Date:         Fri, 21 Apr 1995 10:46:35 -0400
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         drew@interport.net (Derek Drew)
Subject:      battery types (article)

>From: ChrisRosen@aol.com
>Date: Thu, 20 Apr 1995 19:46:56 -0400
>To: drew@interport.net
>Subject: batts
>
>Car Batteries
>
>( by Michael Naum <miken@silvaco.com> July 93 )
>
>>If I remember my physics (or was it chemestry) correctly, batteries will
>>hold a charge better and your electrics will work better in the cold.
>
>The battery will continue to store charge but it will be useless at low
>temperatures.  This is why.
>
>A bit of battery physics....
>
>As temperatures are lowered in a battery, ion mobility (the carriers of
>charge)
>and electron reaction rates are reduced.  Thus most liquid batteries cannot
>produce the same amount of energy at lower temperatures.  If the electrolyte
>freezes then ionic mobility will be lowered to the point that the battery
>is basically useless.  This will probably not happen too often because
>batteries have awfull thermal conductivity so they never reach the ambient
>temperature unless of course you live in Alaska and leave it parked
>on a glacier the entire winter!!   The other interesting thing about 
>batteries is that at lower temperatures there is increased internal 
>resistance.  If you leave something small plugged in (like a radar detector)
>it will draw current.  This current will flow through this internal resistor
>creating heat.  This in turn will keep the battery warm.  But it will drain
>some juice out of your battery. 
>
>Heating a battery produces the opposite effect.  The battery will yield 
>more.  The only problem is the electrons tend to go crazy and cause the
>battery to self destruct.  I had the unpleasant experience of having a
>battery that was boiling BLOW UP in my house garage.  Luckily the hood 
>was up and I was behind my CJ.  There was acid everywhere and my ears
>were ringing for about an hour.  A boiling battery can produce a substantial
>amount of Hydrogen gas.  Thus creating a small non-nuclear H-BOMB capable
>of burning you, your vehicle, and anything in its path.  Avoid a boiling
>battery at all costs...........
>
>
>==============================================================================
>=
>
>Battery Storage Capacity
>
>( by Daniel I. Applebaum <danapple@vicor.com>
>     31Oct94 )
>
>Information from "The Complete Battery Book" by Richard A. Perez.
>Copyright 1985.  ISBN 0-8306-0757-9
>
>Four types of Lead-Acid batteries concern us for vehicular purposes,
>automotive starting, low antimony deep-cycle, high antimony
>deep-cycle, and gel-cells.  I'll go over characteristics of each.
>
>But first, a general note:
>A) The storage capacity (ampere-hour rating) of a battery is a function
>of the surface area of the plates exposed to the chemicals.
>
>1) Automotive Starting Batteries
>It has one job only: to start your car.  An average car uses more than
>300 amps for a few seconds in order to start.  The batteries are
>constructed with a large number of thin plates of lead sponge.  This
>provides maximum surface area.  The batteries handle only very shallow
>cycling, on the order of 1% in normal use.  The starting battery will
>fail after approx. 100 cycles of 50%.  Complete failure at 200 cycles.
>The sponge disintegrates with the repeated full charge and discharge
>chemical reactions.  Lead particles separate from the plates and form
>micro-short circuits inside the battery.  This highly increases the
>self-discharge rate.  Maintenence-free batteries have added calcium to
>the lead sponges to harden them and reduce water loss.  The calcium
>also increases the internal resistance, hence slowing self-discharge.
>The expected lifetime of a starting battery in true starting use is
>3-5 years.  In deep-cycle service, expect less than 2 years.
>
>2) Low Antimony Deep Cycle Batteries
>These are run-of-the-mill "marine/RV deep-cycle" batteries.  It's a
>compromise between a starting battery and a true deep-cycle battery.
>They are much closer to starting batteries, however.  The plates are
>somewhat thicker than starting batteries and have some added antimony.
>It is not designed for powering large loads for a long time.
>Deep-cycling will damage it, over time.  In RV use, with usually no
>more than 20% discharge, the battery should last 200-400 cycles.  If
>cycled 80%, expect a lifetime of less than 200 cycles, or about the
>same as the starting battery.  The thicker plates and antimony add a
>bit of mechanical strength over the standard starting battery.  In
>float service, the battery will last 5-10 years, much greater than
>starting batteries used in float service.
>
>3) High Antimony Deep Cycle Batteries 
>This type is designed to be 80% cycled repeatedly for 5-15 years.
>There is almost no mechanical similarity between this battery and a
>starting battery.  They are massive and huge.  There are very few true
>deep cycle batteries with greater than 6 volts, as they would be too
>heavy to move by hand.  The grids are over 4 times thicker than a
>starting battery's grids.  And there is several times the amount of
>antimony in the grids.  The plates are thick to add lifetime, not
>capacity.  (See A).  The plates are not constructed of sponge, but of
>scored sheets of lead with up to 16% antimony.  The thickness of the
>plates combined with the high antimony content lowers the energy
>density, so this battery is heavier, larger and much more costly per
>kilowatt-hour.  The case is also much thicker, and the plates usually
>leave a 1-3 inch space at the bottom to allow for accumulation of lead
>particles, so that they don't cause micro-shorts.  The top of the case
>also has more space to allow for expansion of the electrolyte.  Plates
>can be removed and serviced.  As the cell interconnect straps are
>exposed, each cell's voltage can be measured individually.  This
>allows the user to determine when an equalizing charge is necessary.
>Some batteries have "wrapped" plates, where perforated plastic is
>wrapped around the plates to keep the lead on them longer.  Such a
>configuration add 25-35% to the lifetime of the battery.  Such
>batteries are mostly used for electric vehicles, which force a fast
>80% or more discharge.  They are then recharge much more slowly.  A
>350 amp-hr 12 volt battery weighs 250 pounds and contains 4.5 gallons
>of sulphuric acid.  They can be cycled 80% between 1000 and 2000
>times.  Lifetime should be 5-15 years.
>
>4) Gel Cells
>This type is designed for portability.  They are small and have a
>jellied electrolyte.  The case is sealed.  The jellied electrolyte
>allows the use of this battery in any orientation.  They are used
>often in aircraft and electronics.  They are supposed to be clean and
>usuable where acid vapors and spills are unacceptable.  They can be
>deep-cycled over long periods.  They must not be charged or discharged
>too rapidly, otherwise it can gas, possibly blowing the sealed case.
>They are prone to sulfation if left discharged for a long time.  With
>proper care, a gel-cell will deliver 1000 cycles over a period of 5
>years or more.
>
>
>
___________________________________
Derek Drew
drew@interport.net (main address for e-mail)
derekdrew@aol.com (alternate/backup address, checked infrequently)