So why did I make a battery charger? Well, it goes back to my very first digital camera. It was a great little point and shoot that ran off of two AA NiMh rechargeable batteries (which were included when I bought the camera). Eventually the day came when they stopped holding a charge. It surprised me because I had only had the camera for a year. However I figured the batteries included with the camera were probably not as good as some awesome new third-party ones. I was pulled in by attractive marketing and went for those with the highest mAh rating. Guess what, they died even faster! I wanted to know why. I didn't know what I was getting into at the time, but this was the start of my battery obsession.
I think a lot of people have wanted to switch over to rechargeables in devices that use AA and AAA alkaline batteries, but for one reason or another have been turned off either by past experiences, the high up-front cost, or... a bunch of other reasons. In my case, I wouldn't mind paying more initially if I had some assurance I was going to get the advertised capacity and number of cycles (or something even close to it) from the rechargeable batteries.
It turns out that chargers are largely to blame for disappointing battery performance: they overcharge the batteries, charge them in pairs (see my video for an explanation of why this is bad), and have inadequate temperature sensing. Are there good chargers out there? Yes, there are. Yet even they tend to be lacking in important areas of design. There is a lot that goes on "behind the scenes" in battery chargers that a user can never know about without a lot of extra equipment and expertise. For instance, what was the charge termination voltage? What was the individual cell temperature during charging? How well did the charger regulate current? What is the actual measured capacity of your cells?
I wanted a battery charger that worked well, handled each cell independently and did so much more than just charge batteries. So I made my own. It has been a huge project (ask my wife) that has taken countless hours and a lot of personal money. I dream of making it even better with more features if this project goes well. By supporting this project you will not only be helping me complete this version, but you will be helping me develop a more completed, commercial ready, version for the future. As a backer I will also be using your input on some of the form and function aspects of my next version.
So what does this version do? First and foremost, it charges AA NiMh batteries. It also cycles new batteries to break them in before their first use to ensure maximum performance. It can refresh batteries that have been in storage or help you identify rechargeable batteries that need to be replaced. It can make sure that batteries are completely drained before recharging them or it can even do a single charge-discharge-charge cycle to report the actual capacity of the battery. Everything including voltage, temperature, current, impedance and estimated health of the battery is stored to an SD card on the bottom of the charger (for viewing and additional analysis on the computer). The file format is designed for easy importing into your favorite spreadsheet program (Excel, Google docs, Open Office etc.). I am also finishing a Processing sketch (check out processing.org if you don't know what it is) to help with visualization of the data and to produce consistent image plots from the data for sharing and comparing.
The final board version will include a small potentiometer for setting the charge current from 200mA up to 1A (note: the highest charge current can only be achieved with one battery in the charger).
If all goes well on Kickstarter then I will make this design all open source (update: It has gone well thanks to all of you! We have passed the pledge goal so everything will be open source and open hardware) and use any money raised for the development of my more feature rich 4 cell version.
You can read more about the project on my blog at: www.paulallenengineering.com/blog.html
Thank you for taking the time to look over my Kickstarter project.
Risks and challenges
Anytime you manufacture electronics there are always risks. Most often the risks are related with the source of parts and getting them in a timely manner. For this reason I am using parts that are readily available from more than one distributor. PCB fabrication and population will take place locally to also help mitigate risk. After that, most of the work has been done, and only minor refinements are taking place. Also depending on the location of overseas backers, it may be more difficult to ensure safe delivery (Message me if you know this might be you).Learn about accountability on Kickstarter
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