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Date: Fri, 16 Mar 2012 12:56:25 -0700
From: Andrew Poelstra <asp11 AT sfu DOT ca>
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Daughter's Science Fair
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On Fri, Mar 16, 2012 at 12:26:15PM -0400, Bob Paddock wrote:
> On Fri, Mar 16, 2012 at 11:33 AM, Rob Butts <r DOT butts2 AT gmail DOT com> wrote:
> > So if I use a 1 watt 15k ohm resistor in series with the nail and an ac
> > outlet that will give me 8ma alternating current and that should light the
> > bulb?
> 
> With no isolation transformer this is not a safe approach for
> something in a Science Fair.
> Anything connected to the AC Line always presents a electrocution
> hazard when not isolated.
> Currents of less than 8 mA across the heart could kill.
> 
> Two identical transformers hooked up back-to-back will get you safety isolation.
> 
> For example in the past 110 in 6.3V out transformers were common.
> Hooking the two 6.3V sides together would get you isolated 110VAC out.

If you're going to go to that trouble, you should probably just use the
6.3V out and light a smaller bulb. ;)

In fact, if you rummage around your house, or garage sales, you can probably
find a 9VAC-or-so wallwart that nobody is using anymore, and you can use the
leads from that to get a safe AC source.

-- 
Andrew Poelstra
Email: asp11 at sfu.ca OR apoelstra at wpsoftware.net
Web:   http://www.wpsoftware.net/andrew
"You shouldn't trust every quote you read on the Internet." -- Socrates