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Max The Magnificent
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Re: Grounding
Max The Magnificent   7/29/2014 12:04:09 PM
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@mhrackin: It turns out that the standard banana plug is a pretty good fit in the standard US U-ground outlet.

Interesting -- I hadn't thought of that -- I'll get one and try it (replace the crocodile/alligator clip on my band with a banana plug)

antedeluvian
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Re: Before you apply power
antedeluvian   7/22/2014 9:11:54 AM
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David, Javi

anti-static mats...

You can get anti-static carpets (which you obvioulsy spread on the floor) which use the self-same ground connections as the table mats.

 

David Ashton
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Re: Before you apply power
David Ashton   7/22/2014 5:17:05 AM
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@Garcia ref Dissipative anti-static mats... while I am not against them per se, I would not like one all over my workbench.  If you happen to be testing a switched mode power supply module (and I occasionally do this with PSUs scrounged from old equipment) you want a good insulating bench area to put them on, as they don't always have a frame and the bottom of the PCB has some nice shocking voltages on it.   I sometimes keep a piece of that plastic corrugated cardboard type stuff for the same reason.   If I'm probing around on the mains side I'll usually get an isolation transformer out too - don't have a death wish yet :-)

David Ashton
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Re: Before you apply power
David Ashton   7/22/2014 5:07:46 AM
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@Crusty... "Why is it that switch mode supplys seem to generate these tingles?"

I've seen, on many schematics of these beasts, a small (1-10 nF) X2 Cap between the common of the mains side and the common of the low voltage side.   I'm not sure why this is needed, but if the common of your mains side happens to be on the live leg, you'd get enough through a few nF to give you a tingle.   If it's for a Laptop or a bedside clock, fine, but if it's for something I'll be touching I much prefer an old-fashioned hunk of iron.

David Ashton
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Re: Before you apply power
David Ashton   7/22/2014 5:03:32 AM
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@Crusty - in addition to giving you tingles, the wall brick will have no or fixed (high) current limiting.   Just in case you make a wrong connection which will cause you to lose the magic smoke in your new board, use your lab power supply and set the current limit to one which will only just supply the board under normal conditions, or even a bit less.  Much safer way to go.  Once you know it's all working, change to the wall wart if you are brave... :-)

Crusty1
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Re: Before you apply power
Crusty1   7/22/2014 3:26:24 AM
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@all, This topic brings me onto! which power supply should I decide to use before I liven up my board?

Do I use the big dual linear power supply, very stable and takes up a lot of my small bench, or do I use the little wall socket, switch mode brick.

After getting one hell of a tingle from the Wall brick via the low volatage side last night I am just begining to think that whilst the wall bricks are usefull I would rather not get that tingle.

Why is it that switch mode supplys seem to generate these tingles, I had a co worker who was leathal to work with, as she always disconnected the ground pin from her scope supply and it always seemed to be me that caught a tingle, so much so, that I ended up wearing insulated gloves when I worked in her lab.

 

Garcia-Lasheras
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Re: Before you apply power
Garcia-Lasheras   7/21/2014 4:47:58 PM
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@elizabethsimon: "the surface of the anti-static mat and the wrist strap are NOT shorted to ground but have some resistance that is sufficient to dissipate the static charge without shocking you."

As far as I remember, my ankle anti-static band is labeled as 1 Mega Ohm between the strap in contact with the skin and the part that touches the floor -- of course, this is useless unless you are on a special dissipative floor such as the one in SMD facilities.

elizabethsimon
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Re: Before you apply power
elizabethsimon   7/21/2014 4:37:21 PM
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I've got a couple of large anti-static mats on my workbench as well as a couple smaller ones that were designed to be used as keyboard mats. The grounding points on these mats have a socket for the ground strap and a wire with a ring terminal. The ring terminal is supposed to attach to the grounded screw between the outlets on a standard duplex wall outlet.

This works well if you have a permanent workbench but it's not practical if you happen to be using a dining table or some such that has to be cleared off when you're done. On the other hand, using the mat to protect the surface of said table is a good idea. What I'd suggest doing in that case is to ground the mat to the power strip that you will be using to power your equipment.

By the way, the surface of the anti-static mat and the wrist strap are NOT shorted to ground but have some resistance that is sufficient to dissipate the static charge without shocking you.

 

mhrackin
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Re: Before you apply power
mhrackin   7/21/2014 2:13:11 PM
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The going rate @1 for most of these is US $11 per square foot for ready-made ones including the grounding point and grounding wire. Typically they have 2 grounding points to allow daisy-chaining of adjacent benches, or attachment of a wrist strap.  I've bought several of these for my lab benches at work. My only beef with them is the grounding conductor attachment sticks up from the surface over 1/2 inch so you can't put any equipment in that area.

mhrackin
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Grounding
mhrackin   7/21/2014 12:43:38 PM
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It turns out that the standard banana plug is a pretty good fit in the standard US U-ground outlet. Most ground straps I see (and the grounding leads of the anti-static mats mentioned above by Garcia-Lasheras) come with a nice black banana plug AND an alligator clip that the banana plug can be plugged into.  The better ones have stacking banana plugs so you can plug both the anti-static mat and the wrist strap into a solid ground.  The alligator clip method is perfect for working on PCs with a metal chassis but not very good for a breadboard!

Added comment: that standard banana plug is a BIT loose, but it's easy to expand the diameter: a 4-way split (common) one will accept taking a small flat-blade screwdriver (the kind every engineer has several "giveaway" ones) under each leaf to expand the effective diameter.  Even the old/cheap plin solid pin versions can be modified with a similar surgery.

 

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