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Creating Sparks with Induction Coils Project

Postby science1 » Mon Nov 12, 2007 6:31 pm

My daughter has a science fair project due in one week and we have been attempting to create sparks with the instructions and material list off of the science buddies web site for this project. We have viewed the ask the expert questions on the list already and have gotten some new parts that some one the experts said needed to be replaced because the ones in the original list will not work (ex: rebar in stead of carriage bolt, insulated wire in stead of bare copper wire, and a different relay switch 275-218). We can get it to chatter, but it will not generate enough energy to create a spark a all, even when we use 18V of energy source. Can you give any suggestions as to what we can do to make sparks. Is there another way to build a similar project. We really don't have time to start over. PLEASE HELP!

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Postby Craig_Bridge » Tue Nov 13, 2007 7:03 am

If it will chatter continuously all on its own, then you probably have a viable primary circuit. One last check of the primary circuit is to measure either the voltage across the primary winding or the current flowing through it to determine that it is changing. Note: This will not be constant unless you interrupt the operation of the relay contacts. Measuring with both open and closed positions should give you different readings.

How many primary turns (around in your case the rebar)?
How many secondary turns?

You need a turns ratio of 750:1 to 1000:1 for a 6 volt primary. If you have a primary of 10 turns, then that is 7500 to 10000 turns. Do you have enough turns?

How wide is your spark gap? Try setting it to about the thinkess of a business / index / recipe card.

Did you use any insulation between the secondary layers? The enamel insulation on magnet wire is subject to cracking and abrasion and can easily break down between layers.

I'm assuming that you used a piece of PVC pipe between the primary and secondary and kept the secondary turns back from the ends of the PVC pipe to avoid other potential dielectric breakdown possibiliities.

With the battery disconnected, what is the resistance of the secondary circuit measured at the spark gap? It should match the current limiting resistors. If it is an open circuit or higher resistance, then you need to check your connections.

Sorry, this one is hard to dignose without seeing it.

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