The Rechargeable Battery "Cycler"
By: Bertrand Zauhar, VE2ZAZ
Published in the September/October 2008 issue of ARRL's QEX Magazine
INDEX
Page last updated: 28/12/2008

INTRODUCTION

This page complements article "The "Rechargeable Battery Cycler" published in the September/October 2008 issue of ARRL's QEX magazine. This page also provides updates to the original article.

The Battery Cycler is an autonomous device that will periodically discharge and recharge Nickel Cadmium (Ni-Cd) or Nickel-Metal-Hydride (Ni-MH) battery packs so that they are always fresh and ready to deliver. 

Please visit this page frequently, and right before assembling the project, as new information may get added regularly.

Once again, I would like to express my gratitude to Jocelyne, my wife.This project took 6+ months of spare time to develop, so she deserves it! Also, thanks Jacques-VE2AZX for beta-testing this system.

Bert, VE2ZAZ
ORIGINAL QEX MAGAZINE ARTICLE

For those who have not read the article yet, this is the best place to start learning about this project.

Reprinted with permission. Copyright ARRL, 2008 all rights reserved. This material originally appeared in QEX: Forum for Communications experimenters (www.arrl.org/qex).

OBTAINING A PCB AND PROGRAMMMED PIC MICRO

Please contact me via email if you would like more information on the following items described in the article:
  • A top quality, fully etched, double-sided bare PCB. The PCB also has solder resist film and component marking.
  • A pre-programmed PIC 18F1220 micro-controller.
I will be happy to provide you with procurement info in my email reply.
THE LATEST NEWS, ERRATA AND IMPROVEMENTS

(Added 28/12/2008)
A version 2 of the Cycler Configuration Software is available for download. This version offers a fix for the battery current display, which overlapped the "mA" label.

(Added 05/11/2008)
The original QEX article is now available here in PDF.

(Added 26/08/2008)
The original QEX article will be available here in PDF form at the end of the month of October 2008. For now, exclusivity is given to the printed magazine.

(Added 26/08/2008)
The LED contour markings on the PCB are inverted for D2 and D3 if using the suggested bi-color LEDs (Digikey 160-1038-ND). See the Assembly Instructions section below.

(Added 26/08/2008)
Hammond Enclosure. I want to warn you that the suggested Hammond enclosure may be too small to work with for some of you (hands full of thumbs?). My goal was to fit everything into the smallest possible enclosure. If you are unsure about your ability to fit everything into the suggested enclosure, just pick a bigger one. The Digikey website catalog shows a list off all the similar aluminum enclosures you can pick one from. Just make sure you select a box that has all its dimensions greater or equal to the one I am suggesting.

I appreciate reading back from experimenters who build this project. This allows me to improve this page by providing additional clarification if necessary. Thanks!
PCB VIEW



Due to space constaints, the top-down view of the PCB layout was not published in the QEX article. Here it is for reference purpose.

Click on the figure to view it in larger size ->


CONFIGURATION SOFTWARE (WINDOWS)

This is the Windows program that provides a user-friendly interface to the Battery Cycler system to configure it. The software provides the following features:

  • Microsoft Windows-based program with single window and tabs,
  • All parameters are set up and saved from within one program,
  • Serial port driven; supports COM1 to COM8,
  • Help provided via mouse cursor hints,
  • Only required at configuration time or whenever log monitoring is desired.
  • Un-install program provided.

This software was developed and tested in a Windows 2000 environment. It was also tested in Windows XP. Previous programs that use the same COM port driver were also successfully used on Windows 98. Since these operating systems cover two main branches of Windows (9x and NT), the software is expected to run in all Windows environments from Windows 95 through Windows Vista.

Version History

Version 2 (December 2008)
This version offers a fix for the battery current display, which overlapped the "mA" label on the initial version.

Version 1 (August 2008)
Initial release.

LEARNING ABOUT AND PROGRAMMING THE PIC FIRMWARE

If you would like to look at the firmware load running inside the PIC micro-controller, well here it is! The ASM file is a text file of the source code I wrote. Beware! This is Assembly language...The code is well documented though. Have fun... ;-)

I also provide the latest HEX file required to upload the firmware load into the PIC 18F1220's program flash. This file is in 8-bit Intel HEX format, which is the industry standard for 8-bit micro-controllers. Note that 5V In-Circuit Serial Programming (ICSP) is not supported on this firmware load. All pins are assigned to external functions, so the low voltage ICSP programming pins could not be spared for that task. In order to accomplish the firmware upload, you need a PIC programmer that can handle the PIC 18F series chips and standard high-voltage programming.

ADDITIONAL ASSEMBLY / WIRING INSTRUCTIONS

  • The TO-220 components (MOSFETS and Power Resisor) can be mounted below the PCB as shown on the figure to the right. Alternatively, they can be mounted above the PCB as long as they make contact to one of the enclosure walls for heat dissipation purpose.
  • The MOSFETS must be mounted with their metal tab (case) "floating". This calls for an an insulation kit for both. Before powering up the Cycler, a final check should be made with an ohmmeter to ensure that the 2 metal tabs are truly floating (high resistance) from the metal enclosure. Resistor R1 does not require electrical insulation since there is no metal on its case. A heat conducting pad or some heat sink compound is required though.
  • The LED contour markings on the PCB are inverted for D2 and D3 if using the suggested bi-color LEDs (Digikey 160-1038-ND). See the figure to the right on how the LEDs should be mounted. The red contours should match the LED shapes.
  • RS-232. The RS-232 connection is a simple 3-wire communication. No handshaking or strapping is required at the PC's end. As well, you do not need to set any COM port parameters within Windows; the software sets these when data exchange occurs. 
Recommended TO-220 components installation
Click on the figure above to view them in larger size.
D2, D3, D6 LED orientation when using Digikey 160-1038-ND
Click on the figure above to view them in larger size.

ADDITIONAL OPERATING INSTRUCTIONS
  • None so far.