Laptop power supply the prong plug

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sii

sii

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Nebraska
Why does my laptop power supply have a the prong plug? There are no exposed metal parts and the output is dc, what purpose does the ground conductor serve?
 
It could provide a ground point for an internal shield that contains RF generated by the switching power supply in the brick.
Is the EGC connected to one side of the DC output that goes to the computer?
I suppose it could be used with a high series resistance to bleed off static electricity.
 
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Cause it stops RF frequencies being radiated from the lap top via the power cable !
They are getting super strict or RF radiation.
Which might not be a bad thing as we see more and more and more
computorised systems every day.
 
GoldDigger said:
It could provide a ground point for an internal shield that contains RF generated by the switching power supply in the brick.
Is the EGC connected to one side of the DC output that goes to the computer?
I suppose it could be used with a high series resistance to bleed off static electricity.
Click to expand...
No, the gc only extends to the brick, it's two wire from the brick to the pc. I hadn't thought of that, I was only thinking if it from the safety standpoint. Thanks.
 
sii said:
No, the gc only extends to the brick, it's two wire from the brick to the pc. I hadn't thought of that, I was only thinking if it from the safety standpoint. Thanks.
Click to expand...

I think he is suggesting that one of the the conductors running to the laptop is grounded.
 
I have seen three prong molded plugs on two wire cords from the factory. The only way to tell for sure what the third prong does is to open stuff up and look. As in doing an autopsy. If the device is working properly, then I would say to just accept the configuration as it is and carry on.
 
Tongue in cheek reply:

It is so when someone pugs in the PS blind under a desk the dongle flops around and shorts against one of the blades as being plugged in and trips breakers--

Have seen this happen, not a conjecture,


Pet peeve: office cubicles with NO outlets above the desktop, all underneath !
 
Until I saw this thread I never noticed my tablet does not have ground prong but my laptop does have a ground prong yet the tablet has exposed metal parts but the laptop doesn't.
 
160608-0903

sii:

The simple experiment to perform is --- measure for continuity between the AC plug EGC pin and either of the two power supply ouput wires. If there is no continutity to either wire, then the EGC is not passed thru to the laptop internal common.

If no continuity is found to the laptop, then you need to open the power supply to see if EGC is used, It might connect to an input noise filter.

.
 
gar said:
160608-0903

sii:

The simple experiment to perform is --- measure for continuity between the AC plug EGC pin and either of the two power supply ouput wires. If there is no continutity to either wire, then the EGC is not passed thru to the laptop internal common.

If no continuity is found to the laptop, then you need to open the power supply to see if EGC is used, It might connect to an input noise filter.

.
Click to expand...

Yup I'm going to do this, just didn't bring it with me to work today, except the "open the power supply" part.....curiosity isn't going to kill this cat.:happysad:
 
160608-1519 EDT

sii:

To investigate the power supply alone without opening it do the following:

1. Do not connect ourput cable to the laptop.
2. Separately measure DC resistance from power plug EGC pin to both the hot and neutral pins. I expect a high resistance, like near infinity.
3. Use a three prong adapter with external EGC wire. Connect a 1000 ohm 1/2 W resistor between the adapter green wire and either neutral or EGC of the wall outlet.
4. Plug the power supply into the adapter and the adapter into the wall outlet.
5. Measure the voltage across the 1000 ohm resistor.

If the voltage is about 5 V, then there is an internal capacitor of about 0.1 ufd between hot and the cord's EGC pin. About 0.5 V and there is an internal capacitance of about 0.01 ufd. Anything in this range would imply and internal input filter that includes the EGC circuit as part of the total filter operation.

.
 
gar said:
160608-1519 EDT

sii:

To investigate the power supply alone without opening it do the following:

1. Do not connect ourput cable to the laptop.
2. Separately measure DC resistance from power plug EGC pin to both the hot and neutral pins. I expect a high resistance, like near infinity.
3. Use a three prong adapter with external EGC wire. Connect a 1000 ohm 1/2 W resistor between the adapter green wire and either neutral or EGC of the wall outlet.
4. Plug the power supply into the adapter and the adapter into the wall outlet.
5. Measure the voltage across the 1000 ohm resistor.

If the voltage is about 5 V, then there is an internal capacitor of about 0.1 ufd between hot and the cord's EGC pin. About 0.5 V and there is an internal capacitance of about 0.01 ufd. Anything in this range would imply and internal input filter that includes the EGC circuit as part of the total filter operation.

.
Click to expand...


Ha ha yeah, I'm not doing that. I really was just curious and my curiosity does not extend this far. Also, it took me years to get a laptop that was actually built to fit my needs and not just a salesman's castoff, I treat that thing better than I treat a couple of my children.

I did however check for continuity between all three plug prongs and the power plug and there is no continuity from one end to the other from any prong.
 
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