OK to hotswap external monitor on a laptop?

vince992004

Junior Member
Sep 15, 2009
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I've always been under the impression that a laptop computer should be turned off before connecting or disconnecting an external monitor. But lately I've come across two people both of whom regularly connect/disconnect monitors with the laptop on. And I expect there are plenty of people who connect projectors to laptops while power is on.

I am going to be setting up my wife's laptop for use with an external monitor, so I'd like to find out what is the correct practice here.

Thanks
 

RaiderJ

Diamond Member
Apr 29, 2001
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I think the concern for hotswapping is to avoid any electrical/static problems. Keep yourself grounded and I can't see why you should have any practical problems.
 

vince992004

Junior Member
Sep 15, 2009
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Thanks for the replies.

I've always assumed that at least part of the requirement in hot swappable was about making sure grounds were connected first. I did some searching and found this page that seems to confirm: http://en.wikipedia.org/wiki/Hot_swapping

Most modern hot-swap methods use a specialized connector with staggered pins, so that certain pins are certain to be connected before others. At one time staggered pins were thought to be an expensive solution, but many contemporary connector families now come with staggered pins as standard; for example, they are used on all modern serial SCSI disk-drives......... Most staggered-pin designs have ground pins longer than the others, ensuring that no sensitive circuitry is connected before there is a reliable system ground. The other pins may all be the same length; in some cases three pin lengths are used.

All the searching I've done still has not come up with a definitive answer. But quite a few people seem to do it, and I've found no reports of anyone that has damaged any hardware through that practice.
 
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veri745

Golden Member
Oct 11, 2007
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Everyone at my work plugs/unplugs vga cables for projectors frequently, and I've never heard of it harming anything. I wouldn't worry too much about hot swapping with VGA or DVI (and certainly not with HDMI)
 

mindless1

Diamond Member
Aug 11, 2001
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There is safest practices/ideals, and then there is real world practicality. Unlike some two-unit combos that share a common earth chassis ground individually, this is not the situation with a laptop so even having ground contact first between the connectors there exists the possibility that the absolute voltage level relative to ground differs between the two.

This means you could have a significant surge upon connection. "Usually" the magnitude is low enough it won't matter, some will accept this small risk for the convenience factor, myself included, but strictly speaking if someone advises against it they are technically correct. You can equalize their ground potentials by touching a grounding strap lead (technician type with high resistance built in) to the ground of either component, and touching the other component's ground (connector shell) with your finger.

Someone might come along and ask, "what about USB, those peripherals are designed hot-swappable". Indeed they are, supposedly, but every now and then with USB peripherals people do see damage from hot swapping especially in environments conducive to static electricity generation.
 
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LokutusofBorg

Golden Member
Mar 20, 2001
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A monitor doesn't ground through the computer, it has a plug into the wall. Grounding is a non-issue for this scenario.
 

mindless1

Diamond Member
Aug 11, 2001
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^ False. Nothing is supposed to "ground through" some other device instead of it's own ground. Rather, you are connecting the ground of one device to the ground of another, and "IF" those grounds are an unequal potential to earth ground, you will have that voltage differential result in a surge.

Grounding is ALWAYS an issue. The only time you can take it for granted when hooking up multiple previously independent circuits is when the design already caused ground to stay at earth ground in all of those circuits.

Remember, you are not guaranteed that the monitor chassis/circuits ground is tied into the earth ground on the AC outlet. On the contrary, many such devices deliberately have a "floating" ground through the (isolation) transformer.
 
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LOUISSSSS

Diamond Member
Dec 5, 2005
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i've pulled vga cables out of my laptop while on over 100 times, nothing ever happened and works for plugging in also. works like usb =]
 

veri745

Golden Member
Oct 11, 2007
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It seems like if it is really a problem, the manufacturers would want to include a small contact point to ground on both components so you could manually tap the grounds together before connecting the actual port.
 

mindless1

Diamond Member
Aug 11, 2001
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^ They do veri745, the contact is the grounded outer shell of both connectors.