Ground loop interference with laptop and external monitor

[davi]

Hi, I'm having a bit of a nightmare. I'm really hoping you can help

We're a small business just moved into an office. We have two laptops connecting to external monitors. Both are the same model laptop (HP DV2530ea) and both monitors are the same (Dell ST2410). The monitor screens flicker like crazy when the laptop is plugged into the mains. When we pull the power lead out they stop flickering.

After reading on the web, we think we have a ground loop problem. We have tried buying shielded monitor cables, HP docking stations, using extension leads but nothing fixes it. The solution offered on other forums is to cut the earth lead in the plug which apparently fixes the problem. But we are quite nervous about this as the earth is there for safety reasons.

Has anyone got any advice please. There must be a solution!

Thanks in advance

 

[septiclecky]

Hi, I'm having a bit of a nightmare. I'm really hoping you can helpWe're a small business just moved into an office. We have two laptops connecting to external monitors. Both are the same model laptop (HP DV2530ea) and both monitors are the same (Dell ST2410). The monitor screens flicker like crazy when the laptop is plugged into the mains. When we pull the power lead out they stop flickering.

After reading on the web, we think we have a ground loop problem. We have tried buying shielded monitor cables, HP docking stations, using extension leads but nothing fixes it. The solution offered on other forums is to cut the earth lead in the plug which apparently fixes the problem. But we are quite nervous about this as the earth is there for safety reasons.

Has anyone got any advice please. There must be a solution!

Thanks in advance

Are they plugged into sockets on different phases by any chance and on NO account should you cut the earth.

 

[davi]

Are they plugged into sockets on different phases by any chance and on NO account should you cut the earth.

Erm, not sure. I have no idea of electrics so don't know if they are on different phases. How would I tell?

Thanks for your response.

 

[Apache]

Ground loop isolator? Can you get them for the mains?

 

[Lurch]

Erm, not sure. I have no idea of electrics so don't know if they are on different phases. How would I tell?Thanks for your response.

First thing is to make sure they are plugged into the same socket outlet. Either plug both the monitor and laptop into the same socket or use an adapter. If they are both plugged into the same socket they are on the same phase.

 

[mojorebel]

you could go for a galvanic isolator these cost about

 

[Lurch]

you could go for a galvanic isolator these cost about

 

[davi]

First thing is to make sure they are plugged into the same socket outlet. Either plug both the monitor and laptop into the same socket or use an adapter. If they are both plugged into the same socket they are on the same phase.

Yep done that, but still the same problem

 

[Lurch]

Looking at this problem a bit more, I think it might be a bit hit an miss as to what will fix it and what won't. There's a fair chance it's a laptop issue so filtering may well fix it, but it may not. You could simply use an isolating transformer to power the monitors and laptops.

 

[davi]

Looking at this problem a bit more, I think it might be a bit hit an miss as to what will fix it and what won't. There's a fair chance it's a laptop issue so filtering may well fix it, but it may not. You could simply use an isolating transformer to power the monitors and laptops.

We have tried another laptop and a different monitor but get the same problem so it's unlikely to be the laptop.

As for the isolating transformer, where would we get one and what are the likely costs?

 

[Lurch]

We have tried another laptop and a different monitor but get the same problem so it's unlikely to be the laptop.

That is odd. I don't think this is somethign I could diagnose from afar seeing as it does it on any monitor or laptop, too much guesswork as there could be an issue somewhere we are unaware of.

As for the isolating transformer, where would we get one and what are the likely costs?

It would depend on the ratings of the equipment, but it would probably be specially made. I usually use a company in Stoke for transformers, http://www.electro-wind.co.uk/

 

[spinlondon]

It is possible to obtain socket-outlets with filters, or even extension leads with filters and surge protection.

However, I would first try using an extension lead with the earth cable disconnected, to ascertain whether it is in fact GLI. This would obviously just be for testing purposes, not as a final solution.

 

[ianmacd]

I would be supprised if the laptop's PSU's even had an earth connection so not sure how they could be causing it directly. Do you get it on both with just one laptop plugged into the mains and one running off battery?

 

[davi]

I would be supprised if the laptop's PSU's even had an earth connection so not sure how they could be causing it directly. Do you get it on both with just one laptop plugged into the mains and one running off battery?

Just to clarify, we get the problem with both laptops.

If we pull one laptop lead out, the flicker/interference disappears from one monitor but doesn't affect the other

If we turn one laptop off the other monitor still shows interference

We have tried alternating different sockets, and leads, and extension combinations

 

[steptoe]

have you got extension leads on the monitor VGA leads(you say the are remote),

if so do the leads have chokes on them?

maybe sounds like the monitor is picking up the field from the laptop PSU

 

[septiclecky]

you could go for a galvanic isolator these cost about

 

[spinlondon]

Whats a supply to a ship got to do with it?

I think you're thinking of a sacraficial anode.

 

[Lurch]

Galvanic isolators are commonly used with shore power supplies on boats and wotnot also.

 

[davi]

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?

 

[septiclecky]

I think you're thinking of a sacraficial anode.

No a galvanic isolator is used when a ship is on shore supply to stop the electrolytic action.