[NSRCA-discussion] Question.

[Bob Richards]

Part of my point was that there is no difference between grabbing the leads of a 300mah 3 cell lipo, or 4 900cca 12v batteries in parallel. It does not matter if the Lipo is 3S 300mah or 3S 5000mah. It does not matter if it is a 12v 7ah gell cell, or 20 12v group 27 batteries wired in parallel. They all have the same voltage potential, and they can all source more current than will possibly flow in human tissue.  None will push more current through human tissue than any of the others.  Simple Ohms law.
 
I'm not doubting you, but I've never EVER felt anything from 12v. When I was in electronics class, we had access to a DC 200v adjustable power supply. My classmates and I, being curious, young AND a bit stupid :-) decided to see how long we could hold onto the leads from this power supply while someone slowly ramped up the voltage. All of us could hold on until the voltage was at least 80v, one guy could go to well over 100v. None of us seemed to feel anything less than 50v. Granted, we were not hot and sweaty.  Oh, one thing we learned very quickly was exactly who we could trust with turning the knob on the power supply. :-)
 
I can believe the FAI rule being based on the 42v level from UL. However, I have to laugh at the 4 digit figure they specify. 42.55V is ok, but 42.57 is not? :-)  On a more serious note, does the specification of 42.56 volts mean that we must have a meter on hand with that much precision? 
 
Bob R.

--- On Fri, 8/20/10, Dowayne Gould <iflyrc24 at gmail.com> wrote:


From: Dowayne Gould <iflyrc24 at gmail.com>
Subject: Re: [NSRCA-discussion] Question.
To: "General pattern discussion" <nsrca-discussion at lists.nsrca.org>
Date: Friday, August 20, 2010, 1:34 PM



I work on trucks that have 4 900cca batteries wired in parallel. On a hot sweaty day 12v running down your arm is down right uncomfortable. Getting hit with a quad flash strobe set up will make a guy mean the rest of the day. 

On Aug 20, 2010 1:10 PM, "Atwood, Mark" <atwoodm at paragon-inc.com> wrote:




>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.  


 
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