Thursday, November 21, 2013

Coffee Maker double hack

Since my daughter Callie really likes to have birds visit our backyard, so she can watch them, figure out what kind each is as well what they like (how to attract even more) I decided to find a way to keep our bird bath from icing over before it really gets and stays cold out here. My objectives are to make it out of parts I have or that I can recycle from old tech, and power it from solar or wind (batteries don't really perform well in freezing temperatures and I really did not want to run an extension cord out to the bird bath).

Solar seemed to be out since the sun is not as bright and the days are getting shorter. Wind seems to be a viable alternative since I learned that stepper motors can be used for generators (I've got a number of stepper motors from older printers that I harvested for parts). 
Something to take note of:
Steppers can generate higher voltage at lower speeds (steppers are generally designed to move slower than other motors and when you use a motor as a generator it will generally only generate the voltage it would run off of when it is spinning at the speed it was designed for - a 12 volt motor designed to rotate at 1000rpm will only generate 12 volts when it is spinning at around 1000rpm). 

I already have a model airplane propeller that I bought earlier this summer (if you want it to face into the wind and spin you need to mount it backwards) and a swivel mount from a small windmill generator I built earlier in the summer as a proof of concept, as well as bridge rectifiers to convert the current generated from AC into DC.  Below is the remains of my test wind mill generator that I built over the summer:

Alternator adapted from old VCR (3 phase motor), Mount made from swivel wheel from a chair, Rectifiers pulled from old electronics.  You might notice the tape in the first picture - a storm blew this over and snapped the connection between the generator and the wind vane so I had to tape it together for the picture..

My only real issue was what to use as a heater. Ideally I needed something water proof that could sit in the bird bath.  My main concerns were:
  1. avoiding electrifying the water (and birds along with it)
  2. overheating the water (cooking the birds) 
I looked up commercial bird bath heaters to get some ideas of how they are designed  .   A small immersion heater would be ideal, I couldn't really find an inexpensive one, or even any designs for making one.

So, I switched gears and decided to find a heating element first and then hopefully be able to figure out a method to insulate it for use in water. I tried finding an old hair dryer thinking I could pull the heating coils out – but I couldn't find one. Next I looked at an old curling iron, I disassembled the handle and could see the heating element but couldn't figure away of getting it out without using a hacksaw to cut down the length.

Finally I settled on an old coffee maker in my basement. I detached the power cords, thermal fuse and water tubing and pulled the heating element out of it rather easily.

At full speed the stepper should generate around 12 volts (it is rated as a 12 volt motor) so I needed the heater to warm up rather than boil water - which it is designed to do at 110 mains voltage.  I decided to test this idea  by attaching a 12 volt battery supply to a the coffee pot heating element to see how hot it gets and to check how much current it draws (to get idea if output of stepper/generator is going to be enough).

  1. Resistance of element: 16.6 ohms
  2. About 600mA current draw at 12 volts (I=V/R Ohms Law)
  3. Element warms up after about a minute. It doesn't seem to get hot, just warm, which should be enough
I'll post the results of this experiment after I finish the build and the weather is cold enough to test it.  If all is well I'll also post the final build instructions up on Instructables .

Now for the double part of the hack. While talking to my wife last night she told me that she wished that her coffee maker could be hooked up to a timer so she wouldn't have to wait for it to brew (she has a Hamilton Beach Scoop - no timer). It seemed like an interesting challenge to me so I starting to think about how I could do it. 

First, of course, I had to check if someone had already done this (why reinvent the wheel - unless you are trying to improve it) and found no one had.

I knew that setting up a countdown timer to trigger a relay is something that I can do but having an actual clock timer would be a lot nicer and the coffee maker that I harvested the heating element from had a functioning timer that would be perfect for the job.  So, I pulled the circuit boards out and started looking at the parts.  The power supply to the heater and the clock/timer were on one board and the clock/timer was a separate board and they are connected by a 5 pin molex ribbon plug (or polarized wafer plug - not to sure of the proper name).

I'll be posting more on this build later, it is a little more involved and I need to write up the math I used for some of it.