Re: [CAD_CAM_EDM_DRO] Re: Ground loop boogieman ... can someone explain this

Ken Jenkins wrote:

> Ground loop boogieman ... can someone explain this in some
> detail or point me to a link that does?
>
> I think I know basically - a "ground loop" is where you have two
> different return paths for your current but they ain't both
> at the exactly the same potential therefore .... problems,
> current flowing in a direction it should not be ... but
> I'd like to understand this (.... better ... or maybe
> "at all" if the above sounds offbase).

Well, the term "ground loop" is used to describe a broad range of
problems, often not fully understood. In analog data acquisition
systems, it can be a very difficult problem, as all signals are
generally referenced to the ground for a zero volt reference.
If there is more than one ground voltage, which one is zero
volts, and what is the other one(s)?

In digital systems, it is much less of a problem, as the difference
between grounds has to be roughly half a volt, often quite a bit
more, before it causes zeros to be read as ones, or vice versa.

> I have created my own breakout board by gutting an old harddrive
> and putting screw terminals on top. I need 5+ vdc to power my
> PacSci 6410 drives and I don't want to bother bringing out another
> line from the PC (it's aesthetically unpleasing :-). So I just
> use the 5+ supply inside the old harddrive making sure to tie it's
> common to the ground pins (18-25) coming from the LPT port ....
> right? ok? no problem? ... or is the ol' ground loop boogieman
> just waiting to bite me with this set up? It's seems electrically
> sound based on what I know (or think I know) but I'm scared of
> the boogieman. What if I plug my harddrive/breakout box and my
> computer into separate outlets? What if my wife uses her hairdryer
> while I'm machining!!!!???

I assume this is an external hard drive box with its own power
supply? As long as the 5 V ground of this power supply is
floating, ie. not attached to case ground, you should have no
problems in that regard. If it is a switching power supply, it may
not function properly with nearly no load. Otherwise, it should
work OK.

Jon