​Click to view in browser​

October 2021

​

Hello Reader,

Wow, It’s October already. And that means it’s been one year since I began this newsletter. Over the past year, I hope you have enjoyed reading as much as I’ve enjoyed writing it, but more importantly, I hope you have learned something.

If you have missed any of the newsletters, they can be found here.

As always, your feedback is welcome and encouraged.

Thanks again for reading.

Rob

​Rob@robdelauter.com ​

​

Thermal Runaway in VRLA Batteries

​

Earlier this month, a customer called with a terrible smell coming from their emergency lighting inverter. He told us it smelled like rotten eggs and the batteries were swollen. Classic signs of thermal runaway.

If not addressed, it could become very dangerous and even lead to fire, though unusual. Figure 1 is the worst case I’ve seen in my career and the fire company was called. Fortunately, no one was injured and no damage outside the battery cabinet.

But what causes this dangerous condition and how can we prevent it?

A battery has internal resistance and when charged, current flows through this resistance generating heat. When the heat is small, the battery can dissipate it. But if it’s too much, the battery heats up.

When the battery heats the current increases, resulting in more heat and more current, a cycle is created, thermal runaway. The only way to stop it is to remove the charging current.

Several things can be done to prevent thermal runaway.

• We can monitor the temperature of the battery and reduce the charging voltage as the batteries warm. This requires a charger capable of temperature compensation, which most modern charges are. But it also requires the proper installation and calibration.
• We also want to limit the charger to an appropriate level for the battery size. Not only does this help with thermal runaway, but it also prevents overcharging the batteries, which leads to cell dry out and early battery failure.
• Proper maintenance by a qualified vendor should be completed at a minimum annually. If the batteries are showing signs of failure, or are end of life, they should be replaced immediately. This will also reduce the risk of load loss.
• Also, be sure the batteries are located in an environmentally controlled space with adequate air circulation.

Thermal Runaway can occur in any size VRLA battery, including the small ones in the UPS system under desks, or the rack mounts located in IT closet. These account for a majority of the thermal runaway incidents we see because they are in warm environments and the batteries are not properly maintained.

However, because the batteries are small and often in unmanned spaces, no one knows until the UPS system fails to support the load during a power outage. When a service tech is dispatched, he finds the batteries swollen and sometimes the telltale smell of rotten eggs.

Thermal runaway can be a scary situation. But with the proper equipment and maintenance, it is preventable.

If you want to know more, below is a link to a paper published by C & D Technologies, a battery manufacturer. It is technical but informative.

​C&D_ThermalRunaway.pdf​

I would also be happy to discuss this in more detail. Send me an email at rob@robdelauter.com

​

​

​