Size of a resistor for static electricity discharge

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

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

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

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

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

Unprotected CMOS gate inputs... tied to either rail internally... have

400 Ohm series resistors. ...Jim Thompson

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