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A shopping cart that accumulates a static charge fits the Charged Device
Model (CDM). It doesn't really matter which direction or polarity the
charge represents from a perspective of being shocked. Unfortunately the
initial discharge pulse would probably blow open an LED with the several
amps of discharge current that occurs. The user and the shopping cart
represent several thousand picofarads of capacitance. And depending on the
type of dielectric material used in the cart wheels and the user's shoes,
the charge can reach many thousands of volts. And it's made worse with
waxed floors. About the only thing you can do is to touch the cart to a
grounded item like a freezer or refrigerator to discharge it and yourself.

In an electronics manufacturing facility we'd use special ESD floor tiles
and carts with drag chains to continuously discharge carts as they were
moved. The entrance to those areas had a sign on the tile floors clearly
saying NO WAX so the housekeeping folks wouldn't defeat the ESD dissipative
floor tiles with a wax coating. But when the carts were used in the common
hallways with non-ESD tiles and waxed floors to use the elevator, we had to
touch the cart to the frame of the elevator door to discharge us and the
cart before we pushed the elevator button.

In our lab, a coworker had sneakers that were really bad about building up
a triboelectric charge and he would draw a 6" to 8" long spark from his arm
or shoulder when he turned the corner (with a grounded wall) into his
cubicle. And that didn't involve a cart. But it clearly exceeded the energy
expected in the Human Body Model of ESD control.

Depends upon the manufacturer. I’ve seen both.

Phenolic is also suitable since it is usually strengthened by application of a mesh to both sides of the material.

Greg


Wed, 08 May 2024 23:57:14 MST Michael A. Terrell wrote:

The insulator is fiber, not Phenolic.

All Caigslist listings give the nearest city in their URL. Ann Arbor is in
Michigan.

On Thu, May 9, 2024 at 2:34?AM David via groups.io <vexorg.calibra=
[email protected]> wrote:

It would really help if people put an approximate location on ads.

Though it seems no location means the seller must be American as they are
the ones that don't bother saying where they live (and not adding to the
stereotype that Americans see themselves as the only place in the world...)

The insulator is fiber, not Phenolic.

On Wed, May 8, 2024 at 3:54?PM radiobero.bb via groups.io <radiobero.bb=
[email protected]> wrote:

This is probably familiar to most people who have ever tried to replace an
old electrolytic capacitor.
It is very easy to make an adapter, at no cost.
It is enough to cut off the edge of the old electrolyte, approximately 3
millimeters from the edge.
You will get an outer ring that fits perfectly back to where it was, and
the bakelite center will serve perfectly to place a modern electrolyte on
it.

Here are pictures of how I usually do it:

/g/TekScopes/album?id=294954

I would suspect their choice of floor wax and the material the cart's
wheels are made from. The equipment is all grounded, so you have to
generate the charge. There are floor waxes made to prevent this, and is
used in Electronics factories. Synthetic rubber and long life plastic
wheels generate static, so together they can cause this problem. Rubbing
two insulators together is the problem. There are ESD ground sraps for your
shoes to help bleed away sartic from your body.

On Sat, May 4, 2024 at 12:31?PM cheater cheater via groups.io
<cheater00social@...> wrote:

Hi all,
I frequent a large grocery market nearby and inevitably every time I
go there I get electrical shocks. I walk around with a cart and often
if I touch a metal fixture (fridge, mesh rack) I get a painful shock.
Sometimes I get a shock if I leave the cart for a few seconds and then
touch its metal mesh.

I was wondering what everyone thought. At first I thought it would be
ESD, but why would it be so extreme? It happens every time. I live in
a place that's pretty dry - RH goes under 20% regularly - and being on
a plain it has a lot of wind, which could create triboelectric
charging. But I'm not really sure about this.

I don't know which way the ESD happens. Is my body discharging into
the cart? Is the cart discharging into my body? Is my body discharging
into the racks or vice versa? How can one check the directionality of
ESD?

One theory about ESD I have is that the fixtures get charged and my
body gets the charge applied to it. This however isn't necessarily
true to me because eg today I got a painful shock from touching the
inside metal surface of a fridge, and that's supposed to be earthed.

Another theory is that as I walk around in the store, as I move around
with the cart, that charges my body. I wear rubber sandals and the
cart has rubber wheels. That would mean I'm a conductor, attached to a
large antenna (the cart's mesh frame), moving through dry air,
insulated from the ground. The ground is made out of some sort of high
impact ceramic-ish tile. But then why would my own cart shock me just
mere seconds after letting go of it? I was unloading my groceries for
the cashier.

My third theory is that this whole facility has a lifted earth
potential. There's an industrial area nearby and they may be dumping a
lot of current into earth which would create a situation where walking
on the ground charges you, and then touching something that's low-Z to
neutral discharges your body (in this case this would be the earthed
fridges etc).

I was wondering how people would approach diagnosing this problem, and
how you would fix it if you had the ability to change anything about
the facility at hand - more as a thought exercise, but if I figure out
what's going on I'm going to write to the company.

Thanks

It would really help if people put an approximate location on ads.

