The Brainstorm is a section of Product Design & Development where we talk with industry leaders to get their perspective on issues critical to the overall design engineering marketplace. In this issue, we ask:
What is the minimum acceptable battery life? Is longer battery life preferred over higher measurement reporting frequency?
Sol Jacobs, Vice President & General Manager, Tadiran Batteries
Determining minimum acceptable battery life is often dictated by application-specific requirements, as product designs must continually adapt to address customer needs as well as keep pace with the competition.
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As a general rule, short-lived batteries can suffice in situations where the product is easily accessible and the costs associated with battery failure are fairly minimal. However, if the device performs a mission- or safety-critical function in a remote location where battery replacement is impossible or not cost effective, then a long-life battery is a must.
For example, when a utility installs a network AMR utility meters in tens of thousands of homes and businesses, then extremely long-life batteries are essential, as a premature system-wide battery changeout can become a logistical nightmare resulting in huge labor expense, disrupted billing cycles, and reduced cash flow. That is why virtually all leading AMR meter manufacturers specify lithium thioryl chloride batteries with a proven service life of over 20 years.
The competing demands of extended battery life versus higher measurement reporting frequency also require application-specific solutions.
In many instances design engineers can achieve both goals simultaneously through the innovative use of power-saving circuitry, low-power RF communication protocols such as ZigBeeand energy-saving product design, such as programming the device to operate in multiple modes, including a sleep or standby mode requiring nil or very low current, an active interrogation/transmission mode where energy demand rises for briefly before returning to sleep or standby mode to conserve energy.
Once again, the application-specific requirements dictate the power management solution.
Dr. Robin Sarah Tichy, Technical Marketing Manger, Micro Power Electronics
During last quarter century, the power demands on portable devices in consumer, business, government and military applications have grown exponentially.
To attempt a better match between the demand and supply of power, design engineers are making great strides in power management technologies. Sleep modes, variable speed disk drives and other technologies have ensured greater efficiencies and less energy waste. Battery technology has attempted, with some success, to keep pace with the demands of the marketplace.
New chemistries have made dramatic improvements in both weight and volumetric measures of cell energy density.
Required battery life is defined by the needs and expectations of the user. Size and weight limitations, the constraints on portable power, are also defined by the usage scenario, so there should be a tipping point where the increase in battery capacity yields diminishing returns in satisfaction. Yet the gap between power supply and demand continues to widen as the market pushes for more functionality and hence higher capacity requirements.
Battery system management and reporting schemes attempt to mitigate the problem. Battery systems engineers and specialists work with design engineers and power management experts to maximize the power available and battery management hardware can report time to empty more accurately than ever before.
Knowledge of remaining battery power may ease user frustration; however, accurate reporting of battery status can never be a substitute for sufficient battery life.
For example, batteries that power barcode scanners for warehouses and large-scale commercial use must last for the duration of a worker's shift. A battery that does not delivery sufficient time introduces inefficiency in the workday and when this inefficiency is multiplied by every worker for several shifts a day, large amounts of money can be lost.
Chris Cooper, Power Technology Specialist, Avnet Electronics Marketing
As I sit here on a plane, strapped in to my mobile “office” and rubbing shoulders with the “sleeping beauty” next to me, I notice I only have 20 percent battery capacity remaining on my laptop.
I can’t help but think that unlimited battery life is the holy grail of all portable devices. Unfortunately, we don’t live in a fairy tale world so we have to tolerate limited battery life. But what is the minimum acceptable amount?
For consumer devices, it must be the point at which the user would rather toss his device in a lake instead of agonizingly plugging it in for yet another recharge. (Battery: 15 percent)
For commercial and industrial products, insufficient battery life now impacts productivity and the bottom line - profit. The amount of acceptable battery life depends on the function that the device is providing and whether it can successfully perform its function without undue interruption. (Battery: 10 percent)
Ultimately, an acceptable battery life ensures the user sees the value or convenience the product provides without the user being consumed by the annoyance of recharging or replacing.
The measurement frequency needs to be adequate so that the device performs the task it was designed for. In most cases, the reporting frequency is a functional requirement. (Battery: 5 percent) Assuming the reporting frequency is sufficient, an increase usually has diminishing returns and, of course, the Holy Grail would be more desirable.
Without an acceptable battery life the device is (Preparing to Standby)….