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Laptops and hum loops

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Laptops and hum loops

Postby ef37a » Tue Dec 24, 2019 5:22 pm

No, I don't have one but I was delivered of a refurbed Lenovo T510 a few days ago and they sent me the wrong charger. No way would the DC plug fit.

I trotted off to my local laptop service shop to see if he had a spare he could sell me. No, only one he keeps for test but he was prepared to lend it to me. Then I mentioned I had seem a 'universal' laptop PSU recently. "Oh we keep those" he said. I told him if it works I 'ave one. "forty quid" never mind, I wanted to get this thing setup and checked out.

Now, the reason for all that preamble is that the supply is Class 2 ins' bi pin and is a Duracell DRAC9006, 90W and looks very well made. Comes with a selection of adaptors, one fits my T510 and another my daughter's Dell. There is also a rectangular one I have never seem before.

So, if anyone has a ground loop problem with a laptop, worth looking at this supply. Not cheap but a spare is never a bad thing anyway.

Dave.
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Re: Laptops and hum loops

Postby Martin Walker » Tue Dec 24, 2019 5:39 pm

Always good to know of a standby like this Dave! :thumbup:


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Re: Laptops and hum loops

Postby Sam Spoons » Tue Dec 24, 2019 6:09 pm

I have a couple of 'universal' laptop PSUs, one is voltage sensing between IIRC 10 and 30 VDC, I have no clue how that works.
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Re: Laptops and hum loops

Postby DGL. » Tue Dec 24, 2019 7:15 pm

Note that some laptops with metal/metallised casing don't work well with ungrounded supplies, primarily the leakage from the rfi filtering is present on the case and can become quite uncomfortable to touch if connected to grounded appliances, my ASUS had that exact problem which went away if used with a grounded supply. This phenomenon was present with 2 genuine ASUS PSU's, with one of them being supplied with teh laptop.
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Re: Laptops and hum loops

Postby ef37a » Tue Dec 24, 2019 8:16 pm

DGL. wrote:Note that some laptops with metal/metallised casing don't work well with ungrounded supplies, primarily the leakage from the rfi filtering is present on the case and can become quite uncomfortable to touch if connected to grounded appliances, my ASUS had that exact problem which went away if used with a grounded supply. This phenomenon was present with 2 genuine ASUS PSU's, with one of them being supplied with teh laptop.

Yes, there is no perfect solution. I offered the Duracell as a good quality, earth free replacement, not every laptop can be found an isolated supply and this universal one might help.

With regard to the 'tingle' effect, if you have a hum loop problem it is likely the USB cable will earth things?

Dave.
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Re: Laptops and hum loops

Postby DGL. » Tue Dec 24, 2019 8:27 pm

ef37a wrote:
DGL. wrote:Note that some laptops with metal/metallised casing don't work well with ungrounded supplies, primarily the leakage from the rfi filtering is present on the case and can become quite uncomfortable to touch if connected to grounded appliances, my ASUS had that exact problem which went away if used with a grounded supply. This phenomenon was present with 2 genuine ASUS PSU's, with one of them being supplied with teh laptop.

Yes, there is no perfect solution. I offered the Duracell as a good quality, earth free replacement, not every laptop can be found an isolated supply and this universal one might help.

With regard to the 'tingle' effect, if you have a hum loop problem it is likely the USB cable will earth things?

Dave.

Yes, I was just putting the PSA out that SOME ungrounded PSU's are not suitable for metal/metallised laptops. Also not that some PSU's communicate with the laptop so watch out for problems there, for example my sisters HP supply will physically fit and power my dell but that laptop won't let it charge the battery displaying a popup to that effect.

The USB cable earthing things was part of my problem, hook up either a USB AI or audio cable and the surface of the laptop became uncomfortable to touch, hooking it up to my projector (which is also grounded) had the same effect. Switching to a grounded supply did create a ground loop but at least the surface was fine to touch.
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