# What condition may cause the plug or the power adapter to become very warm or hot? [closed]

I know that using a power adapter for very long hours (probably more than 24 hours) can cause the plug of a power adapter (or even the power adapter itself) very warm or hot.

However, I am interested to know what other situation(s) can cause the plug and/or its power adapter to become very warm or hot? (and would appreciate if answer can include on how to prevent or solve the situation)

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## closed as off topic by Kellenjb, Leon Heller, stevenvh, W5VO♦Oct 6 '12 at 22:59

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An equivalent formula for Olin's is

Power = Voltage $\times$ Current

and

Energy = Power $\times$ Time

All substances have a heat capacity, which indicates how much temperature rises if you add a certain amount of energy it. For instance, if you dissipate 10 W during 1 second temperature may rise by 1°C. Another second and it rises by another degree. So you would think temperature will keep rising as long as you use the adapter, but fortunately that's not true, as you also have experienced. That's because as heat is added there's also some heat lost to the environment. The higher the temperature difference between the adapter and the surrounding air, the more heat it will lose. So with rising temperature finally you will reach an equilibrium where the amount of dissipated energy equals the amount of lost energy, and then temperature won't rise anymore.

So, this equilibrium depends on temperature difference. If your adapter will go to 50°C in a 20°C room, it will go to 60°C in a 30°C room. It needs the same difference to get rid of the same amount of energy.

The designers of these adapters know that they will get hot, and have accounted for a certain environment temperature at maximum power. In normal conditions you should be safe, but the adapter will no doubt fail quickly when used in a 85°C sauna. That's the reason sauna's normally don't have electronics (I haven't seen any so far); they use the good old hourglass as timer.

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Long term use doesn't cause the heat. This heat simply comes from the current thru it times its little bit of inevitable series resistance. The exact forumulat is:

Watt = Amps² * Ohms

For example, if you are running 10 A thru a adapter plug and it has a series resistance of 25 mΩ, then it will dissipate 2.5 W. You will definitely notice that getting warm. Whether that is a safety hazard depends on whether it can get rid of 2.5 W of heat without getting so hot as to catch fire. The best way to determine that is to look at its rating. Don't let more current run thru it than it is rated to handle.

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When your plug or adapter becomes too hot, it is in an overload condition. Then, some seconds or, at most, a few minutes will be enough to set it on fire.

Your adapter or plug will have reached its thermal steady-state after something like 15...30 minutes, given it is not connected to a load that changes its behavior after this amount of time. If it is still within its limits after this time, it will remain fine even after days or months. (cf. thermal capacity)

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