The Offshore Voyaging Reference Site

Why Lithium Battery Load Dumps Matter

I have been thinking about and researching lithium batteries a lot over the last three months. One of the things that has jumped out at me is the way the load dump problem is being downplayed by both cruisers and industry players.

Now, before I go any further, this is not going to be a tirade against lithium batteries on cruising boats. I’m totally aware of the compelling benefits.

Rather, I’m going to discuss why it’s so important to install a lithium battery system that will prevent load dumps, and then, in the next article, I will cover how to do that.

Let’s start with a quick overview of what load dumps are.

If any of the following limits are violated¹:

  • Over temperature
  • Under temperature
  • Charge over-current
  • Charge over-voltage
  • Too low state of charge
  • Too high state of charge
  • One or more cells in the battery too far out of voltage balance with the others

The battery management system (BMS) will disconnect the battery; in other words, a load dump.

Bonus Tip

The very words “load dump” are misleading since many BMSs, particularly cheaper ones, will disconnect both the loads and charging sources, and smarter ones will more frequently disconnect the charging sources than the loads, so “charge and/or load disconnect” would be more meaningful wording.

The next thing to understand is what we are typically told about load dumps is salesperson-speak at best, and dangerous at worst.

For example, a common reassurance we get when we ask about load dumps is that they are no problem since all we need to do is install an alternator surge suppressor and then load dumps won’t matter since no damage will be done.

First off, the idea that one of these little gadgets will always and repeatedly protect the alternator and the boat’s electronics is suspect at best, but that’s a different article.

¹Some less expensive and less capable BMSs don’t monitor for all of these criteria.

Load Dumps Are High Risk

The second issue, that pretty much universally gets ignored or glossed over, is how dangerous load dumps are, right up to jeopardizing the lives of the crew on the boat.

OK, that sounds dramatic, but let me give you a couple of scenarios to make my point:

More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—Part 1, BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Part 2, Balancing and Monitoring
  32. 11 Steps To Better Lead Acid Battery Life
  33. How Hard Can We Charge Our Lead-Acid Batteries?
  34. How Lead Acid Batteries Get Wrecked and What To Do About It
  35. Equalizing Batteries, The Reality
  36. Renewable Power
  37. Wind Generators
  38. Solar Power
  39. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  40. Battery Monitors, Part 1—Which Type Is Right For You?
  41. Battery Monitors, Part 2—Recommended Unit
  42. Battery Monitors, Part 3—Calibration and Use
  43. Battery Containment—Part 1