Though it seems no location means the seller must be American as they are the ones that don't bother saying where they live (and not adding to the stereotype that Americans see themselves as the only place in the world...)

Try posting on the Logic Analyzers forum on groups.io.

If you're looking for direction, you'll need two of them

I'd be tempted to use a resistor and neon with a one KV diode in series with the neon.? The neon will limit the maximum voltage to about 100 volts or so.

so:? resistor connected to a neon with a series diode, connecting both across each other, and the diodes reversed.

Might be a good idea.

Harvey

Could you use a small (NE-2) neon bulb for this? I recall holding the lead
of one and shuffling across a carpet. I got the bulb to flash.

Steve H.

On Wed, May 8, 2024 at 21:03 Ed Breya via groups.io <edbreya=
[email protected]> wrote:

The LEDs would protect each other from reverse breakdown. They should be
stout enough to take the forward hit and flash. If not, you can put some C
across them or R in series to soften things up (which would also stretch
the pulse for better visibility). Try it and see.

What's really needed to assess part durability is a power rating and an
energy rating. You won't find energy rating for LEDs, so have to
experiment. If you study the HBM you'll have an idea of the energy
available from your own spark. Unfortunately, I don't think there's a spec
for SCM, but you can be sure it would be quite a bit more C, and nearly
zero R. Good luck.

Ed

Very nice. How do you get such a smooth cut of the can?

George KD6NEW

Yes indeed, Steve gets the prize. That's what it would be called if such a thing existed.

Ed

Shopping Cart Model??

Steve Hendrix

Sorry, what's SCM?

On Thu, May 9, 2024 at 3:03?AM Ed Breya via groups.io
<edbreya@...> wrote:

The LEDs would protect each other from reverse breakdown. They should be stout enough to take the forward hit and flash. If not, you can put some C across them or R in series to soften things up (which would also stretch the pulse for better visibility). Try it and see.

What's really needed to assess part durability is a power rating and an energy rating. You won't find energy rating for LEDs, so have to experiment. If you study the HBM you'll have an idea of the energy available from your own spark. Unfortunately, I don't think there's a spec for SCM, but you can be sure it would be quite a bit more C, and nearly zero R. Good luck.

Ed

The LEDs would protect each other from reverse breakdown. They should be stout enough to take the forward hit and flash. If not, you can put some C across them or R in series to soften things up (which would also stretch the pulse for better visibility). Try it and see.

What's really needed to assess part durability is a power rating and an energy rating. You won't find energy rating for LEDs, so have to experiment. If you study the HBM you'll have an idea of the energy available from your own spark. Unfortunately, I don't think there's a spec for SCM, but you can be sure it would be quite a bit more C, and nearly zero R. Good luck.

Ed

Still looking.

Anyone have any experience of the TLA622 logic analyser, trying to sort display issues on one I have aquired

On Wed, May 8, 2024 at 6:29?AM Ed Breya via groups.io
<edbreya@...> wrote:

When one object dumps charge to another with enough energy to make a spark, then you don't need any sophisticated instruments to tell the polarity. A couple of anti-parallel-connected LEDs will suffice. Electrostatics was pretty well figured out by brilliant minds long ago, with comparatively crude instruments, way before tubes and transistors and ICs. Except for scientific curiosity, there's no need to recreate it (aka reinvent the wheel) to answer the question.

Any DMM in its voltage mode can sense the currents flowing in an electrostatic situation, so just bring a handheld DMM in its lowest VDC range, clamped with those anti-paralleled LEDs or regular diodes, and have at it. Use a simple, cheap DMM, like a Harbor Freight one, in case you accidentally discharge into a bad spot. Or, just leave out the DMM and use the LEDs. Don't forget the clipboard, paper, and pen to record the results, and try to look cool while doing it. Don't use a phone - keep it well away from all this activity.

One thing that may help is to look at the various HBM (human body model) electrostatic specifications, to get an idea of magnitudes involved. You can only store so much energy in practical conditions.

Ed

the led idea is pretty good. i was considering something like that for
a moment, but then i thought maybe the voltages involved would just
burn through a silicone junction.

my phone's been in my pocket during each esd event in that store, and
it still works. those things are really well made nowadays.

Hi everyone, I'm searching for some Tektronix 500 series plugins and wondered if anyone on here may have one for sale. They don't need to be working, but do need to be in good cosmetic condition and complete. I'm trying to find :

1l5, 1l10, 1l30, 1l40, 1l60
S type
Q type
1S2

If you have anything, please let me know!

Julian

This is probably familiar to most people who have ever tried to replace an old electrolytic capacitor.
It is very easy to make an adapter, at no cost.
It is enough to cut off the edge of the old electrolyte, approximately 3 millimeters from the edge.
You will get an outer ring that fits perfectly back to where it was, and the bakelite center will serve perfectly to place a modern electrolyte on it.

Here are pictures of how I usually do it:

/g/TekScopes/album?id=294954

@Beros <radiobero.bb@...> added the photo album can electrolytic adapter ( /g/TekScopes/album?id=294954 )