Re: (ET) Battery Question

["Travis Creswell" <ozsolar ipa net>]

Hi Christopher,

For what it's worth I don't anything about drag cars.  But I have been in
the solar business for over 10 years installing and maintaining thousands 
of
batteries and solar panels over that time.

It's not amperage of the loads that would cause the problem that I'm 
worried
about.  Let me take a stab explaining my thought process. The common charge
controller has no provision for hooking up loads so the energy for the load
would still come directly from the battery (via the cars' on board fuse
panel).  A charge controller is designed specifically to prevent a solar
panel from overcharging the battery.  Since solar panels have very limited
current a charge controller is only designed to handle a limited amount of
current and essentially has no provisions to deal with high current sources
such as batteries, battery chargers, unregulated DC power supplies etc. Big
charge controllers are only rated at 40 amps.  The installation manuals 
that
come with charge controllers specifically warn against using them to 
control
anything but solar panels for this reason. 

The simpler Charge Controllers close a relay once the voltage of the 
battery
drops to certain level (commonly ~13.3 volts) connecting the battery to the
solar panel and charging begins.  After the solar panel brings the voltage
up to somewhere around 14.5 the relay opens, disconnecting the solar panel
from the battery to prevent overcharging of the battery.  This process 
might
happen 100's of times day as the battery voltage rises then drops again. 
Charge controllers are specifically sized to the amp rating of the solar
array.

A battery is capable of delivering 1000's of amps.  Once the charge
controllers' relay closes to begin the charging process it will see all of
that amperage as the higher voltage battery attempts to equalize the
voltage.  If the charge controller survives long enough for the battery
being charged to reach the "charged" set point it's relay will attempt to
interrupt a load that could be as large as a thousand amps.  A sudden
catastrophic failure (an explosion) might happen.  Even if it was under a
few hundred amps the Charge Controller just isn't designed for large loads.

Hopefully this explanation clears up my thinking on this.  I might be all
wet but I would not hook two batteries of different nominal voltages
together.

Travis
----------
>From: "Christopher Meier" <mr23 mn rr com>
>To: "Travis Creswell" <ozsolar ipa net>, "Pestka, Dennis J"
<Dennis Pestka TycoHealthcare com>, <elec-trak cosmos phy tufts edu>
>Subject: Re: (ET) Battery Question
>Date: Wed, Jul 17, 2002, 9:14 AM
>

>I was under the impression that dragster are not cranked via a
>starter that is run from the 12v battery; they are spun up by a
>hand held unit that is independently powered.  Please enlighten
>us as to the starting method used on the dragster in question.