4 ms·

Electrovibration in Ungrounded MacBook Pros

5 points by jakerockland 10y ago

aexaey 10y ago
Two small nits about second part of this passage: electrovibration — the rapid attraction and repulsion of the skin to an insulated ground plane (such as brushed aluminum) - Metal in unibody MBPs is sandblasted [1] rather than brushed [2] to give it its texture; - Neither sandblasting nor brushing aluminum gives it thick enough oxide layer (Al2O3), and it is that layer that makes actual insulation. Instead this layer is formed by the way of anodizing [3], complementary and separate process. [1] https://en.wikipedia.org/wiki/Abrasive_blasting https://en.wikipedia.org/wiki/Abrasive_blasting [2] https://en.wikipedia.org/wiki/Brushed_metal https://en.wikipedia.org/wiki/Brushed_metal [3] https://en.wikipedia.org/wiki/Anodizing https://en.wikipedia.org/wiki/Anodizing
gaur 10y ago
Trying to power a metal-shelled computer with a 2-prong plug always seemed to me like an example of Apple painting themselves into a corner. The only two options as far as I know are to leave the case floating (which seems bad) or to tie it to the outlet's neutral pin (less bad, but still not great). The latter presumably leaves you at the mercy of how well the building's neutral pins are grounded. The fact that Apple decided to use fairly puny wires between the power brick and the computer probably doesn't help either. [Also, the link on electrovibration seems to imply it's a capacitive effect, so it's caused by an electric (not magnetic) field.]
- aexaey 10y ago
  First option (ground floating) is actually quite common: A Class II or double insulated electrical appliance is one which has been designed in such a way that it does not require a safety connection to electrical earth (ground). [1] [1] https://en.wikipedia.org/wiki/Appliance_classes#Class_II https://en.wikipedia.org/wiki/Appliance_classes#Class_II
andreiw 10y ago
Experienced same with an iPhone 5s and a three-prong Belkin charger in a Puerto Rico rental. Scared the hell out of me, too. Brushing the metallic back I'd feel sticking. I think I licked it too, and it felt sour.

5 points by jakerockland 10y ago

Two small nits about second part of this passage: electrovibration — the rapid attraction and repulsion of the skin to an insulated ground plane (such as brushed aluminum) - Metal in unibody MBPs is sandblasted [1] rather than brushed [2] to give it its texture; - Neither sandblasting nor brushing aluminum gives it thick enough oxide layer (Al2O3), and it is that layer that makes actual insulation. Instead this layer is formed by the way of anodizing [3], complementary and separate process. [1] https://en.wikipedia.org/wiki/Abrasive_blasting https://en.wikipedia.org/wiki/Abrasive_blasting [2] https://en.wikipedia.org/wiki/Brushed_metal https://en.wikipedia.org/wiki/Brushed_metal [3] https://en.wikipedia.org/wiki/Anodizing https://en.wikipedia.org/wiki/Anodizing

gaur 10y ago

Trying to power a metal-shelled computer with a 2-prong plug always seemed to me like an example of Apple painting themselves into a corner. The only two options as far as I know are to leave the case floating (which seems bad) or to tie it to the outlet's neutral pin (less bad, but still not great). The latter presumably leaves you at the mercy of how well the building's neutral pins are grounded. The fact that Apple decided to use fairly puny wires between the power brick and the computer probably doesn't help either. [Also, the link on electrovibration seems to imply it's a capacitive effect, so it's caused by an electric (not magnetic) field.]

aexaey 10y ago
First option (ground floating) is actually quite common: A Class II or double insulated electrical appliance is one which has been designed in such a way that it does not require a safety connection to electrical earth (ground). [1] [1] https://en.wikipedia.org/wiki/Appliance_classes#Class_II https://en.wikipedia.org/wiki/Appliance_classes#Class_II

andreiw 10y ago

Experienced same with an iPhone 5s and a three-prong Belkin charger in a Puerto Rico rental. Scared the hell out of me, too. Brushing the metallic back I'd feel sticking. I think I licked it too, and it felt sour.