Ground loop interference with laptop and external monitor

[septiclecky]

Quick update, as a test we stripped out the earth from an extension lead, plugged laptop and monitor in and hey presto problem resolved. Obviously this is not a solution but at least we have isolated the issue. Any ideas what this means and if this changes your thinking on how we can resolve it?

Check your building wiring installation.

 

[green-hornet]

Its one of the reasons IT rooms are wired with a clean earth.

I would have an inspection on the wiring and see if there is any leakage on the earth.

The earth may have a lot of "noise" going down it.

 

[spinlondon]

There are socket-outlets with built in filters on the market, don't know if they'll sort it.

There are also extension leads mostly for use with HiFi, that have filters, supposed to cut down earth hum.

Have you considered checking the refresh rates on the monitors? It may be that are out of sync with the Laptops or even the mains supply frequency of 60Hz.

Edit. Sorry it's the Monitors' refresh rates that are generally at 60Hz not the mains supply. As pointed out by Green Hornet.

 

[NozSpark]

Could a UPS sort this out???

 

[green-hornet]

I think it will be down to the power supply quality, and any inbalance should it be three phase.

Multiple earthing points cause hum, as does the circuit boards in some equipment.

If the supply is not a regular 50Hz this could also cause the problem.

I would make sure the installation is fine and that it is balanced, a simple check on the earthing would expose any unwanted voltages, remember though nothing is ever really zero volts.

 

[ianmacd]

remember though nothing is ever really zero volts.

Isnt 0 volts zero volts? :coat

 

[robodan]

I am having the exact same issue, we supply laptops and recently we started to get reports of problems using external displays. Isolating earth does indeed fix the issue.

How safe/dangerous is this?

 

[spinlondon]

On a scale of 1 to 10, probably about a 4.

 

[Lurch]

Well the earth is obviously there as a safety precaution. If there is no problem with the monitor then cutting the earth does indeed make no difference to safety. It's in the event of a problem that the earth is used, with no earth path a fault could leave parts of the monitor at mains potential as rather than the fault current going to earth via the earth cable and popping a fuse it is in fact sitting waiting for something else to complete the path to earth, usually a person, and people don;t last long being parts of electrical circuits.

So in summary, no earth = potentially lethal and I would not be leaving any devices with snipped earth leads in service.

 

[spinlondon]

I thought it was a problem with the earth to the Laptop charger?

 

[Lurch]

I thought it was a problem with the earth to the Laptop charger?

I think you might get a fix if you snip one or the other, or possibly both.

I wouldn;t snip the earth to the laptop charger though for any extended period of time as they tend to drop a bit of current to earth because of the way they are designed (on some) so snipping the earth causes the SMPSU's do do some odd things, usually melt and burn.

If just snipping the earth to the laptop PSU does the job then maybe get some power supplies which are double insulated in the first place.

I think the problem is down to the laptops themselves if monitor and laptop external PSU's have been ruled out. If so I'd be inclined to use different laptops. What are the laptops being used here?

 

[spinlondon]

I thought the supply from the charger to the Laptop did not have an earth, that the charger was one of those separated transformer jobbies.

 

[Lurch]

I thought the supply from the charger to the Laptop did not have an earth, that the charger was one of those separated transformer jobbies.

It is, and the laptop will have further power supply circuitry within it.

And there is no earth from the charger to the laptop, but ground loops aren;t just about travelling up and down earth wires, it's more random, annoying and complex than that under some circumstances.

 

[robodan]

I have used a Universal AC Adaptor and this eliminates the problem, this is possibly the best solution (For me) but is the most expensive.

Another problem this introduces is the cable does not sit firmly enough into the laptop and could potentially damage the connecting pin to the laptop.

Laptops I am having difficulties with are Toshiba L300

 

[ianmacd]

All the ones I have ever seem always seem to be yes. DC and no Earth. So not sure where the fault is bing introdunced unless its a sine wave (or similar) on the 0V side of the transformer that could be linked back so earth if its not true selv. Apple laptop PSU's do not even take CPC.

 

[spinlondon]

So the only option is a conditioned supply, such as provided with a UPS?

What about the sockets with built in filters?

I've had to install them on some jobs, never really knew if they were effective though.

 

[robodan]

could try a UPS actually, will report back in 10 mins

 

[Lurch]

So the only option is a conditioned supply, such as provided with a UPS?

Not neccesarily. That may work, it may not. Other option as has been mentioned is different power supplies or laptops.

If the laptops are for personal use I'd use a different PSU and then if the plugs aren;t so tidy just swap the leads over, bit of heat shrink tubing and soldering would be fine.

If the laptops are for supplying to customers then I'm not so sure that's a decent enough solution. I'd be inclined to supply different ones or get the manufacturer on the case, or both.

 

[spinlondon]

I have used a Universal AC Adaptor and this eliminates the problem, this is possibly the best solution (For me) but is the most expensive.Another problem this introduces is the cable does not sit firmly enough into the laptop and could potentially damage the connecting pin to the laptop.

Laptops I am having difficulties with are Toshiba L300

I've got a Satelite, and use a HP monitor via the HDMI lead.

I also use the monitor for my PC, and leave them both connected.

The only problem I get, is when I have the PC off,and am using the Laptop, I get a Buzzing when there is too much white on the screen. If I remove the Power supply to the monitor, the buzzing goes away.

 

[robodan]

nope, used UPS and still same issue, although UPS is not a particularly great one to be fair