Curing a Hot Battery Pack

Tips for curing overheating battery packs.

The Problem

I got an email not long ago asking for help. An RC pilot has a model with two 3S LiPo battery packs. The packs are sized according to the airplane kit manufacturer specs. Problem is, after a flight the battery packs are scorching hot. He said that he cannot hold them for more than a second or two. He says “this cannot be good.”

Diagnosis

I could not agree more. That cannot be good. He is causing permanent damage to his battery packs with every flight.

It is tempting to start doing computations to confirm the gut reaction. I could have asked him for the battery capacities, C ratings, motor size, propeller size, and wattmeter readings at full throttle. But what would have really been the point of all of that? The problem is obvious, and the sooner he fixes it, the sooner he will prolong the life of his battery packs.

Possible Solutions

I quickly replied to the email with a list of suggestions. First, increase the amount of cooling air to the batteries. It won’t cost him any money, and it should be easy to do.

Second, get new batteries. Either increase their capacity or the C rating or both. That would decrease the performance demand on the batteries.

Finally, try using a smaller propeller. That would decrease the performance level of the airplane, but it may not be by much.

I concluded my email by saying that a combination of the above might be the best solution of all.

Feedback

The pilot replied that he did not think the battery packs were getting any cooling air at all. Then he added that the airplane manufacturer had recommended a higher C rating than what he was using.

Score! That’s exactly what I was thinking.

Then he mentioned that it was a ducted fan airplane. All of a sudden, it all made sense. Electric ducted fans (EDF) are demanding applications. You need lots of power, and getting cooling air to the batteries can be a challenge.

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