----- Original Message -----
Sent: Saturday, October 20, 2001 12:05
PM
Subject: Battery Status &
Charging
See below.
Johnson County, KS has
received 6 AVTS units for demonstration purposes. One of the units says Low for the Battery Status instead of Charging, this unit has been plugged in since they received it, over a week now. Does this mean that the
battery is bad, or that the indication of the battery does not work???
Windows CE 2.12 has a bug where it always reports
the Main Backup Battery as a "Low" Status. This is apparently corrected
in Windows CE 3.0.
A
PIC microcontroller is used to control battery charging/discharging and power
distribution. The PIC monitors the battery and reports a percentage of
the battery's charge capacity to WinCE, but at this time, the
BallotStation software doesn't use the Battery Charge Capacity
Percentage, only the status word (i.e., good, low, very low.) And WinCE
2.12 is stuck on "low". I don't know the outlook for implementing WinCE
3.0. Jeff Dean would be the person to make an inquiry to on that
matter.
They are in the
planning stages of their warehouse, and would like to know what our
recommendations are for charging of the AVTS units. Do the AVTS units
need to be plugged in continously???
No, they don't need to be plugged in
continuously. However, they can if they wish. It won't harm
the unit.
Can the AVTS units need to be
charged on a rotation schedule???
If it is logistically more feasible
for the warehouse staff to use a rotation schedule, then they can do
that. The battery charging circuit only needs AC power attached to
charge the battery. With the unit turned off and AC applied, the system
will be in slow charge mode and will only draw a small amount of AC power
(0.1A @ 110VAC). At that small of a current consumption, quite a few
units can be attached to a single circuit.
NOTE: Sealed lead acid batteries
lose approximately 3% of their charge per month just sitting on the
shelf. If left unused, they should be recharged a minimum of once a
year. Preferable would be once every six months. Obviously, if
they have more frequent elections cycles, and the units are charged before and
after each cycle, this minimum wouldn't be a concern. But if they have
spare units that are always held in reserve and never used, then they should
meet the minimum charging requirements.
Do the AVTS units need to be charged
only 24 hours before an election???
On slow charge, a
discharged battery will be charged in 12 hours. With AC applied and the
unit is turned on and operational, the charging circuit switches
into fast charge mode. This mode will bring a discharged
battery to 85% of full charge within 3 hours. This is done by
applying the manufacturer's maximum recommended charge current into the
battery. The system will switch to slow charge after reaching the 85%
point. Fast charging past that point can reduce the battery's life
expectancy. The purpose behind the fast charge mode is to maximum charge
time in a rolling blackout situation.
When the unit is using fast charge mode,
it will consume more AC power ( 0.3A @ 110VAC).
NOTE: The ballot station operation
takes priority over the charging of the battery. If the ballot station
operation needs to draw power that nears the capacity of the power supply
(e.g, someone plugs in an unapproved PCMCIA device that sucks the power down),
then the battery charging circuit will either reduce to slow charge mode or
stop charging in favor of the ballot station load requirements..
I will be going down to
Johnson County, KS on Tuesday for an all paper election, and they would like
to know the answers to these questions.
Currently, an idle
system will take 5-1/2 hours to discharge a fully charged battery. This
is with the LCD panel displaying constantly. If the software is
developed with a sleep mode for the LCD panel, this discharge time could
be considerably longer. The LCD panel and its backlighting draw the most
power.
The tested configuration
for the 5-1/2 hour discharge time used a 32MB flash memory card as the
only PCMCIA device. Other PCMCIA devices would draw additional power and
therefore shorten the discharge time. Printing a paper tape on
battery power draws considerable power, but that is cyclical and not a concern
for overall discharge time. Unless, of course, it is done
continuously.
On discharge, when the monitored battery
voltage reaches 10.5V, the system will automatically shutdown. This
is the 0% capacity point. Some components in the system require a
minimum of 10.2V for operation and the life expectancy of a sealed lead acid
battery will be reduced if it is used below 10.5V. Life
expectancy on sealed lead acid batteries is 5
years.
I hope that answers your
questions on battery charging (and discharging). Let me know if you
need anything further.
Ian