Re: (ET) charger problem

["Hazen, Dwight L" <hazen indiana edu>]

 You can fret and worry all the time about how to change your batteries. 
The simplest way to be sure is with a hydrometer. You can get one that has 
a thermometer to correct for temperature if you want. The best way for me 
is a simple four ball unit. They are cheap, easy to use and will put you 
in the ball park. I use an Emeter on the tractor that keeps a running 
total or amps in and out. It tells me when I have used 50% of my amps and 
then I drive back to the house to recharge. When the Emeter says I have 
filled them back up I check with the four balls again. If all balls are 
floating and quick to go to the top I know they are fully charged. I 
verify the electronic metering with the four ball unit a few times a year 
and they are always a close match. Be sure and flush/pump the acid in the 
glass tube a few times to get a correct reading in each cell. Unbalanced 
cells are easy to identify this way. Measure twice and worry less.

 Dwight

Dwight L. Hazen

Ham Radio wb9tlh arrl net http://wb9tlh.ampr.us

Light speed computers, starships and ray guns, oh my!



-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu [mailto:elec-trak-bounces 
cosmos phy tufts edu] On Behalf Of David Roden
Sent: Thursday, May 21, 2009 1:58 PM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) charger problem

On 21 May 2009 at 9:51, tbamc wrote:

> I think U. S. Battery recommends about 46.5v for equalization, and as
> far as I know the E-T charger won't get there.

I usually say "ask the manufacturer," but I think USBMC's charging
directions are aimed more at users who need to get the highest possible
capacity from their batteries on every single cycle, and are willing to
sacrifice some cycle life for it.

They recommend constant current to 2.583 volts per cell, then constant
voltage at this point for an additional 2-4 hours.  They suggest to reduce
the voltage by 0.028 Volts per Cell for every 10 deg F above 80 deg F, and
increase voltage by the same amount for temperatures below 80 deg F.
(Following this algorithm to the letter requires a much smarter charger 
than
the GE, by the way.)

I think this is needlessly aggressive for most users.  I wouldn't much
exceed 2.5 volts per cell (45 volts for an ET), and stop the charge when 
the
current falls to 0.05C regardless of time.  I'd probably add an 
equalization
phase of perhaps 2 hours at 0.2C or so for the ET, since it taps the 
battery
pack.  I would still use USBMC's temperature adjustment.


David Roden - Akron, Ohio, USA

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