Science Buddies: "Ask an Expert"

I have everything setup. I am using two baoding metal spheres and a piezoelectric starter. The ground wire (black) is connected to one of the metal plates that came with the starter and the other end is connected to one of the metal spheres. The red wire is connected to the starter and the other end is connected to the other metal sphere. No matter how far or close I put the spheres, I get no sparks. I have also tried the ground wire attached to the starter. Please help.

Hi Diane:
Have you tried this in a dark enough room so that you will be able to see the sparks? I'm also not sure that your piezoelectric starter is connected correctly - how is the

metal plates that came with the starter

connected to the piezoelectric piece?

If your spheres are not getting a spark between them, can you reassemble the starter and get it to work, or is it completely dead? If you can reassemble it and it works, be sure that the 2 wires that go to the

positive electrode (red) and the ground electrode (six "fingers" surrounding the positive electrode)

are what you are connecting to the spheres. Let us know what you find out.

Keith

Hi Diane,

If Keith's excellent suggestions for checking the experimental set-up don't solve the problem, I have two more suggestions that may help with the flying sparks:

1. Clean all of the surfaces with acetone or isopropanol. It's easy to get fingerprints all over the surfaces, and the presence of organic molecules will interfere with spark formation. A thorough cleaning with an organic solvent will solve this problem.

2. If you are doing this experiment in humid weather, you will need to wait for a cold, dry day for really good results. I live in a climate where static electricity and flying spark experiments do not work at all, except on an occasional very dry, windy day.

Please do let us know what solves the problem for you.

Donna Hardy

I have cleaned the spheres and all surfaces.

I have the red wire connected to the piezoelectric starter and the other end touching one the metal spheres. One end of the black wire is touching the other metal sphere. The other end of the black wire is connected to the starter base plate. Please see the attached file which shows how it's set up and let me know what I'm doing wrong.

Thanks so much for the responses. Keep'em coming.

Diane - I didn't see a file with your diagram attached, but a couple of routine things.

1) Does the piezoelectric starter work properly when not attached to the spheres? Can you get a significant spark (usually at least one-quarter inch).
2) Are the spheres truly electrically isolated from each other. As others have suggested, even a high impedence leak between the two spheres will 'ground' the spark.

If you do have a diagram try to repost it. Good luck.

Here is the diagram:

Hi Diane:

Thanks for including the picture. The circuit you are using is not a complete circuit. The piezoelectric device has only the red wire connected to one side of it. The black wire must be connected to the other side of the device. Since I've never seen one of these devices, I'm flying blind here, but the picture in the experimental description shows the red wire coming from the end of the starter and the black wire on the side of the starter. I see that your starter has a red wire on one side. Was the black wire connected originally to the starter? If not, was the metal part in the lower left hand corner of your picture somehow pressed up against the piezoelectric chamber? Or was it in some other way mechanically connected? Let us know what you find out.

Keith

Diane - Thanks for the diagram. As Keith noted, you have an open circuit. I found a similar piezo igniter in may garage (see attachment) and you can see two wires, one mounted on the side, the other coming out the end. Your unit may be missing the side wire and the connection may have been made when it was installed in the metal device that held it. That would have been the natural ground. This should get you to 'sparking'. Good luck.

Finally -- success! My sparks jumped. Thanks to all who responded to my plea for help. I used every suggestion and finally on a cold, dark night with a closed circuit, I saw sparks!

Now I have one more problem. I performed this experiment using different conductors/insulators and different distances between the metal spheres.

I know that the voltage for air = 3kV and the voltage of the piezoelectric ignitor = 17 kV. I don't know how to get the voltage between the balls.

i.e.: Balls are 4 inches apart, with foil between them, there were sparks. How do I calculate the voltage? IS there a formula?

Thanks for our help.

Diane - The dielectric strength (insulation strength) of air is about 3kV/mm. If your igniter is capable of producing 17kV, the approximate length of arc will be about 6mm, or about one-quarter inch. That would be a pretty good basis for estimating the voltage produced. I don't know how you might have observed a 4" discharge between the balls with this type of igniter. A 4 inch discharge in air would require about 300kV. Did the aluminum foil reduce the effective gap to about one-quarter inch?

