Electronic Design

Don’t Let Battery Life “Drain” On The 3D Parade

The “active shutter” glasses used with the latest 3D TVs and gaming applications require batteries to perform two functions: alternately polarize the right and left liquid crystal lenses, and synchronize with the screen. Both functions continuously drain the batteries while viewing. Of the two, polarizing the electro-optical lens shutters between transparent and opaque, at the rate of at least 120 cycles/s (60 for each lens), consumes the most power. 

Different glasses and different batteries naturally possess different power characteristics. Still, they share one thing in common—when the glasses are being used, the batteries will inevitably fail because there’s no way to test the remaining capacity. Therefore, minimizing these occurrences means that battery life is crucial to minimize “draining” the 3D experience. 

Primary Versus Rechargeable
The first major consideration consumers face is whether to splurge on glasses with rechargeable batteries (costing an extra $50 on average) or use glasses with replaceable batteries. Although rechargeable batteries are more “politically correct” among environmentally conscious consumers, most are well aware of their limitations. The main problem is their relatively lower capacity versus non-rechargeable options. As a result, they must be recharged prior to use, especially for a movie or sporting event lasting several hours. If not, the glasses could fail during the event, resulting in the user having to wait for the batteries to recharge to finish watching the event—and that especially isn’t ideal for live activities .

Another problem with 3D glasses is that they use the USB as the power source. This requires storing the glasses near a PC (with it being turned on, of course) or getting a separate USB power supply. Such an arrangement might be fine for gaming applications on a 3D PC monitor, but it’s less than ideal for TV viewing. 

Also considering the additional cost, these disadvantages have shifted the market toward glasses that use replaceable batteries, as evidenced by their 70% (and growing) share. Primary batteries have a very long shelf life, accompanied by a longer service life, which means more 3D viewing time. When properly disposed of (most consumer electronics stores now recycle batteries), they can be just as environmentally friendly as rechargeables. 

Battle Of The Batteries
Not too surprisingly, performance varies dramatically among the different chemistries and brands of today’s primary batteries (see the figure). The tests used to measure energy density are normally performed at a constant drain rate (milliamps of current) to a 2.0-V charge for 3.0-V 2025 and 2032 coin cells.

In addition, most 3D glasses should draw fairly constant power while performing their two functions. What can vary by the type of glasses, however, is the end-of-life battery voltage when proper operation ceases. 

It’s important to note the relative capacity of these primary batteries compared to rechargeables.  While the leading coin cells have energy densities ranging from 170 to 250 mAh or more, the typical rechargeable of comparable size has less than half the energy density, generally in the range of 80 to 100 mAh (see the figure, again). And with their high self-discharge rate, this smaller capacity is depleted fairly quickly between uses. 

Annual Costs—And Savings
The best possible price/performance requires a combination of superior performance and a competitive price. For instance, Contour was able to achieve peak performance by customizing or “tuning” the battery specifically for the operating characteristics of active shutter 3D glasses.  Of equal significance is that customizing batteries for use in specific applications need not increase their cost. In fact, it can actually create a less expensive solution. 

The customized battery’s 33% improvement in average performance, combined with a 17% cost reduction, annually saves the “typical” viewer around $30. This comparison is based on eight hours of viewing per week. In this case, the pair of average batteries would need to be replaced seven times a year at a cost of $42, while the less expensive customized batteries would need to be replaced five times a year at a cost of $12.50, based on the suggested retail price.

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