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Electronics => Projects, Designs, and Technical Stuff => Topic started by: mcn4mee on August 07, 2015, 08:11:18 pm

Title: current through laptop computer on top of esd mat
Post by: mcn4mee on August 07, 2015, 08:11:18 pm

I have an esd mat on my desk and I often set my MacBook Pro on the mat while I'm using it. A few days ago my hard drive failed so I replaced it. The new hard drive is thinner than the old one. As soon as I started using it with the computer on the mat I could feel a mild tingle of current when touching the computer. If I take it off the mat, there's no tingle.

I'm wondering if the old, thicker hard drive was in contact with a ground or something that the new drive, being thinner, isn't contacting.

The old drive was original, a Hitachi 7K500-500. The new drive is a Western Digital WD5000LPLX. Both are 500gb, SATA, 7200 rpm.

Has anyone ever heard of this happening?

Title: Re: current through laptop computer on top of esd mat
Post by: wasyoungonce on August 07, 2015, 11:13:03 pm

I was repairing a CRT TV many years back on an ESD mat (in a workshop) and guys down the bench 1 m from me (same mat) were getting tingling shocks.  The High Voltage was conducting thru the mat.  Surprised the hell out of me as well!

But that was quite HV.   ESD mats are either conductive (<1meg) or resistive/conductive (>10meg ~ 100meg) surface resistance.  I cannot remember what we had, I suspect we were using the conductive mats.   

I'd doubt low voltage would be an issue but that depends upon the mat.   It would be possible for a HDD PCB to conduct from one point to another when in contact with a conductive mat, but unlikely due to the low voltage.

Title: Re: current through laptop computer on top of esd mat
Post by: Berni on August 08, 2015, 04:29:04 pm

This tingling happens due to the mains power supply/charger leaking mains voltage over itself.

I noticed the effect myself on a mac mini before. That one leaked enough current to turn on a LED pretty well if you held one end and touched the metal case with the other.

Title: Re: current through laptop computer on top of esd mat
Post by: timb on August 11, 2015, 10:19:26 pm

Happens to me with my MacBook Air as well. If you want to prevent it, use the three-pronged cord in a grounded outlet (as opposed to the two prong flip down plug).


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Title: Re: current through laptop computer on top of esd mat
Post by: ivan747 on August 16, 2015, 10:06:19 pm

I used tu use a macbook pro. When I plugged it in using the original ungrounded plug, I'd get a tickle while touching the machine and the painted concrete wall. Didn't happen with the grounded extension.

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