Q: My power plug (iPhone) gets very hot while charging the PowerPack battery pack. Is this normal?
A: The heat generated by the power adapter or power plug is determined mainly by the charging current, regardless of what device is on the receiving end of the power. For example, the iPhone square plug will get hot when it stays at close to 1 amp output current, whether it is charging a nearly-depleted iPhone or battery pack. Per the UL safety standard, the upper limit for what’s considered safe is 95 degrees C for plastic and rubber. The hotness sensation depends on both the temperature and the thermal conductivity of the material.
iPhone adapters have built-in safety features that ensure that they will shut off when the temperature is too high. It is known as over-temperature shutoff. Therefore, even though the plug may feel hot to the touch, it is within the design specifications of the plug. That being said, exercising caution and good common sense is always essential when it comes to the safe use of electronics and electrical products.
An iPhone square adapter may feel hotter than a Samsung plug, because of its smaller size. You may compare the two adapters and see the size difference. In general, the larger the size of the charging block, the less hot you feel. Your fingers are simply kept at a greater distance from the hot electrical components inside with more insulation in between.
The bottom line, it is safe to use the iPhone square adapter to charge the battery pack; a Samsung or iPad charging block will work better with the battery pack in terms of recharge time. If the recharging is done faster, the power plug will get a chance to cool off sooner.