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.
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: