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Maximizing the 3D Experience: Don’t Overlook the Batteries

Fri, 11/05/2010 - 10:39am
Eric Lind, VP Business Development at Contour Energy Systems
Eric_T._LindImagine your disappointment when your 3D glasses fail just as the action peaks in a movie or during a game. With rechargeable batteries you’re stuck waiting for the glasses to recharge (having a spare pair is just too difficult to justify given the current high price). With primary batteries, you’re in much better shape: back to viewing after only a brief pause in the action.

This article examines an often overlooked aspect of today’s 3D experience: the need for a power source in “active shutter” 3D glasses. The material begins with a brief explanation of how these 3D glasses work, then compares the different batteries available, including their shelf and service lives, relative price/performance, anticipated costs, and environmental impacts.

Why “Active” 3D?
Simply put: Active 3D glasses provide a quite realistic and, therefore, far superior experience than the previous passive system. Not only were the old-fashioned glasses with red and blue filters embarrassing to wear (witness the humorous photos of people watching movies in a theater), the experience they offered was fairly poor. The 3D effect was limited, colors failed to render properly, and the image was blurry without the glasses (meaning one had to don these ridiculous things to watch). Apparently even the content producers knew the approach was ill-fated because the glasses were always disposable, being made of paper and cheap plastic lenses.

The right way to do 3D requires a “stereoscopic” technique that continuously alternates a left eye image with a right eye image. Because this new approach mimics real-life vision, where each eye has a different perspective, the experience is far more satisfying than was possible with the old red/blue filters, where the two separate images appeared simultaneously, and neither was completely isolated to just one eye.

Isolating the left and right eye images completely requires the new “active shutter” 3D glasses, and these must, therefore, have a power source—a rechargeable or primary battery. The power is required for the glasses to perform their two separate, yet related functions: alternately polarizing or blocking the right and left liquid crystal lenses; and synchronizing this polarization with the left and right images appearing at different times on the screen. Of the two, polarizing the electro-optical lens shutters between transparent and opaque at a minimum rate of 120 cycles per second (60 for each lens) consumes the most power. By contrast, the receiver for the infrared or wireless synchronization signal that is transmitted by the 3D TV consumes very little power. The choice of batteries, therefore, becomes an important part of the 3D experience.

Primary vs. Rechargeable Batteries
Although some rechargeable batteries are made of some pretty toxic stuff, (think NiCad or NiMH) their use is generally considered to be more environmentally friendly. The problem with all rechargeable batteries, however, is their inherent high self-discharge rate. Putting it another way: rechargeables lose their charge pretty quickly when not in use. And that means they must normally be recharged continuously or immediately prior to use, especially for a long movie or sporting event lasting several hours.

The need to ensure that these batteries are fairly fully charged prior to use encounters another problem: the charging system itself. Most rechargeable glasses employ a USB port as the power source, which requires storing the glasses near a PC (with it being turned on, of course), or getting a separate USB power supply. This arrangement might be fine for gaming applications on a 3D PC monitor, but it is far from ideal for TV viewing.

These and other problems with rechargeable batteries (including increased design costs) are the reason why most manufacturers of active 3D glasses offer versions that use primary batteries, and these currently enjoy a 70% (and growing) marketshare. Primary batteries have very long shelf lives, which is why they are always used in smoke detectors and other mission-critical applications. Primary batteries also enjoy a longer service life, which means more 3D viewing time. And as pointed out in the introduction, the batteries can be replaced quickly during the movie or game. But not all primary batteries are created equal.

Comparing the Primary Batteries
Battery life varies greatly among the different sizes, brands and chemistries. Some are “cheap” (a low price with low performance); others are premium (with great performance, but all too often accompanied by a premium price). The chart below shows the energy densities of some popular brands for the two different types of coin cells now used in active shutter 3D glasses. 

These charts show how battery life (measured in milliamp-hours of operation) varies substantially by battery size, chemistry and brand.

It is important to note that the tests used to measure energy density are normally performed at a constant drain rate (milliamps of current) to a 2.0 volt charge for 3.0 volt 2025 and 2032 coin cell batteries. And most 3D glasses should, in fact, draw a fairly constant current from the batteries while performing their two functions. What can vary by the type of glasses, however, is the depleted battery voltage where failure occurs. Some glasses may continue to operate below 2.0 volts, while others may cease operating at a slightly higher voltage.

It is also important note the relative capacity of these primary batteries compared to rechargeable batteries. For example, the leading coin cells shown here have energy densities in the range of 170 to 250 milliamp-hours (mAh) or more, depending on the cell size. But a typical rechargeable battery of comparable size has less than half the energy density, generally in the range of 80 to 100 mAh. And with their high self-discharge rate, this smaller capacity is depleted fairly quickly during storage.

Comparing the Costs
A cost comparison must begin with the glasses themselves. Rechargeable glasses inevitably cost more—up to $50 more. That buys a lot of primary batteries, potentially placing the breakeven point beyond the lifespan of the glasses, depending on viewing habits. And because the internal rechargeable battery cannot be replaced by the consumer, the glasses become useless when the battery ultimately (and inevitably) no longer holds a charge.

“Typical” primary batteries deliver about 60 hours of total viewing time in “typical” 3D glasses. Of course, there is nothing really “typical” in this nascent market, but such conventions need to be used to compare available alternatives on an “apples to apples” basis. Assuming eight hours of viewing per week (e.g. a movie and two sporting events), the typical battery will last a little less than two months, requiring about seven replacements every year. With up to two batteries per pair of glasses and a typical cost of $3.00 each (whether sold individually or in 2-packs), this typical user should expect to pay around $42 per year for batteries. It should come as no surprise that this cost will greatly disappoint the “typical” consumer!

Now consider a battery purpose-built for active shutter 3D glasses that delivers up to 80 hours of viewing time and costs only $2.50 each (in 6-packs). (Yes, such batteries are available for the more conscientious consumers.) These batteries will last nearly three months for the typical user, requiring replacement only five times a year at a total annual cost of just $25. This results in an annual savings nearly $20 over typical primary batteries, and a breakeven period of two years compared to 3D glasses with rechargeable batteries.

These savings also accrue to the environment, of course, with four fewer batteries per user per year being properly disposed of (You do properly dispose of all your used batteries, don’t you?) at your local battery merchant’s place of business or city’s recycling site. While a difference of four batteries per year per user may seem trivial, if any of the various projections about the enormous popularity of 3D TV comes true, the planet stands to benefit tremendously.

Conclusion
While not nearly as important as the choice of TV (and their companion active shutter glasses), the choice of battery type and brand is an important aspect of the 3D experience. After all, batteries always fail only when they are being used. Gamers may prefer rechargeables owing to the ability of the PC’s built-in USB ports to keep them continuously charged. Movie and sports enthusiasts are likely to prefer primary batteries for their longer shelf and service lives, and ease of quick replacement. And the gamer, who is also a movie buff or avid sports fan, will just need to have two pairs of glasses.

About the Author
Before joining Contour Energy Systems as VP of Business Development, Eric Lind was the VP/General Manager of Ultralife Corporation’s Commercial Business, where he led the sales, marketing, and engineering efforts for new and existing products in the automotive, medical, industrial, and other portable power markets. Prior to that Eric was the Director of Business Development in ConocoPhillips’ Emerging Technology group, charged with bringing new technologies from concept to commercialization, and he started his career at Duracell (a division of Procter and Gamble) where he spent eight years in various engineering and management positions within the company’s strategic OEM business group. Eric is a graduate of Duke University with a double major in Biomedical Engineering and Electrical Engineering, and holds an MBA from the University of Connecticut with a concentration in Marketing.
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