Why Lithium Battery Load Dumps Matter

Five minutes before I took the photo this salesman told me that all I needed to do to deal with lithium battery BMS load dumps was to fit an alternator surge suppressor.

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:

  1. One Simple Law That Makes Electrical Systems Easy to Understand
  2. How Batteries Charge (Multiple Charging Sources Too)
  3. How Hard Can We Charge Our Lead Acid Batteries?
  4. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  5. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  6. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  7. The Danger of Voltage Drops From High Current (Amp) Loads
  8. How Lead Acid Batteries Get Wrecked and What To Do About It
  9. 11 Steps To Better Lead Acid Battery Life
  10. 10 Tips To Install An Alternator
  11. Stupid Alternator Regulators Get Smarter…Finally
  12. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  13. Smart Chargers Are Not That Smart
  14. Equalizing Batteries, The Reality
  15. Battery Monitors, Part 1—Which Type Is Right For You?
  16. Battery Monitors, Part 2—Recommended Unit
  17. Battery Monitors, Part 3—Calibration and Use
  18. Do You Need A Generator?
  19. Efficient Generator-Based Electrical Systems For Yachts
  20. Battery Bank Size and Generator Run Time, A Case Study
  21. Battery Options, Part 1—Lithium
  22. Battery Options, Part 2—Lead Acid
  23. Why Lithium Battery Load Dumps Matter
  24. 8 Tips To Prevent Lithium Battery Load Dumps
  25. Lithium Ion Batteries Explained
  26. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  27. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  28. Q&A—Are Battery Desulphators a Good Idea?
  29. Renewable Power
  30. Wind Generators
  31. Solar Power
  32. Hydro Power
  33. Watt & Sea Hydro Generator Review
  34. A Simple, Efficient and Inexpensive¹ 12 or 24 Volt DC Electrical System
  35. 8 Checks To Stop Our DC Electrical System From Burning Our Boat

John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for 25 years, first in yachting magazines and, for the last 20 years, as co-editor/publisher of AAC.

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