Principles of Operation:
LP175 Lithium Battery Pack

NortekUSA's LP175 lithium battery pack increases the duration of deployments by 3-4 times, yet is safe enough to ship the same as a standard alkaline battery pack.

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 without 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

Disadvantages of lithium packs		LP175 improvements
Safety		New safe design
Difficulty shipping		Ship without restrictions
Current limited		Supports 1 A pulse currents
Difficult disposal		Recycling costs are included
Higher cost per watt-hour

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.

Until we get more experience with these packs, or you get experience with your deployments, we recommend that you plan deployments around a capacity of 350% of a standard alkaline pack.

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, which means that you can ship it the same as you would standard alkaline packs.

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.

Power level		Pulse current (ma)
Low		120
Low+		300
High-		800
High		1600

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.

LP175H  

The LP175's maximum pulse current is 1 A, which covers all but high power operation. The LP175H will support up to 4 A current pulses, which is about 3 times the current required for high power operation.

Planning Guidelines  

You may use low, low+ or high- power, but not high power, with Aquadopps, EasyQs, and EasyVs. Because high power draws more than 1 A, voltage could fall sufficiently low to cause failure and loss of data. You can use high power with Vectors. If you plan a deployment to last 30 days or longer, you can deploy the instrument in any water temperature. If your expected duration is 15 days, you may deploy in water temperatures above 10°C, and if your duration is 10 days, you may deploy in water temperatures greater than 20°C.

Estimating remaining capacity  

The change in battery voltage with time, shown in Figure 1, is characteristic of the LP175 battery packs. This includes the slow rise in voltage over most of the deployment and the pause as the voltage falls at the end of the pack's life. The small change over most of the battery's life is not sufficiently large to enable you to estimate the remaining life--changes associated with water temperature and mean current can be larger. However, the beginning of the first rapid voltage drop indicates that the pack has around 15% of its life left, and when the final voltage drop begins, there is only a few percent left.

Recycling  

When you are finished using an LP175, simply mail it to a recycling center in the USA. The costs for recycling are included in the price of the battery pack.