Battery Management Systems for Hand Held Devices

Battery management systems for hand held devices take into account many design considerations including heat dissipation, form factor, weight and load. Feedback to the user on the state of the battery is also critical.



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Video Transcript

Welcome to Engineering.com's series on the design of battery packs and battery management systems.

In the other videos in the series we looked at battery packs and the battery management systems that provide the crucial protection, energy management and cell balancing required to make batteries work. In this video, we're going to take a closer look at some of the unique challenges that battery pack designers face when designing batteries like available space, heat dissipation requirements and form factor or “usability” of a device.

Nowadays, batteries are designed for a huge variety of applications that we use everyday. When designing a battery pack for a hand-held device, several challenges come into play. First of all, the size and weight of the battery is important . The battery pack has to be able to meet the output voltage and current requirements of the device but it can't be too big or too heavy to hold in your hand. Another issue that has to be considered is how comfortable the device is to use. The device may be shaped so it fits comfortably in the average hand and have the center of gravity placed in a certain spot to make it more comfortable to use. Battery pack designers often have to work to accommodate these “form factors” and weight distributions.

For example, take a typical cordless drill. The battery for a cordless drill usually fits on the bottom of the handle but if this battery is too big or too heavy it makes the drill harder to use since the weight of the battery will tend to torque the drill away from the thing you're drilling.

Companies that design and manufacture battery management systems are faced with designing systems that meet complex shape requirements in limited space. System design of the OEM equipment will dictate the budget demands and spatial constraints, and that's where the fun begins, generally, there's not enough space, the space that's available is too small to accommodate the heat transfer, and then designers also have to think about the connectivity of the battery to the device.

This battery management system for an EMS radio battery using a flexible circuit. On the right, you'll see the charge contacts, charge plus, charge minus and temperature thermistor. On the left you'll see the actual contacts for the radio. The entire circuit is flexible since it's designed to wrap around the battery cells and fit within the available space inside the radio.

This battery pack is from a medical application: a patient monitoring unit used to measure a patient's vital signs. It has to be fairly small since it's hand-held and meant to be used in the field and is carried by EMTs in ambulances, so size and mass are design factors. Note the MOSFETs, common to the protector circuit and the control integrated circuit, components common to all battery management systems.

Let's take a look at the electronic circuit that fits onto this pack. Look at the internal construction of the flexible circuit, you'll notice that it has to fit inside a very limited space, so this is a very thin circuit which affects the heat transfer characteristics because thinner boards heat up quicker than thicker ones. Also, note the curve of the pack, no components are placed inside the curve because they'd more likely be damaged in a high-stress area like a curve. Like all battery management systems the components on this flexible circuit are responsible for fuel gauging and protection of the battery.

Now that we've looked at some of the design challenges a battery pack designer faces, you can also check out the other videos in the series to learn about the basic components of a battery management system and what they do, and to look at how at battery packs are design for different large and small-scale applications.



Battery Management Products

Vecture Battery Management Systems
Vecture

Vecture provides design engineering and Battery Management Systems (BMS) manufacturing for the commercial/industrial, consumer, energy, medical, military, and telecommunications markets.