Speaking of LEL, does anyone else get frustrated when they try to explain to people that a full tank of gas will not explode, even if a lit match is thrown in the gas tank?

For combustion to occur one needs:

1) Fuel

2) Oxygen

3) enough heat for ignition ( in exemplia a spark)

 

As luck would have it I ran across the pictures I had of the prototype, so if I can figure out how to get thiem into this post you can see them. You may note that the prototype showed me a few problems that I fixed in the write up.

The first of these was mounting the motor under the support arm. This puts it in the path of heat and fumes, so it would be much better to have it on top of the bar, with a plate directly underneath to block whatever might drift up. (Stepper motors don't have brushes so there's not a fire risk, but they don't like too much heat or corrosive fumes.)

The other correction that comes to mind is the placement of the capacitor. This is a no-brainer and I don't know why I originally put it where it is. It should be back away from the stand and protected inside a container of some sort.

PP

Quote from: Douchermann on August 17, 2009, 06:30:43 AM

Prepuce, being that your motor is running on AC current, a simple dimmer switch might be the answer to your problem.  Try to find a high amp rated one though, as I can't imagine the basic ones are rated much higher than a couple amps, and a strong enough motor will sure as hell fry that with no problem.

Thanks for the suggestion, but because it's a stepper motor that wouldn't work. In fact steppers are ordinarily run with digital signals and require a particular bit pattern to function. The capacitor on the second set of inputs causes a phase shift of the sine wave, making the motor turn.

So, what you'd actually want would be a trimmer capacitor (variable capacitor, the capacitor equivalent of a dimmer switch). They don't really go up beyond the picofarad range, however.

What was the actual total capacitance of the circuit? Ceramic caps that are physically large in size are often of fairly low capacitance, with a high voltage rating. If the caps have markings like "103" on them, that tells us what their values are.

As far as digital signals go, I know that the Arduino community (www.arduino.cc) has a lot of members doing things with digital control of stepper motors. With an Arduino and a potentiometer you could easily regulate the speed of the stirrer.