T&T: Batteries? - detailed and long

[2elnav at netbistro.com]

----- Original Message ----- 
From: "Paul W. Weakley" <jweakley at visi.net>
>I just read a portion of Steve Dashew's article on batteries.  >>>>>> snip 
><<<<<<
> But, my primary question is the "Traction Battery" and how does it differ
> from a high quality deep discharge made by many reputable manufacturers?
>
> Paul

REPLY
A true traction battery will have thicker plates compared to ordinary 
batteries.  Even when compared to so caled deep cycle batteries by Concorde 
and Exide.
I have dismantled so called "deep cycle"  batteries that are not true deep 
cycle.  Sadly marketing got hold of the term and started  applying it 
indiscriminately.  Many so called deep cycle  batteries will stand up to one 
or two deep cycles  wihtout harm. But not repeated daily cycles.
However,  traction batteries are designed to deliver nearly continuous full 
output current  until 80% discharged.  The term comes from the application 
of driving traction motors in fork lifts, floor sweepers/polishers and golf 
carts.

Typically these batteries are supplied to a user along with a dedicated 
charger  designed specifically  for that battery bank size. For industrial 
use, the 8 hour shift  becomes a defining time limit.  A fork lift  should 
recharge in one 8 hour shift period.  But  I do recall working with some 
back in the sixties that had a 16 hour charge cycle as the norm. This time 
includes the finish float stage  to completely bring up the charge to 100% 
full.  In those days  chargers were mostly  SCR type and single stage.
In addition to  heavier plates; traction batteries will have larger fluid 
resevoirs for the electrolyte. BTW until recently  traction batteries were 
always wet flooded cell type. This added electrolyte helps with heat 
dissipation as well as providing  the extra amount of liquid to prevent 
running dry  during elevated temperatuers during eother  use or recharging.
 In the case of fork lift batteries I have discovered that modern 
manufacturing methods include the use of polypropylene cases.  These cases 
are soft and somewhat pliable. The final battery pack requires an external 
case - usually steel - to give physical support to the plate stack inside. 
AS  aconsequence these bateries typically weigh in at around a ton.
Rolls makes small 2V  cells and have formatted he case size to neatly stack 
up inside  th esame foot print  as the ubiqutous  8D size so beloved by 
boat builders and designers for many decades.  one 8D weighs in at around 
160 lb.  Handling ease is the biggest justification for the Rolls  product. 
In addition they make the case stronger and more rigid compared to the 
bigger  cells.

Today you can also get sealed  "deep cycle" batteries  using either the Gel 
or AGM  technology.   Gel will discharge deply without damage but the 
gelling agent is silica sand, a non conductive media.  The addition of non 
conductive material to the electrolyte does not speed up  charging. If 
anything it slows it down. for  emergency back up  or UPS  operation thsi si 
quite acceptable.   for marine use  which may include  frerquent recharging 
from a genset, this long period of recharge is not acceptable. The fuel 
burned  by the gnerator is terribly expensive.
The next development was described as AGM  - absorbed glass mat.  Instead of 
a liquid bath of electrolyte, the sulphuric acid  electrolyte is soaked into 
a bloter sheet consisting of glass strands  similar to ( although not 
exactly the same as  the mat used in boat construction)  fiberglass matt 
you se used in boat building.
The big advantage of AGM is the high  current discharge  ability combined 
with the eaqually rapid recharge rate.  The trade off  being the reduced 
number of cycles compared to  flooded cell of equal amp hour capacity.
The reapid recharge means  reduced genset run time.
AGM are typically described as deep cycle and some are in fact  also sold as 
Traction batteries.  AGM when fully discharged each cycle wil give you 
300  - 400 cyucles.
Reduce that Do D to 50% and the life expectancy  increases to  about 1500 
cycles and  if you keep the DoD to less than 30%  you can get somethign liek 
3000 cycles.
The curve is not linear.   Companies like Concorde Lifeline publish  curves 
and most brands will be similar in cyurve shape if not in actual  value 
points on the graph.

Now we have a new technology. Also touted as deep cycle and also 
demonstrating many of the good characterisitcs  of AGM. It is called thin 
plate technology.  Odyssey and Northstar  are the most familiar brand names 
that you will have seen.  some of you have seen Meridian and Energy1 as 
brand names.  These bateries have one huge advantage. For the same given Amp 
hour capacity  they have  a footprint of approximately half the size.
although the manufacturers are cloe mouthed about actual details,  some 
things can be deduced from appearance.  Thin plate technology can deliver 
high  current surges for the same reason  starting batteries  deliver big 
start current  for short duration.  Because the Thin Plate batteries also 
use the glass mat like an AGM battery  they have good deep discharge  and 
fast recharge capabilities.  Thin plate batteries have not been on the 
market for long enough to determine if they will stand up to  a decade or 
more of heavy use.
I remember playing around with AGM batteries starting back in the mid 
eighties when a 25 A-H Cyclon  Gates battery cost $400 each.  I obtained 
some  that were already 4 years old. I kept them in service  in my sailboat 
for 15 years.  Having no charging facility on board I ran them flat. then 
brought them home for recharging.  I used a common garage type charger. 
Despite this abuse they performed sterling service. Its hard to find a worse 
or harsher  service condition  than that.
Optima  are a close copy of these early  Gates tubular construction 
batteries.

Hope this helps.

Arild