[NSRCA-dist7] NSRCA-dist7 Digest, Vol 99, Issue 3 [RCA 18-09 - 12S Voltage]

[Peter Vogel]

There was *originally* a safety concern because the Euro guys argue 42v is
enough to kill you (it's a voltage limit, not a cell count limit, so even
the 4.37v lipo cells at 10s are illegal).  But FAI abandoned that concern
when they started allowing 12 and 14s in the helicopter classes (i.e.
F3C).  I would argue what Billy Crystal's character said in *Running
Scared: *"It's not the volts that kill you, it's the amps".  A taser, as an
example, delivers about 10,000v and doesn't kill you.  Fundamentally if you
let as little as 0.1 amps cross your chest from source to ground you begin
to be at risk of death, at the very least you are going to have serious
difficulty breathing.

This article reproduces what I was taught in high school:
https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

But that leaves aside the resistance of skin, etc. the reality is that I =
V/R, so the higher the resistance of the skin the higher the voltage you
can handle before allowing that 0.1 - 0.2 amps across your heart.  With dry
(not sweaty) hands the resistance from hand to hand (worst-case scenario of
source to ground going across the chest) is 1M ohms so it would take about
20kV to get the current needed to kill, but with sweaty hands it drops to
17,000 ohms and 340V will kill you, add a wedding ring or a tool with a
metal surface you are gripping tightly and the number could drop to 1000
ohms and 20V will kill, 17V would cause ventricular fibrillation.

In short, 42V was based on a very elementary "rule of thumb" analysis and
is pretty arbitrary and makes a ton of assumptions.

That said, I don't think AMA rules should move to 12S until FAI rules do...

Peter+

On Wed, Aug 23, 2017 at 4:38 PM, Bill Polits via NSRCA-dist7 <
nsrca-dist7 at lists.nsrca.org> wrote:

> Derek K, John G,
>
> The only objection I have in the past heard with respect to increasing the
> electric power system limit to 12S is the issue of safety at the higher
> voltage (at least it's my impression that to some degree, safety was the
> reason for the original limit). I have no opinion either way, but just
> wanted to comment that it seems to me that a discussion of the matter of
> safety would be appropriate to include in the rule change proposal.
>
> Best regards,
>
> Bill Polits
> NSCRA 4445
>
> On Tue, Aug 22, 2017 at 1:00 PM, <nsrca-dist7-request at lists.nsrca.org>
> wrote:
>
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>> Today's Topics:
>>
>>    1. Current Rules Proposals (Derek Koopowitz)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Tue, 22 Aug 2017 10:45:11 -0700
>> From: Derek Koopowitz <derekkoopowitz at comcast.net>
>> To: <nsrca-dist7 at lists.nsrca.org>
>> Subject: [NSRCA-dist7] Current Rules Proposals
>> Message-ID: <85A2E9C4-8753-4C3B-9E10-39AEDD3A082B at gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>>
>>
>>
>>
>>
>>
>> Hey everyone,
>>
>>
>>
>> It is time for me to vote on the rules proposals that are before the
>> contest board ? I would like your input on these please.  You can view the
>> current proposals here:
>>
>>
>>
>> http://www.modelaircraft.org/events/ruleproposals/rcaero.aspx
>>
>>
>>
>> The cross proposals that were accepted to move on to the final vote can
>> be seen here:
>>
>>
>>
>> http://www.modelaircraft.org/events/ruleproposals.aspx#2018-2019
>>
>>
>>
>> I?d like your input by early September please.  All votes need to be sent
>> to the AMA by 9/15.
>>
>>
>>
>> Thanks!
>>
>> -Derek
>>
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>
>
>
> --
> Bill Polits
> bpolits at gmail.com
> 510-528-2341 <(510)%20528-2341>
> 510-390-1419 <(510)%20390-1419> cell
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-- 
Director, Fixed Wing Flight Training
Santa Clara County Model Aircraft Skypark
Associate Vice President, Academy of Model Aeronautics District X
Treasurer, National Society of Radio Control Aerobatics (NSRCA)
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