Figure 1. Battery voltages measured during deployments of three different Aquadopp Profilers. The deployment duration varied from 60-100 days and the water temperature varied from 6-17°C. The source of the small differences in voltage among the three deployments is unknown, but could arise from differences in the instruments’ calibration, the water temperature or the battery packs themselves. The actual pack voltage is about 0.5-0.6 VDC higher because the measurement is made after a voltage drop across a diode inside the isntrument.

Figure 2. Comparison of typical lithium and alkaline battery pack voltages during deployments. The solid line represens the normal pack voltage and the dashed line the voltage when loaded by the transmit pulse (see below). The voltage of the alkaline pack falls more because of the pack’s internal resistance.

Figure 3. Current in a 2 MHz Aquadopp Current Profiler. The profiler transmits up to 23 pulses each s, each pulse using about 0.8 A of current and dissipating about 0.01 J of energy. Between pusles, profiler operation uses around 55 ma of current. Users can reduce the number of pulses each s by adjusting the measurement load; after the profiler has completed its allotted pulses, it goes into a “wait state” in which it uses only 6.5 ma. When the instrument is finished with a measurement average, it goes to sleep, using around 0.1 ma until it is time to start another measurement. The critical factors for the battery design are the overall energy used and the 0.8 A peak current. The above assumes a voltage of around 12 VDC.

Figure 4. Prototype pack under rapid depletion. Standard packs should not be depleted in less than about a month. We have developed a new pack, which can be depleted in about a week. The voltage curves at the left were measured in a Vector Velocimeter running continuously. One pack was left at room temperature and another was placed in a refrigerator. The dashed black line (“Long Deployment”) is the green curve from Figure 1, but with the time axis scaled to deplete in about 7.5 days.