From: billp@Syntex.COM (Bill Putney)
Newsgroups: rec.radio.amateur.misc
Subject: Re: 12volt Marine Battery Use
Date: 7 Oct 92 19:48:07 GMT
Article-I.D.: synseer.1992Oct7.194807.6150
Reply-To: billp@Syntex.COM
Distribution: na
Organization: Syntex U.S.A. - Palo Alto, CA

In article 718141469@mik.uky.edu, johnr@mik.uky.edu (john s roberts) writes:
>I have an old marine battery that I was using for an audio application, but
>the idea of using it with ham radio sounds great.  For the past few years
>it has been sitting with a trickle charge.  The other day I turned off the
>charger and used the audio piece that I had and the battery did not supply
>any power.  I was wondering if there was anyway to jumpstart a battery.  I
>have heard about putting old nicads in the freezer, but would this work for
>a marine battery?  Hope this doesn't start something like the concrete 
>discussion....
>
>John
>
>--
>  --==+  John S. Roberts, Jr.    Internet: johnr@mik.uky.edu (NeXT)  +==-- 
>  --==+  Lexington, Kentucky        Other: mtbb136@ms.uky.edu        +==--
>  --==+  Home: (606) 272-1417         Ham: pending 146.760-          +==--
>  --==+  Work: (606) 257-6100         DoD: trying                    +==--


John, 

Usually the reason lead/acid batteries don't supply any power is that
they have sulphate crystals grown over the plates from disuse.  Another 
cause might be that the battery is dry or that the cells are shorted.  

Use safty glasses while working around batteries!

Check the electrolyte level in the cells.  If the level looks good connect, 
an ampmeter in the charging circuit.  If there is a reasonable amount of
current flowing, the cells are probabily shorted.  Take the battery with
you to use as a "core" when you buy a new one or dispose of it at a toxic
waste dump.  If there isn't much (or any) current flowing, the plates are
sulphated.  I have had some luck with small batteries using a current 
limited power supply to knock off (or probabily break down) the crystals.  

**********************************************************************
*** I think this may be kind of a dangerious thing to try with a  ****
*** large battery.                                                ****
**********************************************************************

What I did was to use a bench supply that had a current limiter.  I set the 
current limit for some small percent (To be safe I'd say no more than 5%) of 
C (C is the capacity of the battery in Ampere/hours), connect the battery 
like you would if you were going to charge it and turn the voltage up until 
you start to see some current flowing (not to exceed twice the normal battery 
voltage).  This will take a while to show any results (maybe a day or so). 
 
This process was about 50% effective in bringing back some really dead ones.

What I have observed is that the current will start to rise as the crystals
are broken down.  When the current reaches the limit the voltage will start
to decline as the battery resistance decreases.  Once the battery takes as 
much charge as is is going to take the voltage will start to go back up.
You should turn the voltage down on the supply as it falls.  By the end of
this proceedure the battery voltage should be at a high float voltage (no
more than 14 volts).

If you have some sort of load, I would cycle the battery a couple of times
down to 11 volts on the load and back up to float on a normal automotive
charger.  This will get rid of any lingering crystals of sulphate and give
you a chance to estimate the batteries new capacity value.

Better yet, if you wait a while and watch the newspaper ads, Sears will have 
a sale on their marine Die Hard batteries.  I have seen these on sale for 
under $50.00.

Good luck
-Bill
---
=====================================================================
#  Bill Putney                     |  billp@Syntex.COM              #
#  Syntex U.S.A.                   |  {oliveb|decwrk}!synseer!billp #
#  M.S. A5-6                       |--------------------------------#
#  3401 Hillview Ave.              |  P.O.T.S.  (415) 855-1259      #
#  Palo Alto, CA  94303            |  FAX       (415) 855-5301      #
=====================================================================