.
  • Linear cells (L Type): These cells are stacked end to end with a welded nickel strip over the terminals.

These are some of the standard battery pack configurations. Keep in mind that the customer could select small cells to improve the aesthetic appearance of the battery pack but will require multiple packs based on the product's power needs. You could also select large cells when fewer batteries are needed.

Certifications and Industry Requirements

A customer should always abide by all industry standards regarding the development, shipping, and transportation of the battery packs provided within their products. Certain industries, such as medical, may require serializing every battery pack and component of the product. For the aerospace industry, special in-house testing and documentation is necessary. In addition, certification and testing may be required based on the battery chemistry, as this is required for all lithium-based batteries.

There are a range of organizations that require certifications. These certifications can increase both battery pack development lead times and battery testing costs based on the specific certification. Organizations that require certification include:

  • UN/DOT: Certification is required for all lithium battery products that will be shipped as air freight
  • CE Marking: The CE marking applies to battery pack's safety requirements that are sold in the European Union
  • International Electrotechnical Commission (IEC): Provides key standards and certifications for primary and secondary lithium-based cells, primary and secondary rechargeable lithium-based cells, and batteries and secondary cells consisting of alkaline or non-acid electrolytes.

Underwriters Laboratories (UL): As an independent product safety certification organization, they provide certifications for batteries used in electric vehicles, lithium-based cells, primary rechargeable cells that are portable, and rechargeable secondary batteries used as power sources in products.

In addition, there are other organizations that provide a range of safety requirements, consensus-based standards, and guidelines that a customer can review. These organizations are: International Air Transport Association (IATA), the American National Standards Institute (ANSI), the Society of Automotive and Aerospace Engineers (SAE), and the Institute of Electrical and Electronics Engineers (IEEE). Contacting these organizations or reviewing the most current standards on their website can help customers ensure that they are following all safety and testing requirements.

Summary

When developing a product that requires a custom battery pack solution, it is not always easy to figure out the type of battery chemistries, number of cells, pack configurations, or the enclosure requirements. Even when having limited information, our technical team and engineers can help you figure out the specifications that are needed so we can supply you with the appropriate and safe battery pack that will power your product or application.


Topics: Battery Packs


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