[NSRCA-discussion] Question.

Fri Aug 20 09:09:55 AKDT 2010

From Underwriter Lab documents….

Testing in 1950s determined that a
shock and let-go value of not greater than 42.4 volts was
an acceptable level in most dry locations and would not
be lethal to a person in contact with the circuit. This
value of 42.4 volts peak would not be acceptable in a wet
location since the resistance of a person’s body would be
much lower in a wet condition.

It’s extremely person to person dependent.  Our skin resistance varies wildly and the difference between Dry skin and Wet skin is something like 100,000 ohms to 1,000 ohms.  Sort of a wide range.

But again, the “generally accepted” safe low voltage is 40V, or in the case of UL Listing, 42.4.

I have to believe that played a big role in the FAI guideline initially of not exceeding 42V.

AC current is different, both more and less lethal.  More because it fibrillates the heart, but less because you have a chance of letting go.  Very situation dependent.

Mark Atwood
Paragon Consulting, Inc.  |  President
5885 Landerbrook Drive Suite 130, Cleveland Ohio, 44124
Phone: 440.684.3101 x102  |  Fax: 440.684.3102
mark.atwood at paragon-inc.com<mailto:mark.atwood at paragon-inc.com>  |  www.paragon-inc.com<http://www.paragon-inc.com/>

From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Bob Richards
Sent: Friday, August 20, 2010 12:01 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Question.

>>>The voltage in a battery is not the lethal element, current of Amperage is.<<<

So are you saying that a 1 cell 5000mah pack is dangerous enough to kill 1000 people? :-)

A 12v car battery can put out hundreds of amps. It does not kill anyone from electrocution since the human body is a terrible conductor (high resistance) and 12v is not enough voltage to cause a significant current to flow through human tissue. So, it takes a high enough voltage to overcome the resistance of the human body before enough current flows to cause problems.

On the other hand, a Tesla coil can produce over a 100k volts, but a person can touch it because there is so little current produced - not enough to hurt someone.

It takes a source with a high enough potential (voltage) to overcome the human resistance, along with enough current capacity, before harm can be done.

The exact values that can be considered dangerous can be debated. 50ma will not always be dangerous - it won't feel good, however. OTOH, less than 20ma under the right circumstances can be lethal.

Bob R.

--- On Thu, 8/19/10, Randall Bearden <rbearden56 at bellsouth.net> wrote:

The voltage in a battery is not the lethal element, current of Amperage is.  I believe the voltage is to limit the number of cells that can be used for the power source.  Each will have 3.6 volts so you can see that 11  cells in series can will have  39.6 volts.  The number of cells in parallel will add up to the current you need for the engine to produce power.  Letha current is about 50 mA or 0.05 Amps of current.

On 8/19/10 3:22 PM, "Atwood, Mark" <atwoodm at paragon-inc.com> wrote:
I can’t answer the “checking” question, as I have never had mine checked, but I “think” I was told they did at the worlds.  As to why the limit on voltage, that’s simply a safety issue.   40V dc is generally accepted as the threshold for non-lethal dc voltage.  Your skins natural resistance will prevent enough current from going through you at that voltage to kill you (though as many have experienced, it can burn the crap out of your fingers).   That said, if you had electrodes poked through the skin, it could still toast you.

There has been talk about raising that limit to accommodate 12s batteries which FAI has done for the Heli F3C competitions.  I doubt you’ll see it go above that.   I’m actually surprised that the AMA hasn’t put an upper limit (or maybe they have and I’m unaware) for the same safety reason.

I can only imagine what a good old fashioned electrocution would do for our image.   Big bird fun fry…

Mark Atwood
Paragon Consulting, Inc.  |  President
5885 Landerbrook Drive Suite 130, Cleveland Ohio, 44124
Phone: 440.684.3101 x102  |  Fax: 440.684.3102
mark.atwood at paragon-inc.com <mailto:mark.atwood at paragon-inc.com<http://us.mc11.mail.yahoo.com/mc/compose?to=mark.atwood@paragon-inc.com>>   |  www.paragon-inc.com <http://www.paragon-inc.com/>

From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org<http://us.mc11.mail.yahoo.com/mc/compose?to=nsrca-discussion-bounces@lists.nsrca.org>] On Behalf Of Tim Taylor
Sent: Thursday, August 19, 2010 3:13 PM
To: nsrca-discussion at lists.nsrca.org
Subject: [NSRCA-discussion] Question.

   4. Model Aircraft Requirements:
  4.1: Propulsion source limitations: Electrically-powered model aircraft are limited to a maximum of 42.56 volts for the propulsion circuit, measured prior to flight while the competitor is in the ready box.

  I see Electrics have a "Displacement" limit, why are they limited and the IC engines not?

  I also see they must be checked in the ready box prior to each flight, anyone ever have this check done? Even at the worlds?

  Or is this another ignored rule?

  Tim

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