Wednesday, December 26, 2012

Plastic Welding and First Steps Towards Lithium

The first tangible step towards converting my DIY electric car from lead to lithium batteries was accomplished today. I welded the first of two plastic battery boxes from sheets of PVC. Cutting was done on a table saw, and I used a cheap $40 plastic welding tool from harbor freight along with some PVC welding rod to complete the box.
The tool has a built in heating element, and requires quite a lot of compressed air. It has it's own regulator and air pressure is the only way to regulate temperature. A pressure of 4 PSI gives a stream of air at around 600 degrees Fahrenheit which is the recommended temperature for welding the PVC I was using. The process is fairly straightforward and once you get a feel for how far and at what angle to hold the torch, things go quite smoothly. The first box went from a 4'x4' sheet of PVC to finished in about 2 hours.
Here you can see one of the welds in the box where I was still getting the hang of it. Despite some discoloration due to overheating in some areas, the edge is very strong and I cant seem to break it with my hands alone. This box will be dropping in to an existing frame used for the lead batteries, while the next box  needs to be designed from scratch to fit between the frame under the car. I'll also need to weld an angle iron frame to support that one. This is the first step of many, the batteries get here in five weeks, so it will be an ongoing process until then. More to come soon.

Duracell Powermat Surgery

Alright, here goes my first post of substance. Today I found myself in possession of a Duracell Powermat wireless charging kit and case for a Samsung Galaxy S3. The charging mat, as I guess one would call it, is very well built. It's made of machined aluminum and the bottom has grippy rubber strips so it doesn't slide around on a desk. The case that accompanies it however leaves a lot to be desired.

The case adds quite a bit of thickness and height to the device and it's made of a cheap-feeling white plastic. The rubber sides make the lock and volume buttons all but impossible to press, and let's face it, it's damn ugly if you don't have a white Galaxy S3. Samsung is supposedly going to release a wireless charging system of their own that replaces the back cover of the phone and adds no thickness, and there are even contacts for such a thing on the back of the phone under the cover. This was all it took to convince me to crack open the case (which split in two pieces in a matter of seconds) to discover that there was just a small circuit board with a sticky back in the center. There was only one logical way to continue.

Further research revealed that I wasn't the first to attempt a DIY wireless charging modification and there were even instructions to use old Palm pixi/pre back covers and chargers as sacrificial parts for under $20. This process could be used to make just about any device support inductive charging, and the contacts on the S3 make it even easier. After some fiddling with copper tape and soldering, I had it working. I won't go too far into details as the XDA post linked above does a good job of explaining the process with pictures.

So if you have a Duracell Powermat and want to make your device sleeker, crack open the case and give this a try. A few tips if you decide to attempt this:

  • The ferrite circle on the back of the PCB is necessary for the charger to work when against the back of the device. It seems Duracell uses something at a higher frequency to get the power to the device (judging by the slight high pitch buzz) that the phone itself will interfere with, unlike the Palm circuit used in the XDA link.
  • The red and black wires are positive and negative respectively, just as you'd expect. The yellow wire is connected to the shield of the USB connector and wasn't necessary for operation.
  • On the Galaxy S3, the pin towards the top of the device is positive, something they failed to mention in the XDA post, and I now know that connecting them backwards will have no ill effects because of this oversight.
Thanks, for reading! Let me know if you attempt this or have any info/suggestions.

Tuesday, December 25, 2012

Introduction

Hi! I'm Nolan. I'm a sophomore at Cal Poly in San Luis Obispo, CA studying computer engineering, because I couldn't choose between my love of software, electronics, and physics. I plan on posting any cool projects I happen to be working on as well as using this as a log for the ongoing project that is my DIY electric car. Thanks to Kenneth Finnegan (http://blog.thelifeofkenneth.com/) for persuading me to start this.

Now more about me: I'm an active member of the Cal Poly Amateur Radio Club (http://w6bhz.org) and I have a lot of fun playing with radios and making use of my recently acquired call sign, KK6ADS. I converted a Toyota RAV4 into a fully electric vehicle during my sophomore year of high school with the help of my dad, and I am now in the process of upgrading the lead batteries to lithium (more on that in later posts). I have fun writing android apps, and maintain one to check meal plan balances at Cal Poly (http://goo.gl/tJgWH). I also speak a fair amount of German, as I took four years of it in high school (and actually tried to learn it). That's all for now folks!