Principles of Operation:
LP175 Lithium Battery Pack

NortekUSA has developed a lithium battery pack for use in many Nortek products.  The "LP175" lithium battery pack increases the duration of deployments by 3-4 times, yet its safe enough to ship to most locations (on non-passenger aircraft).

Lithium battery packs have long been used to extend the duration of ocean deployments, but at the cost of greater risk because they are capable of storing so much more energy than alkaline packs. Because they have traditionally represented a safety risk, Lithium packs have also been much harder to ship. NortekUSA's LP175 lithium pack is a new design, produced by Tadiran Batteries. This pack retains high total capacity, yet improves its safety, which enables you to ship the pack with fewer restrictions.

The LP175 has been designed specifically for Nortek's instruments (up to high-power) and is optimized to support long deployments. The LP175H battery pack supports high power operation.

Advantages of lithium packs compared with alkaline packs

• Increase deployment durations by 3-4 times
• Capacity is less sensitive to operational temperature
• Lighter weight

Figure 1. Battery voltage vs. time from two LP-175 deployments. The deployment duration is shown in units relative to the duration forecast for a standard alkaline battery pack (dashed line).

Deployment duration  

Laboratory tests indicated that the LP175 would have an effective capacity of around 175 watt-hours, or about 3.5 times a standard 50 watt-hour alkaline battery pack. Figure 1 shows the results from two deployments, one which depleted the battery pack and a second which used about 90% of its capacity. The LP175 lasted (or would have lasted) about 4.5 times as long as a standard alkaline pack.

For most typical measurements we recommend that you plan deployments around a capacity of 350% of a standard alkaline pack.  For  more aggressive sampling configurations (duty cycle greater than about 90%, such as continuous sampling with a Vector), we recommend that you plan deployments around a capacity of about 250%.

Safety and Shipping  

The LP175's lithium cells use a new packaging design that makes the pack far more stable and safer than most other lithium packs. The LP175 has been tested with a rigorous (and expensive) series of tests, following standards set by the United Nations. By passing these tests, the LP175 qualifies for unrestricted shipping (on non-passenger aircraft)

Performance characteristics  

One consequence of the new design is that the LP175 supplies relatively low current. The LP175 can easily supply the average current typically required by a Nortek instrument, but these instruments also require short-duration high-current pulses (Table 1) when they transmit sound. The LP175 handles these current pulses with small rechargeable cells (Figure 2). These cells store relatively little energy, but they supply the current needed for these short pulses.

Table 1. Transmit current vs. power level. A typical transmit duration is 1 ms.

Figure 2. Simplified schematic of the LP175 design. Lithium cells (A) provide most of the energy storage, but supply relatively low current. Rechargable cells (B) provide short-term current pulses up to 1 A. The LP175H will use larger rechargable cells, increasing pulse currents to 4 A. Diode C is for protection, and resettable fuse D prevents excessive current.