For the boater, the old adage “You reap what you sow” usually rings true. Having peace of mind while out on the water is the ideal experience, and something all boaters desire. But it is important to pay close attention to detail, especially when it comes to the boat’s electrical systems. Some issues can be easily prevented by a thorough inspection of your electrical systems, and one of the most important of these issues is thermal runaway.
Thermal runaway occurs when chemical reactions generate heat, and this increase in heat causes the original reaction to accelerate, thereby generating more heat, and so on. When a boat’s batteries are charging, they heat up—this is completely normal. However, as the charge rate increases, so does the amount of resistance to the charging process. At a certain point, if the heat induced with charging is not dissipated enough, the battery begins a process called thermal runaway.
When a battery reaches this level of heat, even the previously used charge rate causes the battery to overheat. As this cycle of overheating continues, the process escalates. If the charging device does not sense that the battery or batteries are overheating, they could catch fire or even explode.
Thermal runaway is common not just on boats, but also in other applications. A few years ago, laptop manufacturers had to recall thousands of laptops because of this issue.
While performing electrical audits, we often see instances of preventable thermal runaway. Therefore, we strongly recommend constantly checking and questioning the integrity of a boat’s electrical systems. In many cases, by looking at the causes of thermal runaway, it can be prevented before the process even starts. Here are two common causes:
Taking care of your boat’s batteries is usually simple, but some issues are hard to detect. The following tips are easy to implement for most boaters. However, the safety and reliability of your electrical systems should not be taken for granted, so if you are unsure or need guidance, contact a professional for assistance.
To better demonstrate the causes and effects of thermal runaway, here are some scenarios we have seen over the years:
Scenario #1: Approximate Cost - $5,500
A boat owner had a three-by-three battery setup (nine batteries in one battery bank) on his boat. To measure the temperature of a group of batteries accurately, the temperature sensor must be mounted on the warmest battery, in this case the one in the middle. Unfortunately, the temperature sensor was mounted incorrectly on one of the four corner batteries. Under high charging and thermal runaway, the middle battery swelled so much that it practically warped into a balloon shape. Five of the nine batteries were completely ruined, and the four remaining corner batteries were left in mediocre condition. It cost the owner $5,500 just to replace the batteries, teaching him a curt lesson in the importance of positioning the temperature sensor in the correct place.
Scenario #2: Approximate Cost - $2,400
Having just installed a new battery charger, the old temperature sensor was refitted with the new charger. This setup seemed to work fine. However, the temperature reading showed approximately 303 degrees F when it should have read 72 degrees F. This resulted in the battery being constantly undercharged. Eventually the battery bank was damaged and had to be replaced, costing approximately $2,400.
Thermal runaway can be easily prevented if the necessary steps are taken early enough. It’s easy to relax and enjoy the sights and sounds of the open waters worry-free, after having paid attention to the small details—especially when you know your battery system is healthy.
About the author: Jeff Cote is a systems design engineer and owner of Pacific Yacht Systems, a full service shop delivering marine electrical and navigation solutions for recreational boats. Visit their website and blog for info and articles on marine electrical systems, projects and more: www.pysystems.ca.