Overheating Equipment in the Trunk?

My last few entries have been about changes to my stereo and ham radio projects. I’ll finish the series by answering a frequently asked question: “Doesn’t your equipment get hot or risk overheating under the trunk floor?” I considered that possibility after feeling a hot Helix amplifier and had even designed a forced ventilation system to help mitigate any unseen problems. I had some fans on hand, but decided to wait for the car’s first warm weather to watch the assess the setup. The summer of 2017 came and went without a single problem. Sure, the amplifiers felt warm, one was even hot, but how bad was it? I added a remote temperature sensor to the trunk in 2018 to make a better analysis. The results were surprising…

I bought an indoor/outdoor thermometer and placed the “outdoor” sensor in the trunk. At first, I just tossed it in an open spot near an amplifier. I drove the car for about an hour to heat-up the amplifiers and give the trunk temperatures time to rise. I placed my hand on each amplifier to see which one was warmest. It was the Helix amp. I used a laser thermometer, shown above, to verify my findings by measuring each metallic object in the space. I then placed the remote temperature sensor directly against the Helix amp. I think this location yields a slightly unrealistic readout because it’s measuring the temperature of the amplifier casing instead of the air temperature of the equipment space. But I stuck with it because I wanted to measure a worst case scenario.

Oddly enough, the Helix amp wasn’t terribly hot. I attribute the perception that the amps are “hot to touch” on the fact that our hands are much cooler than anything inside a hot car. My laser thermometer indicates that the surface of my hands is ~92°F and my fingertips are 85°F. It’s only natural that a 110-degree amplifier can feel hot to touch, but still be operating within its design limits. Think about it: Engineers know that cars get hot inside. So wouldn’t it stand to reason that they’d design automotive electronics with that in mind? For example, my ham radio’s published operating range is 14-140°F. Might audio amplifiers have similar capabilities? If so, is any of my equipment in real danger of overheating?

See the various photos below to see my measurements. Some of my measurements were taken with a cold car in the morning, some where of a cold car in the afternoon, and some were after the car was hot and had been driven around with the amplifiers heating the trunk cavity. In some photos, I was able to capture the outdoor temperature on the dash, the “IN” temperature of the passenger compartment, and the “OUT” temperature of the equipment area. This photo shows that the temperature in the passenger compartment (“IN”) rose to 94°F, even on a cooler day, but the equipment space (“OUT”) was still at its morning temperature of 74°F. This is a good indicator of how well the trunk floor insulates the area beneath it. Read the description of each photograph to see what I was comparing.

The trunk never really gets “cool” on a hot summer day. Still, I was surprised to discover that the trunk floor does a very good job of isolating the 120-degree interior from the electronics. The temperature below the trunk floor consistently matches the outdoor temperature within a few degrees after sitting for more than 4-5 hours. It matches the outside temperature each morning. On a hot day, the car’s interior can soar to over 120°F when parked. However, the space below the trunk floor still falls within a few degrees of the outdoor temperature. With that in mind, why would I want to set up a ventilation system that pumps hot air into my electronics area?

Once the car is driving and the air conditioner has finally cooled the interior,  the amps heat the equipment space around 20°F over the outdoor temperature, even less when the outdoor temperature is below 90°F. In short, the highest temperature I’ve ever seen the hottest amplifier in my cache reach is 120°F, which is probably below its design limit. Now that I’ve run this setup for two full summers, I find very little reason to add external cooling. Of course, that’s how I see things on my modest 700-watt setup. Someone driving much more power may see different results.

I’ve placed a photo with each paragraph just to break up the page. There’s not much rhyme or reason to their placement. HAHA! See the descriptions in the album below to see what was measured in each photo.

Not Too Hot,

Scott

 

About Scott

I grew up near Houston, TX and served in the U. S. Coast Guard for over 30 years. I have an electronics background and continue to work in the electronics engineering field. I taught myself the basics about automotive systems as well as how to perform some of my own maintenance (cars and bicycles). I became involved with Amateur Radio and computers in 1995. The explosion of technology has made my job and several of my hobbies quite interesting. My hobbies include Volkswagens, bicycling, photography, electronics, amateur radio, web management, and reptiles. Visit my websites to learn more.
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