Rick

Rick:

Here are my observations:
At 5" - 6” apart – no sparks with air, foil, plastic bag, wet or dry paper.
At 4” apart – no spark with air or dry paper; sparks with foil, wet paper, and plastic bag.
At 3” apart – sparks with air, foil, plastic bag, and wet paper; no sparks with dry paper.
At 2” same as 3”

What Sparks looked like:
At 2 – 4”; sparks = tiny sparkle of light appeared at the negative electrode ball with air, foil, plastic bag & wet paper
Except, at 2" w/foil; spark was a brilliant flash of light at the negative electrode ball.

My questions:
1. Did I truly see sparks at 3-4 inches or just at 2 inches w/foil?
2. What is the formula to determine how far the sparks jumped between the balls at each distance?

Thanks for you help,
DianeB

At 2 – 4”; sparks = tiny sparkle of light appeared at the negative electrode ball with air, foil, plastic bag & wet paper Except, at 2" w/foil; spark was a brilliant flash of light at the negative electrode ball.
1. Did I truly see sparks at 3-4 inches or just at 2 inches w/foil?

If you saw a "tiny sparkle" of light, then you saw something producing light. With semiconductor materials, photons can be emitted when electrons switch between relatively low energy levels. It is very easy to end up with small amounts of semiconductor materials from finger prints, cleaning agent residues, dust coatings, etc. Given that you saw a significant difference in behaviors between 2 inches with foil and 2 inches with air and 3 inches with everything, I suspect that you might have something other than a spark discharge producing the light. If you have time, you should repeat the experiment with an air gap and slowly decrease the distance until you get that brilliant spark you saw with the foil. This distance and the air temperature and humidity and barometric pressure will give you an indication of how much voltage you are developing. Unfortunately, the air gap distances per voltage formulas are based on sharp point air gaps to provide the minimum breakdown voltage for concentrated charge gaps. With your ball structures, you have a distributed charge density which will have a higher breakdown voltage, unfortunately, I can't predict by how much without knowing a lot more about how many electrons your piezo generator is producing and how many are leaking (being lost). The guestimates that others have provided for your piezo generator probably assume a given spark gap; however, the maximum voltage a given piezo generator can produce maybe considerably more if the leakage resistance is low and the dielectric breakdown paths will withstand a higher voltage before breaking down.

Aluminum foil is definitely a conductor so you definitely changed your distance and probably changed your charge density geometry as well when you tested it. The amount of light produced by an arc discharge is primarily a factor of the amount of current in the discharge. In any case, what you saw for this foil case was definitely light from a spark arc discharge.

2. What is the formula to determine how far the sparks jumped between the balls at each distance?

I don't understand your question. By definition, if a spark discharge occurred between the two balls with an air gap at some measured distance between them, then the measured distance between them is by definition the distance the spark traveled or jumped or arced.

If you are attempting to measure the relative dielectric properties of paper, wet paper, plastic wrap, etc with respect to air, then you need to find a way to hold the test material between the two balls without the test material contacting either and determine how much closer the two balls can be without arcing through the test material (vs arching around the test material).

I HAVE CONDUCTED THE EXPERIMENT REPEATEDLY AN CAN NOT GET THE SPARK TO GO ANYWHERE NEAR THE BALLS. WHAT CAN I DO?

DianeBrown wrote:I have everything setup. I am using two baoding metal spheres and a piezoelectric starter. The ground wire (black) is connected to one of the metal plates that came with the starter and the other end is connected to one of the metal spheres. The red wire is connected to the starter and the other end is connected to the other metal sphere. No matter how far or close I put the spheres, I get no sparks. I have also tried the ground wire attached to the starter. Please help.

TNX 4 THE IDEA BUT IT STILL WONT WORK?

Hello and welcome to the forum - is this a new thread instead of a continuation of the old one? If so, let us know so we can break it off (and give you more attention.)

As in the previous problems you noted, a compete circuit is required for the starter to give you a spark. Could you post a picture of how your starter is connected? What do you mean that you cannot

GET THE SPARK TO GO ANYWHERE NEAR THE BALLS

? Is the starter producing a spark somewhere else? This makes it sound like you have not dismantled the starter and connected it up to the balls? Please give us more information so we can help you.

Keith