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I forgot to add, what its suppose to do

- Programmable battery discharge analyser
- Analyses batteries 1V to 15V
- Discharges 0-2500mA (about 10mA resolution)
- Programmable termination by voltage, time, capacity, or dV/dt.
- Logging of data (capacity, voltage etc) to SD card, to CSV file
- Uses Arduino libraries for easy modification of firmware by hobbyists
- Spare I/O ports broken out so users can add custom features
- USB port access (via FT232RL chip), can be left empty if no USB required
- TTL-UART terminals for serial interface (when built without USB)
- Discharge in constant current, constant resistance, constant power modes
- Internal resistance test (by multiple constant current discharge steps)
- 16x2 LCD display showing current status
- 4-way key pad navigation
- Stand-alone operation, no need to connect to computer
- Can be powered by USB or external DC jack
- Calibration via serial port terminal
- MOSFET mounted externally, using appropriate heatsink for battery voltage and current discharge. This is so the user can customise their own mounting options.

Good recognition I originally decided to make this to test my third party battery packs for my 1Ds. As I believed I may have gotten a few dodgy ones from eBay and wanted to test its discharge characteristic.

Unlike the Maha C9000 AA/AAA charger, it does not do any charging, only discharge. So it doesn't do cycling etc. I did think about this, and to do it would add considerable cost to it. I have one of those Maha chargers too! But I think the Maha charger is pretty good.

I guess the people its targeted to, are people who rely on batteries a lot and need to check its condition regularly. Such as people using cameras, the RC crowd and their toys, hobbyists wanting to see a visual graph of the discharge characteristic. I doubt it has any real general-population commercial use.

It would be nice to have a computer program to see the plot without having to import the files to Excel etc, but I couldn't write a Windows GUI program (e.g .NET, VB, etc) to save my life!

So if I open source it, maybe some enthusiastic person could build on it.

It uses an AVR Atmega328 chip, the SD read/write code is done using Arduino sdfatlib. I originally tried writing straight AVR code using Chan's FatFs and i couldn't get it working. PetitFS worked okay, but wasn't really suitable for writing data in a practical way. So to sdfatlib for Arduino it was. The output from the MCU (5V) is level converted to 3.3V and drives the SD card.

On a practical note, I did use it and found some battery packs with a out of balance cell, which was discharging to zero (falling off the wall) before the rest and managed to improve it signficantly by doing a few cycles (charging manually 16hrs 0.1C, discharge 0.1C).

thats pretty cool! how much power can you dissipate and what mosfet did you use? i'd like to replace my west mountain discharger with something bigger at some point.

you could use processing to write a quick gui. arduino spawned from processing and wiring so its very similar to work with.

OR, u could use logview. http://www.logview.info/vBulletin/ highly configurable, works great!

I originally decided to make this to test my third party battery packs for my 1Ds. As I believed I may have gotten a few dodgy ones from eBay and wanted to test its discharge characteristic.

in the name of hell! few you said? third party? why the 1Ds owner need a "few 3rd party" batteries? and built a discharger to find out the dodgy one. its funny and i dont get it, except if you just want to do it for hobby or have plan to sell it. my "late" 1D have 2 original pack, and i never needed the second one, in any of my projects, so i cannot imagine how big is your project that need a "few" battery pack. why dont you get original pack instead of 3rd party? dont tell me its expensive. well that an OT rant, i hope you are not offended.

anyway, have you successfully distinguished between the good one and the dodgy one? my normal way of doing is fully charge it, and see how many charge (volt) left after 1 day to 1 week not used.

But I think the Maha charger is pretty good.

yes it is good, except at restoring dead battery, even its own brand battery.

It would be nice to have a computer program to see the plot without having to import the files to Excel etc, but I couldn't write a Windows GUI program (e.g .NET, VB, etc) to save my life!
So if I open source it, maybe some enthusiastic person could build on it.

i can help you with that. but more complicated graph needs more time to develop.

It uses an AVR Atmega328 chip, the SD read/write code is done using Arduino sdfatlib...

thanx for the interesting info. looking forward to use the library in my next project.

On a practical note, I did use it and found some battery packs with a out of balance cell, which was discharging to zero (falling off the wall) before the rest and managed to improve it signficantly by doing a few cycles (charging manually 16hrs 0.1C, discharge 0.1C).

have you done test on AA size NiMH?

I don't know how much interest there would be out there, so I was wondering if anyone out there had any input on whether this might be worth forking out the dollars for a real board etc, as-in, would anyone buy it? Is there a market potential here in the maker, hobbyist area?

it all depends on the pricepoint i geuss, you should be looking at least cost * 2 as pricepoint. most likely the RC market is the biggest potential.
you have very cheap chargers who do discharging , some of the more expensive are still only 80 $ (can only discharge 20 watt) but those can be connected to logview and get you plots of charge/discharge cycles.

The main selling point of yours would be that anyone can customize the firmware at their wishes of course.

Nice project, i like it.