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110 volts on your computer



- My laptop is beating an electric shock, I feel a slight tingling sensation. Do not know what's the matter?

When for the tenth time I heard a debate about the causes of this phenomenon among programmers with macbooks, it became clear that it was time to write an article. Sometimes this effect manifests itself as a slight vibration when touching the skin and metal parts of the laptop, sometimes as a tingling sensation.

Short answer: your computer case is under voltage ~ 110V (half of the mains voltage), but because of the small current strength you are not hit too hard.

For electrical engineers, this is commonplace: for the same reasons, in a house with old wiring, a washing machine can be shocked when you touch the bath, the case of a stationary computer, etc. This topic has been raised many times on the Internet, but so far most people are not aware of the causes of this phenomenon. The situation is complicated by the fact that the design of the power supply in European macbooks does not allow to get rid of this phenomenon !

Why is this happening?



Usually unpleasant tingling sensations occur when a person touches some grounded metal surfaces, for example, a radiator of a battery under a table and at the same time holds his hands on a metal part of a computer. In my case, it was a grounded metal edge of the countertop. If you simultaneously touch the edge of the countertop and macbook, a tangible tingling sensation appeared in the hands.

And this is a completely normal situation. The fact is that in the circuit of the computer’s power supply there is an interference filter, the filter input is made on two capacitors connected on one side to each of the wires of the 220-volt network, and on the other their common point is connected to the case. The result is a voltage divider of 220 volts in half. From here 110 volts appear on the case.


Simplified noise filter circuit of a computer power supply

The picture above shows a simplified diagram of the interference filter in the power supply. As you can see, both capacitors are connected to protective earth (yellow wire E), which in turn is connected to the device. If the power supply is plugged into the outlet without grounding, then half the voltage from the mains voltage appears on the case. At the same time, the current in this circuit flows small, but it is quite enough to cause unpleasant sensations or slight sparking if you touch it with another device with the correct grounding. So you can observe small sparks when you try to connect two devices with a cable in cases where one of them is connected to an outlet with ground, and the other without.

Apple Power Supplies


As we have already found out, the voltage on the case appears only if the devices are connected to an outlet without grounding. There are many such outlets in houses with old wiring, where grounding in outlets is simply absent.

However, even in buildings with modern wiring, where the outlets have a properly connected ground, for some reason, the MacBooks continue to be shocked. It's all about the features of Apple power supplies.


Grounding contact on the power supply from the MacBook. This contact is connected to the laptop case.

All MacBook power supplies have removable plugs for different countries. You can carry only a small adapter with you on travel and change it if necessary. Complete with a macbook there is always a short plug, which is inserted immediately into the body and a long plug on the wire. So in the European, American and Chinese short forks there is no ground contact. It is only in the British fork.


Apple short European plug does not have a ground contact

UPD: the UK short plug also does not have a ground contact inside, although there is a ground plug. Proof .


And only an elongated plug with a cable has a grounding contact. This can be checked by looking at the place of attachment of the plug-nozzle to the power supply, inside there should be contacts that clamp the grounding washer. If not, the laptop is guaranteed to be shocked. This is often found on Chinese fake power supplies, even on an elongated power outlet with cable.


Ground contact inside detachable plug

Conclusion


Despite the banality of this problem, I constantly hear new theories of its origin, even among IT-employees. If you google it, there are dozens of topics where people complain about the MacBook under stress. The same problem holds true for iPhones connected to a charger.

1. How to properly ground a MacBook Pro
2. Electric shock coming from the edges of my macbook
3. MacBook Pro at 220 volts, could feel current through aluminum case

If you are concerned about this problem, here are a couple of tips:

  • Verify that your power outlet is grounded. Sometimes extension cords may not have a grounding contact, although there is one in the wall outlet.
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UPDATE:



, (20V) . , , .





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