![\"newbatterycover\"](\"http:\/\/stereo.thurstons.us\/content\/wp-content\/uploads\/2015\/02\/newbatterycover.jpg\")
<\/a> is designed to use two SR44 cells which is a slightly odd choice. Given that the camera is already more than 2kg, why not provide the option of a larger capacity battery bank? I suspect it was just assumed that this new camera should be fed like any other camera, and the designer defaulted to button cells. The downsides of this choice are:<\/p>\n- \n
- Low power capacity<\/li>\n
- High replacement cost<\/li>\n<\/ul>\n
The silver-oxide SR44 cells typically have a power capacity between 150 and 170mAh, and cost about $2 each. A similar battery, the alkaline LR44 carries between 100 and 150 mAh and commonly costs about $1 each. A very different, but interesting alternative, the zinc-air PR44 carries 600mAh and costs about $1 each.<\/p>\n
Current Requirements<\/h1>\n
The battery supplies power to the camera meter and shutter. The meter will draw power while the button under the left thumb is pressed, or when the shutter is cocked and the shutter button is half-pressed. The shutter draws power as long as it is open. A long exposure requires a lot of battery capacity.<\/p>\n
The meter draws .010 amps (10ma). The shutter draws .023 amps (23ma). If both the shutter and meter are active, the draw is .032 amps (32ma). In normal operation, the meter is not<\/em> drawing power while the shutter is open. This scenario was contrived only for demonstration purposes.<\/p>\n
Without an operational battery, the camera meter will not work and the shutter will only work at its fastest rate (1\/500th of a second).<\/p>\n
Voltage Requirements<\/h1>\n
Batteries are not a constant-voltage power supply. Their voltage will vary with age, use, temperature, and load. Typically the voltage drops with age and use, but at what voltage will the TL120 cease working?<\/p>\n
Using a variable-voltage power supply, it was observed that the shutter could be opened with approximately 1.2v and would close at approximately 1.0v. At these very low voltages, it was observed that the two shutters often did not close simultaneously. The shutters were not<\/span> timed in these low voltage tests. Real-world observations make me expect that timing accuracy suffers at low voltages.<\/p>\n
1.2V may be the minimum to operate the shutter, but I estimate that 2.0 is the minimum voltage at which the camera will reliably operate. This is an estimate<\/em>. This has not yet been determined experimentally.<\/p>\n
Battery Performance<\/h1>\n
Different battery chemistries have different discharge characteristics. These characteristics also vary between brands and manufacturers. The discharge characteristics can be determined by experiment, and is sometimes available from the major manufacturers. Choosing the correct battery for a specific use requires matching battery characteristics to the project.<\/p>\n
Documented<\/span><\/h2>\n