Date: Wed, 28 Mar 2012 14:02:03

Author: Bill Norwood

Subject: Re: Nakamura Van De Graaff "Raijin" - Safety

Post:

Hi George,

My revised question(s):

1. "Is it true that a human will draw 10 amps for a microsecond if the human is grounded (even sloppily grounded) if he comes comes close enough for a spark to jump from a VdG sphere of 20cm diameter, charged to 200,000 volts?"

2. "Also, isn't it true that the capacitance of the human does not manner in this case, because he is operating as a straight wire to ground?"

Thanks, Bill

-----Original Message-----
From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of George Herold
Sent: Wednesday, March 28, 2012 12:13 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] Nakamura Van De Graaff "Raijin" - Safety

Hi Sam, Unless you've got a VdG with a big 'dome' the human body capacitance should be bigger than the VdG. But you are right in that the VdG capacitance will have the major effect on the amount of charge.
(Since it's the smaller of the two.) (So please ignore my previous
guesstimate.)

I first think we should clarify the question. I was thinking that the question was, "How much charge is transfered when an uncharged human touches a charged VdG?"

So if I remember way back... The capacitance of a sphere is 4*pi*epsilon-zero*R

For a 30cm diamter dome I get about 15pF.

George

> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu
> [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Sam Sampere
> Sent: Tuesday, March 27, 2012 12:43 PM
> To: 'tap-l@lists.ncsu.edu'
> Subject: Re: [tap-l] Nakamura Van De Graaff "Raijin" - Safety
>
> C of the VdG. C for a person is tiny.
>
> Add a person to the VdG and you have tons of corona. You won't charge
> the VdG up to the full potential.
>
> You also need to look at the energy. 1/2 C V^2 is pretty small for a
> VdG with a 30 cm dome.
>
> --------------------------
> Sam Sampere
> Syracuse University
> Department of Physics
> 201 Physics Building
> Syracuse, NY 13244
> 315-443-5999
> 315-443-9103 (fax)
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu
> [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Bill Norwood
> Sent: Tuesday, March 27, 2012 12:18 PM
> To: tap-l@lists.ncsu.edu
> Subject: Re: [tap-l] Nakamura Van De Graaff "Raijin" - Safety
>
> 1. Are we talking about the capacitance of the VdG sphere or the
> human?
> 2. Capacitance of the human doesn't matter, since he/she is
> essentially just a straight wire (as a tree is with
> lightning) to ground?
> 3. The voltage of a VdG can be 100 to 500 Kv, and it would be at that
> voltage at the time of its discharge to the human.
> Bill
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu
> [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Sam Sampere
> Sent: Tuesday, March 27, 2012 11:19 AM
> To: 'tap-l@lists.ncsu.edu'
> Subject: Re: [tap-l] Nakamura Van De Graaff "Raijin" - Safety
>
> You can do a back of the envelope calculation.
>
> C is about 10^-12 F. If V = 100,000 V, which it isn't when you attach
> a human, then you can calculate Q, (.1 microC). If you want to assume
> a delta t of 1 microsecond, you can calculate I. Using these numbers,
> I get 0.1 A.
>
> You can check my numbers, though, I did this quickly.
>
> Sam
>
> --------------------------
> Sam Sampere
> Syracuse University
> Department of Physics
> 201 Physics Building
> Syracuse, NY 13244
> 315-443-5999
> 315-443-9103 (fax)
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu
> [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Bill Norwood
> Sent: Monday, March 26, 2012 2:55 PM
> To: tap-l@lists.ncsu.edu
> Subject: Re: [tap-l] Nakamura Van De Graaff "Raijin" - Safety
>
> Hi Taplers,
> -Is it correct that one can "draw" through body about 10 amps for
> about 1 millionth of a second from a VdG discharge?
> Bill Norwood, U of MD at College Park
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu
> [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of Jerry DiMarco
> Sent: Monday, March 26, 2012 2:36 PM
> To: tap-l@lists.ncsu.edu
> Subject: Re: [tap-l] Nakamura Van De Graaff "Raijin" - Safety
>
> I wonder if this modification bypasses any safety features of
> that VDG, such as current limiting. The low current limit is one of
> the measures that keeps VDGs safe...
>
>
> Jerry D
>
> At 3/23/2012 02:08 AM, you wrote:
> >......
> >Ok, the SF VdG comes with a large dome, that's why I bought
> it in the
> >first place. Look at the lower combs. They are floating! That is,
> >insulated from the base with insulating washers! So, remove
> the washer
> >and replace them with metal ones AND also attach a wire
> connecting the
> >comb to ground.
> >
> >Why the extra wire? The base is painted.
> >......
> >
> >Sam
>
>
>
>
>
>
>

Back