Newsgroups: rec.radio.amateur.misc
Subject: Re: more about ham legends
From: julian@bongo.UUCP (Julian Macassey)
Date: 7 Sep 92 19:44:17 GMT
Organization: The Hole in the Wall  Hollywood California U.S.A.




In article <i672588@pro-haven.cts.com> phantom@pro-haven.cts.com (Tiffany Keller) writes:
>Ok....
>In <1992Sep4.153146.20014@cs.rose-hulman.edu>
>derry@NeXTwork.Rose-Hulman.Edu (John Derry) writes:
	Stuff deleted
>
>% 4.  If you set a car battery on concrete it will discharge it much
>%     faster than if you set it on wood.

>        Number 4 however.....
>        I used to work for a security alarms company (we installed them...)
>and we used lead-acid batteries (such as car batteries...).  The owners and
>managers have been installing these systems for about 10 years and I was
>told Emphatically *NOT* to set these batteries on the sidewalk while
>unloading the truck.....I asked why and they told me that the concrete is
>an *excellent* earth ground and drains the battery in a hurry.....I didn't
>pay much attention to this....Until I left a charged battery at a site for
>a day or so, came back and it was mostly discharged (couldn't even power
>the system.....They don't lose their charge *that* fast normally.....)
>        Btw.....we used these batteries as a backup in case of a power
>outage......They can power the system for up to 36 hrs.....(just a
>sidenote...)

	Now, let me see if I have this right. Set a lead acid battery
on concrete and it will discharge. Set it on wood and it won't.

	Now if concrete is an excellent "earth ground" we can assume
two things: 1. A conductor on the base of a battery causes it to
discharge. If "earth ground" means "conductor". 2. Proximity to to a
ground plane somehow causes a battery to discharge if "earth ground"
means ground plane.

	So let's assume 1. If that is true. I think that "concrete is a
conductor" is what is meant. I am not even going to discuss whether
concrete, dry or wet, is a conductor. For the purpose of discussion, we
will assume it is. So, if placing a battery on a conductor would discharge
it, then we will use for our example some known conductors. What if a
battery is placed on a sheet of steel? Would that make it discharge
also? This is easy to test. Get three similar batteries, place one on
concrete, one on a plank of wood and one on a sheet of steel. Monitor
all three.

	Note, that most cars are made of steel, the battery compartment
is also made of steel. Has anyone managed to improve battery
performance in the family chariot by building a wood/plastic battery
compartment?

	Furthermore, what is the discharge path? A lead acid battery
has a case made of glass, ebonite (hard rubber) or plastic (ABS,
polysulfone etc). The tops of non plastic batteries are usually sealed
with pitch (bitumen). These materials are chosen for their insulating
properties and resistance to sulphuric acid. So is there something in
concrete that makes these impervious insulators into conductors?

	So what is the discharge path? If one exists, then we can
measure it and decide whether concrete really discharges lead acid
batteries.


	Now mode 2. I have no idea how proximity to a ground plabe
would affect a chemical battery. If it does, all those batteries the
telco uses in its underground vaults are in trouble. Then again simple
to test. Three batteries - identical. Hang one from a tree, place another
in a hole in the ground and as a control, one standing on concrete.
Measure. See if there is a pattern of discharge.

	Finally, concrete. Now most concrete is made from Portland
cement and aggregate (sand and pebbles). Reinforced concrete has iron
bars running through it. But it is not known as a conductor. Note that
antenna towers on concrete need grounding rods to provide a gound path
for the tower. The only thing that normally conducts lightning through
concrete is the rebar (iron bars). They alas usually vaporise under 
the current and blow the concrete apart.

	But. I stand willing to be shown the error of my ways. Could
someone explain how concrete makes a discharge path through a plastic
battery or point me to literature where measurements have been made.
Until then, we should leave this to alt.folklore.urban.

-- 
Julian Macassey, julian@bongo.info.com  N6ARE@K6VE.#SOCAL.CA.USA.NA
742 1/2 North Hayworth Avenue Hollywood CA 90046-7142 voice (213) 653-4495