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Battery Status & Charging

See below. 
 
 -----Original Message-----
From: owner-support@gesn.com [mailto:owner-support@gesn.com]On Behalf Of Jeff Hintz
Sent: October 20, 2001 9:17 AM
To: Support Team (E-mail)
Subject: Johnson County, KS - Battery Status & Charging

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