Many subsea engineers accustomed to mechanical hydraulics and/or tethered umbilicals have a concern that "You Cannot Reliably Use Batteries Under Water", so convincing them otherwise is a daily task for battery manufacturer Southwest Electronic Energy (SWE). The company manufacture five standard SeaSafe® battery packs that can be used at an ocean depth of over 6,000m.
Here, we examine three major challenges to the reliable usage of subsea batteries and show how SWE addressed them:
Electrical Connections |
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| CHALLENGE | SOLUTION |
| • Electrical connections do not endure water well • Water conducts electricity, especially salt water - Enables short circuits in cables or connectors or batteries where water may enter unintended |
• All subsea water related electrical connections of battery modules use subsea characterized cables and connectors proven reliable for subsea use… to keep the water out. • Battery modules configured in either a 1 ATM pressure vessel or pressure balance oil filled (PBOF) case are NOT SUBJECT TO SUBSEA WATER • Battery modules inter-wired within the 1 ATM pressure vessel or PBOF case have bulkhead connectors on the external subsea side of the vessel or case that meet subsea requirements • OR battery modules themselves are watertight and use subsea cables and connectors that are suitable for subsea use |
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Subsea Pressure |
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| CHALLENGE | SOLUTION |
| • Integrated circuits and battery cells do not typically withstand high pressure - Designed to work in 1 atmosphere of pressure where we live and breath • Subsea pressure grows higher as a linear relationship to depth - For every 33ft (~10m) you go down, pressure increases by one atmosphere (~14.7 psi) |
• Integrated circuit PCBs are proprietary designed and custom-made for pressure tolerance • Battery cells are custom selected and tested/characterized for pressure tolerance • Battery modules are proprietary manufactured for pressure tolerance • Pressure tolerance rating – SeaSafe® is 6,000m depth |
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Reliable & Automatic Battery Management
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| CHALLENGE | SOLUTION |
| • Built in, distributed management of battery safety to automatically cut off electricity based on violating safe use conditions • Condition based monitoring to know state of health and remaining capacity |
• SeaSafe® BMS built into every battery module - Built in, distributed management of battery safety to automatically cut off electricity based on violating safe use conditions - Condition based monitoring to know state of health and remaining capacity - Distributed battery management to avoid possible single point of failure bringing down all battery management |
As you can see, batteries can be specifically designed and tested to ensure they can cope with subsea conditions and keep the water out. However, this is just the first step on the journey to powering subsea vehicles and equipment. Selecting the right chemistry can make a huge difference, and SWE's SeaSafe® Lithium-ion battery packs offer 4x Longer Mission Run Time and 6x Longer Battery Life Time compared to Sealed Lead Acid (SLA).
