Re: (ET) NiCD powered Elec-trak report

["David Roden" <etpost drmm net>]

Nicads love the cold.  The loss of capacity is minimal.  OTOH, nicads are 
not so keen on hot weather - frequent operation above about 40 deg C tends 
to reduce their cycle life.  They are thus an excellent choice for those 
in 
the northern parts of the US and Canada, but they require somewhat more 
effort for use in, say, Phoenix. You have to provide ample cooling - don't 
pack the cells into the boxes; leave some space for air circulation and 
perhaps add a fan.  You should monitor cell temperatures carefully during 
the summer if you are operating in ambient temperatures over about 85 deg 
F.

They also maintain very stable voltage until they are almost flat, at 
which 
point the voltage falls off a cliff.  This is both a blessing and a curse. 
 
You have plenty of power for a long time.  However, when they're flat, 
you're pretty much done.  With lead batteries a voltmeter (such as the ET 
uses) tells you very roughly how much charge you have left.  With nicads a 
voltmeter tells you that you're going to be walking. ;-)  Christopher is 
using E-meters to deal with this matter.

There is also very little "limp home" capability in nicads, unlike lead 
batteries; with the latter you can let them rest a few minutes and you'll 
generally regain just enough capacity to get back to the garage.  

But they have plenty of advantages : longer cycle life, no sulfation 
damage 
if they are stored in a discharged state, more tolerant of deep 
discharges. 

The flooded type especially are relatively easy to charge with a 
moderately 
smart charger : just put back as many amp hours as you took out at about 
C/5, then drop to C/20 and add another 20%.  Alternatively, set a timer to 
zero, then charge constant current at C/5 until voltage reaches 1.6vpc.  
Reduce current to C/25, reverse the timer, and charge until the timer 
counts 
down to zero.  (Based on charge instructions for Saft STM range modules.)

BTW, just to be clear, Christopher has 60 nicad CELLS, not 60 batteries.  
The BB600s are often sold as individual cells, though sometimes you find 
them assembled into batteries.  These cells are hopelessly expensive if 
purchased new, but you can often find them offered as surplus for 
reasonable 
prices.


David Roden - Akron, Ohio, USA

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