Size of a resistor for static electricity discharge

[Bill Gill]

I keep zapping myself when I reach for the tone arm on
my new turntable. So I need to put a discharge point
on the table so I can get discharged before I hit the
tone arm. What size resistor should I use? I was
thinking about 1 megohm.

Thanks,
Bill

 

[Kaz Kylheku]

On 2014-02-25, Bill Gill <billnews2@cox.net> wrote:

I keep zapping myself when I reach for the tone arm on
my new turntable. So I need to put a discharge point
on the table so I can get discharged before I hit the
tone arm. What size resistor should I use? I was
thinking about 1 megohm.

Grounded wrist-straps have resistors in them. Why aren't they just
zero ohm? Probably for safety. You wear these things continuously while
handling sensitive devices. You don't want to be grounded while working on
electronics, because you're providing a conductive through yourself if you
touch a high voltage.

One megohm is small enough to provide a reasonable discharge time between the
time you put one the wrist strap and touch anything sensitive, and to keep you
continuously discharged.

Let's think about body capacitance C, the resistance R and the RC constant
thereof.

Wikipedia on body capacitance: "the [c]apacitance of a human body in normal surroundings is typically in the tens to low hundreds of picofarads. "

If your body capacitance is 100 pF, five RC constants with 1M = 500
microseconds.

The R may be big, but the C is very tiny, so the discharge time is more than
reasonable, with plenty of headroom to handle unusually values of C.

Still, I would say, make things simple and provide a simple conductive,
grounded point. Just don't touch that if you suspect that some other part of
your body is connected to a high voltage.

However, the same caveat already goes for any device that has a metal, grounded
chassis, making it pointless to fuss about. If your turntable had such a
chassis, you could just touch that! Or maybe some other component in your
stereo rack has a grounded chassis.

 

[Tim Wescott]

On Tue, 25 Feb 2014 08:10:30 -0600, Bill Gill wrote:

I keep zapping myself when I reach for the tone arm on my new turntable.
So I need to put a discharge point on the table so I can get discharged
before I hit the tone arm. What size resistor should I use? I was
thinking about 1 megohm.

To protect the turntable, or to keep your arm from cramping up?

When I worked in fiberglass manufacture, we used wooden-handled
screwdrivers (pulling fiberglass parts from molds generates lots of
static electricity). On dry days you could get a quiet but discernable
shriek from the process as the spark oscillated in the audio at a rising
frequency.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

Bill Gill <billnews2@cox.net> wrote:

I keep zapping myself when I reach for the tone arm on my new
turntable. So I need to put a discharge point on the table so I can
get discharged before I hit the tone arm. What size resistor should
I use?

Go to the hardware store and buy one of those voltage testers that
consists of a small neon lamp and a resistor in a housing, with two
short wire probes sticking out. At home, ground one of the probes and
touch the other one to 1) discharge yourself and 2) get a free light
show. To a certain extent, a bigger charge results in a brighter or
longer flash of the lamp.

Matt Roberds

 

[John Larkin]

On Tue, 25 Feb 2014 08:10:30 -0600, Bill Gill <billnews2@cox.net>
wrote:

I keep zapping myself when I reach for the tone arm on
my new turntable. So I need to put a discharge point
on the table so I can get discharged before I hit the
tone arm. What size resistor should I use? I was
thinking about 1 megohm.

Thanks,
Bill

1 meg, axial, is about what is used on esd wrist straps. I'd put a few
smaller ones in series, to reduce the chance of arc-over if you came
in really charged-up, like ten kilovolts or something.




--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Michael Black]

On Tue, 25 Feb 2014, Kaz Kylheku wrote:

On 2014-02-25, Bill Gill <billnews2@cox.net> wrote:
I keep zapping myself when I reach for the tone arm on
my new turntable. So I need to put a discharge point
on the table so I can get discharged before I hit the
tone arm. What size resistor should I use? I was
thinking about 1 megohm.

Grounded wrist-straps have resistors in them. Why aren't they just
zero ohm? Probably for safety. You wear these things continuously while
handling sensitive devices. You don't want to be grounded while working on
electronics, because you're providing a conductive through yourself if you
touch a high voltage.

One megohm is small enough to provide a reasonable discharge time between the
time you put one the wrist strap and touch anything sensitive, and to keep you
continuously discharged.

Let's think about body capacitance C, the resistance R and the RC constant
thereof.

Wikipedia on body capacitance: "the [c]apacitance of a human body in normal surroundings is typically in the tens to low hundreds of picofarads. "

If your body capacitance is 100 pF, five RC constants with 1M = 500
microseconds.

The R may be big, but the C is very tiny, so the discharge time is more than
reasonable, with plenty of headroom to handle unusually values of C.

Still, I would say, make things simple and provide a simple conductive,
grounded point. Just don't touch that if you suspect that some other part of
your body is connected to a high voltage.

However, the same caveat already goes for any device that has a metal, grounded
chassis, making it pointless to fuss about. If your turntable had such a
chassis, you could just touch that! Or maybe some other component in your
stereo rack has a grounded chassis.

I figured he's hoping to avoid the bite. Discharging through a resistor
may lessen the "shock" of touching metal when statically charged.

The alternative is a humidifer and/or no rugs and/or rugs that don't build
up a static charge.

Michael

 

[Bill Gill]

On 2/25/2014 3:51 PM, Michael Black wrote:

I figured he's hoping to avoid the bite. Discharging through a resistor
may lessen the "shock" of touching metal when statically charged.

The alternative is a humidifer and/or no rugs and/or rugs that don't
build up a static charge.

Michael

I don't want to damage the turn table. I don't like the shock, but
I can live with it. I figure I should use a resistor to
reduce the size of the surge, which has a greater chance of
causing damage.

What I was planning was to fasten a small piece of metal to the
lid of the turntable where I pick it up so that I would
automatically be discharged when I opened it up. That way there
is much less chance of forgetting to discharge myself before
changing the record.

I don't have carpet. I think it is my chair that is doing it
to me.

Bill

 

[Jim Thompson]

On Tue, 25 Feb 2014 08:10:30 -0600, Bill Gill <billnews2@cox.net>
wrote:

I keep zapping myself when I reach for the tone arm on
my new turntable. So I need to put a discharge point
on the table so I can get discharged before I hit the
tone arm. What size resistor should I use? I was
thinking about 1 megohm.

Thanks,
Bill

Unprotected CMOS gate inputs... tied to either rail internally... have
400 Ohm series resistors.

...Jim Thompson
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